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© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 83
NUMERICAL INVESTIGATION OF HEAT TRANSFER &
FLUID FLOW IN A SOLAR AIR HEATER DUCT USING
GAP IN V-SHAPED RIBS ON ABSORBER PLATE
Jouhri Kumar Akale1, Dr. S.k. Nagpure
2
M.tech. Scholar1, HOD2 Department of Mechanical Engineering
Scope College of Engineering, Bhopal, India
Abstract — In a Computational Fluid Dynamics (CFD), the
trial has been conducted on the heat transfer and friction
factor, for a solar air heater with Circular ribs with
different relative gap width. In the CFD investigation it
was assumed that, the rib height is 2mm, the pitch of the
rib (P) is 20, the Relative Roughness pitch (P/e) is 10, and
the angle of attack (α) is 60°. This investigation was
carried out on a Reynolds Number ranging in between
3000-15000.
When the desired heat transfer was carried with smooth
and rough ribs with symmetrical gaps it was found that;
I. The smooth ribs could not transfer the desired
heat due to absence of friction; so, they are not preferred
practically.
II. The rough ribs were efficient enough to transfer
the desired heat, but they are not economical and are very
complex in design and construction. Whereas, the Circular
ribs with different relative gap width gives more area of
contact. So, there is enough time to transfer the heat from
the ribs to the passing air which touches the ribs and the
heat transfer takes place efficiently. Thus, the Circular
ribs with different relative gap width, when compared with
the smooth and rough ribs with symmetrical gaps, it was
concluded that the related Nusselt Number and Friction
Factor for Circular ribs with different relative gap width
was more efficient as well as economical, than that of
smooth and rough ribs with symmetrical gaps for flow
Reynolds Number.
Keywords— CFD analysis, FLUENT, UNIGRAPHICS,
Solar Duct, Friction factor, and Nusselt number.
I INTRODUCTION
Due to depletion of fossil fuels and the fuels like coal, crude
oil which produces petrol, LPG,coal tar etc. for energy
generation like electrical energy ,mechanical energy and in
aerospace applications preferably harms the environment and
ozone layer of our earth due to this hazardous effect takes
place in our environment and causes the effect of green house
,major issues like for ventilation in industries ,offices ,houses
basically an air conditioning system is preferred and other
criteria if we see in refrigeration system cloroflouro carbon is
used this substance is also used in aeroplanes and satellites launching systems this substance plays an important role in
these such applications as a major part of fuel combustion to
avoid these effects a solar energy plays an important role now
a day’s solar panel operated aeroplanes were manufactured to
conserve our fossil fuels and to protect our environment from
harmful fuel combustion fume in ventilation and air drying
process solar duct plays an important role the assembled view
of solar duct
1.1 About the solar duct
1.2.1 DUCT –Ducts are used in HVAC system and ventilation
process in industries ,offices ,houses they consists of an plate
assembled in circular rib with different relative gap width or
rectangular form with roughness for better conductivity to
increase heat transfer rate during operation.
Most appropriate way to analyze the solar heater air duct with
different Geometry is to analyze each of the geometry on CFD
and compare the results obtained with the results of
experimental investigation done by Rajesh Maithani and
J.S.Sainiand find out the best geometry having more heat
transfer of air in solar heater air duct
Figure 1.1: Solar Air Heater
1.2.2 SOLAR ENERGY COLLECTORS
Solar collectors are the key component of active solar-heating
systems. Solar collectors gather the sun's energy, transform its
radiation into heat, then transfer that heat to water, solar fluid,
or air. The solar thermal energy can be used in solar water-
heating systems, solar pool heaters, and solar space-heating systems.
Solar energy collectors are classified as:
(1) Flat plate collectors.
(2) Concentrating collectors.
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 84
If the area of interception of solar radiation is same as the area
of absorption, the collector is known as flat plate collector.
II PERFORMANCE EQUATIONS FOR A SOLAR
COLLECTOR
The performance of solar collector is described by an energy
balance that indicate the distribution of incident solar energy
into useful energy gain (Qu) and heat losses like bottom (Qb)
and top (Qt) as shown in Fig.1.2. The details of the
performance analysis of a solar collector are discussed by
Duffie and Beckman [31] and Goswami [41].The heat transfer
in a solar collector takes place by simultaneous radiation,
convection and conduction. The heat transfer from the top takes place by convection and radiation while from the side
and bottom is by conduction. The net rate of useful energy
collected per unit area is the difference of the amount of solar
energy absorbed and the energy loss by the collector to the
surroundings.
Objective of the Work
The main objective of the current work is
The main objective of our proposed work is
validation of the solar duct models by comparing the
shows simulated outcome.
To predict nusselt no. and friction factor for different
Relative gap width on the Circular rib with different
relative gap width roughened solar duct.
To simulate the Circular rib with different relative
gap width roughened solar duct of the different
Circular rib with different relative gap width
roughened profile and constant velocity for constant heat input.
To define average heat transfer coefficient, Nusselt
number and friction factor for the Circular rib with
different relative gap width roughened solar duct of
the different relative gap width and constant velocity
and constant heat input.
Predict temperature distribution along the Duct.
Problem Formulation
The survey of different previous works we predict the
friction factor is higher as compared to present study is shown
in our base paper. The purposes of this study reduce the
friction factor and increase the Nusselt no. at various relative
gap widths. Thus Chosen Circular rib with different relative
gap width shaped roughened solar duct absorber plate of the
different relative gap width in place of circular roughened
duct.
III LITERATURE REVIEW
3.1 CATEGORIZATION OF LITERATURE
Literature is divided into following categories:
1. Concept of artificial roughness
2. Roughness geometries used in solar air heater ducts
The thermal efficiency of solar air heaters (SAHs) has been
found to be generally poor because of the inherent poor
thermal conductivity of air. In order to make the solar air
heaters economically viable, their thermal efficiency needs to
be improved by enhancing the heat transfer coefficient. There
are different factors affecting the SAH efficiency, for example
collector length, collector depth, type of absorber plate, glass cover plate, wind speed, and so forth.
The shape factor of the absorber plate is the most important
parameter in the design for any type of SAH. Increasing the
absorber plate shape area will increase the heat transfer to the
flowing air. On the other hand, it will increase the pressure
drop in the collector; this increases the required power
consumption to pump the air flow crossing the collector [1].
Sahu and Bhagoria(2005) [1]], The investigation had been
done on this paper is the heat transfer coefficient by using 90˚
broken transverse ribs on absorber plate of a solar air
heater,the roughened wall being heated while the remaining three walls are insulated. We found the entire range of
Reynolds number and Nusselt number is also increases attains
a maximum for artificial roughness pitch of 20 mm and
decreases with an increase of artificialroughness pitch.The
experimental values of the thermal efficiency of the three
roughened absorber plates tested have been compared with the
smooth plates. A plate having roughness pitch 20 mm and
plate gives the highest efficiency of 83.5%.
Anil Kumar et al.(2009)[2]–- Stated artificial roughness in
the form of repeated ribs is one of the effective way of
improving the performance of a solar air heater ducts. It has
been carried out to determine the effect of different artificial roughness geometries on heat transfer and friction
characteristics in solar air heater ducts. The objective of that
study is to review various studies, in which different artificial
roughness elements are used to enhance the heat transfer co-
efficient with little penalty of friction factor. On the basis of
correlations developed by various investigators for heat
transfer coefficient and friction factor, an attempt has been
made to compare the thermo-hydraulic performance of
roughened solar air heater ducts. It has been found that lot of
experimental and analytical studies reported in that paper.
Kumar and Saini[3] carried out CFD based analysis to fluid flow and heat transfer characteristics of a solar air heaters
having roughened duct provided with artificial roughness in
arc shaped geometry. The heat transfer and flow analysis of
the chosen roughness element were carried out using 3-D
models. Authors reported that Nusselt number has been found
to increase with increase in Reynolds number where friction
factor decreases with increase in Reynolds number for all
combinations of relative roughness height (e/D) and relative
arc angle (á/90).
Karmare and Tikekar [4]- performed a CFD simulation of
fluid flow and heat transfer in a solar air heater duct with
metal grit ribs as roughness elements employed on one broad wall of a solar air heater. The circular, triangular and square
shape rib grits with the angle of attack of 54°, 56°, 58°, 60°
and 62° were tested for the same Reynolds number. Authors
reported that the CFD results give the good agreements with
experimental results. Hence, CFD techniques can be used for
analyzing and optimizing complex type of roughness surface.
Soi et al. presented a CFD based investigation of heat transfer
and friction characteristics of artificially roughened duct of a
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 85
solar air heater. K-shaped (combination of transverse and V-
up) roughness geometry was used as an artificial roughness.
Authors observed, for a given type of artificial roughness,
Nusselt number increases with an increase in Reynolds
number for smooth as well as roughened plate. Sharma et al.
designed a solar air heater duct in order to carry out CFD based investigation. CFD based performance analysis of solar
air heater duct provided with artificial roughness in the form
of square type protrusion shape geometry was reported. 2-D
computational domain and grid were selected. Non-uniform
meshing was generated over the duct.
Sharma and Thakur [5] conducted a CFD study to
investigate the heat transfer and friction loss characteristics in
a solar air heater having attachments of V-shaped ribs
roughness at 60° relative to flow direction pointing
downstream on underside of the absorber plate. Authors
observed,Nusselt number increases with increase in Reynolds
number where friction factor decreases with increase in Reynolds number for all combinations of relative roughness
height (e/D) and relative roughness pitch. In the present work
a computational investigation of turbulent forced convection
in a two-dimensional duct of a solar air heater having
rectangular rib roughness on the absorber plate is conducted.
The upper wall is subjected to a uniform heat flux condition
while the lower wall and two other side walls, except inlet and
outlet are insulated.
Sachin Chaudhary et al. [6] - having more concern with
enhancement of heat transfer coefficient using artificial
roughened absorber plate on solar air heater. The increment in heat transfer also leads to increase in friction factor which
leads to increase in pumping power. In this study M shape
geometry has been studied which is having different
orientation. The effect of roughness parameters relative
roughness height (e/D), relative roughness (P/e) and angle of
attack (á) on Nusselt number and friction factor have been
seen. The range of Reynolds number 3000-22000, e/D, P/e
and á are 0.037-0.0776, 12.5-75 and 30-60° respectively. It
has been found out that providing the artificial roughness of M
shape increases heat transfer upto 1.7-1.8 times over the
smooth duct
V COMPUTATIONAL FLUID DYNAMICS (CFD)
5.1 INTRODUCTION: Computation Fluid Dynamics (CFD)
is the branch of fluid science which deals with a variation
occurs on fluid flow, basically computational fluid dynamics
opt an finite volume method as methodology and for base
equation it follows the eulerian equation, i.e. when gravity
forces were not consider, pressure force and viscous force are
used to simulate the desired fluid flow problem.
VI MODEL FORMULATION
6.1 PREPARATION OF THE CAD MODEL
The measurements of the computational area sun based pipe
depended on the work by Rajesh Maithani, J.S. Saini. After
this procedure the imperative are connected and along these
lines the model is accomplished in demonstrating
programming UNIGRAPHICS The accompanying section
(4.1.1) demonstrates the parameters of sun based air radiator
channel roughened misleadingly with V-ribs and Semi-
circular V-ribs.
6.2 Pre-processing
6.2.1 To prepare A CAD model and geometry
dimension
Figure 6.1: Figure 4.2 Duct with different circular gap width
absorber plate
6.2.2 Meshing
Type of meshing: - Tetrahedral No. of element: - 106660
No of face: - 163801
No of nodes: -57141 Interval Size: - 1
Figure 6.2: Meshing of under floor air distribution system
VII DATA REDUCTION 7.1 The procedure of calculation of above mentioned parameters are given below:
Velocity of air through duct
The velocity of air is calculated from the knowledge of mass
flow rate and area of flow as,
V=m/(ρ.W.H)
(ii) Equivalent hydraulic diameter
The hydraulic diameter of the rectangular section of the duct is
determined from the relationship as given below,
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 86
D = (4 x Area of flow)/ Perimeter
(iii) Reynolds number (Re)
The Reynolds number of air flow in the duct is calculated
from the following relationship,
(iv). Nusselt Number for roughened duct
Nu = h D /K
Where k is the thermal conductivity of air andD is the
hydraulic diameter.
(v) Nusselt Number for smooth duct
Nusselt Number for smooth roughened duct can be obtained
by Dittus–Boelter correlation
Nus = 0.023 Re0.8Pr0.4
(vi). Friction factor for roughened duct
f=(ΔP/L)D/(2ρV^2 )
Average pressure drop (∆P) can be obtained directly from
FLUENT.
(vii). Friction factor for smooth duct
Friction factor for smooth roughened duct can be obtained
byBlasius correlation
f_s=0.079 R_e^(-0.25)
(viii). Thermal enhancement factor
Thermal enhancement factor=(Nu⁄Nu_s )/(f⁄f_s )^(1/3)
VIII RESULT AND DISCUSSION The effects of relative gap width (g/e) and Reynolds
number(Re) on the heat transfer and friction characteristics for
flow of air in a roughened rectangular duct are presented
below.The results have been compared with experimental value of same parameter and also compare with smooth ducts
operating under similar operating conditions to discuss the
enhancement in heat transfer and friction factor on account of
artificial roughness.
Figure 8.1 Comparison of different relative gap width (2, 2.5,
3, 4) for Nusselt no
Table No. 8.1.1 Comparison of experimental, Relative gap
width (g/e)= 4 and smooth plate for Nusselt No.
Reynolds
No.
Nusselt No. of
experimental
Nusselt No
of Relative
gap width
(g/e) = 4.
Smooth
3000 41 65.184 60.481
5000 81 120.346 120.412
7000 143 208.749 200.347
9000 159 220.563 208.963
11000 168 229.761 225.852
13000 171 230.753 234.743
15000 173 239.851 241.916
Figure 8.2 Compare with experimental in g/e=4 result with
smooth
Figure 8.3 Temperature coloured contour plots of air at outlet
at Reynolds number 3000
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 87
Figure 8.4 Temperature coloured contour plots of air at outlet
at Reynolds number 5000
Figure 8.5 Temperature colored contour plots of air at outlet at
Reynolds
Number7000
Figure 8.6 Temperature colored contour plots of air at outlet at Reynolds number 9000
Figure 8.7 Temperature coloured contour plots of air at outlet
at Reynolds number 11000
Figure 8.8 Comparison of different r.g.w. for Friction Factor
Table no.8.1.2 Comparison of experimental, CFD, smooth
plate for Friction Factor
Reynolds No. Friction
Factor in
EXP.
Friction
Factor in
CFD
Smooth
3000 0.0333 0.0389 0.0396
5000 0.0300 0.0359 0.0357
7000 0.0280 0.0320 0.0348
9000 0.0265 0.0330 0.0342
11000 0.0260 0.0308 0.0308
13000 0.0260 0.0310 0.0310
15000 0.0260 0.0318 0.0315
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
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Figure No.8.9 Comparison of experimental, CFD, smooth
plate for Friction Factor
IX CONCLUSION
Average deviation of result obtained
from CFD for smooth & circular geometry for Nu
number & Friction factor lies within the range,
average Nu Number is deviate 3.76% for smooth
plate and Average Friction factor is deviate 3.91% for
smooth plate as compared to experimental work of
the Author.
Average deviation of results obtained for different circular gap width from CFD in Nu Number is
deviated by 17.01 % i.e., Nu Number increases for
circular geometry at each Reynolds number taken for
analysis.
Average deviation of result obtained for different
circular gap width from CFD in Friction factor is
deviated by 20.15% i.e., Friction factor increases for
circular geometry at each Reynolds number taken for
analysis.
Thermo-Hydraulic performance increases at
Reynolds number 3000 for different circular gap width by 6.7%; and for Reynolds number 3000, 5000,
7000, 9000, 11000, 13000, 15000it increases by
18.63%, 24.12%, and 19.35%, 16. 97% respectively.
This CFD analysis clearly indicates that different
circular gap width 3roughness increases the
turbulence in the air; and at the contact, the heat
transferring area of air is increased which results in
the increase in Nu Number and Friction factor as
compared to circular geometry.
FUTURE SCOPE:-
For the future works in this area the following outlines are -
Simulation could be done for the solar duct of roughened circular rib with different relative gap width profiles by
varying the Relative gap width or no. of gap.
Simulation could be done for the solar duct of roughened circular rib with different relative gap width profiles by
varying heat input.
Simulation could be done for the solar duct of roughened
circular rib with different relative gap width profiles by
varying all three parametersi.e. relative gap width, no. of gap, roughened profile, and velocity.
Simulation could also be done by varying Angle of Attack.
Appendix
Sample calculations for circular rib q = 1000 W/m2, e= 2mm, P= 20mm, g/e=2 and Re = 3000 are given below:
1. Hydraulic Diameter (D)
= (2×W×H)/(W+H) =(2×0.3×0.025)/(0.3 + 0.025)=0.046154 m
2. Velocity of air (V)
V=Re (ν)/D=1.3 m/s
3. Heat Transfer Coefficient (h)
Average heat transfer coefficient (h) can be obtained directly from FLUENT.
h= 23W/m2K
4. Nusselt Number for roughened duct
Nu = h D /K= 45.76523
5. Nusselt Number for smooth duct
Nusselt Number for smooth roughened duct can be obtained by Dittus–Boelter correlation
Nus = 0.023 Re0.8Pr0.4 = 60.481
6. Pressure drop (ΔP)
Average pressure drop (∆P) can be obtained directly from FLUENT.
∆P= 6 Pa
7. Friction factor for roughened duct
Friction factor for smooth roughened duct can be obtained byBlasius correlation
f=(ΔP/L)D/(2ρV^2 ) =0.0492
8. Friction factor for smooth duct
f_s=0.079 R_e^(-0.25) =0.0396
© 2017 IJRTI | Volume 2, Issue 4 | ISSN: 2456-3315
IJRTI1704021 International Journal for Research Trends and Innovation (www.ijrti.org) 89
9. Thermal enhancement factor
Thermal enhancement factor=(Nu⁄Nu_s )/(f⁄f_s )^(1/3) =1.712
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