bse public cpd lecture – seminar on liquid desiccant · 2010-08-31 · seminar on liquid...

BSE Public CPD Lecture – Seminar on Liquid Desiccant A Seminar on Liquid Desiccant delivered by Professor Zhang Xiaosong and Mr. Chang Liang was held on 3 August 2010 (Tuesday). Over 120 participants attended this public CPD lecture co-organized by PolyU Department of Building Services Engineering and The American Society of Heating, Refrigerating and Air-Conditioning Engineers-Hong Kong Chapter (ASHRAE-HKC).

Powerpoint file of the CPD lecture Professor Zhang is the Associate Dean of the School of Energy and Environment at Southeast University. He has engaged with the research on liquid desiccant for over 10 years. His research areas include novel dehumidifier, the heat and mass transfer in the liquid desiccant system, solar energy based regenerator, liquid desiccant based novel air conditioning system and the liquid desiccant based ice making. Mr. Chang is a PhD candidate in Building Energy Research Centre at Tsinghua University. He has been doing consulting work in US, Hong Kong and mainland China for 5 years. His research works are related to new technologies applications including liquid desiccant applications with goals of saving energy and low carbon footprint.

Professor Zhang

Mr. Chang

The liquid desiccant system, as an energy-efficient, environmentally friendly and healthy means of air dehumidification, can be used to achieve the decoupling of the air latent load and sensible load removal. The driving force of moisture removal by the liquid desiccant is the water vapour pressure difference between the desiccant solution and the air. The moisture in air is absorbed by the strong desiccant solution rather than condensed by low temperature coolants. In addition, the sensible load can be removed by relatively high temperature coolants. Therefore, COP of chilling equipment can be improved and considerable energy can be saved. In the lecture, the two speakers introduced the state-of-the-art research and applications of liquid desiccant. Various kinds of commonly used liquid desiccants were discussed.

Introducing the new liquid dehumidification air-conditioning

systems

Presentation by Dr. Xiao

In addition, Dr. F. Xiao of BSE introduced her research project on application of liquid desiccant based air conditioning system in Hong Kong which is supported by Hong Kong Environment and Conservation Fund (ECF). In the Q&A session, participants interacted with our speakers on their research works and presentations.

Interaction   

BSE News 2010 CPD 100803

Fundamental research progresses Fundamental research progresses about the liquid dehumidification about the liquid dehumidification

airair--conditioning systemconditioning system

School of Energy & EnvironmentSoutheast UniversityAug 3th, 2010，Hong Kong

Prof. Xiaosong Zhang

1933:

2000:

2006:

1902成立

1988

1952南京工学院

1928国立中央大学

九龙湖新校区

AUTHOR’S INTRODUCTION

Vice dean of the School of Energy and Environment, Southeast University.Director of the Education Ministry affiliated engineering center “low-carbon

construction environment equipments and energy-conservation systems”；Board members of (IIR)E2, Director of the Chinese Society of Engineering

Thermophysics， of Chinese Association of Refrigeration, Vice Chairman of Jiangsu Province Institute of Refrigeration；

Special expert of the national twelfth five year plan addressing climate change challenge, Leading young talent of Jiangsu Province"333 high-level personnel training project” and the first winners of several awards tem-level scientific and technological achievements，Including the second prize of the Jiangsu Science and Technology Progress Award three times, second prize of the Ministry of Education Science and Technology Invention one time. Obtained 39 national invention patents, authored more than 100 articles.

Prof. Xiao-Song Zhang,

OUR TEAM

Dr. Yong-Gao Yin: PhD., Lecturer, School of Energy and Environment, Southeast UniversityProf. Shu-Hong Li: PhD., Research Fellow, School of Energy and Environment, Southeast UniversityDr. Cai-Hua Liang: PhD., associate professor, School of Energy and Environment, Southeast UniversityDr. Xiu-Wei Li: PhD., Lecturer, College of Power Engineering, Nanjing University of Science and TechnologyDr. Dong-Gen Peng: PhD., Lecturer, School of Civil Engineering and Architecture, Nanchang UniversityMiss. Guo-Ying Xu: PhD Student，…….

Research projects conductedTime series chart of fundamental research projects

in the recent decade

01-03 04-06 07-09 10-13 07-09 08-10

Liquid dehumidifi

cation+

Evaporation cooling

air-conditionin

g system

Liquid-desiccant

-based potential energy storage technolo

gy

Deep-liquid-

dehumidification

assisted ice slurry

production method

Liquid-desiccant based air-

conditioning system with independent

heat and humidity control

Energy storage

mechanism of high density

potential energy storage

technology

Building energy

conservation and

equipments in the

“summer –hot-winter-cold area”

Key project funded by Ministry of Education

Support project of the 11th five year plan

07-09

Heat source

assisted solar

power utilizatio

n

863

95 1500 05 10

Not form a complete decoupling

environmental heat and moisture control system and its thermodynamic

analysis

European and American scholars

suggested independent control of heat and

humidity

Humidity treatment and control: we conceived a new liquid dehumidification air-conditioning system

Academician Jiang, TsinghuaUniversity, used liquid

dehumidification to treat fresh air and promotes the independent

humidity control method

We propose a new air-conditioning system

integrated liquid dehumidification with

radiant cooling

With experiments, Professor of American Goswami proved the energy conservation effect of independent

liquid dehumidification

Research Track: liquid dehumidification air-conditioning system

Outline

Traits and merits of liquid dehumidificationMass transfer mechanism and theoretical models of liquid dehumidificationUtilization of low grade heat in liquid desiccant regenerationNovel liquid-dehumidification based air-conditioning systems and equipmentsApplication of liquid dehumidification in new scientific areas

1. Traits and merits of liquid dehumidification

Traits and merits of liquid dehumidification

Dehumidification Technology：Condensing dehumidification, solid dehumidification, liquid dehumidification

0

10

20

30

40

50

60

0 0.005 0.01 0.015 0.02 0.025

含湿量 /(kg/kg)

温度

/o C O－被处理空气O

RS

转轮除湿

溶液除湿

冷凝除湿

R－室内空气

S－送风状态

5

10

15

20

25

30

35

0 0.005 0.01 0.015 0.02 0.025

含湿量 /(kg/kg)

温度

/o C

被处理空气

空气露点

Working range of condensing Working range of condensing dehumidificationdehumidification

Comparison between different Comparison between different dehumidification methodsdehumidification methods

Temperature of the heat source driving liquid dehumidification process

Liquid desiccant：LiCl-H2O

p v/k

Pa

The temperature of the heat source can be low（60-80℃）, many renewable energy can be efficiently used, like solar energy or geothermal energy.

Temperature of the heat source driving liquid dehumidification process

Independent humidity treatment systemHigh efficient air-conditioning system:

independent treatment of heat and humidity

新风

再 生器

稀 溶液

储液罐

浓溶液

…

溶液泵

溶液泵

除湿器 ( 新风机)送

风

…

辐 射板 或风 机盘管

18℃冷水

冷

水

Raise COP; Fine temperature Raise COP; Fine temperature and humidity control in a wide and humidity control in a wide rangerange

Analysis and intensification of the heat and mass transfer process for liquid

dehumidificationthe heat and mass transfer process between air and desiccant

solution

Air Tair Desiccant Ts

Sensible heat transfer

Air humidity ωair Desiccant ω s

Concentration change

Latent heat of phase change and heat released from

mixing process

Moisture transferMoisture transfer

Moisture transfer driven by water vapor pressure difference

2. Mass transfer mechanism and theoretical models of

liquid dehumidification

Heat and mass transfer mechanism and intensification of the liquid dehumidification process

Status quo – varieties of models for heat and mass transfer

1 Efficient correlation model

2Complex model (in consideration of the heat and mass transfer resistance of the liquid layer)

Volume average finite difference model3

4 Linear-based quasi-analytical model

Humidity/temperature efficient definition

ineina

outainam

,,

,,

ωωωω

ε−

−=

insina

outainat tt

tt

,,

,,

−

−=ε

ineina

outainah hh

hh

,,

,,

−

−=ε

Temperature efficient

Humidity efficient

Total heat efficientInlet Inlet

airairOutlet

desiccant solution

1 Efficient correlation model

Inlet desiccant solution

TEGLiCl

不规则

Martin and Goswami

LiBr叉流

Liu et al.

平均误差±10%TEGLiCl

不规则

Chung and Luo

平均误差±7%TEGLiCl

不规则

Chung

TEG规则Abdul-Wahab et al

Application rangeDesiccant solutionStuffCorrelationReference

,0.601 0.25 0.00072 0.0107y s w a inM a Tε = + − − 77 200wa< <0.174

,

,0.184 1.68

,

,3.388

0.205 exp 0.9851

( )

0.152 exp 0.6861

a ina

s s in

wy

a in

s in

TMM T

a ZTT

ε

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠−Γ

=⎛ ⎞−⎜ ⎟⎜ ⎟

⎝ ⎠−Γ

0.6,

,0.185 0.638

,

,21.498

0.024 exp 1.0571

( )

0.192 exp 0.6151

a ina

s s in

wy

a in

s in

TMM T

a ZTT

ε−

−

⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠−Γ

=⎛ ⎞−⎜ ⎟⎜ ⎟

⎝ ⎠−Γ

0.2804 0.36570y a sC M Mε −=

0.1,

,0.537

,

,1.558

0.642 exp 0.21

0.496 exp 0.9451

a ina

s s in

sy

a in

s in

s

TMM T

XTT

X

ε

⎛ ⎞⎛ ⎞−⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠−

=⎛ ⎞−⎜ ⎟⎜ ⎟

⎝ ⎠−

( )

0.751(0.396 1.573),

,

(0.033 0.906)

1 48.345s

c

s

c

rr

a insy

a s in

rr

w

hMM h

a Z

ε−−

−

⎛ ⎞⎛ ⎞= − ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

0.893 /2.273

s aM M<

<

0.420.49

sX<<

3.5 /15.4

s aM M<

<

2 Complex model (in consideration of the heat and mass transfer resistance of the liquid layer)

Full developed laminar flow/falling film flow

Des

icca

nt Air

H

x

ys

x

ya

δaδs

ua

us

δ

2

2 0ss

s

ugy

ν ∂+ =

∂

2

2

1 aa

a a

upx y

νρ

∂∂=

∂ ∂2

2a a

a aT Tux y

α∂ ∂=

∂ ∂

2

2s s

s sT Tux y

α∂ ∂=

∂ ∂2

2Da ad dux y

∂ ∂=

∂ ∂2

2Ds sux yξ ξ∂ ∂=

∂ ∂

a a s s

a sa a a fg s

a a sy y

T TdD hy y y

δ δ

λ ρ λ= =

⎛ ⎞∂ ∂∂− − =⎜ ⎟∂ ∂ ∂⎝ ⎠

a a s s

a a s sa sy y

dD Dy y

δ δ

ξρ ρ= =

∂ ∂− =

∂ ∂

momentum

energy

mass

boundary conditions of

the layer

Rahamah,1998; Ali et al., 2003,2004; Dai et al., 2004; Yin et al., 2006;

Volume average finite difference model3

Factor and Grossman, 1980; Stevens et al., 1989; Khan, 1994, 1998; Goswami et al., 2002, 2003; Liu et al., 2006; Yin et al., 2008;

dx

dy

Ts Xs Gs

Ts+dTs Xs+dXs Gs+dGs

Ga

Ta

ω

Ga+dGa

Ta+dTa

ω+dω

x

y=L

空气进口 溶液进口 ininsins Xtm ,, ,,inainaa tm ,, ,, ω

Xtm ss ,,

outoutsouts Xtm ,, ,,outaoutaa tm ,, ,, ω

aaa tm ω,,

空气出口 溶液出口

x+dx

H

0

4 Linear-based quasi-analytical model

Chen et al., 2006; Ren, 2007, 2008; Davoud and Meysam, 2009.

Based on Model III- Volume average finite difference modelThe relationship between the desiccant temperature and the air humidity is assumed linearMinor factors are neglected according to the characteristics of the heat and mass transfer process

Precision depends on the assumptions

Popularity is poor

Not good at analyzing the ongoing state of the heat and mass transfer process

Question is？

1, What will be the conclusion in the

case of coupled heat and mass transfer？

2, Will the evaluation method of logarithmic mean temperature difference still OK for the coupled heat and mass transfer process

Treatable area partition determined by the initial air state

10

15

20

25

30

35

40

0 5 10 15 20

含湿量 /(g/kg)

温度

/o C

湿空气饱和线

A2

A5

A11

A1

s

A3

A6

A9

A10 A12

A8

56

10 1112

除湿区域

除湿或再生

再生区域A7

8

A4

2

43

9

Application of the treatable partition

10

15

20

25

30

35

40

0 5 10 15 20

含湿量 /(g/kg)

温度

/o C

s in

湿空气饱和线

A区

B区

C区

D区

RulesRules

PartitionPartition A and A and Partition CPartition Ccountercurrent flow has the best countercurrent flow has the best

mass transfer effect while the mass transfer effect while the concurrent flow has the worstconcurrent flow has the worst

boundary: boundary: ωω = = ωωe,ine,in

Partition A：Dehumidification partition; same direction of heat and mass transfer

Partition B：regeneration partition; opposite direction of heat and mass transfer

Partition C：regeneration partition; same direction of heat and mass transfer

Partition D：Dehumidification partition; opposite direction of heat and mass transfer

PartitionPartition B and B and PartitionPartition DDconcurrentconcurrent flow flow has the best has the best

mass transfer effect while the mass transfer effect while the countercurrentcountercurrent flow flow has the worsthas the worst

boundary: boundary: ωω = = ωω**

Research progress about the heat and mass transfer features of liquid dehumidification (II)Development of evaluation method and theoretical model for

coupled heat and mass transfer performanceC

D a

hLeh Cp

= D t w

a

h V aNTUM

=

cc

m

QhS T

=⋅Δ

vD

m

MhS ω

=⋅Δ

take the method used to solve the conventional heat transfer problems

max min

max minln /mT TT

T TΔ −Δ

Δ =Δ Δ

max min

max minln /mω ωωω ω

Δ −ΔΔ =

Δ ΔRight？

Rem nSh a Sc= ⋅ ⋅

Pr Rep qNu b= ⋅ ⋅

Coupled heat and mass transfer is different from the pure heat transfer

Countercurrent flow dehumidification－Fumo (2002)

Cross flow regeneration (2006)

29

30

31

32

33

34

0 2 4 6 8 10实验数据点

温度

/o C

24

26

28

30

32

34

0 2 4 6 8 10实验数据点

温度

/o C

Inlet desiccant

Inlet air

Outlet Outlet desiccantdesiccant

Outlet airOutlet air

Inlet air

Inlet desiccant

Outlet air

Outlet desiccant

Temperature of the outlet desiccant is higher than that of any inlet desiccant

Temperature of the outlet desiccant is lower than that of any inlet liquid

Ratio=ΔTlogm/ΔTm Ratio=Δωlogm/Δωm

除湿工况D1；D2；D3 0

1

2

0.1 1 5R

Counter Flow Parallel Flow Cross Flow

除湿工况D4；D5；D6

再生工况R1；R2；R3

Will the evaluation method of logarithmic mean temperature difference still OK for the coupled heat and mass transfer process？How can we evaluate the coupled heat and mass transfer coefficient based on the heat and mass transfer model ？

Conclusion：The conventional evaluation method of logarithmic mean temperature difference is not OK for the coupled heat and mass transfer process.

Question 2：Evaluation of the coupled heat and mass transfer coefficient

In consideration of the transfer coefficient distributed along with the transfer potential difference

0 L

ωa

Solution

Air

x

ωa(x)

x

( )v

D L

o

mhx dxω

Δ=

Δ∫

( )C L

o

QhT x dx

Δ=

Δ∫

DM hω=Δ ⋅

( )1a s dS

Sω ω ωΔ = −∫∫

CQ h t= ⋅Δ

( )1a st t t dS

SΔ = −∫∫

hD-Le separation measurement method

, 1 , , , ,( , , , , , , , )deh out deh deh air deh air deh deh sol deh deh sol Df L G T G X T hω ω=

Assume Le

, 1 ( , , , , , , , , )deh out deh a a a s s s Df L G T G X T h L eω ω=

, 2 ( , , , , , , , , )a out deh a a a s s s DT f L G T G X T h L eω=

, 3 ( , , , , , , , , )s ou t deh a a a s a s DT f L G T G X T h L eω=

Calculate hD

, 2 ( , , , , , , , , )a out deh a a a s s s DT f L G T G X T h Leω= Real Le

(Southeast Univ.，Yin Y.G.)

Liquid dehumidification experiment with packing stuff type dehumidifier

cross flow孔板送风

焓差室内环境

试验台本体

电加热器

电加湿器

蒸发器

压缩机

风机

来自节流机构去冷凝器

溶液除湿模块

Influence of air flow rate on the coupled heat and mass transfer process

h C/

W/(

m2·°C

)

Le

h D/

g/(m

2 s)

Influence of air humidity on the coupled heat and mass transfer process

Fresh idea for developing the model of coupled heat and mass transfer process

Ta

显热交换Qs

ωa ωs

传质湿差Δω

耦合传质系数hD

潜热交换 质交换Mw

Ma Ms

Xs

传热温差ΔT

耦合传热系数hC

Ts

The key!

(Southeast Univ.，Yin Y.G.)

3. Utilization of low grade heat in liquid desiccant regeneration

Solar regeneration

mode

Separated type

Direct heating

Indirect heating

Combined type

Solar powered regeneration method

Natural convection C/R

Collier (Unglazed) (1978) Nelson (Glazed) (1990)Gandhidasan (Partly glazed)(1994-1998)

Forced convection C/R

Gandhidasan (Arabia)(1982)Ru Yang (Taiwan)(1994-2001)Saman (Australia)(2002)

Solar powered regeneration process

Experiment platform

Validation of the glass plate temperatureValidation of the glass plate temperature Validation of the outlet regeneration parametersValidation of the outlet regeneration parameters

Multi-stage regeneration systemRegeneration of desiccant solution of different concentration and with

different collector/regeneratorFirst stage: regeneration of the desiccant solution from the pre-

dehumidifier, outdoor air is directly used for regenerationSecond stage: regeneration of the desiccant solution from the dehumidifier,

pre-treated air is used for regeneration

Performance of multi-stage regeneration with different climate parameters

环境湿度 Y0/ g·kg-110 12 14 16 18 20

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

40

60

80

100

120SC - 直接再生ΨSC - 预处理再生ESPESC

25 26 27 28 29 30 31 32 33 34 3515

20

25

30

35

40

45

50

0.20

0.24

0.28

0.32

0.36

606162636465SC- 直接再生Ψ

SC- 预处理再生ESPESC

环境温度T0 /℃

品质

系数

Ψ/-

有效溶

液比

ESP/%

蓄能密度

SC，ESC/

MJ·m-

3

SC- 直接再生ΨSC- 预处理再生ESPESC

蓄能

密度

SC，ESC/MJ·m-

3

品质

系数

Ψ/-

有效

溶液

比ESP/%

太阳辐射Ic /W·m-2650 700 750 800 850 900 950 1000 1050 1100

0

10

20

30

40

50

60

70

80

0.0

0.2

0.4

0.6

60

65

70

75

80

0 60%φ >

Utilization of low grade waste heat

Waste heat utilization

Humidity distribution with different inlet desiccant temperature

Ts=28 ºC Ts=32 ºC Ts=35 ºC

Requirement of the minimum inlet desiccant temperature under the efficient regeneration working condition

( ),min,a s sf X Tω =

Humidity difference distribution between the desiccant surface and the air

Influence of the air flow rate on the regeneration performance

Regeneration thermal efficient is minus: air is dehumidified rather than regeneratedFor a certain desiccant flow rate, air flow rate should be large enough and there exists a best working range

0 5 10 15 20 25

0

1

2

3

4

5

6

7

R

Ms=0.04 kg/sMs=0.08 kg/sMs=0.12 kg/sMs=0.16 kg/s

4. Novel liquid-dehumidification based air-conditioning systems and equipments

Internal cooled/heated dehumidification/regeneration apparatusExperiment system development

Influence of the internal cooled water temperature on the dehumidification process

2.55

2.6

2.65

2.7

2.75

2.8

19 20 21 22 23 24Tw /°C

20

21

22

23

24

25

26

19 20 21 22 23 24

Ts,out Tw,out

Tw /°CInfluence of the air flow rate on the dehumidification

process

1.5

2

2.5

3

0.048 0.06 0.072 0.084 0.096

Ma /kg/s

内冷 绝热

Influence of the desiccant inlet temperature on the dehumidification process

1.5

2

2.5

3

3.5

20 22 24 26 28 30 32

Δω

/ g/

kg绝热除湿‐a

内冷除湿‐a

绝热除湿‐b

内冷除湿‐b

Ts /°C

Performance comparison between the internal heated regeneration method and the adiabatic

regeneration method

36

38

40

42

0.036 0.048 0.06 0.072 0.084 0.096

T a,out

/°C

Ma /kg/s

内热再生绝热再生

The outlet air temperatures are almost equal, which implies a higher regeneration efficient

Influence of the inlet desiccant temperature on the regeneration process

Δω

/ g/

kg

Desiccant solution

Moist AirMoisture

Original dehumidifier

silica gel

Saturated

New surface

Combined dehumidifier

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

时间 (s)

溶液除湿器3: 纯 CaCl

2溶液

混合溶液

ti=27 oC di=15.5 g/(kg air)

除湿量(g/(kg air.s))

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

时间 (s)

除湿量(g/(kg air.s))

溶液除湿器2 溶液除湿器3 ti=27oC di=14.5 g/(kg air)

Dehumidification effect enhancement

5. Application and future of liquid dehumidification in new scientific areas

Development of new liquid dehumidification air-conditioning systemslow operation cost solar-powered refrigeration /dehumidification/air conditioning systemsdeep-liquid-dehumidification assisted evaporative-supercooling method for ice slurry production High efficient air-conditioning system with independent heat and humidity controlLiquid-desiccant-based potential energy storage technology

Development of new liquid dehumidification air-conditioning systems

N

O

D

S100%

T

d

`

冷却水

太阳能集热器

空调房间

回风新风

排风

绝热

加湿器除湿器再生器

冷却水

`

外界环境空气

排放

Liquid dehumidification cooling system driven by solar energy

蒸发

冷却器回热器 除湿器 QdQe 12

3

4

给水

6

5

78

9

10 储液器

再生器

换热器

1712 13 14

15

Qh

储液器16

11

18

其他热源

Integrated system of liquid dehumidification and air conditioning

Humidity Control and Regulation

Steel-making wet blast off---humidity control

Humidity pretreatment of the fresh air

Industrial humidity control and regulation

Evaporative super-cooling method for ice slurry production

Ice storage：the methods for ice slurry productionPrinciple of evaporative super-cooling method for ice slurry production

Evaporation

When the air humidity is very low and the wet bulb

temperature is below 0℃, the water droplets can be super-cooled and form ice particles

Liquid dehumidification canLiquid dehumidification candecrease the air humidity decrease the air humidity

and consequently and consequently decrease the water vapor pressuredecrease the water vapor pressure

Water above 0℃,spray in the chamber

Cooling effect

Renewable energy input

Reutilization of the rejected heat from the condenser

Renewable energy input

Experiment platform

Produced ice particles

High efficient air-conditioning system with independent heat and humidity controlNo dew-point controlRaise the temperature of cold source, No requirement of reheat, Significant energy conservation effectRegeneration process can be driven by varieties of low grade heat sources (like solar energy), as well as the rejected heat from the condenser

高温冷源

除湿器

再生器

太阳能集热器

100%

L

O

N

SC Wh

焓

含湿量d

Liquid-desiccant-based potential energy storage technology

Large storage density, 3 times more than ice storage Long-distance transport, storage at room temperatureLow grade thermal energy storage (65-85oC)

能量输送

蓄能

谢谢！

ThanksThanks！！

rachpe@seu.edu.cn