performance analysis of a new developed a thesis in
TRANSCRIPT
![Page 1: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/1.jpg)
PERFORMANCE ANALYSIS OF A NEW DEVELOPED
DESICCANT IN A PACKED TOWER
by
SEDEF KAVASOGULLARI, B.S.
A THESIS
IN
MECHANICAL ENGINEERING
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
IN
MECHANICAL ENGINEERING
Approved
Accepted
May, 1991
![Page 2: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/2.jpg)
ACKNO\"'LEDGEMEJ\'TS
The author would like to thank Dr. Atila Ertas for his direction, counseling, valu
able advice, and support throughout this research, and to Dr. P. G andhldasan for
his help, advice, and direction. The author would like to express her appreciations
to Kham.is R. Al-Balushl for hls help during this study and to ~orton Company for
their continuous support. Special thanks are also extended to Dr. Herbert Carper
and Dr. Edward E. Anderson for serving as members of this thesis committee.
The author expresses her sincere gratitude to her Mother, Beyhan Kavasogullari,
for her support, and love. Special thanks for Michael J. Benson, for his support,
help and encouragement.
Financial support for this study has been provided by the state of Texas under
Energy Research in Application Program, Project # 309.
11
![Page 3: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/3.jpg)
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................... u
ABSTRACT ............................................................. vii
LIST OF TABLES ...................................................... viii
LIST OF FIGURES ...................................................... ix
NOMENCLATURE ...................................................... Xl
CHAPTER
1. BACKGROUND AND LITERATURE SURVEY .................... 1
1.1 Introduction .................................................... 1
1.2 Desiccants ...................................................... 2
1.2.1 Solid Desiccants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 Liquid Desiccants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Gas Liquid Contact Devices ..................................... 6
1.3.1 Regular Packings ......................................... 10
1.3.2 Random Packings ......................................... 10
1.3.3 Selection of Packing Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.3.1 Raschig Rings ....................................... 12
1.3.3.2 Snowflake Packings .................................. 12
1.4 Proposed Dehumidification System ............................. 13
2. COMPARISON OF HEAT AND MASS TRANSFER COEFFICIENTS OF LIQUID DESICCANT MIXTURES IN A PACKED COLUMN ............................ 19
2.1 Introduction ................................................... 19
2.2 Evaluation of Heat and Mass Transfer Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
lll
![Page 4: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/4.jpg)
2.3 Results and Discussion ......................................... 23
2.3.1 0.5 in. Ceramic Raschig Ring .............................. 24
2.3.2 1.0 in. Ceramic Raschig Ring .............................. 25
2.3.3 1.5 in. Ceramic Raschig Ring .............................. 25
2.3.4 2.0 in. Ceramic Raschig Ring .............................. 26
3. EVALUATION OF THE PERFORMANCE OF THE DEHUMIDIFICATION PROCESS IN A PACKED COLUMN ........................................... 36
3.1 Introduction .................................................... 36
3.2 Evaluation of Heat and Mass Transfer Coefficients ........................................... 37
3.2.1 Holdup Calculations ...................................... 37
3.2.2 Interfacial Surface Area Calculations ...................... 37
3.2.3 Volumetric Heat and Mass Transfer Coefficients ........... 39
3.3 Simultaneous Analysis of Heat and Mass Transfer in the Packed Column ................................. 40
3.4 Computational Procedure ...................................... 44
3.5 Results and Discussion ......................................... 45
4. APPLICATIONS OF DEHUMIDIFICATION SYSTEMS FOR AIR CONDITIONING UNITS ................................. 62
4.1 Introduction ................................................... 62
4.2 Air-Conditioning in Supermarkets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3 Concept of the Proposed Cooling System ....................... 64
4.4 Description of the Model ....................................... 65
4.5 System Analysis for the Supermarket ........................... 66
4.5.1 Supermarket .............................................. 66
4.5.2 Mixing of Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
IV
![Page 5: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/5.jpg)
4.5.3 Dehumidification Tower ................................... 67
4.5.4 Vapor-Compression Unit .................................. 68
4.5.5 Solar Regenerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.5.6 Heat Exchangers .......................................... 69
4.5. 7 Auxiliary Heater .......................................... 70
4.6 Results and Discussion ......................................... 70
4. 7 Economic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.7.1 Targeted Energy Savings .................................. 71
4.7.2 Savings ................................................... 71
4.7.2.1 Pumps .............................................. 72
4. 7 .2.2 Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7.2.3 Vapor-Compression System .......................... 73
4.7.2.3 The Conventional AirConditioning Unit .............. 73
4.7.2.4 Comparison of Energy Requirements ................. 73
5. CONCLUSIONS AND RECOMMENDATIONS .................... 79
REFERENCES .......................................................... 83
APPENDICES
A. COMFORT ZONE ................................................ 87
B. CALCULATIONS ................................................. 88
Mixing of Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Vapor Compression Unit ....................................... 89
Solar Regenerator .............................................. 91
Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Auxiliary Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
v
![Page 6: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/6.jpg)
Pump Energy Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Fan Energy Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Vapor Compression Unit Energy Calculations .................. 98
Energy Calculations for Conventional System . . . . . . . . . . . . . . . . . . . . . . . 99
Saving Calculation ............................................... 100
C. REGENERATOR COVERED "WITH GLASS BUT BOTH ENDS ARE OPEN .................................. 103
D. MATERIAL COST .............................................. 104
E. CONVENTIONAL SYSTEM PROCESSES ON THE PSYCHROMETRJC CHART ........................... 106
VI
![Page 7: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/7.jpg)
ABSTRACT
Dehumidification of air using desiccants is a developing topic in the last decade
as result of energy shortage considerations. In this study, a theoretical method is
employed to analyze a liquid desiccant packed tower system. A new desiccant (Cost
Effective Liquid Desiccant, 'CELD') is introduced which is a 50% LiCl and 50%
CaCl2 mixture. The heat and mass transfer coefficients of LiCl, CaCl2 , and CELD
solutions are compared. The packed column performance of the CELD is calculated
using a new snowflake packing material. After showing that the CELD is a stable
liquid desiccant, a numerical model of a dehumidification system is combined with
a vapor compression unit to form a hybrid cooling unit to study the energy savings
for a supermarket.
In this study, it is shown that the CELD is promising to be a cost effective sta
ble liquid desiccant. The snowflake packing is an efficient packing material. Conse
quently, liquid desiccant hybrid cooling systems is a new alternative for conventional
air conditioning units with economical benefits.
Vll
![Page 8: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/8.jpg)
LIST OF TABLES
2.1 Constants for calculating static and total holdup .......................... 30
2.2 Constants for calculating interfacial surface area. . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1 Additional. cost of ~he proposed hybrid cooling system on conventional uru t. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4
Vlll
![Page 9: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/9.jpg)
LIST OF FIGURES
1.1 Packed Tower ........................................................... 15
1.2 Some random packings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.3 Plastic lntalox® snowflake packing ....................................... 17
1.4 The proposed system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1 Schematic of the closed cycle drying system .............................. 31
2.2 Effect of liquid flow rate on volumetric liquid phase mass transfer coefficient for 0.5 in. ceramic raschig ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.3 Effect of desiccant concentration on volumetric liquid phase mass transfer coefficient for 0.5 in. ceramic raschig ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4 Effect of liquid inlet temperature on volumetric liquid phase mass transfer coefficient for 0.5 in. ceramic raschig ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.5 Effect of liquid fl.ow rate on volumetric liquid phase heat transfer coefficient for 0.5 in. ceramic raschig ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1 Total holdup versus liquid inlet flow rate for lntalox® snowflake packing .. 49
3.2 Differential section of a packed tower .................................... 50
3.3 Dehumidification performance of the packed column with lntalox® snowflake packing .............................................. 51
3.4 Change of air outlet temperature with the packing height for the lntalox® snowflake packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.5 Change in the exit humidity of air with the liquid flow rate for Intalox® snowflake packing . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.6 Change in the liquid and air temperature with the desiccant flow rate for Intalox® snowflake packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.7 Change in the air outlet humidity with the increase in the desiccant inlet temperature for lntalox® snowflake packing ........................ 55
3.8 Change in the desiccant and air outlet temperature with the increase in the desiccant inlet temperature for Intalox® snow:A.ake packing .............. 56
lX
![Page 10: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/10.jpg)
3.9 Change in the air outlet humidity with the change in desiccant inlet temperature for 40% and 45% concentrations, with 3 and 4 GPM flow rate of desiccant for Intalox® snowflake packing . . . . . . . . . . . . . . . . . . . . 57
3.10 Change in the air humidity with the increase in the air inlet temperature for Intalox® snowflake packing ............................. 58
3.11 Change in the desiccant and air temperatures with increase in the air inlet temperature for Intalox® snowflake packing with 100% saturated air ..... 59
3.12 Change in the outlet humidity with the change in the inlet humidity of air for Intalox® snowflake packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.13 Change in the outlet temperatures of desiccant and air with the change in air inlet humidity for Intalox® snowflake packing ..................... 61
4.1 Schematic of the proposed cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2 Processes on the psychometric chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.3 Air-desiccant and desiccant-desiccant heat exchangers . . . . . . . . . . . . . . . . . . . . 77
4.4 Desiccant-water heat exchanger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
X
![Page 11: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/11.jpg)
a
c
ds
E
Energy
Fc,FL
g
G
G'
h' a G
H,
NOMENCLATURE
specific interfacial surface area for absorption, desorption, (m2 /m3 )
specific interfacial surface area for vaporization, (m2 /m3)
molar density, (kmoljm3 )
heat capacity of dry air, (J/kmol K)
heat capacity of water, (J/kmol K)
heat capacity of liquid, ( J /kmol K)
specific heat, (kJ /kg°C)
diffusivity of liquid (m2 /s)
diameter of the sphere that has the same surface, (m)
effectiveness, dimensionless
energy, (kW)
mass transfer coefficient for air and liquid respectively, (kmol/m2 s)
gravitational acceleration, (m/s2)
superficial molar gas mass velocity, (kmol/m2s)
superficial gas mass velocity (kgdryair/m2s)
molar velocity of dry air, (kmol/m2s)
enthalpy, (kJ /kg)
saturation enthalpy for gas phase, (kJ /kg)
latent heat of evaporation, (kJ /kg°C)
heat transfer coefficient for air and liquid respectively, (W /m2K)
volumetric heat transfer coefficient for the gas phase corrected for
the mass transfer, [Ackermann Correction], (W /m3 K)
integral heat of solution per mole of solution, (kJ /kmol)
Xl
![Page 12: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/12.jpg)
HL
HG
JD
JH
K'
KG
kG,kL
kth
L'
L
m
p
p·
Pt
PBM
PrG,PrL
Power
liquid phase molar enthalpy, (kJ /kmol)
gas phase molar enthalpy, (kJ /kmol)
mass transfer group, dimensionless
heat transfer group, dimensionless
overall mass transfer coefficient on mass basis, (kg/m2 s)
overall mass transfer coefficient on molar basis, (kmol/m2 atm s)
mass transfer coefficient for gas and liquid
respectively (kg/ m 2 s)
thermal conductivity of liquid (W /m2K)
superficial liquid mass velocity (kg/m2s)
superficial liquid molar velocity (kmol/m2 s)
mass flow rate, kg/s
molecular weight of water vapor, kg/kmol
molar flux of water relative to a fixed surface, (kmol/m2 s)
pressure, (Pa)
vapor pressure, (Pa)
total pressure, (Pa)
mean partial pressure, (Pa)
Prandtl number for air and liquid respectively
power, (kWh)
heat flow rate, (k W)
heat flow in the evaporator, (kJ /kg)
heat flux for the gas phase, (kJ /m2 kg)
Schmidt number for air and liquid respectively
air temperature (°C)
Xll
![Page 13: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/13.jpg)
T.-1
w
X
Yc
Yci
Yc
z
p
Subscripts
A
cd
com
D
liquid desiccant temperature (°C)
interfacial temperature, (°C)
ambient temperature, (°C)
humidity ratio, (kg/kg)
desiccant flow rate, (kg/hr)
concentration of water in liquid phase, (kmol H20 /kmol liquid mixture)
value of Xc at the interface, (kmol H20/kmol liquid mixture)
concentration of water in the gas mixture, (kmol H2 0/kmol gas mixture)
value of Yc at the interface, (kmol H20/kmol gas mixture)
concentration of water in gas phase, (kmol H2 0/kmol dry air)
height of the packing from the bottom, (m)
liquid desiccant concentration (%)
fractional void volume in a dry packed tower, dimensionless
operating void space in the packing, dimensionless
viscosity of air and liquid, respectively, (kg/m s)
molar latent heat of vaporization of water at the
reference temperature, (kJ /kmol)
liquid operating, static, and total holdup respectively, (m3 /m3)
density, (kg/m3)
efficiency
ambient air
condenser
compressor
desiccant
Xlll
![Page 14: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/14.jpg)
E vapor compression unit
£1" evaporative cooler
F fan
M air mixture
n new system
0 old system
p pump
PD desiccant pump
PW water pump
R room
ref refrigerant
WB wet bulb
XlV
![Page 15: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/15.jpg)
CHAPTER 1
BACKGROUND AND LITERATURE SURVEY
1.1 Introduction
Increasing energy costs in the last decade have resulted in an increased attention
to dehumidification systems. Dehumidified air has potential uses in many fields, e.g.,
air-conditioning, crop-drying, meat and fish drying, etc.
Dehumidification of air can be achieved in many different ways, such as refrig
eration, mechanical compression, and using desiccants. The refrigeration method
is widely used in air-conditioning units. In conventional air conditioning units, air
is cooled below the saturation temperature, which is below the comfort conditions,
to condense the excess moisture. For comfort conditions, air is reheated over the
condenser. This is a very expensive way of dehumidifying the air. Mechanical com
pression is another way of dehumidification. When air is compressed mechanically,
the moisture in the air can be condensed due to high vapor pressure even at high
temperatures. However, this is only suitable for dehumidifying small amounts of
air and the need for a large amount of cooling water makes the system impractical
and costly. The third method of uses desiccants. This was studied in detail in this
project. Desiccants are materials that have the ability of extracting moisture from
different media.
The goal of this thesis was to conduct a theoretical study of the performance of
a liquid desiccant packed tower system using a newly developed desiccant called
1
![Page 16: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/16.jpg)
2
'Cost Effective Liquid Desiccant' (CELD). CELD is a mixture of 50% lithium chlo
ride and 50% calcium chloride. The heat and mass transfer coefficients for CELD
will be calculated, and the results will be compared with those of lithium chloride,
and calcium chloride. Then the performance of CELD in the packed tower will
be evaluated, and the results will be discussed. Two hybrid cooling systems that
use CELD as the desiccant for dehumidification were modelled, and an economic
analysis of the model was undertaken.
In this chapter, a background for desiccants, towers and packing materials will
be presented and the proposed dehumidification system will be discussed.
1.2 Desiccants
Desiccants are the materials that have a high affinity for water vapor. As a
result of absorbing moisture, some desiccants change their chemical structure or
become diluted. To be able to reuse the desiccant, regeneration is necessary. The
regeneration of the desiccant can be accomplished by using solar energy or fossil fuel.
Regeneration temperatures can be as low as 50°C or as high as 250°C depending on
the type of the desiccant. Desiccants have many areas of applications. Desiccants
can be broadly classified as solid and liquid desiccants.
1.2.1 Solid Desiccant
Lithium chloride, silica gel, activated alumina, and activated carbon are some
examples of solid desiccants. The solid desiccant that has a porous structure picks
up the moisture from the air and forms a hybrid of the desiccant. Regeneration
is accomplished either by reheating the solid desiccant or by passing the heated
air through the desiccant bed to absorb the moisture in the desiccant. A model
that uses a solid desiccant in the dehumidification chamber of an air-conditioning
![Page 17: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/17.jpg)
3
unit (hybrid cooling system) in a supermarket has been designed and operated by
Manley et al. (1985). In this system, the solid desiccant is gel tapes that are covered
with solid lithium chloride which is shaped like a rotary wheel that is casted in a
net. This shape allows the air to pass through the desiccant. One third of the bed
is isolated from the other part, and this portion is used for integrated regeneration
of the desiccant. In the regeneration part, air that is heated by a natural gas heater
passes through the desiccant wheel to pick up the moisture.
In another study, the recovered heat from the condenser is used for the regen
eration of the desiccant (Macdonald, 1983). Whitehead (1985) suggested a similar
system for a hot and humid climate. In this system, outside air is dehumidified
below comfort conditions and then mixed with the returning air from the room.
This system decreases the amount of air that needs to pass through the desiccant
wheel and requires less power for operation. Hybrid cooling systems that use solid
desiccants promise up to a 60% savings over conventional vapor compression units
(Macdonald, 1983). In the hybrid cooling system, the only power required is to
blow the air through the desiccant and sensibly cool the air a few degrees. In many
of these studies, the desiccants are highly stable, but the stability is very much de
pendent on the contaminants in the air used (Burns et al., 1985). For this reason,
air passing through the desiccant is filtered. This creates additional pressure drops,
which mean higher power blowers. Solid desiccant hybrid cooling systems have been
analyzed theoretically in many studies. Systems are shown to have "coefficient of
performance" (COP) as low as 0.8 and as high as 2.48(Kettleborough et al., 1986).
But the number of experimental studies are limited, and there is not enough com
mercialization. These are a few of the reasons why hybrid cooling systems are not
widely used.
![Page 18: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/18.jpg)
4
1.2.2 Liquid Desiccants
Moisture can be removed from the air by using a solution of lithium chloride,
calcium chloride or bromide. "Then the air and liquid desiccants are brought into
contact, depending on the concentration of the liquid desiccant, moisture tends
to move from the gas phase to the liquid phase. The driving force in this phase
change is the difference between the vapor pressure of the liquid desiccant and vapor
pressure of the air. So in such a contact system, maintaining a proper desiccant
concentration will result in dehumidification regardless of the moisture in the air.
Many chemicals can be used as liquid desiccants, e.g., lithium chloride, calcium
chloride, monoethylene, sodium or potassium hydroxide, zinc chloride or bromide,
sulfuric acid, phosphoric acid, etc. There are some characteristics which need to be
considered for the choice of liquid desiccants. First, liquid desiccants should have
a low vapor pressure for effective drying. It should be regenerated easily at low
temperatures. There should be a large solubility range on the temperature scale to
prevent precipitation and it should be nontoxic. Most importantly, it should also
be inexpensive.
Some advantages of liquid desiccants over their solid counterparts are their abil
ity to be regenerated separately from the dehumidification process and liquid des
iccants can be cooled or heated through heat exchangers. Moreover, the liquid
desiccant will clean up the air from contaminants and disinfect it. This has not
only the advantage of the lower blower power but also the advantage of clean air
(Kettleborough et al., 1986).
In the present study, a liquid desiccant system was chosen because of the fore
going advantages and lack of research in this area. The liquid desiccants have many
potential areas of application. Drying crops is one of the primary examples. Air
during the dehumidification process is warmed up to a few degrees above the am-
![Page 19: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/19.jpg)
5
bient temperature, as a result of released latent heat of vaporization. This warm
and dry air can be used for batch-drying operations for the post-harvest handling
of crops. The process has considerable economical advantages over conventional
natural gas systems in which the air is only sensibly heated.
Liquid desiccants can also be used as heat pumps ( G andhidasan, 1989). Heat
can be stored and recovered by diluting and reconcentrating the liquid desiccant.
Power generation is another potential area for the use of liquid desiccants. Solar
energy and liquid desiccants can be combined to produce high pressure steam to
keep a turbine running.
Another field of application is in the food-processing industry ( Gandhidasan,
1989). Foods spoil mainly because of their high water content. Liquid desiccants
can be used for drying red meats or fish, concentration of citrus juices, and the
cooling and freezing of solid foods. Biswal et al. (1982) developed a mathematical
model of a packed tower for a solar-driven food-processing application.
The regeneration of liquid desiccants can be achieved by either solar panels or
by using natural gas and a regeneration tower. Gandhidasan (1983) suggested a
parallel-flow solar regenerator for the reconcentration of the liquid desiccant in his
theoretical study. It is found that preheating the liquid will increase the performance
of the regenerator. The other controlling parameters in the system are insolation
of solar panel, ambient temperature, water vapor pressure in the ambient air, and
the ratio of liquid flow rate to air flow rate. Peng et al. (1984) studied the different
types of solar regenerators and concluded that in hot and humid climates open
regenerator performance is very low. Leboeuf et al. (1980) used a packed tower to
reconcentrate a lithium chloride solution for absorption cooling using solar heated
air. Gandhidasan (1990) derived a simple expression to calculate the mass of water
evaporated from the weak desiccant in a packed tower using hot air.
![Page 20: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/20.jpg)
6
In the present study, a new desiccant is proposed, which is called CELD. It is a
mixture of 50% lithium chloride and 50% calcium chloride. Calcium chloride is the
cheapest desiccant (around 15 cents per pound) and easily available. It promises
dehumidification up to 25% for concentrations around 40%. However it is very
unstable with the inlet conditions of the air and desiccant. Lithium chloride is
a very strong and stable liquid desiccant, but it is very costly (around $8.00 per
pound). It promises dehumidification up to 60% for concentrations of 40%. The
mixing of these two substances produces a optimal desiccant (i.e., effectiveness and
cost saving of around 50% is achieved compared to lithium chloride). The 50%
combination of the two desiccants was chosen according to the vapor pressure of
the mixture. Detailed information about CELD solutions can be found in Ertas et
al. (1990a). CELD is used for the first time in this project.
1.3 Gas Liquid Contact Devices
The contact of liquid and gas can be achieved in parallel or counter flow towers
such as the wetted-wall towers, spray towers or chambers, fin tube surfaces in a
column, and packed towers.
Wetted-wall towers are used for controlled mass transfer operations. The liquid
runs down inside a vertical pipe where the gas may flow in either direction. Al
though the gas phase pressure drop is very low, the interfacial surface area is just
equal to the inner surface of the pipe. This surface area is insufficient for effective
dehumidification.
Liquid is sprayed into the gas stream by a nozzle in the spray to·wers. The
flow can be a countercurrent in a vertical column, or cocurrent in a horizontal
column. Even though the gas phase pressure drop is small, it requires a large
amount of pumping power to disperse the liquid into fine droplets. In addition,
![Page 21: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/21.jpg)
7
liquid tends to entrain with the gas in large amounts. Mist eliminators are needed
for most of these operations. Grifford (1957) suggested a dehumidification system
for an air-conditioning unit. In this system, two spray towers are used-one for
dehumidification and one for regeneration. The cooling water circulated in the
dehumidifying tower keeps the operation temperature around 80°F. Similarly, hot
water inside the regeneration tower keeps the temperature of regeneration between
200°F and 270°F. Even though the economic savings are not a considerable amount,
the author suggests the system because of the sterile atmosphere it provides. Gupta
et al. (1978) proposed a 3-ton air-conditioning unit that uses a spray tower, solar
regenerator, and direct type evaporative cooler. The system was designed for hot
and humid climates. The only drawback of the system was the corrosive liquid
desiccant. Corrosion is especially important in the solar panels. The system COP
was calculated to be around 0.2. Queiroz et al. (1984) have used the Markel
integral approach to calculate the mass transfer coefficient for the dehumidification
operation in a spray tower.
Peng et al. (1981) studied a fin tower. The individual heat and mass transfer
equations were derived. The interfacial surface area is assumed to be equal to the fin
surface as long as the liquid flow occupies less than 20% of the volume. However, in
the experimental studies there were many problems because of the flooding which
is coupled with choking. The reason for this is the structure of the fins and the
liquid desiccant ( triethylene glycol, TEG). They modelled a dehumidifying tower
suitable for a 3-ton air conditioning load. The theoretical and experimental results
were in close agreement. However, the theoretical model needs to be reevaluated
for different initial conditions. The liquid is sprayed over the tubes of the fin tube
surfaces in a column where the air is blown upward through the column. The cooling
water that circulates inside the fin tube keeps the operation isothermal. However, in
![Page 22: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/22.jpg)
8
some cases, extremely large air flow rates are required, and it is difficult to control
the liquid film over the fin tubes.
Packed towers are useful for cases where continous contact between the gas and
liquid phases are required. Towers can be filled \vith packings or devices that will
provide the required interfacial surface area, as shown in Fig. 1.1. The liquid is
distributed over the packing and covers it as a thin liquid film. For the dehumidifi
cation processes, the recommended design is the countercurrent flow column. The
desiccant falls down through the packing because of gravity while the gas moves
upwards due to the pressure difference created by the blower. There is a consid
erable pressure drop in the gas phase, whereas for the liquid phase the only power
requirement is for pumping the liquid up to the top of the tower. Sherwood et al.
(1939) correlated the heat and mass transfer coefficients of the packed tower us
ing 0.5, 1.0, and 1.5 in. ceramic raschig rings with water and air. The experiments
were conducted for different absorption and desorption cases and different heights of
packing. McAdams et al. (1949) studied a packed column with 1 in. carbon raschig
rings, theoretically and experimentally. They calculated the heat and mass transfer
coefficients in both modes and concluded that overall transfer coefficients should
not be used in the evaluation of tower performance. Treybal (1969) calculated the
mass and heat transfer performance of a packed column, using individual phase
coefficients. The heat and mass transfer is calculated through the mass and energy
balance through the tower. The tower height is calculated for the desired level of
performance. Factor et al. ( 1980) calculated the performance of a packed tower the
oretically and experimentally with ceramic lntalox® saddle packing. The difference
between the methods of Treybal (1969) and Factor et al.'s study is the interfacial
surface temperature. Treybal calculated the interfacial surface temperature using
an iterative method. Factor et al. assumed the interfacial surface temperature was
![Page 23: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/23.jpg)
9
equal to the water bulk temperature. Monoethylene glycol (MEG) and lithium bro
mide (LiBr) were used in the experimental studies. MEG gave very unstable results
because of its structure. LiBr gave not only stable results but it was also consistent
with theoretical calculations. The only problem they had was the large pressure
drop across the packed column. They suggested the use of different packing mate
rials. Lof et al. (1984) measured the heat and mass transfer coefficients of a packed
column with 1 in. ceramic raschig rings and compared their experimental results
with the ~vlcAdams' equation {1949). They give different reasons for the inconsis
tency of the results. However, McAdams' equations were correlated using carbon
raschig rings. Gandhidasan et al. (1987) used a method similar to Treybal (1969)
for the calculation of performance of the packed tower. In this study, they assumed
that the resistance to mass transfer exists in both phases and that the interfacial
surface temperature was equal to the liquid bulk temperature. Ullah (1986) used
the same method to evaluate the dehumidification effectiveness of a packed column
with calcium chloride. This method was developed for the performance analysis
of an air-conditioning unit which used a dehumidifying tower. The effectiveness
method reduces the high computational cost. Other components of the system are
an evaporative cooler, a solar roof pool regenerator, and a cooling water system. An
absorption cooling system column mechanism was analyzed by Collier {1979). In
this system instead of heating the regeneration environment, liquid desiccant was
heated in the open solar regenerators. The system performance was calculated ac
cording to the performance of the solar regenerators. The amount of water that can
be removed in the solar panel "\vill correspond to the amount of latent load that will
be absorbed in the absorption tower. The open solar regenerators brought many
problems to the system. Gandhidasan, {1990), derived a simple expression which
determines the performance of a solar-desiccant air-conditioning unit with the given
![Page 24: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/24.jpg)
10
initial conditions. The unit consists of an evaporative cooler, solar regenerator, de
humidifying tower, and cooling water system. This approximation provides a broad
idea about the performance of the system under given conditions.
The packed columns are chosen to work with in this study because they provide
large interfacial surface areas and ease of operation. Due to the insulation on the
walls oft he column, the heat and mass transfer processes can be treated as adiabatic.
The packing material for columns are classified into two major groups according to
their structure.
1.3.1 Regular Packings
This type entails a large group of packing. Counter flow trays, stacked raschig
rings, structured packings, and expanded-metal-lath packings are some examples of
regular packing. The material can be metal, plastic, ceramic or the combination of
these types. They usually provide a lower pressure drop than random packings and
controlled interfacial surface areas. The controlled surface area provides controlled
mass transfer in the volume. Their structure changes according to design purposes.
They provide an efficient media for countercurrent liquid gas flow. However, their
prices are very high.
1.3.2 Random Packings
Random packings are simply materials that are dumped inside the tower irreg
ularly. In the past, the packing materials used were broken stones, gravel, or lumps
of coke. Even though they have lower cost, they cause larger pressure drops in
the gas phase as a result of their structure. Today various packings with differ
ent structure and materials are available. Some examples of widely used packings
are: raschig ring, berl saddle, super Intalox® saddle, maspac packing, Tellerette®
![Page 25: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/25.jpg)
11
packing, pall ring, hy-pak packing, and IMTP® packing. Some of the packings are
shown in Fig. 1.2 (Strigle, 1987). Most of these packings are available in metal,
plastic, and ceramic form and in many sizes, e.g., raschig rings are available from 6
to 100 millimeters (mm) in diameter (Treybal, 1980). The packing materials that
have been designed in the last five years are primarily available in plastic. The
reason for this can be summarized as: new plastics are resistant to heat and heavy
loads and inert to most chemicals; they have light weight and low cost; and they
can be cast giving larger void space and interfacial surface areas.
1.3.3 Selection of Packing Material
Packings are chosen according to following properties:
1. Packing material should provide a large interfacial surface area for
the contact of liquid and gas.
2. Packings should have sufficient void space for the liquid and gas to
move along the tower.
3. Packings material should be inert to liquid which is being processed.
4. Packings should resist the structural loads and also should be easy to
handle.
5. Packings should have a low price.
The packing material choice in this study was made according to the above
mentioned factors and the availability of data. Ceramic raschig rings and Intalox®
high-performance snowflake packings are studied.
![Page 26: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/26.jpg)
12
1.3.3.1 Raschig Rings
These are thin walled hollow cylinders. Their sizes are determined by the diam
eter of the cylinder. Even though they are available in many different sizes from 6
mm to 100 mm, in the present study only 13 mm (0.5 inches, in.) 25 mm (1 in.),
38 mm (1.5 in.), and 50 mm (2 in.) will be used. Ceramic raschig rings of these
sizes were studied previously by Shulman et al. (1955) and the available data was
reorganized in Treybal (1980). The availability of the data was one of the reasons
these packing materials were used in this study. The comparison of heat and mass
transfer coefficients for lithium chloride, calcium chloride, and CELD was done us
ing these packing materials. As raschig rings are made of ceramics, in addition to
their high weight, they are liable to be broken during the dumping into the tower.
1.3.3.2 Snowflake Packings
This is a new product of the Norton Company. Its nominal diameter is 94 mm,
and height is 30.5 mm. Snowflake packing provides approximately 95% \'oid space
and a surface area of 4.54 m 2 /m3• Packing elements are shaped like a snowflake
as shown Fig. 1.3 (Norton, 1987). Larger void space allows more gas and liquid
to move along the tower with smaller pressure drops and also results in smaller
holdups. This is an advantage for dehumidification systems, because the stagnant
liquid inside the tower gets saturated in a short time and this causes a decrease in
the mass transfer performance of the system. In addition to the above mentioned
properties, polypropylene snowflake packings are easy to handle and are resistant
to corrosion and high temperatures and have a low price.
![Page 27: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/27.jpg)
13
1.4 The Proposed Dehumidification System
The proposed system is formed by a dehumidifying tower, a droplet separator,
two heat exchangers, a water cooling tower, an auxiliary heater, two desiccant
tanks, and a desiccant regeneration system as shown in Fig. 1.4. The figure will
be completed in the following chapters by adding the pumps and fans that are
necessary for circulating the liquid and air, respectively.
The dehumidifying tower is a packed column that is filled with plastic snowflake
packing material. The tower is a 24 in. diameter thin walled PVC pipe. The height
of the tower will be decided according to the performance of the CELD solution.
Two packing holders restrict the packing from the upper and lO\ver ends and also
control the gas and liquid flow distribution. The liquid distributor distributes the
liquid on the packing material evenly. The height of the tower is suggested to be at
least 2 feet longer than the packing height. If desired an additional few feet below
the packing can be used as a desiccant tank.
The droplet separators are needed because the liquid tends to be entrained the
leaving gas. The heat exchangers, cooling water and the cooling tower, and the
auxiliary heater are necessary for heating the weak desiccant corning from the de
humidifying tower and cooling the desiccant returning from the regeneration system.
The regeneration system is needed to concentrate the diluted desiccant back to
the desired concentrations. Regeneration can be achieved by using solar energy
or fossil fuel. Solar panels that are covered with glass, with the upper and lower
ends open to the atmosphere, can be used in the regeneration of the desiccant. A
detailed study of this type of solar panel is given by Mullick et al. (1974). As the
liquid falls down from the upper end of the panel, it is heated by the solar radiation.
The heating process increases the vapor pressure of the desiccant. The air 'vhich
has a lower vapor pressure than liquid desiccant, picks up moisture in the panel. :\
![Page 28: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/28.jpg)
14
liquid temperature around 60°C is sufficient for the performance of the solar panel.
A natural gas auxiliary heater can be used during the time periods when the solar
radiation is not available.
Another way of regeneration is to use packed columns. The mass transfer at the
of liquid and gas contact is a result of the vapor pressure difference of the two phases.
If the vapor pressure of the liquid desiccant increases above the vapor pressure of
the ambient air, water will be transferred from the liquid phase to the gas phase.
This can be achieved in two methods. The first method is to heat the air. When
air is heated, its relative humidity is decreased. During the contact in the column
air transfers heat to the liquid phase. This method has been studied previously by
Leboeuf et al. (1978). A second mode of dehumidification is suggested where the
liquid desiccant is heated. By this way, the vapor pressure of the desiccant solution
rises above the ambient air vapor pressure.
After studying the performance of the new liquid desiccant CELD, the above
dehumidification system will be analyzed as a part of a hybrid cooling system for a
supermarket in a hot and humid climate.
![Page 29: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/29.jpg)
15
Tower
Liquid Distributer
~~;~~m~~~~~~~- Packing Holder
Packing Suppon
Liquid Out -
Figure 1.1 Packed tower.
![Page 30: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/30.jpg)
,
(a) (b) (c) (d) (e)
(f) (g)
Figure 1.2 Some random packings (a) raschig ring, (b) lessing ring, ' c 1
partition ring, (d) berl saddle, ( e )Intalox® saddle, (f) telleret te. (g) pall nng.
16
![Page 31: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/31.jpg)
17
Figure 1.3 Plastic Intalox® snowflake packing.
![Page 32: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/32.jpg)
Hct;cncralinn Sys1cm -
Li!juid Dcsiccanl ====
Wa1cr
-Ueal
l
-=;!JE"hm'"I-J j ~--~:ling : f Tuwer l f
·--l &nr~A l
-
~-AirOu1
:~6)!t!m~~ ~~:~~. ~~ ;~ ~~ ~!-~.. . . ~. -• .!,..!~.!·.!~~:~!-·!-P-!e;.~~-~~.¥.~:!-~-!! ;ic Packed Tower:;; h~5~!;i~!~i!i!!!! .!~6~--~ .!:!~~a;~-!-;.! .!~~?~a!i!~:.!~~;e ._a;a!(~;~..A" ~.!~ e;.! ~9!%
.MJn
l>roplcl Scpcralnr
Figure 1.4 The proposed system.
t--'
00
![Page 33: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/33.jpg)
CHAPTER 2
COMPARISON OF MASS AND HEAT TRANSFER
COEFFICIENTS OF LIQUID DESICCANT
MIXTURES IN A PACKED COLUMN
2.1 Introduction
Dehumidification processes have important applications in batch-bin drying sys
tems. A liquid desiccant closed cycle drying system is shown in Fig. 2.1. The basic
concept of the system is to reduce the moisture content and warm up the air which
can be used for drying, a few degrees above the ambient temperature. This system
essentially consists of three processes: a batch drying process, a dehumidification
process, and a regeneration process. The liquid-phase falls downward due to gravity,
while the gas-phase moves upward through the packed tower due to the pressure
differential created by the blower. During the air-liquid contact, the air assumes
the vapor pressure of the desiccant solution. The vapor pressure of the desiccant
solution is lower than that of the humid air; hence, moisture transfer will occur
from the air to the solution. During the process there is a rise in air temperature,
due to the release of the latent heat of vaporization. Meanwhile, since moisture is
being absorbed, the desiccant is diluted. To reuse the desiccant in the process, it
must be regenerated to an acceptable level of concentration. The heat required for
regeneration can be supplied by any solar regenerator or an auxiliary heater. Then
19
![Page 34: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/34.jpg)
20
the concentrated, hot desiccant transfers heat to the dehumidified air in a liquid
to-air heat exchanger and returns to the storage tank. The warm, dry air is sent
to the batch-bin dryer, and the concentrated desiccant is cooled and supplied from
the tank to the top of the tower.
The system mentioned above is an example of a dehumidifying packed column
application. In order to analyze the performance of packed columns for dehumidifi
cation processes, calculation of the mass and heat transfer coefficients of the packing
material used in the column is necessary. Queiroz et al. {1984) have used the Markel
integral approach to calculate the mass transfer coefficient for the dehumidification
operation in a spray tower. Recently, Lof et al. {1984) conducted experiments to
calculate the overall heat and mass transfer coefficients in a packed tower using
a lithium chloride solution. A recent report by Gandhidasan (1985) is related to
the present study. For an adiabatic operation in packed towers, he si:lggested the
use of individual phase-coefficients rather than overall coefficients. In this chapter,
calculations are performed according to this method.
This chapter is concerned with the interface transfer of heat and mass v.·hen
air is brought into contact with liquid desiccant mixtures. A theoretical study of
heat and mass transfer analysis in an air-desiccant dehumidification contact system
(packed column) employing liquid desiccants, namely calcium chloride (CaCl2),
lithium chloride (LiCl), and a new liquid desiccant mixture CELD (Ertas et al.,
1990a) is studied. This new liquid desiccant assures no solidification, and it is
stable. To be able to compare the behavior of the CELD solution with the other
two desiccants, calculations will be done using ceramic raschig rings. As mentioned
in the previous chapter, the characteristics of 0.5 in., 1.0 in., 1.5 in., and 2.0 in.
ceramic raschig rings are studied by Shulman et al. {1955) and Treybal (1980).
![Page 35: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/35.jpg)
21
2.2 Evaluation of The Heat and Mass Transfer Coefficients
Many investigations of heat and mass transfer in fluid-solid systems have indi-
cated that the void space, fLo, is an important variable for the evaluation of the
heat and mass transfer coefficients. A knowledge of liquid holdup and the effec-
ti\·e interfacial areas is necessary to determine the void space in a packed tower.
"Holdup" refers to the liquid retained in the tower as film wetting the packing and
as pools caught in the crevices between packing particles (Treybal, 1980). There
are three different types of liquid holdup. The total holdup, cPLt, defined as the total
liquid in the packing under operating conditions, is expressed as the volume of the
retained liquid per unit volume of packing. The static holdup, cPL., is defined as the
liquid in the packing which does not drain from the packing when the liquid supply
to the column is discontinued. The operating holdup, cPLo, defined as the difference
between the total and static holdups, represents the liquid that will drain from the
packing and is also a measure of the liquid flowing through the packing when the
tower is in operation (Shulman et al., 1955).
The relation between the three holdups is given by
(2.1)
The void space, fLo, available for air flow in the packing is the difference of the void
space, f 1 , for the dry packing material and the total holdup. It is given as (Treybal,
1980)
(2.2)
For the purpose of estimating the total and static holdups the following empirical
equations are recommended (Shulman et al., 1955)
(2.3)
![Page 36: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/36.jpg)
22
(2.4)
where /3 = 1d.s 9 and d.s is the diameter of a sphere with the same surface area as
a single packing particle. The constants, a, /, 8, 8, and ). are given in Table 2.1
(Treybal, 1980). The gas-phase mass transfer coefficient is given by (Shulman et
al., 1955)
Fe = 1.195G[d.sG' I ~c(1 - ELa)r0-36
(ScG)0.667
The liquid-phase mass transfer coefficient is given by (Shulman et al., 1955)
or
where C is the molar density of the desiccant.
(2.5)
(2.6)
(2.7)
For vaporization, the interfacial area is proportional to the total holdup and the
relationship is given by (Shulman et al., 1955)
<PLt a= 0.85aA-,
<PLo (2.8)
where aA is the interfacial area for the absorption or desorption with water or
aqueous solution and given by
_ [808G'] n(L')P aA- m p~5 , (2.9)
where m, n, and pare empirical constants, given in Table 2.2(Treybal,1980). Through
the heat-mass transfer analogy, the gas-phase heat transfer coefficient can be cal
culated assuming ~ = 1. (This assumption is reasonable because, during the
![Page 37: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/37.jpg)
23
dehumidification process, the water vapor evaporates from the air stream and is
absorbed by the aqueous solution. Also, during the regeneration process, the wa
ter vapor evaporates from the aqueous solution and is absorbed by the air stream.
Hence, this can be approximated as a water-air system and a Lewis number of unity
can be assumed for this purpose.) The result is
hG _ l.195G'Cs[dsG' I JLG(1 - t:Lo)r0
.36
- ( PrG )0.667 ' (2.10)
where J D is the mass transfer group and is equal to (Shulman at al., 1955)
FG( ScG )0.667
JD = G ' (2.11)
and J H is the heat-transfer group given by
(2.12)
Similarly, the liquid-phase heat transfer coefficient is given by
h kth[dsL'Jo.4s(P )o.s L = 25.1- -- TL .
ds J.LL (2.13)
The corresponding volumetric coefficients can be obtained by multiplying equations
(2.5), (2.i), (2.10), and (2.13) with a, as obtained by equation (2.8).
2.3 Results and Discussion
As indicated in the above analysis, mass and heat transfer coefficients were calcu-
lated theoretically for the air-phase and liquid phase using 0.5, 1.0, 1.5, and 2.0 in.
ceramic Raschig rings. Calcium chloride, lithium chloride, and CELD solutions were
used as liquid desiccants and the results are correlated in the following equations
![Page 38: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/38.jpg)
24
(for correlation, a 'Statistical Analysis System', (SAS), non-linear regression model
is used and the mean square error in the analysis is found to be approximately
0.0079).
2.3.1 0.5 in. Ceramic Raschig Rings
Calcium Chloride Solution
hLa _ 292575.38( L')o.s2 e-o.oo132TL eo.oo24e ( G')O.l37.
FLa 0.04 7( L')o.s2 e-o.oonsTL eo.oo64e ( G')o.137.
hGa 4072.53(L')O.l89eO.oolosTG( G')0.777.
0.158( L')O.l89 eo.ooo9sTG ( G')o.111.
CELD Solution
hLa 28321 1.25( L')o.s2 e -o.oo1TL eo.oo29e( G')0.137.
FLa _ 0.0809( L')o.s2 e-o.oousTL eo.oos1e ( G')0.137.
hGa _ 4072.53(L')0.189e0.00105TG(G')o.777.
0.158( L')o.1s9 eo.ooo9sTG ( G')o.111.
Lithium Chloride Solution
hLa 273489.14( L')o.s2 e-o.oo1TL eo.oo41e( G')0.137.
FLa 0.0960( L')o.s2 e-o.oon7TL eo.oosse ( G')O.l37.
hGa 4072.53( L')O.l89 eo.oo1osTG ( G')o.111.
0.158( L')o.1ss eo.ooossTG ( G't777.
(2.14)
(2.15)
(2.16)
![Page 39: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/39.jpg)
2.3.2 1.0 in. Ceramic Raschig Rings
- Calcium Chloride Solution
hLa _ 261963.44( L')0.63 e-0.00132TL eo.oo24e( G')o.o74.
FLa _ 0.042(L')0.63e-o.oonsh eo.oo64e( G')o.o14.
haa 3668.29( L')0.2eo.ooo9sTG( G')o.n.
0.142( L')o.2 eo.ooossTG ( G')o.n.
CELD Solution
hLa 253580.59( L')0.63 e -o.oo1TL eo.oo29e ( G')o.o14.
FLa _ 0.072(L')0.63e-o.oonsheo.oos7e(G')o.074.
haa 3668.29( L')o.2 eo.ooogsTG ( G')o.11.
Lithium Chloride Solution
hLa 244873.51( L')0.63e-o.ooiTL eo.oo4te( G')o.o14.
FLa _ 0.086( L')0.63e-o.oon7heo.oo6se( G')o.o14.
haa 3668.29( L')o.2 eo.ooo9sTG ( G')o.n.
2.3.3 1.5 in. Ceramic Raschig Rings
Calcium Chloride Solution
hLa 149066.3( L')o.73 e-o.oot32TL eo.oo24e ( G')o.oo9.
FLa 0.024( L')0.73 e -o.oonsTL eo.oo64e ( G')o.oo9.
haa 2294.20( L')0.29 eo.ooossTG ( G')o.6s.
0.089( L')0.29 eo.ooo1sTG ( G')o.6s.
25
(2.17)
(2.18)
(2.19)
(2.20)
![Page 40: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/40.jpg)
26
- CELD Solution
hLa 144294. 77( L')o.13e-o.oo1TL eo.oo29e( G')o.oo9.
FLa 0.041 ( L')0.73e-o.ooush eo.oos7( ( G')o.oo9.
he a _ 2294.20( L')0.29 eo.ooossTG ( G')o.6s.
0.089( L')0.29 eo.ooo7sTG ( G')o.6s. (2.21)
- Lithium Chloride Solution
hLa 139341.84( L')0.73e-o.ooiTL eo.oo41e( G')o.oo9.
FLa _ 0.049(L')o.73e-o.oou7TLeo.oo6se(G')o.oo9.
he a 2294.20( L')0.29 eo.ooossTG ( G')o.6s.
0.089( L')o.29 eo.ooo1sTG ( G')o.6s. (2.22)
2.3.4 2.0 in. Ceramic Raschig Rings
- Calcium Chloride Solution
hLa 128416_56( L')o.66 e-o.ooi32TL eo.oo24e.
FLa - 0.021 ( L')o.66 e-o.oousTL eo.oo64e.
he a 2013.24( L')0.233 eo.ooos4TG ( G')0.64.
Fe a - 0.078( L')0.233eo.ooo77TG ( G')0.64. (2.23)
- CELD Solution
hLa 124306( £')0.66 e-O.OOlTL e0.0029e.
FLa 0.0355( L')0.66 e -O.OOliSTL eo.oosn.
he a 2013.24(L')0.233eo.ooos4TG( G')0.64.
Fe a 0.078( L')0.233 eo.ooonTG ( G')0.64. (2.24)
![Page 41: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/41.jpg)
Lithium Chloride Solution
hLa - 120040.99( L')o.ss e-o.oo1TL eo.o041e.
FLa - 0.042( L')o.sse-o.oon7TL eo.oosse.
hGa - 2013.24( L')0.233 f0.00084TG ( G')0.64.
FGa - 0.078( L')0.233 f0.00077TG ( G')0.64. (2.25)
The following parameters were used to find the above correlation equations
G' = 0.3 to 1.1 kg/m2 .s;
L' = 0. 7 to 6. 7 kg/m2 .s;
TG = 25 to 70°C;
TL = 26.66 to 60°C;
~ = 32.5 to 40%.
27
It is believed that these parameters are reasonably free of end effects and can be
used in further calculations.
In the present study, data for the viscosity and density of lithium chloride and
calcium chloride, which are necessary for the evaluation of heat and mass transfer
coefficients, are obtained from Ertas et al. (1990b ).
The effect of some of the liquid desiccant parameters, such as concentration, ~,
temperature, TL, and flow rate, L', have been presented in the correlation equations
2.14-2.25. To better understand the effect of these parameters, the results are also
presented in Figs. 2.2 to 2.5.
The typical plot of Fig. 2.2 shows that lithium chloride has the higher rate of
change of liquid phase mass transfer coefficient, when compared with the calcium
chloride and CELD solutions. For a particular air flow rate, the volumetric liquid
phase mass transfer coefficient also increases as the solution flow rate increases. It
![Page 42: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/42.jpg)
28
is apparent from this figure that the rate of the mass transfer coefficient increase
for the three desiccants is greater over the first 1 kgf(m2 x s) of liquid desiccant
mass flow rate. Although the CELD solution is a mixture of 50% lithium chloride
and 50% calcium chloride, a considerable increase in liquid mass transfer coefficient
is evident compared with the calcium chloride.
The effects of desiccant concentration on the liquid phase mass transfer coeffi
cient are shown in Fig. 2.3. The mass transfer coefficient increases with the increase
of desiccant concentration. However, as shown in Fig. 2.2, the mass transfer coef
ficient of the liquid desiccants is a stronger function of desiccant flow rate rather
than the concentration.
The liquid phase mass transfer coefficient as a function of liquid desiccant inlet
temperature is given in Fig. 2.4. From the figure, the mass transfer coefficient
decreases as the desiccant inlet temperature increases. This is expected because, as
the liquid desiccant temperature increases, the desiccant vapor pressure increases,
thereby reducing the performance of the liquid desiccant. Although the traces
from this figure revealed that the effect of inlet temperature on the mass transfer
coefficient is not significant, it is known that desiccant inlet temperatures should
be kept at a certain level for the best system performance.
The change of the liquid phase heat transfer coefficient with mass flow rate of
the liquid desiccant is given in Fig. 2.5. This figure indicates that the heat transfer
coefficient is a strong function of the desiccant flow rate. However, as can be seen
from the figure, the change of the heat transfer coefficients is almost the same for
all three desiccants.
From correlation equations 2.14-2.25, it is clear that the liquid phase mass and
heat transfer coefficients decrease as the ceramic raschig ring size increases for the
![Page 43: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/43.jpg)
29
same operating parameters. This is due to the decrease in total surface area per
unit volume.
The CELD desiccant solution in a packed column greatly improves the mass
transfer as compared to a calcium chloride desiccant solution. This improvement is
nonlinear which suggests that the lithium chloride and calcium chloride do not act
independently in the solution. It is also apparent that the solution inlet temperature
and concentration do not significantly affect the mass transfer in the ranges expected
for air drying. The CELD desiccant solution demonstrates the same liquid phase
heat transfer as the pure lithium chloride and calcium chloride solutions. This
suggests that the solvent dominates the liquid phase heat transfer rather than the
solute.
In this chapter, we demonstrated the behavior of the CELD solution in compar
ison to its two components. The tower analysis of the CELD solution will be made
using the new Intalox® snowflake packing material.
![Page 44: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/44.jpg)
30
Table 2.1: Constants for calculating total and static holdups
RASCHIG RINGS Porcelain Ceramic Carbon
a 2.09 x10 6 2.09 X 10-6 7.34x1o-6
I 1.508 1.508 1.104 b 2.47x10 4 2.47x1o- 4 5.94x10-4
() 0.376 0.376 0.376 ,\ 1.21 1.21 1.21
Table 2.2: Constants for calculating interfacial surface area.
Nominal size of Packing Range of L'
mm 1n. kg/ m2 • s m n p
13 0.5 0.68-2.0 28.01 0.2323 L' - 0.30 -1.04 2.0-6.1 14.69 0.01114 L' + 0.148 -0.111
25 1.0 0.68-2.0 34.42 0 0.552 2.0-6.1 68.2 0.0389 L' - 0.0793 -0.47
38 1.5 0.68-2.0 36.5 0.0498 L' - 0.1013 0.274 2.0-6.1 40.11 0.01091 L' - 0.022 0.140
50 2.0 0.68-2.0 31.52 0 0.481 2.0-6.1 34.03 0 0.362
![Page 45: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/45.jpg)
Debumldltler
Wet Air -......... . . .. .. . . .. . . . . .. .. . . . . . . . . . . . ...... . .. . . . . .. . . . . . ...... . . . . . . . . . . . . . . . . . . . . . . . . ...... . .. . . . . . . . . . . . .. . .. .
I
Pump. Batcb-BID 1
Dryer L~-
--Dry, Warm air
.Pump
Heat Exchar~~er
Weak Desiccant r-- '':
Strong Desiccant
Figure 2.1 Schematic of the closed cycle drying system.
31
![Page 46: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/46.jpg)
0.29524
0.0
- I i /"1 -~": i
~~)~· -< :· I """"--(.~:: . v
I : ... ~ ~-. I/
rv~··.- / I ,c',-W
/ v ·,\.e. -/ / r'l: ~ t-.o:,.... 4~r·~ ,.. ,.,e,, ~ "/ ~
;~~ !' v TL. = 31°C :/ v 1/ "(
0.0
l; m = 40% ,. G' = 0.7 kg/ m2 s
I I
Superficial Liquid Mass Velocity, kg I m2 s
I
l
7.00
Figure 2.2 Effect of liquid flow rate on volumetric liquid phase mass transfer coefficient for 0.5 in. ceramic raschig ring.
32
![Page 47: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/47.jpg)
0.22869 -
0.10509
32.5
I Lithi ~mC ~lorid~
I I
I
rl=:T n I i
~ I
I
TI..· = 31°C L m = 3 kg/m2 s G' = 0.7 kgfm2s I
r~lr 11m C hlori be
Desicant Concentration, Weight%
I j
I
40.0
Figure 2.3 Effect of desiccant concentration on volumetric liquid phase ma.:>s transfer coefficient for 0.5 in. ceramic raschig ring.
33
![Page 48: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/48.jpg)
0.17593 IL
.:;;: [C
-J\...
0.08276 I
25.0
~h-l I l I
IOl Ide
l
:L l[)
I i
I ~ =40% L' =) kglm2s a· = 0. 7 kg!m2s
I IICIU n< :h orin~ I
I
Desicant Inlet Temperature, degree C
I ,-
I I f-
:-
I
60.0
Figure 2.4 Effect of liquid inlet temperature on volumetric liquid phase
mass transfer coefficient for 0.5 in. cerarrric raschig ring.
34
![Page 49: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/49.jpg)
894587
0.0
0.0 Superficial Liqutd Mass Velocity, kg I m2 s
7.0
Figure 2.5 Effect of liquid flow rate on volumetric liquid phase heat transfer
coefficient for 0.5 in. ceramic raschig ring.
35
![Page 50: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/50.jpg)
CHAPTER 3
EVALrATIOI\ OF THE PERFORMANCE OF THE DEHUMIDIFICATION
PROCESS IN A PACKED COLUMN
3.1 Introduction
The dehumidification process in a packed tower is a result of simultaneous heat
and mass transfer. The difference in the vapor pressure of the desiccant solution
and the air, at the interfacial surface, is the driving force for mass transfer. As the
moisture transfers from the gas phase to the liquid phase latent heat is liberate.
This increases the temperature of the flow stream. The heat and mass transfer
coefficients that are calculated in the second chapter, F Ga, F La, hGa, and hLa are
the individual phase coefficients. The second chapter deals with the comparison of
heat and mass transfer coefficients for CELD and its two components, namely CaC12
and LiCl with four different size raschig rings. The individual phase coefficients are
recommended for use in packed column performance evaluations (McAdams, 1949).
The performance of the packed column will be evaluated by using Intalox® snowflake
packings. This new material is promising as an efficient new packing material.
In this chapter, the heat and mass transfer coefficients for CELD, using lntalox®
snowflake packing material will be calculated, and the performance of the dehumid
ification process in a packed column will be evaluated. Similar studies have previ
ously been done in which the liquid phase resistance to mass transfer was assumed
to be negligible (Lof et al., 1984). In this study, the resistance of mass transfer
36
![Page 51: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/51.jpg)
37
will be taken into consideration, and evaluations will be made using the method
suggested by Gandhidasan, (1985).
3.2 Evaluation of Heat and Mass Transfer Coefficients
The Intalox® snowflake packing material is a relatively new packing material.
The data for the characteristics of the packing are not available in an organized
form. The properties of the packing are calculated from the information which is
obtained from the packing manufacturer.
3.2.1 Holdup Calculations
The total holdup plot for Intalox snowflake packing obtained from Norton,
(1987), is shown in Fig. 3.1. As seen in the figure, the pressure drop across the
packing is an important criteria for determining the holdups. Approximately 0.5
in. of water column pressure head is anticipated for every foot of packing of the de
humidification process (Ertas et al., 1990c). The total holdup equation is (Norton,
1987)
cPLt = 2.9 X 10-3 L'l.07,
where L' is in kg/(m2 x s) and cPLt is in m3 /m3•
(3.1)
The snowflake packing is especially designed for lower static holdups. The static
holdup is assumed to be 2% of the total holdup.
3.2.2 Interfacial Surface Area Calculations
The snowflake packing material provides 91.8 m2 /m3 of dry surface area (Norton,
1987). However, during the operation, the effective interfacial surface area for the
mass and heat transfer is actually much less than this value. Shulman et al. (1955)
![Page 52: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/52.jpg)
38
calculated the effective interfacial surface area by taking the ratio of kGa and kG,
where these values are experimentally measured. They conducted these tests for
ceramic raschig rings and berl saddle packings. Treybal (1980) correlated these data
from the figures in the form of non-linear equations (i.e., effective interfacial surface
area is given as a nonlinear function of liquid and air flow rate).
In this study, a similar procedure will be followed for the calculation of the
effective interfacial surface area for snowflake packing material. The overall mass
transfer coefficient on a mass basis, K'aA, as obtained from the snowflake packing
manufacturer (obtained by personal contact from Norton Chemical Process Prod
ucts Company, John R. Sauter, Chamberlain Labs. Stow, Ohio 44224) , is
K' a A = 0.209205( L')0.4364( G')0.695' (3.2)
where L' and G' are in terms of lb/(ft2 x hr) and K'aA is in terms of lb/{ft3 x hr).
The above equation is obtained through a chilled water dehumidification experi
ment. In this study, it is assumed that during the dehumidification process desiccant
air contact system behaves like a water-air contact system. K'aA also satisfies the
equation
J dHG = K'aA z. H(;-HG G'
(3.3)
The overall transfer coefficient, K'aA, is related to the KGaA, which is a overall
transfer coefficient on a molar basis, by the equation (McAdams, 1954; Kern, 1950)
(3.4)
![Page 53: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/53.jpg)
39
where Pt is the total pressure and Mv is the molecular weight of water vapor.
Even though KcaA is the overall mass transfer coefficient, it can be converted to
individual phase transfer coefficients by the relationship (Shulman et al., 1955)
1 1 m --=--+--K caA kcaA kLaA'
(3.5)
where m is Henry's constant. It can be calculated using Henry's law as (Treybal,
1980)
(3.6)
where the p· is the gas phase vapor pressure, and Pt is gas phase total pressure. kc
can be calculated from (Shulman et al., 1955)
Fe kc = --,
PsM (3.7)
where F G is given by equation (2.5) and kL is given by equation (2.6). The interfacial
surface area is calculated from the equation (3.5). For the calculations of PsM and
m, air phase is assumed to be dry but at the interface, it is assumed to be saturated
with water vapor. The effective interfacial surface area, a, can be calculated from
equation (2.8). The heat and mass transfer coefficients are obtained from equations
(2.5), (2. 7), (2.10), and (2.13). The corresponding volumetric coefficients can be
obtained by multiplying these equations by the result of equations (3.5) and (2.8).
3.2.3 Volumetric Heat and Mass Transfer Coefficients
The results of the above equations are calculated for CELD solution and are
correlated using a SAS non-linear regression model. The mean square error for the
![Page 54: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/54.jpg)
40
calculations are: for FLa is 0.00345; for Fca is 0.00107; for hLa is 0.00344; and for
hca is 0.00105. The correlated equations for snowflake packing with CELD solution
are
hLa 130507( L')0.44e-o.ooo1sTL eoms~ ( G')o.69.
FLa - 0.0373( L')0.44e -o.ooo3TL eo.o2n~ ( G')o.s9.
he a - 187 .5( L')O.o4eo.osTG ( G')l.33.
Fe a - 0.00727( L')o.o4eo.osTG ( G')l.33.
The above equations are valid for the following ranges
G' = 0.3 to 1.1 kg/m2 s;
L' = 0. 7 to 6. 7 kg/m2s;
Tc = 25 to 70°C;
TL = 26.66 to 60°C;
~ = 32.5 to 40%.
(3.8)
The physical properties of the CELD that are used in these calculations are
obtained from Ertas et al. (1990a).
3.3 Simultaneous Analysis of Heat and Mass Transfer in the Packed Column
Vilhen air and desiccant come in contact in the packed column, because of the
difference in their vapor pressure, heat and mass transfer occurs, until a certain
equilibrium is reached. As the liquid falls down through the tower, it absorbs the
moisture from the air and its vapor pressure increases. In contrast, as the gas
moves up in the column, its vapor pressure decreases with its water vapor content.
The following equations obtained from Treybal (1969) are used to simulate the
![Page 55: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/55.jpg)
41
performance of a packed column. The following assumptions are necessary for the
calculations of an adiabatic desiccant-air contact system:
1. Heat loss through the walls is negligible.
2. Interfacial surface temperature is equal to the temperature of the bulk
liquid. The order of error due to this assumption is very small and
can be seen in Treybal, (1969).
3. Packing.is adequately irrigated and, therefore, the interfacial surface
area is the same for both heat and mass transfer.
4. No axial dispersion occurs in the packed tower. Co et al. (1971)
studied the mixing in the packed column by using adequate liquid
distribution and showed that assuming constant properties in a hori
zontal section of the packing is reasonable.
A differential section of a packed tower is shown in Fig. 3.2. The following equa
tions are derived using basic heat and mass balances in the section. The enthalpy
of the liquid is given by
HL CL(TL- To)+ ~H.,
dHL - CLdTL + d~H •.
(3.9)
(3.10)
In the calculations, the change of ~H. with the concentration is neglected, since its
effect on the performance of the column is very small. Similarly for air
Ha - CB(Ta- To)+ Yc[Cc(Ta- To)+ >.to],
dHa - CBdTa + YcCcdTa + dYc[Cc(Ta- To)+ >.to]·
(3.11)
(3.12)
![Page 56: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/56.jpg)
42
The direction of the heat and mass flux is taken positive in the direction of air to
liquid. The mass transfer at the interface of air and liquid is
Ncadz = Fe ln C1 adz= -GBdYc, [ 1- y '] 1- Yc
(3.13)
or
dYe=_ Feazn[1- Yci]. dz GB 1- Yc
(3.14)
The heat transfer at the interface is
(3.15)
Applying the Ackermann correction for simultaneous heat and mass transfer gives
dl' h' GB[Cc7z] ea = -1- exp[GB(C/r" )fheaJ"
(3.16)
The transfer of moisture to the liquid from the interface is
Ncadz = FL ln c adz. [ 1- X ]
1- Xci (3.17)
A mass balance in the control volume in Fig. 3.2 gives the result
(3.18)
An energy balance on the air side of the Fig. 3.2 gives
![Page 57: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/57.jpg)
43
Combining equations (3.12) and (3.19) reduces them to
(3.20)
or in reduced form
h(;a(TG- Ti) --=-Gs(Cs + YcCc)"
dTG dz
(3.21)
The liquid temperature gradient given is derived in a similar way.
(3.22)
The interfacial condition can be obtained by equating equations (3.13) and (3.17).
Yci = 1 - (1 - Yc) [ 1
- Xc] ~ · 1- Xci
(3.23)
The above equation can be solved simultaneously with vapor-liquid equilibrium
data for CELD solution. Using a SAS linear regression model the available vapor
pressure data is correlated in the following equation. (The root mean square error
is 0.0000327.)
0.05720066 Yci = 0.07983109 + 0.00172330877: - ----
Xci (3.24)
Equations (3.23) and (3.24) are solved simultaneously for Yci and Xci, for every
section of the column. The analysis presented above will evaluate the performance
of the column with the given: liquid inlet temperature and concentration; air inlet
temperature and concentration; exiting air humidity or desired level of dehumidi-
fication; flow rates of liquid and air. The output will be the height of the packed
![Page 58: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/58.jpg)
44
column, exiting au temperature and humidity, and liquid temperature and con
centration. Equations (3.14), (3.21), and (3.22) are used to define liquid and air
properties in every section of the column. This method is called the 'incremental
research method'. The calculation starts at the bottom of the tower where z=O.
3.4 Computational Procedure
The computation starts with reading the inlet conditions of air and liquid, and
the exit humidity of the air. A reference temperature is assumed. Calculations start
by assuming the exit temperature of the liquid . Then the packing height is divided
into N sections. N is chosen as 100. The liquid and gas exit conditions are calculated
from the mass and heat balance in every section. The program is initialized from
the bottom of the tower with the guessed liquid exit temperature. First the heat
and mass transfer coefficients are calculated and then interface moisture condition
is calculated. The concentration and temperature gradients are calculated along
the z direction. After this step the incremental tower height is calculated for the
given change in the absolute humidity. Then for the next incremental tower section,
the air and liquid properties are updated.
The same calculation of interface moisture conditions are repeated for each sec
tion. When the ( N + 1) cross section or Nth tower section is processed, the program
reaches the top of the column. Here the calculated liquid inlet temperature is corn
pared with the given value. If the difference of the two values is larger than a given
error, a new appropriate liquid exit temperature is assumed and iterations are re
peated until the convergence is reached. An over relaxation method is used for this
iterative calculation. The 'Successive Over Relaxation' (SOR) is equal to 1.5.
![Page 59: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/59.jpg)
45
The results are liquid and gas temperatures, liquid concentration, air exit hu
midity and tower height. The liquid and air humidity profile can also be determined,
if desired.
3.5 Results and Discussion
As explained in the procedure, the computer simulation gives the height of the
packed column as the output for the desired level of performance. The performance
of a column is analyzed in order to find the optimal design for the tower. An
important criterion for the optimal column is the packing height. Fig. 3.3 shows
the performance of packed columns for different packing heights. As the packing
height increases, the outlet humidity of the air decreases. However the relationship
between the two is not linear. As the packing height increases, the rate of decrease
of humidity decreases. This is a result of a decrease of the vapor pressure of the air.
When the tower reaches a certain height, the air which is close to the top of the
tower will be dehumidified, and as a result of this, its vapor pressure will decrease.
Even though the desiccant is strong (i.e., has a low vapor pressure), the driving
force (i.e., the difference between the vapor pressure) will be very low. This will
result in a lower mass transfer. A 0.5 m. packing height is chosen to work with
for constant height calculations; because after this height, the rate of decrease of
humidity becomes smaller.
Most of the applications of dehumidification processes have special air outlet
temperature requirements. The change of outlet air temperature with the packing
height is shown in Fig. 3.4. The air temperature increases with the packing height
for the first 1.3 m. of the packing. After that the air temperature starts to decrease.
It is simply because after the first meter of packing, there is a very low mass transfer
rate (i.e., the latent heat production is very low). Air which is about to leave the
![Page 60: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/60.jpg)
46
tower loses heat to the entering liquid. As a result of low latent heat production, air
loses heat to the liquid desiccant whlch is at a lower temperature. Liquid and air flow
rates, liquid and air inlet temperatures, air inlet humidity, and liquid concentration
at the inlet are other factors that affect the packing tower performance.
The effect of some of these parameters will be discussed to be able to understand
the behavior of the tower under different operating conditions. Fig. 3.5 shows the
change in the performance of the column for a fixed height of packing. The air outlet
moisture keeps on decreasing with the increase in the liquid flow rate. However,
similar to the packing height, the rate of decrease of humidity decreases with the
increasing liquid flow rate. The reason for thls is that the larger liquid flow fills
up the void space available for air flow, w hlch causes a decrease in the interfacial
surface area. As a result, the mass transfer decreases.
The increasing desiccant flow rate causes a decrease in the exit temperatures of
liquid and gas phases (Fig. 3.6). Thls is due to the increased amount of liquid which
absorbs the produced latent heat. The decreasing rate of latent heat production
also affects the change in the temperature of both phases. As seen from the figure,
air temperature is affected less than liquid temperature. The increasing liquid
temperature is an advantage for the regeneration process.
Fig. 3. 7 shows another important factor of analysis, the column performance
versus increasing liquid inlet temperature. As the liquid inlet temperature increases,
the air outlet humidity also increases. Increasing liquid temperature causes an in
crease in the vapor pressure of the solution which results in a lower mass transfer
rate. The effect of increasing liquid temperature on air and desiccant outlet tem
peratures can be seen in Fig. 3.8. Even though there is a larger difference between
the liquid and air temperatures, the rate of increase in both phases are similar.
![Page 61: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/61.jpg)
47
The liquid phase absorbs the latent heat that has been produced during the phase
change.
The comparison of the performances of a 0.5 m. packed column with 3 and 4
GPM flow rates for 40% and 45% desiccant concentrations are shown in Fig. 3.9. As
seen for both concentrations, increasing liquid inlet temperatures causes a decrease
in the performance of the packed column. All four cases show a decrease in the
performance; however, 4 GPM flow rate with 45% concentration has the highest
slope. The 4 GPM flow rates are affected by the increase in the liquid temperature
more than 3 GPM flows. This behavior can be observed from the slope of the
curves.
Fig. 3.10 shows the effect of increasing air inlet temperature on the change of
humidity for 100% saturated air. As shown in the figure, increasing air temperature
causes an increase in the change of humidity. However, the exit humidity also
increase. An increase in the air inlet temperature causes a decrease in the change
of air temperature and an opposite effect on the change of liquid temperature, as
seen in Fig. 3.11.
The performance of the packed column for different climates with different hu
midities is another important factor. Fig. 3.12 shows the performance of the col
umn in three different climates in the United States; Florida, Texas, and Okla
homa. The performance of the column decreases for increasing humidities. How
ever, the amount of the extracted moisture increases (~humidity(Oklahoma)=3.21
10-3 kg/kg, ~humidity(Texas)=4.88 10-3 kg/kg, ~humidity(Florida)=6.57 10-3
kg/kg). The effect of increasing moisture in air on the outlet liquid and air tem
peratures can be seen in Fig. 3.13. The increase in temperature in both phases is
evident. However, the rate of increase in liquid phase is considerably larger than
the rate of increase in the gas phase.
![Page 62: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/62.jpg)
48
Some of the parameters that affect the performance of the packed column are
discussed above. However the change in the air flow rate is another important
factor. Computer runs show that air flow rate has an opposite effect to liquid flow
rate. The increasing flow rate requires a longer tower for a desired level of operation.
![Page 63: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/63.jpg)
10 0 0 0 e o
;::;- 0 E ; 0 ~
=?
8 c.
s. 4
.3
2
.I ::lo ~08 a: .06 w ..... ~ 0
0
0
4
3
2
00 1
WATE~ L!OUID RATE. lbff11• h
891000 2 :: J S6 79910000 2 3 4 567 0 ~-I
I
I
I I
: I
I :
! j
I ' ~ ~ '
' .J i""L_
'
, v I "' // I
' ~ / I I I .I llv
' ? i ! '
'
~E
t::=g ./8 /A
0 ~-
8 6 5 4.., 3=
-v
l.n
I~ ~
2' ~ :;,
0 c ~a
OS::t 06a::
w ..... 04~ 3 0
2 0
0. 2 3 .; : 6 78910
01 2 3 ~ 56 789100
WATEF= LIQUID RATE. kgfm2 • s
AP
mm H20/m in. H20/ft
A-0 0.0
8-42 0.5
C-83 1.0
0-125 1.5
E- 167 2.0
Figure 3.1 Total holdup versus liquid inlet flow rate for lntalox~ snowflake
packing.
49
![Page 64: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/64.jpg)
'
Interfacial Surface
Area adz
Ga Yc+ dYe TG +dTG
•I'
50
--~-~-~~~:~:~-~--~-~:~:~-~-~:~:~--~-~:~:~-~--~-=:~:~-~~=-~--~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~----z+dz ~ ----------------
I
Ti _..!, -I
Liquid Desiccant Air I
Xci I _ .... "j ..:, Yci I I I
I ~-----------------1 ~--------------------~-------------------------------~~~~~~~~~~~~~---z --------- ____________________ i ________ _
'If L+dL
TL + dTL Xc + dxc
Ga Yc TG
Figure 3.2 Differential section of a packed tower.
![Page 65: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/65.jpg)
.... :0: ..... 38 Tc = 34.44°C 0 t:ll)
TL = 32.22°C ~ - L' = 4.0GPM .... ~ ct:
G'= 1091 CFM ~ 33 ~ = 40% ..... 0
Wj = 38.6 10·3 kg/kg t:ll) ~ ..., c >.. 28 -"'0 .... .... .... -.... t> 23 -= 0 .... <
18 4-------~-----------r---.--~------~--~--~ 0.0 0.5 1.0
Packing Height, m.
Figure 3.3 Dehumidification performance of the packed column "·ith Intalox® snowflake packing.
51
![Page 66: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/66.jpg)
u c Q.) .... ::l --1:.: Q.) Q. .... .... . o I:"'"
u -::l 0 .... <
37 ~-----------------------------------------,
36
35
34 0 J 0.5
Ta = 34.44°C TL = 32.22°C L' = 4.0GPM G' = 1091CFM ~ = 40% wi = 38.6 w-3 kg/kg
1.0 1.5
Packing Height, m.
figure :).-1 Change of air outlet temperature with the packing height for the I nt alox:8 snowflake packing.
52
![Page 67: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/67.jpg)
...: co:: Tc = 34.44°C '-0 TL = 32.22°C Cll 28.5
...:..:: G' = 1091 CFM - ~ = 40% ... ~ Wj = 38.6 w-3 kg/kg eo: ~ Packing Height = 0.5 m '-0 Cll
...:..:: 27.5 "" ----i-:-9 ,.. c: :::::
:I: 26.5 -~ -6 ... -<
25.5~~~--~~~~~~~~~~~~~~--~~--~
2 3 4 5 6 7 8
Desiccant Flowrate, GPM.
Figure 3.5 Change in the exit humidity of air with the liquid flow rate for Intalux® snowflake packing.
53
![Page 68: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/68.jpg)
44
cJ 0
~ :l ~ ... 0 c. ,.. c: ~ 39
~ :l 0
34
2 4
Ta = 34.44°C TL = 32.22°C G' = 1091 CFM
~ = 40% Wj = 38.6 w-3 kg/kg Packing Height = 0.5 m
6
Desiccant Flowrate, GPM.
8
Figure 3.6 Change in the liquid and air temperature with the desiccant flow rate for lntaloxiB snowflake packing.
54
![Page 69: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/69.jpg)
32 ...
Tc = 34.44°C c-:: '- L' = 3.0GPM 0 c..o 31 G' = 1091 CFM ~
~ = 40% -... wi = 3R.6 1 o-3 kg/kg ~
ee Packing Height = 0.5 m ~ 30 .._ 0 c..o ~
....., 29 ----
;;:., -=s! 28 ,... = :I
::r: ts - 27 6 ... <
26 i-~~~----r-~~----~--~------~--------~ 25 30 35 40 45
Desiccant Inlet Temperature, °C.
figure 3.7 Change in the air outlet humidity with the increase in the desiccant inlet temperature for lntalox® snowflake packing.
5.5
![Page 70: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/70.jpg)
TG = 34.44°C 48 L' = 3.0GPM
G' = 1091 CFM ~ = 40%
cJ Wi = 38.6 } Q·3 kg/kg 0 Packing Height = 0.5 m ~ ::::;
43 i:o ... a) Q..
E ~ 4) -::::; 0 38
33 ,_------~----~--~--~--------~------~--~ 25 35 45
Desiccant Inlet Temperature, °C.
Figure 3.8 Change in the desiccant and air outlet temperature with the incrPase in the desiccant inlet temperature for Intalox® snmdlake packing.
56
![Page 71: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/71.jpg)
<
22 ~-----------------------------------------------.
21
20
19
18
:7
16
Tc = 32.22°C G' = 1091 CFM Wj = 24.18 1 o-3 kg/kg Packing Height = 0.5 m
15 ~--~----~--~----~--------~--~--~----~--~ 28 30 32 34 36 38
Desiccant Inlet Temperature, °C.
Figure 3.9 Change in the air outlet humidity with the change in desiccant inlet temperature for -!0% and 45% concentrations, ,,·ith 3 and 4 GPI\J flow rate of desiccant for Intaloxl3 snowflake packing.
![Page 72: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/72.jpg)
.... C':l '-0 eLl ~ -.... ~
~ ~ '-0 eLl ~
,...., -._.
>.. -:-2 E :::: -.... c: ~ Oll c: co:
..::: u
l2.5
11.5
10.5
9.5
8.5
7.5
31 32 33
TL = 32.22°C L' = 3.0GPM G' = 1091 CFM
~ = 40% Packing Height = 0.5 m
34 35
Air Inlet Temperature, °C.
36
Figure 3.10 Change in the air humidity ·with the increase in the air inlet temperature for lntalox~ snowflake packing.
58
![Page 73: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/73.jpg)
cJ c
c:
13 ~------------------------------------------~
11
9
3 Air
TL = 32.22°C L' = 3.0GPM G' = 1091 CFM ~ = 40% Packing Height = 0.5 m
1 C:==:===::::::::~ 31 32 33 34 35 36
Air Inlet Temperature, °C.
figure 3.11 Change in the desiccant and air temperatures with increase in ti1t' air inlet temperature for lntaloxl8 sno,\·fiake packing with lOOo/c saturated air.
59
![Page 74: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/74.jpg)
~ ~
...; .... ~
eo: '- TL = 32.22°C c eJ) To = 32.22°C .:.t:. - 21 L' = 4.0GPM ...
G'= 1091 CFM ~ ;:
~ = 40% ~ '- Packing Height = 0.5 m 0 eJ) 20
.:.t. ,..., -._.
>.. -~ 19 .... = ....
::c .A Florida 0 ::I 18 0 Texas 0 ... < c Oklohama
17 20 22 24 26 28
Air Inlet Humidity, 10·3 kg of water I kg of air.
Figure 3.12 Change in the outlet humidity with the change m the inlet humidity of air for Intalox® snowflake packing.
60
![Page 75: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/75.jpg)
3E
TL = 32.22°C TG = 32.22°C
37 L' = 4.0GPM G'= 1091 CFM ~ = 40%
cj 36 Packing Height = 0.5 rn c
~ ::; ::; 35 ... ~ c.. ,.. c: ~ ~ 34
-::; 0 Air
33
32 +-------~~----~----~--------~------~~ 20 22 24 26 28
Air Inlet Humidity, 10·3 kg of water I kg of air.
Figure 3.13 Change in the outlet temperatures of desiccant and air with the change in air inlet humidity for Intalox~ sno"·fiake packing.
61
![Page 76: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/76.jpg)
CHAPTER 4
APPLICATIONS OF DEHUMIDIFICATION SYSTEMS
FOR AIR CONDITIONING UNITS
4.1 Introduction
In many southern states, the summer electrical load is significantly influenced
by the use of air-conditioners. The energy required to operate these units create a
daily late afternoon peak load. These electrical demand curves reach even higher
peaks during the hottest summer days. One of the most attractive features of
the proposed project, which uses solar energy to provide comfort cooling, is the
incidence of maximum solar radiation when the need for cooling is greatest.
Different types of solar cooling systems are described in the literature and they
can be broadly classified as closed-cycle and open-cycle systems. Much attention
has been given to closed-cycle systems, particularly absorption refrigeration and
vapor compression systems while comparatively little attention has been given to
open cycle space cooling systems.
Absorption refrigeration systems have been extensively studied by many in
vestigators and successful combinations are LiBr-H 2 0 and H20-NH 3 systems. In
the absorption system, solar energy need not be converted into mechanical energy.
Hence this system seems to be more attractive. However, the major disadvantages
of this system are the requirement of a large amount of cooling water for remov
ing the waste heat from the condenser and absorber and the low vacuum pressure,
62
![Page 77: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/77.jpg)
63
which must be maintained in the evaporator and absorber at all times. The vapor
compression system consists of the Rankine cycle heat engine, which produces me
chanical output to drive a conventional air-conditioning compressor. It has been
studied and the conclusion is that this system would out perform the absorption
system when coupled with a focussing collector. The conversion efficiency would
be low and the requirement of a sun tracking concentrator makes the system more
expensive and cumbersome.
The proposed hybrid desiccant cooling systems combine a desiccant dehumidi
fier with a vapor-compression unit to meet the supermarket air-conditioning load.
The proposed hybrid cooling system utilizes the desiccant to meet the latent load
and a vapor-compression unit to handle the sensible load. The system uses solar
energy for the regeneration of the liquid desiccant. One of the major advantages
of this system is that the required temperature of 50°-65°C for regeneration of the
absorbent solution can be easily obtained by using a simple solar regenerator. In
this chapter, the concept, design, and cycle analysis of the proposed cooling system
is described.
4.2 Air Conditioning in Supermarkets
Supermarkets have special requirements for air-conditioning. Because of open
refrigeration stands and a high moisture production rate, the latent load to sensible
load on the air-conditioning system is very high. In most cases, a conventional
system uses central air-conditioning for sensible cooling and refrigerated cases for
the latent load, moisture removal. To be able to condition the air to the required
level, a large amount of air flow rate is needed. This is a very inefficient way of
using energy. Supermarkets consume approximately 4% of U.S (Burns et al., 1985).
electrical energy. The proposed hybrid cooling system promises a very efficient way
![Page 78: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/78.jpg)
64
of air-conditioning in supermarkets. The proposed system, first dehumidifies the air
through a packed tower which handles the latent load, and then sensibly cools the
air through the vapor-compression unit that has a high COP due to a low cooling
rate. As the air is not being reheated in the proposed system, there is no waste
energy.
4.3 Concept of the Proposed Cooling System
In southern parts of the United States, both temperature and humidity are high
in summer months and hence both dehumidification and cooling are necessary. In a
vapor compression unit, the humid air is first drawn over an evaporator, chilled to
the dew point, often to a temperature below that is desired in the occupied space.
Then the chilled air is drawn over the condenser coil, where it is reheated. In the
proposed system there is no need for reheating. The primary energy input into the
system is in the form of heat required to regenerate the absorbent solution. This
temperature is considerably lower than that required for operation of vapor com
pression systems. The proposed hybrid desiccant cooling system is an alternative
to a conventional vapor compression system as a means of reducing electrical en
ergy consumption and energy costs. Since the vapor compression unit in a hybrid
system only has to remove a portion of the load, the electrical energy consumption
is substantially reduced over that of a conventional system. Further, since the va
por compression unit no longer has to cool the air below dew point temperatures,
the evaporator temperature may be raised. This increases the COP of the vapor
compression unit and reduces energy input to the compressor. By separating the
performance of latent and sensible cooling into two different components, it is now
possible to reduce humidity without simultaneously reducing the supply air temper
ature below desired levels. Dehumidification is no longer dependent on the limits
![Page 79: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/79.jpg)
65
of the Yapor-compression unit. Various designs for liquid desiccant dehumidifiers
have been proposed and studied. However the present work considers a packed bed
dehumidifier and CELD as the liquid absorbent for the proposed cooling system.
4.4 Description of the Model
The proposed system is designed to provide cooling for a supermarket. The
schematic of the system is shown in Fig. 4.1, and the processes are shown on the
psychrometric chart in Fig. 4.2. The system consists of a conventional vapor
compression unit, an auxiliary heater, a solar regenerator, three heat exchangers,
a dehumidifier, a cooling tower, pumps for the solution and water, two fans and
the ducts. The assumed ambient conditions are 32.22°C and 70%RH. The indoor
design conditions of the conditioned space are 23°C and 0.0086 kg of water /kg
of air (Appendix A). The mixture of return air from the supermarket and fresh
air from the atmosphere enters the dehumidifier at 'd' as shown in the Figure.
After the dehumidification process, the air is warmed up and dried, which is not
suitable for comfort conditions. Hence, after removing the latent cooling load in
the dehumidifier, the dried air at condition 'a' is passed over the evaporator coil
in the conventional vapor compression unit. The air is sensibly cooled to condition
'b', and the conditioned air is then delivered to the building.
A simple system using atmospheric air through the solar regenerator is con
sidered in the proposed cooling system. An open solar regenerator is simple and
effective, but in humid climates the evaporation rate is low. The weak desiccant
from the dehumidifier is pumped through heat exchangers to the solar regenerator.
The regenerator consists of a single galvanized iron sheet painted black, over which
the weak absorbent solution flows as a thin film. The collector is insulated on the
underside. To reduce heat loss, it is covered by a single glazing of 3 mm thickness.
![Page 80: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/80.jpg)
66
·water evaporating from the liquid surface is removed by wind gusts. The heat re
jected by the condenser of the vapor compression unit is used to preheat the weak
desiccant after the dehumidification process.
4.5 System Analysis in the Supermarket
The proposed system for the supermarket will be analyzed, component by com
ponent, for complete performance.
4.5.1 Supermarket
For an average supermarket, one can assume a surface area of 2,800 m2, and
it produces moisture at a rate of 11.3x 10-3 kg/s (Manley, 1985). However, the
supermarket temperature needs to be kept below 24°C and 55% relative humidity
or 0.010244 kg of water/kg of air absolute humidity (Burns, 1985). Because of the
open refrigeration stands, the latent load to sensible load ratio is very high. In order
to maintain the comfort in the supermarket, air is cooled down to 23°C and dried
to 0.0086 kg of water/kg of air (Burns, 1985). Air is drawn from the building at a
rate of 6.95 kg/s and is mixed with 10% of the outside air (0.695 kg/s).
4.5.2 Mixing of Air
The air coming from inside the building mixes with the outside air. The following
conditions were used.
Air leaving the building
mass flow rate - 6.95 kg/s (1314 7 cfm),
temperature - 24°C,
absolute humidity - 0.010244 kg of water/kg of air.
![Page 81: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/81.jpg)
Outside air
mass flow rate- 0.695 kg/s (1315 cfm),
temperature - 32.22°C,
absolute humidity - 0.02142 kg of water/kg of air.
Mixed air
mass flow rate- 7.645 kg/s (1315 cfm),
temperature - 24. 70°C,
absolute humidity- 0.01126 kg of water/kg of air.
The detailed calculations are given in Appendix B.l.
4.5.3 Dehumidification Tower
67
The dehumidification tower has a diameter of 48 in. and is packed with snowflake
plastic packings to a height of 1 ft. The dehumidifier is modeled according to
calculations in Chapter 3. The inlet and outlet conditions of the to·wer are as
follows.
Air inlet
TA - 24.7°C,
wA - 0.01126 kg of water/kg of air,
G' 7.645 kg/s = 14462 cfm.
![Page 82: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/82.jpg)
68
Air exit
TA - 27.262°C,
WA 0.0086 kg of water/kg of air,
G' - 7.6246 kg/s = 14424 cfm.
Desiccant inlet
TD 32.22°C,
~D - 40%,
L' 0.5258 kgjs.
Desiccant exit
TD - 41.638°C,
~D 38.5%,
L' 0.5462 kg/s.
4.5.4 Vapor-Compression Unit
Air passes over the coils of the evaporator which uses refrigerant-12 as the re
frigerant. Air enters the evaporator at
T 27.262°C,
![Page 83: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/83.jpg)
69
w - 0.0086 kg water /kg air,
m 7.6246 kg/s.
and leaves the evaporator at
T 23.ooooc,
w 0.0086 kg water/kg air,
m - 7.6246 kgjs.
The heat absorbed in the evaporator is Q EV = 32.64 k Vv (kilowatt) and the heat
rejected at the condenser is Qed= 36.11 kW. The refrigerant flow rate is 0.2834 kg/s.
Detailed calculations are given in Appendix B.2.
4.5.5 Solar Regenerator
The amount of water that should be removed from the desiccant is 73.44 kg/hr,
and the solar panel surface area required for this operation is 95.37 m 2 • Detailed
calculations are given in Appendix B.3.
4.5.6 Heat Exchangers
From the information given in Appendix C, we know that the solution leaves
the regenerator at 60°C. The hot desiccant at the outlet of the regenerator needs
to be cooled down prior to entering the dehumidifier. The weak desiccant which
comes out from the dehumidifier can first be heated with the warm condenser air in
the air-to-desiccant heat exchanger, and then with hot desiccant in the desiccant
to-desiccant heat exchanger. The heat rejected from the condenser produces air at
45.0°C and at 2.81 kg/s. This air is used for heating the weak desiccant at 41.64°C
![Page 84: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/84.jpg)
70
to 43.80°C in an air-desiccant heat exchanger. Detailed calculations are g1ven m
Appendix B.4.1.
Further, the cooler weak desiccant and warmer strong desiccant transfer heat in a
desiccant-to-desiccant heat exchanger, shown in Fig. 4.3. After passing through the
desiccant-to-desiccant heat exchanger, the weak desiccant is warmed up to 56.76°C
and is sent to the solar regenerators. The strong desiccant is cooled to 46.53°C, and
it needs to be cooled further to 32.22°C. Detailed calculations are given in Appendix
B.4.2. The cooling of strong desiccant can be achieved with a cooling water system.
The cooling water system carries water at 0.6 kg/s mass flow rate. The inlet
temperature of the water is 28.70°C and the outlet is 36.50°C, as shown in Fig. 4.4.
A cooling tower is used to cool the warm water. Detailed calculations are given in
Appendix B.4.3.
4.5.7 Auxiliary Heater
An auxiliary heater is used during the time in which the performance of the solar
regenerator is lower than given in Appendix C. It is assumed that the regenerator
only performs at the highest operating conditions for four hours every day and at
half of the highest performance for another four hours. During the rest of the day
the contribution of sun is negligible. Then, the auxiliary heater should heat the
desiccant from 56.76°C to 60.00°C which is in heat terms, 4.59 k'V. The average
energy requirement for the auxiliary heater is 3.44 k W.
4.6 Results and Discussion
From the above analysis, it is seen that the proposed hybrid desiccant cooling
system, a combination of liquid desiccant dehumidifier with a vapor-compression
unit, will provide comfort conditions in hot, humid climates. Only by adding the
![Page 85: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/85.jpg)
71
dehumidification cycle, the existing system can be converted to a hybrid cooling
system. For the new supermarket buildings, this system promises additional sav
ings with the lower air flow rate (e.g., smaller blower and duct size). The solar
regenerator is simple in construction and in operation. The additional cost of the
system on top of the conventional vapor-compression unit is given in Table 4.1. The
references for the price list are given in Appendix E.
4. 7 Economic Analysis
The econorruc analysis of the system will include the energy savmgs, yearly
money savings, and the payback period of the proposed system.
4. 7.1 Targeted Energy Savings
According to the Public Utility Commission of Texas, Electric Division, "End
Use Modeling Project Interim Report", through the years 1990-1999, the average
yearly commercial end-use electricity consumption for air-conditioning is 18,048
GWH (Gega Watt-Hours). The total energy consumption through these years is
180,480 GWH/year. It is assumed 40% of energy will be used in supermarkets (Pub.
Ut. Com., 1990). By using ERAP conversion factors, this is equal to 8.37 x 1014
Btu's targeted for energy saving.
4.7.2 Savings
The saving that are introduced by the new system in energy and in money will
be calculated. The energy saving factor, yearly saving of money, and payback period
of the proposed system will be calculated. The savings factor is the percent energy
savings of the proposed system over the conventional system. Energy required for
the proposed system
![Page 86: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/86.jpg)
Energy required to run the pumps - Energyp
Energy required to run the fans - EnergyF
Energy required to run the vapor- compression unit EnergyE
72
Energy required for auxiliary heater Energyauxil.heater
Energy = Energyp + EnergyF + Energyauxil.heater + EnergYE·
The overall energy needed for the system will be calculated from the energy
requirements for each part. The energy requirement for the conventional unit will
be calculated from the energy required for the state changes of air.
4.7.2.1 Pumps
In the system there are three pumps-two for the desiccant and one for water
circulation. One of the desiccant pumps is placed on the strong desiccant line, and
the energy required to run this pump is 0.01768 kW. The other desiccant pump is on
weak desiccant line and the energy required for this pump is 0.0185 kW. The \vater
pump which is on the cooling water line requires 0.0138kW. Detailed calculations
are given in Appendix B.6.
4. 7.2.2 Fans
In the system, there are two fans-one is a blower to circulate the air corning
from the building and the other is a fan for the cooling tower. The energy required
for the blower is 15.9 kW. The energy required for the cooling tower fan is 0.0062
kW. The detailed calculations are given in Appendix B.7.
![Page 87: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/87.jpg)
73
4. 7.2.3 Vapor-Compression System
The energy required for the compressor can be calculated from the assumption
that the condenser is working at 45°C and the evaporator at 18.0°C. The energy
required for the unit is 3.46 kW. Detailed calculations are given in Appendix B.S.
4.7.2.4 The Conventional Air Conditioning Unit
Conventional air-conditioner operation can be investigated in two steps. The
first step is cooling the air to the saturation state and condensing the excess humid
ity. The second step is warming up the air to a comfortable condition. The energy
required for the unit is 44.32 kW. The energy required for the blower is 15.9 kW.
The detailed calculations are in given Appendix B.9.
4.7.2.5 Comparison of Energy Requirements
Energy needed to run conventional system
Energyo = 60.22 kJ/s = 60.22 kW
Energy needed for the proposed system
Energyn = 22.85 kJ /s = 22.85 kW
Energy saving = 60.22 - 22.85 = 37.37 kW.
( 4.1)
( 4.2)
The savings factor, SF, is the percentage of the energy that will be saved with
the installation of the proposed system. The proposed system's saving factor is
62%. The yearly savings are $5712 and the payback period for the unit is 18.75
months. Detailed calculations are given in Appendix B.10.
![Page 88: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/88.jpg)
Table 4.1: Additional cost of the proposed hybrid cooling system on conventional unit.
I Item I Unit I Unit Cost I Total Cost $ + Tax j Solar Panel 2952.57 2952.57 Pumps; Desiccant 2 108 216
Water 1 108 108 P.V.C. pipe 338 338 Dehumidification Tower 1 77 77 Cooling Tower Fan 1 48.08 48.08 Cooling Tower Frame 1 50 50 Droplet Separator 1 75 75 Diffuser, Packing Supporter, Packing holder, Tower table 150 150 Heat exchanger
Desiccant-Desiccant 1 600 600 Desiccant-Water 1 550 550 Desiccant-Air 1 350 350
Desiccant Tanks 1 113 113 Desiccant 1363 1363 Packing Material 80 80 Auxiliary Heater 190.77 190.77 Miscellaneous 300 300 Labor to Manufacture (54 hr) $ 8 per hr 432 Labor to Assemble 150 150
Total Retail Cost 8143.42 From Retail to Wholesale Conversion 20% -1626.68 Wholesale Conversion Total Cost 6514.73 Assuming 15% Profit +977.21
I Tax +456.03
I Retail Sale Price 7947.97
74
![Page 89: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/89.jpg)
States:
1- Air G'= 6.95 kg/s t = 240C w = 0.0102441eg water/kg air
2-Air G'= 7.645 kg/s t = 24.70C w = 0.01126 leg water/kg air
3-Air G'=7.625 legis t=27.2620C
w = 0.0086 leg water/kg air 4-Air
G'=7.625 legis t = 230C
w = 0.0086 leg water/leg air
5- Desiccant L' =0.5258 legis t= 32.220C ~=40%
6-Desiccant L' = 0.5462 kgls t = 41.6380C
X= 38.5%
7-Desiccant L' =0.5462 legis t = 43.SOC ~=38.5%
8- Desiccant L' =0.54621egls t = 56.760C ~= 38.5%
9- Desiccant L' =0.5258 legis t = 600C ~=40%
10-Desiccant L' = 0.5258 legis t = 46.530C ~=40%
11-Cooling Water L'=0.6q/s t =28.70C
12-Cooling Water L' = 0.6 leg/s t= 36.50C
13-Ambient air G' =0.695 t= 32.220C
{;)
Solar Regenerator
Refrigerant
Air
- Desiccant Water
w = 0.02142 kg water/kg air
fiuure 4.1 Schematic of the proposed cooling system. 0
![Page 90: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/90.jpg)
60%
23.00 24.00 24.70
Temperature, OC
76
.. ·;::; '-
Cl)
~ tJ
3 11.260 <;;
·c; E '-
10.244 0
E Cl)
~ 8.600
:.0 ·e ::I
:X: u
;..=
t en
27.26 32.22 a-b, Vapor-Compression System
b-e, Room
c-d-e, Mixing with Ambient Air
d-a, Dehumidifier
Figure 4.2 Processes on the ps~rchometric chart (not to scale).
![Page 91: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/91.jpg)
Waste Heat Desiccant-desiccant from heatexchanger
the Condenser
~~28~~siccant I• M1 :tW Desiccant-air 43.SOOC
heat exchanger Weak Desiccant
60°C Strong Desiccant
Figure 4.3 Air-desiccant and desiccant-desiccant heat exchangers.
I I
![Page 92: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/92.jpg)
32.22°C Strong Desiccant
Water-desiccant heat exchanger
46.530C Strong Desiccant
Figure 4.4 Desiccant-\'l.·ater heat exchanger.
78
![Page 93: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/93.jpg)
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
In this project, dehumidification of air using liquid desiccants has been carried
out. The heat and mass transfer coefficients are calculated for the packed column
using CaCl2 , LiCl, and a newly introduced liquid desiccant CELD solution for four
different sizes of ceramic raschig rings. The performance of the CELD solution in a
packed column filled with plastic snowflake packing, which was a new packing, was
also evaluated. The performance of the CELD solution in a packed column filled
with 1.5 in. ceramic raschig rings was also calculated and the performance of the
two was compared. A hybrid cooling system, which uses a CELD solution and a
packed column with snowflake packing to absorb the latent load of air is modelled.
Regeneration is accomplished in a semi open solar regenerator. A basic economic
analysis of the model was performed.
The following conclusions were drawn from this study:
1. CELD is a 50% CaCl2 and 50% LiCl mixture, and its performance
is above the pure CaCl2 solutions and below the LiCl. However the
behavior is not related to the concentration linearly.
2. CELD is a promising, inexpensive, and stable liquid desiccant for
dehumidification and hybrid cooling systems.
79
![Page 94: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/94.jpg)
3. Heat and mass transfer coefficients for the CELD-air contact system
using snowflake packing are calculated. The gas phase coefficients
are strong functions of gas phase mass velocity, and liquid phase
coefficients are strong functions of both liquid and gas phase mass
velocities.
4. The effect of liquid and gas temperatures and liquid concentration on
the heat and mass transfer coefficients are comparably smaller than
the liquid and gas flow rates, for the range in which the coefficients
are evaluated.
5. The performance of the CELD solution in the packed tower filled with
snowflake packing material showed that a 40% CELD solution in a
0.5 m packing height will create 11.9 x 10-3 kg of water I kg of air
change in the humidity. For the same flow rate, 1.0 m packing height
will create 16.6 x 10-3 kg of water I kg of air change in the humidity.
For optimum operation, it may be desirable to the increase packing
height to 1.0 m. However increasing the height above 1.0 m will not
create any significant change in the outlet humidity of air. It should
be kept in mind that these values are liable to change with the change
in the air and liquid flow rates.
6. The calculations showed that for the same level of dehumidification
of air, plastic snowflake packings require a higher tower than 1.5 in.
ceramic raschig rings. However, snowflake packing is found to be
superior because of its low price and weight, lower pressure drops
and ease of installment.
80
![Page 95: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/95.jpg)
7. After observing the stable performance of CELD solutions, a hybrid
cooling system is modelled for a supermarket in a hot and humid cli
mate which uses a snowflake packing material with the CELD solution
as a desiccant in a column. Additional dehumidification and regen
eration cycles are proven to introduce savings over the conventional
units up to 62% with a payback period of less than 2 years. This
shows that liquid desiccant hybrid cooling systems are cost-effective
alternatives for conventional air conditioning units.
The following are recommendations for future studies in this area:
1. The mass and heat transfer coefficients that are calculated in this
study can be compared with the experimental evaluations. The per
formance of the tower can also be compared with the experimental
results.
2. The properties of snowflake packing material, v.-hich is available in
this study, can be reorganized and evaluated.
3. The liquid desiccant hybrid cooling system model can be restudied
for different air and liquid temperatures to optimize the efficiency of
the system.
4. The solar regenerator can be replaced by a packed regeneration col
umn where the heat to the system is obtained from a natural gas
heater which heats the liquid. Even though this system may have
lower energy savings as the heat for evaporation is obtained from the
heater, it will increase the stability of the regeneration cycle.
81
![Page 96: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/96.jpg)
5. Similar liquid desiccant hybrid cooling units can be developed for
residential or smaller size commercial business uses (e.g., fast food
restaurants)
6. An experimental setup for a liquid desiccant hybrid cooling system
can be developed and the performance of the system can be analyzed.
Similar studies have been conducted using solid desiccants. An ex
perimental setup can bring more attention to liquid desiccant hybrid
cooling systems.
7. Similar models can be developed for different areas in which liquid
desiccant dehumidification systems may be used (e.g., low tempera
ture batch drying operations, etc.)
8. The noncorrosive materials are recommended to use for hybrid cooling
system, specially for heat exchangers. However, this will increase the
payback period.
82
![Page 97: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/97.jpg)
REFERENCES
Annual Financial Review: The Annual Report of the Supermarket Companies, 1987-88, A 4950-2.
Biswal, R. !\ .. et al., 1982, "Modeling a Packed Tower for Solar Driven Food Processing," American Society of Agricultural Engineering, Paper No. 82-6511.
Burns, P. R., Mitchell J. Vt.T., and Beckman, Vt,T. A., 1985, "Hybrid Cooling Systems in Supermarket Applications," ASHRAE Transactions, vol. 91, part 1b, pp. 457-468.
Co, P. and Bibaud, R., 197L " Longitudinal Mixing of the Liquid Phase in Packed Columns with Countercurrent Two Phase Flow," The Canadian Journal of Chemical Engineering, vol. 49, pp. 727-731.
Collier, R. K., 1979, " The Analysis of a Open Cycle Absorbtion Refrigeration System," Solar Energy , vol. 23, pp. 357-366.
Ertas, A., Anderson, E. E., and Kiris, I., 1990a, "Properties of a New Desiccant Solution-Lithium Chloride and Calcium Chloride Mixture," Proceedings of the 1990 Annual Conference of American Solar Energy Society, Austin, pp. 535-
540.
Ertas, A., Anderson, E. E., and Kavasogullari, S., 199Gb, "Comparison of Mass and Heat Transfer Coefficients for Liquid Desiccant 1\fuc:tures in a Packed Column," Proceedings of the 1990 ASME Winter Annual Meeting, Dallas, pp. 55-60.
Ertas, A., Anderson, E. E., Gandhidasan, P., Kiris, I., and Kavasogullari, S., 1990c, "Development and Investigation of a Liquid Desiccant System and Use of a Solar Regenerator for Hot and Humid Climates," A report prepared for Texas Higher Education Coordinating Energy Research in Application Program, ERAP-2-#309.
Factor, H. M., and Grossman, G., 1980, "A Packed Bed Dehumidifier/Regenerator for Solar Air Conditioning with Liquid Desiccant," Solar Energy, vol. 24, pp. 541-550.
Fair, J. R., 1970, "Comparing Trays and Packing," Chemical Engineering Progress, vol. 66, no. 3, pp. 45-49.
Gandhidasan, P., 1983, "Thermal Performance Prediction and Sensitivity Analysis for a Parallel Flow Solar Regenerator," Transactions of ASME Journal of Solar Energy Engineering, vol. 105, pp. 205-228.
83
![Page 98: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/98.jpg)
84
Gandhidasan, P., 1985, "Low Temperature Drying Using Liquid Desiccants," report submitted to Fulbright/LASPAU.
Gandhidasan, P., 1989, "Potential Use of Liquid Desiccant in Solar Application," Proceedings of ISES Solar World Congress, Kobe, Japan.
Gandhidasan, P., 1990, "Reconcentration of Aqueous Solution in a Packed Bed: A Simple Approach," Transactions of ASME Journal of Solar Energy Engineering, vol. 112, no. 4, pp. 268-272 .
Gandhidasan, P., Ullah, M. R., and Kettleborough, C. F., 1987, "Analysis of Heat and Mass Transfer between a Desiccant-Air System in a Packed-Tower," Transactions of ASME Journal of Solar Energy Engineering, vol. 109, pp. 89-93.
Grifford, E. W., 1957, "Dehumidification by Liquid Sorbents," Heating, Piping, and Air Conditioning, April, pp. 156-169.
Gupta, M. C. and Gandhidasan, P., 1978, "Open Cycle 3-ton Solar Air-Conditioner: Concept, Design, and Cycle Analysis," Proceedings of the International Solar Energy Conference, New Delhi, pp. 1991-1996.
Hougen, 0. A., and Dodge, F. W., 1947, The Drying of Gases, J. V·l. Edwards.
Kern, D. Q., 1950, Process Heat Transfer, McGraw-Hill.
Kettleborough, C. F., Ullah, M. R. and Waugaman, D. G., 1986, "Desiccant Cooling Systems - A Review," Proceedings of the Third Annual Symposium on Infraring Energy Efficiency in Hot and Humid Cliamtes, Arlington Tx, Nov. 15-18, 1986.
Kreith, F., 1965, Principles of Heat Transfer, International Textbook Company.
Leboeuf, C., and Lof, G. 0., 1978, "Analysis of LiCl Open-Cycle Absorption air Conditioner which Utilizes a Packed Bed for Regeneration of the Absorbent Solution Driven by Solar Heated Air," a report prepared for the U.S. Department of Energy, Solar Energy, C00/4546-1.
Leboeuf, C., and Lof, G. 0., 1980, "Open Cycle Absorption Cooling Using Packed Bed Absorbent Reconcentration," Proceedings of the Annual Meeting of the American Section of ISES, pp. 205-209.
Lof G. 0. Luez, T. G., and Rao, S., 1984, "Coefficients of Heat and Mass Transfer ' in ~ Packed Bed Suitable for Solar Regeneration of Aqueous Lithium Chlo
ride Solution," Transaction of ASME Journal of Solar Energy Engineering, vol. 106, pp. 387-392.
Macdonald, N. J ., 1983, "Utilization of Condenser Heat for Desiccant Dehumidification in Supermarket Applications," ASHRAE Transactions, vol. 89, part 2a, pp. 225-235.
![Page 99: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/99.jpg)
85
I\1anley, D. L., Bowlen, K. L., and Cohen, B. M., 1985, "Evaluation of Gas-fired Desiccant Based Space Conditioning for Supermarket,'' ASHRAE Transactions, vol. 91. part lb, pp. 44i-456.
McAdams, V•l. H., Pohlenz, J. B., and St. John, R. C., 1949, "Transfer of Heat and Mass between Air and 'Water in a Packed Tower," Chenilcal Engineering Progress, vol. 45, no. 4, pp. 241-252.
McAdams, '~7 • H., 1954, Heat Transmission, McGraw-Hill.
Mullick, S. C. and Gupta, M. C., 1974, "Solar Desorption of Absorbent Solution," Solar Energy, vol. 16, pp. 19-24.
Norton Company, 1987, Intalox High Performance Snowflake Packing, 2M-132200302-8/88 Bulletin ISPP-1R.
Peng, C. S. P. and Howell, J. R., 1981, "Analysis and Design of Efficient Absorbers for Low Temperature Desiccant Air Conditioning," Transaction of ASME Journal of Solar Energy Engineering, vol. 103, pp. 67-74.
Peng, C. S. P. and Howell, J. R., 1984, "The Performance of Various Types of Regenerators for Liquid Desiccants," Transactions of ASME Journal of Solar Energy Engineering, vol. 106, pp. 133-141.
Public Utility Commission of Texas, Electric Division, 1990, End-Use Modeling Project Interim Report.
Queiroz, A. G., et al., 1984, "Performance Analysis of an Air Drier for a Liquid Dehunildifier Solar Air Conditioning System," ASME ~7inter Annual Meeting, 84-WA/Sol-6.
Sherwood, T. K. And Holloway, F. A. 1., 1939, "Performance of Packed TowersExperimental Studies of Absorption And Desorbtion," American Institute of Che:mlcal Engineers, pp. 21-37.
Shulmann, H. 1., Ullrich, C. F., Proulx, A. Z., and Zimmerman, J. 0., 1955, "Performance of Packed Columns, Part I,II, and III," A.I.Ch.E Journal, vol. 1,no. 2, pp. 247-264.
Strigle, Jr. R. F., 1987, Random Packings and Packed Towers, Design and Application, Gulf Publications.
Thuesen, G. J. and Fabrycky, W. J., 1989, Engineering Economy, Prentice-Hall International Series in Industrial and Systems Engineering.
Treybal, R. E., 1969, "Adiabatic Gas Absorption and Stripping in Packed Towers," Industrial and Engineering Chemistry, vol. 61, no. 7, pp. 36-41.
Treybal, R. E., 1980, Mass Transfer Operations, Me Graw-Hill.
![Page 100: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/100.jpg)
86
rllah, M. R., 1986, "Analysis of a Counterflow Indirect Evaporative Cooling and Liquid Desiccant Dehurrildification System,'" a Ph.D. dissertation submitted to Texas A&M University.
'\\:"hitehead, E. R., 1985, "Outdoor Air Treatment for Humidity Control in Supermarket," ASHRAE Transactions, vol. 91, part lb, pp. 434-440.
![Page 101: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/101.jpg)
: .......... . COMIOAT ZCNE OE'TAil.
I 1} '" ,,,.. •••• ., ONy tor;, • II
'2l We1-ou10 lines "aHa Oftty rort .. • i,
''t
: 00 ..
3 >O' ;; f o ...
APPENDIX A
COMFORT ZONE
I !/ H
r r E lO E
l! . 0 5t ..
f "' " 0
i
\0
Sl•nd•rd Err~cliv~ T~mpenlurt •nd lhr ASHR.-'f. Cnmfnrl Lonn
87
![Page 102: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/102.jpg)
APPENDIX B
CALCULATIONS
B.1 Mixing of Air
The humidity ratio is calculated as
WA-ambient - WM 10 WAf- WR 1
0.02142- WM 10 WM - 0.010244 1 '
and
WM = 0.01126 kg of water/kg of air.
Temperature of the mixture is calculated from the enthalpy equation
H = Cp X t + w X HE.
The ambient air enthalpy
HA-ambient 1.005 X 32.22 + 0.02142 X 2560.26
HA-ambient 87.22 kJ /kg.
The room air enthalpy
H R - 1.005 X 24.00 + 0.010244 X 2545.37
HR 50.19 kJjkg.
The mixed air enthalpy can be calculated from the ratio
88
(B.1)
(B.2)
![Page 103: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/103.jpg)
H A -ambient - H M
HM-HR 87.22- HM HM- 50.19
The enthalpy of mixed air
H M = 53.55 kJ /kg.
10 1
10
1
89
(B.3)
Hence from the enthalpy equation the temperature of the mixed air is calculated.
53.55 = 1.005 X TM + 0.01126 X 2546.64,
The mixture enters the dehumidifier at 24.7°C and 0.01126 kg of \Yater/kg of
dry air.
B.2 Vapor Compression Unit
Air passes over the coils of the evaporator which carries freon-12 as refrigerant.
Air enters the evaporator at
w 0.0086 kg water /kg air,
m 7.6246 kg/s,
![Page 104: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/104.jpg)
90
and leaves at 23°C. The heat flow is
(B.4)
Q - 7.6246 X 1.005 X 4.262 = 32.65 kW.
Assuming the evaporator temperature is 18.0°C and the condenser temperature
as 45.00°C, heat absorbed by the evaporator is calculated as
(B.5)
qL 194.842-79.647 = 115.195 kJjkg.
Mass flow rate of the refrigerant is
m = 32·65 kJ/s = 0.2834 k /s. 115.195 kJ /kg g
The air leaves the evaporator at
T - 23.00°C,
w 0.0086 kg water/kg air,
m 7.625 kg/s.
The heat rejected by condenser can be calculated as
Q in~H,
Q 0.2834 X (207.074- 79.647),
Q 36.11 kW. (B.6)
![Page 105: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/105.jpg)
91
B.3 Solar Regenerator
The amount of water to be removed from the solution can be calculated to obtain
0.5258 kg/s of 40% CELD solution.
Amount of Desiccant
0.4 x 0.5258 = 0.2103 kg/s.
Amount of Water
0.6 x 0.5258 = 0.3155 kg/s.
The amount of desiccant in the 38.5% CELD solution is
X= 0.2103 0.385
X = 0.5462 kg/ s.
Amount of water entering into the solar regenerator = 0.5462-0.2103=0.3359 kg/s.
Amount of water to be removed =0.3359-0.3155=0.0204 kg/s or 73.44 kg/hr.
From the solar regenerator calculations (Appendix C), the surface area needed
to remove 73.44 kg/hr water is
73.44 - 9 37 2 - 5. m. 0.77
![Page 106: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/106.jpg)
B.4 Heat Exchangers
B.4.1 Air-Desiccant Heat Exchanger
92
The heat rejected by the condenser is 36.11 k\V. Assuming that air will pass
over the condenser and warm up to 45°C, this air will be used to warm up the weak
desiccant. The amount of air that will be needed can be calculated as
Q - (mC,D.t)ai,.
36.11 - mai,. X 1.005 X ( 45.00 - 32.22)
mA - 2.81 kg/s.
This air will be used to warm up the desiccant at 41.638°C, by assuming an
effectiveness of 0.65. (m x C,)ai,. > (m x C,)D the effectiveness equation is (Kreith,
1965)
E -
0.65
Tout-A
(m x C,)A x (Tin-A- Tout-A) (m X C,)D X (Tin-A- Tin-D) (2.81 X 1.005) X ( 45.00- Tout-A)
(0.5462 X 2.594) X ( 45.00- 41.638)
43.90°C.
The desiccant outlet temperatures can be calculated from the heat balance.
( mC,D.t)D - ( mC,D.t)ai,.
0.5462 X 2.594 X (Tout- 41.638) 2.81 X 1.005 X ( 45.00- 43.90).
(B.7)
The weak desiccant leaves the heat exchanger at 43.8°C. The recommended
design for the heat exchanger is a 36 in. diameter, 2-foot high cylinder where the
air is blown through the coils of the desiccant from the bottom of the cylinder.
![Page 107: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/107.jpg)
93
The heat exchanger uses the blower of the condenser. Further, the cooler weak
desiccant and warmer strong desiccant transfers heat in a desiccant to desiccant
heat exchanger.
B.4.2 Desiccant-Desiccant Heat Exchanger
The strong desiccant enters the heat exchanger at 60°C and the weak desiccant
enters at 43.80°C. The effectiveness of the heat exchanger is assumed as 0.8. The
flow rates of the desiccant are close to each other and their C'P is assumed to be the
same. Thus the effectiveness of the heat exchanger is
~T --=0.8. l::t.Tma.z
(B.8)
The inlet solution temperature from the heat exchanger to solar regenerator can
be calculated as
T.t,.ong-de• - 43.80 = 0.8 60- 43.80 '
Solution enters the solar regenerator at 56. 76°C. The strong desiccant outlet
temperature can be calculated from the heat balance.
0.5462 X 2.594 X (56.76- 43.80) 0.5258 X 2.594 X (60 - T).
![Page 108: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/108.jpg)
94
T:::46.53°C is the temperature at which the strong desiccant leaves the heat
exchanger. The recommended design is a tube-tube or a shell tube heat exchanger.
The strong desiccant needs to cool down to 32.22°C.
B.4.3 Cooling \Vater System
This system is designed to cool the desiccant from 46.53°C to 32.22°C. The
water flow rate is assumed as 0.6 kg/s and the heat exchanger effectiveness as
0.8. The recommended design is a plate-tube or a shell tube heat exchanger. As
(m x C,)wate .. > (m x C,)D, the heat exchanger effectiveness is (Kreith, 1965)
E ( m X C,)wate .. X (Tin-water - Taut-water)
( m X C,)D X (Tin-D - Tin-water)
q - ( m X C,)D X !lTD :::: 19.51 kJ /s
q EX (m X C,)D X (Tin-D- Tin-water)= 19.51 kJ/s
T. = 28.7°C in-water
q (m X C,)wate,. X !lTwate,. = 19.51 kJjs
(B.9)
The approach of the cooling tower is 1.5, and the range is 7.8. A redwood
counter flow cooling tower is used with spray diffusers and splash filling. The forced
draft is suggested. The air flow rate is 0.03 kg/ s with the air exit temperature of
34°C.
B.5 Auxiliary Heater
The auxiliary heater should heat the desiccant from 56.76°C to 60.00°C. In heat
terms
![Page 109: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/109.jpg)
D.T
m
= 60.oooc- 56.76°C
2.594 kJ kg oc
0.5462 kg/s
Q 4.59 k'W.
Then, taking the average energy requirement of the auxiliary heater
Energyauzil.heater 4.59 X 4 X 0.5 + 4.59 X 16
24
Energyauzil.heater - 3.44 kW.
B.6 Pump Energy Calculations
Energy required to run the pump is
A 1 . 1 Energyp = I..J.p x - x m x -.
p ,
Assuming that the pressure head is around 10 ft. of water column
D.p = 10 ft. of water= 3023.87 kg/m2•
For the weak desiccant pump
m 0.5462 kg/s
p 1246.8 kg/m3•
95
(B.10)
(B.ll)
![Page 110: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/110.jpg)
96
For the strong desiccant pump
m - 0.5258kg/s
p = 1259.0 kg/m3•
Energy needed for the weak desiccant pump
EnergyPDl 1 1
3023.87 X 1246
_8
X 0.5462 X O. 7
EnergyPDl - 1.893 kgm/ s
EnergyPDl 0.0185 kW.
Energy needed for the strong desiccant pump
1 1 EnergypD2 3023.87 x
1259_ x 0.5258 X O.
7
EnergypD2 - 1.804 kgm/s
EnergypD2 - 0.01768 kW.
For the water pump
m - 0.6 kg/s
p 996.9 kg/m3
~p - 1511.93 kg/m2•
Energy needed for the water pump
Energypw 1511.93 X -1
- X 0.6 X -1-
996.9 0.7
Energypw 1.299 kgm/s = 0.0127 kW.
![Page 111: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/111.jpg)
as
97
B. 7 Fan Energy Calculations
Energy required to run the fan that circulates the air in the building is calculated
E . A 1 1 nergyF = m x ~..Jt.P x - x -.
Paif' TJ
m 7.645 kg s
D.p - 0.2 m of water
kg PA - 1.177 3
m
TJ - 0.8.
kgm EnergyF1 = 1618.8 -- = 15.9 kW.
s
Energy required for the fan of cooling tower
m - 0.03 kg s
D.p 0.02 m of water
kg Paif' - 1.177 3
m
TJ - 0.8.
kgm EnergyF2 = 0.635 -- = 0.0062 kW.
s
(B.12)
(B.13)
![Page 112: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/112.jpg)
98
B.8 Vapor Compression Unit Energy Calculations
Energy required for compressor can be calculated from the assumption that the
condenser is working at 45°C and evaporator at 18.0°C. From the freon 12 tables
p - 1.0843 MPa
s - 0.68837 kJ/kg K,
and the state is calculated as
H - 207.074 kJ /kg.
Heat rejected by the condenser
Qed - 36.11 kJ js.
Heat absorbed by the evaporator
Qcooling - mair X !:lH
Qcooling - 32.65 kJ /s.
Energy needed for the compressor IS simply the difference between the heat
rejected at the condenser and heat absorbed at the evaporator.
. . Energycom Qed- Qcooling
Energycom - 3.46 kJ/s = 3.46 kW.
(B.14)
(B.15)
![Page 113: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/113.jpg)
99
B.9 Energy Calculations for the Conventional System
The air that enters the evaporator will be cooled below the dew point temper-
ature. The dew point temperature of the entering air with the inlet humidity of
0.01126 kg of water/ kg of dry air, is 15.9°C. Enthalpy of this state can be read from
the psychrometric chart as 12.85 kcal/kg. The desired level of absolute humidity
is 0.0086 kg of water/ kg of dry air. The corresponding dew point temperature is
11.8°C. Enthalpy of this state is 8.00 kcal/kg. Appendix E shows the state changes
during the operation on the psychrometric chart. The air outlet temperature from
the evaporator is considerably low for comfort conditions (given in Appendix B).
The condenser heat is utilized for the reheat of the air which returns to the building.
The energy absorbed in the condenser can be calculated from the enthalpy changes
in two states, a and b.
The saturation state of the entering air can be found from steam tables.
EnergyEv - 155.13 kW.
(B.16)
(B.17)
The COP of the vapor compression units for high latent load applications (i.e.
supermarkets) in hot and humid climates is between 2.3 to 3.5 (information obtained
from AirTech Company). In this calculation COP will be taken as 3.5. The energy
required to run the compressor is the ratio of the energy absorbed in the evaporator
and COP.
Energycom
Energycom
EnergyEv
COP 44.32 kW.
(B.18)
(B.l9)
![Page 114: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/114.jpg)
100
The energy required to run the fan needs to be added
EnergyF = 15.9 k\,V.
B.10 Saving Calculations
Saving Factor
Savings factor, SF, is the percentage of the energy that will be saved by the
installation of the proposed system.
SF - ( Energyn) 1- X 100 Energyo
(B.20)
SF ( 22.85) 1--- X 100 60.22
SF 62%.
Thus, the new system promises up to 62% energy savings.
Yearly Savings
Assuming that the price of natural gas is $3.84/million Btu (from Energas,
Industrial Prices, Lubbock, TX, 1990), and the price of electricity is $0.04 /kWh
(from Ranking of Electricity Prices), daily saving that the current system will bring
can be calculated. For the proposed system, natural gas is used in the auxiliary
heater. The power needed to run the auxiliary heater for a day
power auzil.heater 4.59 X 4 X 0.5 + 4.59 X 16
power auzil.heater 82.62 kWh/day= 281694.5 Btu/day
Costauzil.heater - $1.08/day. (B.21)
![Page 115: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/115.jpg)
101
Power needed to run pumps, fans, and the vapor-compression unit for the pro
posed system is
Powerothe... - 19.41 X 24
Powerothe... 465.84 kWh/day
Costothe .. • $18.63/day.
The total cost of running the proposed system for a day is $19.71.
For the conventional system the power needed to run the vapor-compression
unit and the fans
Powero
Powero
Casto
60.22 X 24
1445.3 kWh/day
$57.80/day.
Thus, the new system will provide saving = $57.80- $19.71 = $38.08 per day.
Yearly savings can be calculated from the daily savings assuming that the air
conditioning unit will be used from May to September, for five months. The total
saving for a year is
A - 5 months/year x 30 days/month x $38.08 per day
A - $5712 /year.
(B.22)
![Page 116: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/116.jpg)
102
Payback Period
Payback is the period of time required for the cumalitive cash in flows from a
project to equal the initial cash outlay. The interest rate during this period and the
salvage value of the equipment will be taken into consideration. The method used
is called 'Capital Recovery with Return' (Thuesen, 1989). The initial investment,
P, is $7947.97. The salvage value of the pumps, desiccant tank, auxiliary heater and
fans is calculated from 20% of the initial costs. The initial total cost of these pieces
are $ 675.85, and the salvage value, F, is $135.17. Currently, the interest rate, i,
for the commercial loans is 11% for large businesses ( N CNB Texas National Bank).
The payback period can be calculated from the following equation (Thuesen, 1989)
n -ln [ A-ix1P-F)]
ln(1 + i) n - 1.56 years = 18.75 months.
The total payback period is 1.56 years.
(B.23)
![Page 117: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/117.jpg)
APPENDIX C
REGENERATOR COVERED WITH GLASS
BUT BOTH ENDS ARE OPEN
Assume ambient temperature is 32.22°C, desiccant temperature is 60°C, partial
pressure of water vapor in ambient air is 24.8 mm Hg. Assume convection heat
transfer coeff. is 5.25 x 10-3 kW /m2°C, based on Mullick et al. (1974), energy
transfer by convective heat transfer is 0.14595 kW /m2• Assuming h/k based on
Dropkin's measurement, convective mass transfer coef., k, is 19.5 kg/hr m2 (~y).
~pis 45.2 mm Hg, or !::l.y is 0.0393. Mass Transfer is k x /j.y, 0. 77 kg water/hr m2•
103
![Page 118: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/118.jpg)
APPENDIX D
MATERIAL COST
1. \Vater pumps and desiccant pumps are obtained from Grainger cat
alog Chemical-Resistant Magnetic-Drive Centrifugal Pumps, manu
facturers model 3-MD-SC, stock no. 2P038.
2. Cooling tower fan from Grainger catalog 12 in. diameter ring fan
Dayton, stock no. 2C107.
3. Dehumidifying tower 48 in. diameter 90 psi pvc pipe from Diamond
Plastic Co., Lubbock, TX.
4. PVC pipe as ducks 12 in. diameter 50 psi pvc pipe from Diamond
Plastic Co., Lubbock, TX.
5. Liquid desiccant 0.5258 kg/s of solution is equal to 0.21032 kg/s
CELD flow rate. The LiCl is $2.99/lb, from LitCo Co., Gastonia
N. C. and CaCl2 is $0.2766/lb, from Mayfield Paper Co., Lubbock
TX. This is equal to Sl.633/lb or $3.6/kg for CELD. 30 minute supply
of CELD is
CostcELD = 0.21032 x 3.6 x 30 x 60 = $1363
The cost of CELD solution is $1363.
6. Desiccant Tank 200 gallons plastic tank, from Lee Co. Idalou TX.
7. Intalox® snow flake packing from Norton Co., Akron OH.
104
![Page 119: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/119.jpg)
8. Nat ural gas liquid heater from Me MasterCarr Catalog, no. 3598K51.
9. Cost of each m 2 collector is calculated as: From General Steel Co,
Burch Glass Co, Selle Insulation, Lubbock, TX
Description Total Cost
16 Gage Galvanized Steel Sheet 2 x $6.17 per m2
16 Gage Window Glass $17.216 per m2
2" Fiberglass Insulation $1.4 per m2
Total Material Cost $30.956 per m2
Total Cost of Solar panel of 95.37 m 2 $2952.57
10. Heat exchangers approximate prices from Southwestern Refrigaera
tion Co., Lubbock, TX.
•
105
![Page 120: PERFORMANCE ANALYSIS OF A NEW DEVELOPED A THESIS IN](https://reader035.vdocument.in/reader035/viewer/2022081418/62a095a2fa3cbd623517aa9a/html5/thumbnails/120.jpg)
'"j .. .. .. .. " ..... .. .. ..
% • .. 0 ..
I .. ! ..
~ " ~ . ~ . : . 'C ,, ...
APPEXDIX E
CO~VENTIONAL SYSTE:..IS PROCESSES
ON THE PSYCHROMETRIC CHART
PHYS1'ROMETRIC qHART rS~OitCUI'Cl Of,...IIJIWI".C It'• I..,,.. riO''"" llfJ
. . • • •.
..i ..
l()(j
.••
.JO .. .. ..
.70
. .. ..
~ .