A cfd investigation and pressure correlation of solar air heater

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
401
A CFD INVESTIGATION AND PRESSURE CORRELATION OF
SOLAR AIR HEATER
Anup Kumar*, Anil Kumar Mishra**
* Dept. of Mechanical Engineering, Birla Institute of Technology, Mesra, India
**Dept. of Mechanical Engineering, Birla Institute of Technology, Mesra, India
ABSTRACT
The intent of the present work is to study the behavior of solar air heater with and
without porous media and also to compare their performance under different set of
conditions, obtained by changing various governing parameters like air mass flow rate, inlet
air temperature, spacing between top cover and absorber plate and intensity of solar radiation.
The problems have been solved by the Finite Difference Method. This study presents the
mathematical model for predicting the heat transfer characteristics and the performance of
solar air heater with and without porous media. The solar air heater with porous media gives
higher thermal efficiency than without porous media. The thermal conductivity of porous
media has significant effect on the thermal performance of the solar air heater. The work has
been carried out on GAMBIT and FLUENT software as it is standard tool for flow analysis
and widely acceptable. A double pass flat plate solar air heater model is prepared subjected to
the relative loads and constraints and results are obtained for the proposed models.
Keyword: Solar Air Heater, Porous Media, Pressure Drop, CFD
1. INTRODUCTION
Energy is a vital need in all aspects and increasing demands for energy is not
sufficient for basic requirement. Therefore, human being is looking for renewable source of
energy such as solar energy, geothermal energy, and wind energy. Humans have always used
the Solar energy is the radiation produced by nuclear fusion reactions in the core of the sun.
This radiation travels to earth through space in the form of energy called photons. Solar
energy collectors are special kind of heat exchangers that transform solar radiation energy to
internal energy of the transport medium. The major component of any solar system is the
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 2, March - April (2013), pp. 401-417
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402
solar plate collector. This is a device which absorbs the incoming solar radiation converts it
into heat, and transfers this heat to a fluid (usually air, water, or oil) flowing through the
collector. The solar energy thus collected is carried from the circulating fluid either directly
to the hot water or space conditioning equipment or to a thermal energy storage tank from
which can be drawn for use at night and/or cloudy days. Solar collector may be classified
according to their collecting characteristics, and the way in which they are mounted and
depends on the type of working fluid which is employed into the collector. A collector
generally uses liquid or a gas as working medium to transfer heat. The most common liquids
are water or a water-ethylene glycol solution. The most common gas is air.
Figure 1 Exploded view of the Flat plate collector
Depending upon the air passage in the solar air heater the air heaters can be classified in the
following ways-
Single glass cover air heater- In this type of solar heater there is only one glass surface on
the top and the absorber is below the glass plate. The air flows between the glass plate and
the absorber plate. (Figure 2)
Double glass cover air heater- This type of air heater includes two glass cover on the top
surface and the air flows between the glass cover and the absorber plate. (Figure 3)
Double pass air heater without porous matrix- In this type of solar air heater, air flows
between two glass plate in one direction and then between the glass plate and the absorber
plate in the opposite direction. (Figure 4)
Double pass air heater with porous matrix- The constructional part of solar air heater with
porous media same as solar air with non- porous media but only difference is that the porous
material is used in second pass of air flow. Porous materials have become increasingly
attractive for application in high temperature heat exchangers. The high effectiveness of the
heat exchange mechanism is mainly due to the intimate contact in the interstices between the
gas particles and porous plate. (Figure 5)

403
A porous medium is a material containing pores (voids). The skeletal portion of the material
is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or
gas). The skeletal material is usually a solid, but structures like foams are often also usefully
analyzed using concept of porous media. A porous medium is most often characterized by its
porosity. It is also observed that thermal efficiency of solar air heater can be increased by
minimizing heat loss from collector to maximize heat transfer from absorber [8]. To provide
a counter flow passage an extra top cover can be provided to increase volumetric heat transfer
co-efficient.
2. MATHEMATICAL FORMULATION
In the present study, at first mathematical model is obtained by the application of the
governing conservation laws. The heat balance is accomplished across each component of
given solar air heater i.e., the glass covers, the air stream and the absorber plate. The heat
balance for the air stream yields the governing differential equations and the associated
boundary conditions. The main idea is to minimize heat losses from the front cover of the
collector and to maximize heat extraction from the absorber. Porous media forms an
extensive area for heat transfer, where the volumetric heat transfer coefficient is very high; it
will enhance heat transfer from the absorber to the airstream. In the design of this type of
collector, this combines double air passage and porous media pressure drop should be
minimized[11]. The basic physical equations used to describe the heat transfer characteristics
Figure 2 Single glass cover air heater Figure 3 Double glass cover air heater
Figure 4 Double pass air heaters without
porous matrix
Figure 5 Double pass air heaters
with porous matrix

404
are developed from the conservation equations of energy. The heat and fluid flow are
assumed steady and one dimensional. It is because of the radiation heat exchange terms that
render the problem non-linear hence making the exact solution cumbersome. So a numerical
approach is applied which would give a solution with a fairly good accuracy.
The model is based on the assumption made by Naphon and Kongtragool[2] -
Flow of air is steady.
Outside convective heat transfer coefficient is constant along the length of solar air
heater.
Inside convective heat transfer coefficient is constant along the length of solar air
heater.
Thermal conductivity of the porous media is constant along the length of solar air
heater.
The temperatures of the cover and plates vary only in the direction of fluid flow (x-
direction);
The side losses are negligible and leakage of air to/or from the collectors is negligible.
Ideal gas with constant specific heat.
The air flow is forced, steady and one-dimensional and the thermo-physical properties
of air and packed bed are independent of temperature.
The plug flow condition exists throughout the length of heater, i.e., the air velocity in
the channel at any section is constant.
The porous absorber and the air stream are in thermal equilibrium because the value
of volumetric heat transfer coefficient in the pores of the porous matrix is very high.
2.1 Factors Affecting Efficiency of flat Plate Solar Air Heater
2.1.1 Porous Medium - The solar air heater with the porous media gives 25.9%
higherthermal efficiency than that without porous media. The thermal conductivity of porous
media has significant effect on the thermal performance of the solar air heater [2].
Asporous mediumis characterized by its porosity or measure of voids and the skeletal portion
of the material is often called the "matrix" or "frame". The measure of void isa fraction of the
volume of voids over the total volume, between 0–1, or as a percentage between 0–100
percent. There is also a concept of closed porosity andeffective porosity, i.e., the pore space
accessible to flow.[7]
2.2.2 Transmissivity-Absorptivity Product-Transmissivity-Absorptivity product is defined
as the ratio of the flux absorbed in the absorber plate to the flux incident on the cover system,
and is denoted by the symbol (τα). Out of fraction τα transmitted through the cover system, a
part is absorbed and a part reflects back diffusively. Out of the reflected part, a portion is
transmitted through the cover system and a portion reflected back to the absorber plate. The
process of absorption and reflection at the absorber plate surface (figure 6) goes on
indefinitely, the quantities involved being successively smaller.
Thus, the net fraction absorbed (τα) = ταሾ1 ൅ ሺ1 െ αሻρୢ
ሺ1 െ αሻଶ
ρୢ
ଶ
൅ ‫]ڮ‬
ൌ
τα
ଵିሺଵିαሻρౚ
(1)

405
Figure. 6 Process of Absorption and Reflection
2.2.3 Overall Loss Coefficient- The heat loss from the collector in terms of overall loss
coefficient defined by the equation
qଵ ൌ UଵA୮൫T୮୫ െ Tୟ൯ (2)
The heat loss from the collector is the sum of heat loss from the top, bottom and the sides.
Thus
qଵ ൌ q୲ ൅ qୠ ൅ qୱ (3)
q୲ ൌ U୲A୮൫T୮୫ െ Tୟ൯ (4)
qୠ ൌ UୠA୮ሺT୮୫ െ Tୟሻ (5)
qୱ ൌ UୱA୮ሺT୮୫ െ Tୟሻ (6)
Uଵ ൌ U୲ ൅ Uୠ ൅ Uୱ (7)
2.2.4Top loss coefficient ‫܃‬‫ܜ‬- The top loss coefficient is evaluated by considering convection
and radiation losses from the absorber plate in the upward direction. For the purpose of
calculation, it is assumed that the transparent covers and the absorber plate constitute a
system of infinite parallel surfaces and that the flow of heat is one-dimensional and steady. It
is further assumed that the temperature drop across the thickness of the covers is negligible
and the interaction between the incoming solar radiation absorbed by the covers and the
outgoing loss may be neglected. The outgoing re-radiation is of larger wavelength. For these
wavelengths, the transparent cover is assumed to be opaque.Sukhatme [3] suggested thatheat
transferred by convection and radiation at different layers as follows-
(a) The absorber plate and the first cover;
୯భ
୅౦
ൌ h୮ିୡଵ൫T୮୫ െ Tୡଵ൯ ൅ σ
ሺ୘౦ౣ
ర ି୘ౙభ
ర ሻ
ଵ
஫౦ൗ ାଵ
஫ౙൗ ିଵ
(8)
(b) The two glass covers;
୯భ
୅౦
ൌ hୡଵିୡଶሺTୡଵ െ Tୡଶሻ ൅ σ
ሺ୘ౙభ
ర ି୘ౙమ
ర ሻ
ଵ
஫ౙൗ ାଵ
஫ౙൗ ିଵ
(9)
(c) The second glass cover and the sky;
୯భ
୅౦
ൌ hୟሺTୡଶ െ Tୟሻ ൅ σεୡሺTୡଶ
ସ
െ Tୱ୩୷
ସ
ሻ (10)

406
Sukhatme [3] also suggested the empirical relation for the top loss coefficient as-
U୲ ൌ ሾ
୑
൬
ి
౐౦ౣ
൰ቀ
౐౦ౣష౐౗
౉శ౜
ቁ
బ.యయ ൅
ଵ
୦౗
ሿିଵ
൅ ሾ
σሺ୘౦ౣ
మ ା୘౗
మሻሺ୘౦ౣା୘౗ሻ
భ
ε౦శబ.బబఱ౉ሺభషε౦ሻ
ା
మ౉శ౜షభ
εౙ
ି୑
] (11)
Where, f ൌ ሺ1 െ 0.04hୟ ൅ 0.0005hୟ
ଶሻሺ1 ൅ 0.091ሻM
C ൌ 365.9൫1 െ 0.00883β ൅ .0001298βଶ
൯
M=number of glass covers
2.2.5Heat transfer coefficient at the top cover- The convective heat transfer coefficient
(hୟ) at the top cover has been calculated from the following empirical correlation suggested
by McAdams [4],
hୟ ൌ 5.7 ൅ 3.8V (12)
Where, V is the wind speed in m/s.
An another important dimensionless correlation have been suggested by Sparrow and
hiscoworkers [5] given as,
j ൌ 0.86ሺRe୐
‫כ‬ ሻିଵ/ଶ
; (13)
Where, j=j-factor given by
୦౗
ρେ౦୚
Prଶ/ଷ
Re୐
‫כ‬
= Reynolds number based on the characteristics dimension
L ൌ 4Aୡ/Cୡ
Aୡ=Collector gross area
Cୡ=Circumference associated with the collector gross area.
2.2.6Sky Temperature- As suggested by Sukhatme [3] Sky temperature is usually
calculatedfrom empirical relation in which temperature are expressed in Kelvin
Tୱ୩୷ ൌ Tୟ (14)
2.2.7Bottom loss coefficient(Ub)-The bottom loss coefficient is calculated by considering
conduction and convection losses from the absorber plate in the downward direction[6]. It
will be assumed that the heat flow is one dimensional and steady (Fig.7). In most cases, the
thickness of thermal insulation is provided such that the thermal resistance associated with
conduction dominates. Thus, neglecting the convective resistance at the bottom surface of the
collector casing.
Uୠ ൌ K୧/δୠ
Where, k୧=Thermal conductivity of the insulation
δୠ= Thickness of the insulation.

407
Figure 7. Bottom and side losses from a flat-plate
2.2.8 Side loss coefficient (‫܃‬‫ܛ‬)-The assumptions applied for side loss coefficient is
conduction resistance dominates and that the flow of heat is one dimensional and steady state.
The one-dimensional approximation can be justified on the grounds that Uୱis always much
smaller than theU୲.
If the dimensions of the absorber plate are L1 x L2 and the height of the collector is L3 and
assuming that the average temperature drop across the insulation is (T୮୫ െ Tୟሻ/2 andthe
thickness of this insulation isδୱ.
qୱ ൌ
2LଷሺLଵ ൅ Lଶሻk୧ሺT୮୫ െ Tୟሻ
2δୱ
Uୱ ൌ
2LଷሺLଵ ൅ Lଶሻk୧ሺT୮୫ െ Tୟሻ
LଵLଶδୱ
2.3 Governing Equation
Under steady state operating conditions, the energy balance for the conventional and
counter flow collectors as suggested by Mohammad [1] and applying the finite difference
method on the proposed double-pass flat-pate solar air heaters without and with porous media
which are as follows:
For top glass cover:
G.E:Iαୡ ൌ hୟሺTୡଵ െ Tୟሻ ൅ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୰.ୡୡሺTୡଵ െ Tୡଶሻ...(15)
For down flow air stream:
G.D.E.: mc
ୢ୲౜భ
ୢ୶
ൌ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୤ୡଶሺTୡଶ െ T୤ଵሻ…(16)
For second glass cover
G.E.:
Iαୡτୡ ൌ h୰.ୡୡሺTୡଶ െ Tୡଵሻ ൅ h୤ଵୡଶሺTୡଶ െ T୤ଵሻ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ h୰.୮ୡሺTୡଶ െ T୮ሻ
…(17)
For up follow air stream:
G.D.E.: mc
ୢ୘౜మ
ୢ୶
ൌ h୤ଵୡଶሺTୡଶ െ T୤ଶሻ ൅ h୤ଶ୮ሺT୮ െ T୤ଶሻ...(18)

408
For absorber plate:
G.E.: Iα୮τୡ ൌ h୤ଶ୮൫T୮ െ T୤ଶ൯ ൅ h୰.୮ୡ൫T୮ െ Tୡଶ൯ ൅ UୠሺT୮ െ Tୟሻ…(19)
Double-pass flat-pate collector with porous media
For top glass cover:
G.E: Iαୡ ൌ hୟሺTୡଵ െ Tୟሻ ൅ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୰.ୡୡሺTୡଵ െ Tୡଶሻ...(20)
For down flow air stream:
G.D.E.: mc
ୢ୲౜భ
ୢ୶
ൌ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୤ୡଶሺTୡଶ െ T୤ଵሻ…(21)
For second glass cover
G.E.:
Iαୡτୡ ൌ h୰.ୡୡሺTୡଶ െ Tୡଵሻ ൅ h୤ଵୡଶሺTୡଶ െ T୤ଵሻ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ h୰.୮ୡሺTୡଶ െ T୮ሻ ...(22)
For up flow air stream:
G.D.E.:
mc
ୢ୘౜మ
ୢ୶
ൌ Kୣ୤୤
ୢమ୘౜మ
ୢ୶మ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ UୠሺTୟ െ T୤ଶሻ ൅ Iα୮τୡτୡ...(23)
For the sake of convenience the heat transfer coefficients between the air stream and the
covers and between the air stream and the absorber plate are assumed equal and can be
calculated as follows:
h୤ଵୡଵ ൌ h୤ଵୡଶ ൌ h୤ଶୡଶ ൌ h୤ଶ୮ ൌ h୤…(24)
The air density: ρ ൌ
୔౗
ୖ୘౗
…(25)
Kinematic viscosity: ν ൌ
µ
ρ
…(26)
Thermal diffusivity: α ൌ
୩
ρୡ౦
…(27)
Prandtl number: P୰ ൌ
ν
α
…(28)
Hydraulic diameter: D୦ ൌ
ସ୅౜
୔
ൌ 2D…(29)
Reynolds number: Rୣ ൌ
ρ୙ୈ౞
µ
ൌ
ଶ୫
µ
…(30)
Grashof Number =
௚ఉ∆்య
௩మ …(31)
Nusselt number; Nu ൌ 0.0333 Rୣ
଴.଼
P୰
଴.ଷଷ
…(32)

409
Convective heat transfer coefficient between any two surfaces
h୰ଵଶ ൌ
σሺ୘భା୘మሻሺ୘భ
మା୘మ
మሻ
భ
εభ
ା
భ
εమ
ିଵ
…(33)
When the air flows through the channel in the air heater, due to friction the air pressure drop
along the of the flow channel. This pressure drop across the duct is given by the:
p ൌ f ቀ
୫య
ρ
ቁ ቀ
୐య
ୈయ
ቁ…(34)
Where, f ൌ f଴ ൅ yሺ
ୈ
୐
) …(3.40)
The value of f଴ and y are:
f଴=24/Re, y=0.9 for Laminar flow (Re<2550) …(34)
f଴ = 0.0094, y =2.92Re-0.15
for transitional flow (2550<Re<104
) …(35)
f଴ = 0.059 Re-0.2
, y =0.73 for turbulent flow (104
<Re<105
) …(36)
So far as pressure drop (pumping power) is concerned, the counter flow solar air heater has a
U-turn section and extra-length for air passages. Hence the extra pressure drop is introduced
by this design. The pressure drop in the u-section can be calculated as:
ᇞ p ൌ
୏୫మ
ଶρୈమ…(37)
K=1forU-section
The pumping power can be calculated asW ൌ
୫ᇞ୮
ρ
…(38)
3. MODELING AND ANALYSIS
The finite difference method (FDM) is used to solve the differential equations and
hence to simulate a given solar air heater. In FDM technique, the first step involves the
transformation of the actual physical domain into the computational grid. Second step is to
transform the differential equations into difference equations, which along with the equations
obtained by heat balance across the covers and the absorber are the simultaneous nonlinear
algebraic equations. The next step is to solve those numerically using gauss elimination
method. The solution is obtained in the form of nodal temperatures for the covers, the air
streams and the absorber. Study has been extended by changing the various governing
parameters like the air mass flow rate, the inlet air temperature, the depth of the collector duct
and the intensity of solar radiation and finally the performance characteristics have been
obtained. A computer program is developed using Dev C++ programming language based on
algorithm and flow chart.

410
3.1 Technical Specifications
Input Parameters and Constants for the proposed model.
Sl.No. Input Parameters Values
1. Length of solar air heater, L(m) 2.0
2. Width of solar air heater, w(m) 1.0
3. Depth of upper channel solar air heater, D1(cm) 4.5,5.5,6.5
4. Depth of lower channel solar air heater, D2(cm) 4.5,5.5,6.5
5. Emissivity of glass covers, εୡ 0.92
6. Emissivity of absorber plate and packed bed,ε୮ 0.92
7. Transmissivity of glass cover and absorber,߬௖ ‫ݎ݋‬ ߬௣ 0.92
8. Absorptivity of glass cover,αୡ 0.06
9. Absorptivity of absorber,α୮ 0.92
10. Inlet air temperature, Ti(K) 288,303
11. Air mass flow rate per unit width, m (kg/m s) 0.01-.2
12. Back insulation thickness(m) 0.05
13. Side insulation thickness(m) 0.05
14. Porosity of Porous medium( Glass wool) 0.8
15. Plate Type Flat Plate
3.2 Proposed Model
The design of thermal equipment must focus on a combination of numerical and
experimental techniques hence, a three-dimensional numerical model was developed using
the CFD numerical package FLUENT. The proposed model is modeled by using CATIA V5
R19 which is used for analysis by applying boundary conditions. An analysis of proposed
model is also performed by using CFD package as CFD is concerned with the efficient
numerical solution of the partial differential equations that describe fluid dynamics. A model
for virtual prototyping of thermal equipment must be detailed enough in order to consider all
the main physical phenomena that are taking place as well as giving results in a reasonable
computational time. The mesh size is critical for CFD analysis, especially when dealing with
natural convection.
3.3 Algorithm for Computer Program
Following steps are involved in the simulation of double pass flat plate solar air heater:
Step 1: Enter values of m, L, D, Tୟ, pୟ, R, hୟ, µ, Uୠ, αୡ, α୮, τୡ, σ, c୮, k୤.
Step 2: Select the type of heater.
Step 3: Calculateν, P୰, Rୣ, N୳, h୤.
Step 4: Initialize with T୤ሾ0ሿ ൌ T୧, h୰.ୡୡሾiሿ ൌ 5, h୰.୮ୡሾiሿ ൌ 5 for all i.
Step 5: Solving the finite difference equations for a given solar heater to calculate the nodal
temperatures by using the appropriate boundary conditions and gauss elimination method for
solving the simultaneous equations as described above. After that following parameter are
calculated.
P ൌ f ቆ
mଷ
ρ
ቇ ቆ
Lଷ
Dଷ
ቇ
η ൌ
mc୮∆T
IA

411
Step 6: Once all these temperature are obtained, the following performance characteristics are
obtained:
1. ∆P Vs m
2. η vs ܶ௣
3. η Vs m
4.
ୢ୘
୍
Vs m
5. ߟ ܸ‫ݏ‬
ௗ்
ூ
Figure 8. 3-D Model of Solar Air Heater
Figure 9. Mesh generation of 3-D Model

412
3.4 Flowchart for the simulation of double pass flat plate solar air heater
Start
Obtain the following characteristics
1. ΔP Vs m
2. η vs ܶ௣
3. η Vs m
4.
ୢ୘
୍
Vs m
5. ߟ ܸ‫ݏ‬
ௗ்
ூ
End
ΔT୥ ൌ maxሺTୡଵሾiሿ െ Tୟሻ
Δܶ௣௙ ൌ max ሺܶ௣ሾ݅ሿ െ ܶ௙ሾ݅ሿሻ
P ൌ f ቆ
mଷ
ρ
ቇ ቆ
Lଷ
Dଷ
ቇ
ߟ ൌ
݉ܿ௣ሺܶ଴ െ ܶ௜ሻ
‫ܫ‬ሺ‫ݔܮ‬ሻ
;
Obtain:
Input the Values of
݉, ‫,ܮ‬ ‫,ܦ‬ ܶ௔, ‫݌‬௔, ܴ, ݄௔, ߤ, ܷ௕, ߙ௖, ߙ௣, ߬௖, ߪ, ܿ௣, ݇௙
Substituting these values in the set of equations obtained by
energy balance for a given solar air heater and solving them
simultaneous by gauss-elimination method to evaluate
Tୡଵ, Tୡଶ, T୤ଵ, T୤ଶ and T୮
n; ρ; ν; ߙ; ܲ௥; ܴ௘; ܰ‫ݑ‬
Calculate

413
4. RESULT AND DISCUSSION
The majority of the heat transfer occurred at the bottom section of the solar air
heater,rather than near the level between the inlet fluid temperature and the fluid inside
thesolar air heater.The variation of pressure drop with different mass flow andefficiency
withmass flow rate, plate temperature, solar radiation for both solar air heater without porous
and with porous media are shown in graph 10, 11, 12, 13 and 14.The pressure drop increases
in both solar air heater without porous and with porous media with increase in mass flow rate.
Figure 10. Variation of Pressure with Mass flow rate
Figure 11. Variation of efficiency with Mass flow rate

414
Figure 12. Variation of efficiency with plate temperature
Figure 13. Variation of efficiency with dT/I
Figure 14. Variation of dT/I with mass flow rate

415
Figure 15. Variation of Pressure Drop across solar Air Heater
Figure 16. Variation of Air Velocity across Solar Air heater
5. CONCLUDING REMARKS
The variations of pressure in solar air heater model with different mass flow rate for
non-porous and porous media are shown in figure 10 for different depth, inlet temperature
and solar radiation. It is concluded that outlet temperature is decreasing with increase in mass
flow rate. It is found that the use of porous media in lower channel increases the outlet
temperature. The use of porous media in solar air heater increases the system efficiency and
outlet temperature. This increase, results an increase in the pressure drop for solar collector
with porous media, which means increasing of the cost of the pumping power expanded in
the collector. But this factor has no significant for low flow rates.

416
Nomenclature
Af-Front Area
Cp- Specific heat capacity
D-Depth of the duct
Dh-Hydraulic Diameter
L-Length of the duct
n1-Refractive index
h-Heat transfer coefficient
m- Mass flow rate
k- Thermal conductivity
I- Intensity of solar radiation
U- Overall heat transfer coefficient
T- Temperature
V-Ambient Air velocity
W-Pumping factor
GREEK LETTERS
߳-Emissivity
߬ -Transmissivity
ߙ- Absorptivity
ߚ-Diffusivity
ߟ- Thermal efficiency
߮- Porosity
ߩ- Extinction coefficient
∆Difference of two quantities
SUBSCRIPTS
a- Ambient
b- Bottom
c- Cover
e-Effective
f- Fluid
p- Packing plate
t- Top
1- First glass cover
2- Second glass cover
REFERENCE
[1]Mohamad.A.A,“High efficiency solar air heater”, solar energy vol.60 No.2, pp.71-76,
1997.
[2]-Naphonparison,“Effect of porous media on the performance of the double pass flat plate
solar air heater”, solar energy, Vol.12 No.1, pp.90-99, 1996
[3]Sukhatme S.P., “Solar energy”, 3rd ed., 1984, Tata McGraw Hill, New Delhi.
[4] McAdams.W.H, “Heat Transmission”, 3rd ed.., McGraw Hill, New York, 1954.
[5] Sparrow, E.M., and Tien, K.K., “Forced convection heat transfer at an inclined and yawed
square plate application to solar collectors”, Heat transfer, Vol. 99 pp.507-522, 1977

417
[6] Raja shekhar,Y.,Sharma,K.,V.,,Rao,M.,B.,“Evaluation of heat loss coefficients in solar
flat plate collectors”,ARPN Journal, Vo. l4,No.5, pp. 15-19,2009.
[7] Languri,E.,M.,Taherian, H.,“Enhanced double –pass solar air heater with and without
porous medium”, International Journal of green Energy, Vol. 8, pp. 643-654,2011.
[8] Pradharaj,M.,Velmurugan,V., Moorthy, H., “Review on porous and non-porous flat plate
air collector with mirror enclose”, International journal of Engineering and Technology, Vol2
pp.4013-4019,2010
[9] Yousef.BAA, Adam.NM, “Performance analysis for flat plate collector with and without
porous media”, Journal of energy in Southern Africa, vol.19 No.4, pp.32-42, 2008.
[10] Zhao, Q., Salder, G.W., Leonardo, J.J., “Transient simulation of flat-plate solar
collectors”, Solar Energy, Vol.40, pp.167-174, 1988.
[11] Lansing.F.L,Reynold.R, “High performance flat plate solar collector”, solar energy
vol.24 No.2, pp.90-99, 1996.
[12] Ajay Kumar Kapardar and Dr. R. P. Sharma, “Experimental Investigation of Solar Air
Heater using Porous Medium”, International Journal of Mechanical Engineering &
Technology (IJMET), Volume 3, Issue 2, 2012, pp. 387 - 396, ISSN Print: 0976 – 6340,
ISSN Online: 0976 – 6359.
[13] Yogesh C. Dhote and Dr. S.B. Thombre, “Parametric Study on the Thermal Performance
of the Solar Air Heater with Energy Storage”, International Journal of Mechanical
Engineering & Technology (IJMET), Volume 3, Issue 1, 2012, pp. 90 - 99, ISSN Print:
0976 – 6340, ISSN Online: 0976 – 6359.
[14] Ajay Kumar Kapardar and Dr. R. P. Sharma, “Numerical and CFD Based Analysis of
Porous Media Solar Air Heater”, International Journal of Mechanical Engineering &
Technology (IJMET), Volume 3, Issue 2, 2012, pp. 374 - 386, ISSN Print: 0976 – 6340,
ISSN Online: 0976 – 6359.

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