Ijetae 0413 59

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 4, April 2013)

337

CFD Analysis of Solar Flat Plate Collector Prof. P.W.Ingle

1, Dr. A. A. Pawar

2, Prof. B. D. Deshmukh

3, Prof. K. C. Bhosale

4

1Assistant Professor Mechanical Engineering Department, S.R.E.S. College of Engineering, Kopargaon, Maharashtra,

2Professor Mechanical Engineering Department, RSCOE, Thathwade, Pune,

3,4Assistant Professor Mechanical Engineering Department, S.R.E.S. College of Engineering, Kopargaon, Maharashtra

Abstract - This thesis attempts to present numerical

simulation of solar collector developed exclusively for grape

drying. Solar drying of grapes is much feasible technically and

economically. There has been a remarkable achievement in

solar drying of grapes due to sustained research and

development associated with the adoption of advanced

technologies.

Simulation is an important tool for design and operation

control. For the designer of a drying system, simulation makes

it possible to find the optimum design and operating

parameters. For the designer of the control system, simulation

provides a means to device control strategies and to analyze

the effects of disturbances.

In the present thesis the computational fluid dynamics

(CFD) tool has been used to simulate the solar collector for

better understanding the heat transfer capability. 3D model of

the collector involving air inlet, wavy structured absorber

plate,glass cover plate, and pebble block is modeled by

ANSYS Workbench and the unstructured grid was created in

ANSYS ICEM. The results were obtained by using ANSYS

FLUENT software.

The objective of this work is to compare theoretically and

experimentally work done with the work done by using

computational fluid dynamics (CFD) tool with respect to flow

and temperature distribution inside the solar collector. The

outlet temperature of air is compared with experimental

results and there is a good agreement in between them

Keywords—Solar Collector, Drying, Temperature ANSYS,

CFD

I. INTRODUCTION

Solar energy is the most considerable energy source in

the world. Sun, which is 1.495x1011

(m) far from the earth

and has a diameter of 1.39x109 (m), would emit

approximately 1353 (W/m2) on to a surface perpendicular

to rays, if there was no atmospheric layer. The world

receives 170 trillion (KW) solar energy and 30% of this

energy is reflected back to the space, 47% is transformed to

low temperature heat energy, 23% is used for

evaporation/rainfall cycle in the Biosphere and less than

0.5% is used in the kinetic energy of the wind, waves and

photosynthesis of plants.

Solar energy systems consist of many parts. The most

important part of these systems is the solar collector where

the heat transfer from sun to absorber and absorber to fluid

occurs. In order to affect the performance of these systems,

generally modifications on solar collectors are performed.

With the rapid development in civilization, man has

increasingly become dependent on natural resources to

satisfy his needs. Drying fruits and vegetables such as

grapes, pepper, pawpaw, etc is one of those indispensable

processes that require natural resources in the form of fuels.

Solar dryer is fast becoming a preferred method of drying

fruits, food grains considering the potential of saving

significant amounts of conventional fuel. The major factor

that limits the solar energy for drying application is that it

is a cyclic time dependent energy source. Therefore, solar

systems require energy storage to provide energy during

the night and overcast periods. In addition, one of the major

requirements in using solar energy for drying application is

the development of a suitable drying unit, which should be

fast and energy efficient[1].

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 solar collector. Of all the solar

thermal collectors, the flat plate collectors though produce

lower temperatures, have the advantage of being simpler in

design, having lower maintenance and lower cost. To

obtain maximum amount of solar energy of minimum cost

the flat plate solar air heaters with thermal storage have

been developed. Solar air heater is type of solar collector

which is extensively used in many applications such as

residential, industrial and agricultural fields.[2]

Solar collectors are the key component of active solar-

heating systems. They gather the sun's energy, transform its

radiation into heat, then transfer that heat to a fluid (usually

water or air). The solar thermal energy can be used in solar

water-heating systems, solar pool heaters, and solar space-

heating systems.



338

A. Flat-plate collectors

Flat-plate collectors are the most common solar collector

for solar water-heating systems in homes and solar space

heating. A typical flat-plate collector is an insulated metal

box with a glass or plastic cover (called the glazing) and a

dark-colored absorber plate. These collectors heat liquid or

air at temperatures less than 80°C.

The objective of present study is to perform CFD

simulation of flat plate collector with air flow. The CFD

model was validated with experimental results. Based on

the results of the experiments CFD analysis of air on solar

flat plate collector is carried out. There are certain

limitations for experimental results thus data at each and

every point cannot be obtained, hence CFD is the tool

which handles complex situations where experimental is

not applicable because of limitations and cost effectiveness

problem. The overall aim of this work is to understand the

flow and temperature distribution of air through solar flat

plate collector[3].

II. PROBLEM STATEMENT

The objective of present study is to perform CFD

simulation for solar air collector. The results obtained by

CFD simulation are been validated with experimental

results.The experimental conditions taken for solar air

collector, the same has been used for CFD simulation. The

overall aim of this work is to understand the flow behavior

and temperature distribution of air inside the solar collector

and compare the outlet temperature of air with

experimental results.

The 3D model consisting of the solar air collector

involving air inlet, wavy structured absorber plate , glass

cover plate, and pebble block is model by ANSYS

Workbench and the unstructured grid was created in

ANSYS ICEM. The results were obtained by using

ANSYS FLUENT software

The overall dimension for solar air collector is

2000X1000X130 mm3 with 4 mm thick glass plate which is

placed at around 126 mm from the top side of the collector.

The wavy structured absorber plate of 2000 mm length,

1000 mm wide and 2 mm in thickness. Inlet of solar air

collector is of circular cross section with diameter of 70

mm. There are two outlets to the solar collector with

circular cross section having diameter 60 mm.

Fig.1 Isometric view of Solar flat plate collector

III. NUMERICAL SIMULATION BY SOFTWARE

Computational system dynamics is the analysis of the

systems involving fluid flow, heat transfer and associated

phenomenon such as chemical reactions by means of

computer-based simulation. The technique is very powerful

and spans a wide range of industrial and non-industrial

applications areas. Some examples are: aerodynamics of

aircrafts and vehicles, hydrodynamics of ships, combustion,

turbo machinery, electrical and electronic engineering,

chemical process engineering, external and internal

environment of buildings, marine engineering,

environmental engineering, hydrology and oceanography,

metrology, biomedical engineering etc. from the 1960s

onwards, the aerospace industry has integrated CFD

technique into design, R & D and manufacture of aircrafts

and jet engines. More recently the methods have been

applied to the design of internal combustion engines,

combustion chambers of gas turbines and furnaces.

Furthermore, motor manufacturers now routinely predict

drag forces, under bonnet airflow and the in-car

environment with CFD. Increasingly CFD is becoming a

vital component in the design of industrial products and

processes.

The ultimate aim of development in the CFD field is to

provide a capability comparable to other CAE (Computer-

Aided Engineering) tools such as stress analysis codes.



339

The main reason why CFD has lagged behind is the

tremendous complexity of the underlying behavior, which

precludes a description of the fluid flows this is at the same

time economical and sufficiently complete. The availability

of affordable high performance computing hardware and

the introduction of user friendly interference have led to a

recent upsurge of interest and CFD is poised to make an

entry into the wider industrial community in the 1990s.

Clearly the investment costs of a CFD capability are not

small, but the total expense is not normally as great as that

of a high quality experimental facility. Moreover, there are

several unique advantages of CFD over experimental-based

approaches to fluid systems design.

1. Substantial reduction of lead times and costs of new

design.

2. Ability to study systems where controlled experimental

are difficult or impossible to perform. (e.g. very large

systems)

3. Ability to study systems under hazardous conditions at

and beyond their normal performance limits. (e.g. safety

studies and accident scenarios)

4. Practically unlimited level of detail of results.

In contrast CFD codes can produce extremely large

volumes of results at virtually no added expense and it is

very cheap to perform parametric studies, for instance to

optimize equipment performance[4].

A. Basics in CFD

CFD codes are structured around the numerical

algorithms that can tackle fluid flow problems. In order to

provide easy asses to their solving power all commercial

CFD packages include sophisticated user interfaces to input

problem parameters and to examine the results. Hence all

code contains three main elements:

1. Pre-processor

2. Solver

3. Post-processor

B. Numerical Modeling of solar air collector

The procedure adopted to simulate the solar air collector

by CFD tool is as follows:

a. The 3D model is been modeled by using ANSYS

WORKBENCH software as shown in Fig.2

b. After creation of 3D model, the unstructured grid is

been created by using ANSYS ICEM software as

shown in fig 3 and fig.4

c. The unstructured grid created consist around 1.5 crore

elements.

d. The unstructured grid which is created then imported

in ANSYS FLUENT software and the experimental

conditions are used while simulating the solar air

collector.

e. The model was defined by using 3D segregated solver

with steady condition, energy equation, and K-epsilon

of viscous model.

f. The fluid chosen to simulate solar collector is air. The

air properties used in this simulation is shown in table

no.1

g. The boundary conditions used in this simulation are

shown in table no.2 and 3.

h. After setting all boundary conditions in fluent

software, to solve the numerical equations the

initialization by inlet is to be done.

i. To visualize the residuals of iterations verses

convergence limit, the residual monitor is set to be in

ON state condition.

j. To get the final results the numbers of iterations are

set around 10000. The results for these simulations

were converged at around 4000 to 6000 iterations.

k. As the number of elements are more to get the

converged results the time taken for these simulations

will be more with single processor.

l. Finally after getting the proper converged results the

air flow distribution and heat transfer inside the solar

air collector is been plotted in the form of Contour

plots.

m. The outlet temperature is been calculated from

ANSYS FLUENT after getting converged results and

been compared with the experimental results.

Fig.2. 3D model of solar air collector visualizing the absorber plate



340

Fig.3 3D mesh of Solar Flat Plate Collector

Fig. 4 Meshing by using ANSYS fLUENT

TABLE 1.

PROPERTIES OF AIR

Property Value

Mass flow rate of air 0.0105 Kg/sec

Density 1.165 kg/m3

Thermal Conductivity 100 W/m K

Specific Heat 1005 J/kg K

TABLE 2

PROPERTIES OF PEBBLE BLOCK

Property Value

Density 1350 Kg/m3

Thermal Conductivity 100 W/m K

Specific Heat 300-600 J/kg K

TABLE 3

PROPERTIES OF GLASS

Property Value

Density 1000 Kg/m3

Thermal Conductivity 1.75 W/m K

Specific Heat 910 J/kg K

C. Assumptions considered for simulation

1. Air is used as working fluid, it is compressible

fluid.

2. Problem is considered 3D and steady state.

3. Surface considered in geometry are smooth air

flow over it is frictionless.

4. Ambient temperature is considered constant.

5. Flow is assumed to be turbulent.

6. Turbulence specification method of turbulent

intensity and viscosity ratio with 5 % and 10

respectively. By default these values are can be

taken 3 % and 3 respectively or calculated as per

model. Here it is been assumed that turbulence will

be more so approximately value has been taken by

doing trial and error for convergence of model

results[5].

IV. RESULT AND DISCUSSION

The results obtained from the CFD analysis of solar flat

plate collector are presented in this section. The simulation

is carried out for different times of the day i.e.9 am to 5

pm. Then the results obtained by this simulation compared

with the experimental results as shown in fig 4. The curves

are plotted to indicate experimental and simulated outlet

temperatures versus time. From fig 4 it seems that the

difference between experimental and simulated outlet

temperature for different times is almost 5˚C.



341

TABLE 4

COMPARISON OF EXPERIMENTAL AND CFD RESULTS

Time Hrs

Solar Intensity

(W/m2)

Ambient temperature

(0C)

Collector temperature

obtained by

CFD(0C)

Collector temperature

(0C)

9 am 621.7 32.5 60.87 55.7

10

am

750.5 34.7 73.75 60.5

11

am

879.5 37 85.34 67.4

12 909 38.9 93.38 76.5

1 pm 948 38.5 96.10 78.1

2 pm 909.5 41.1 93.40 75.2

3 pm 790 40 84.84 68.8

4 pm 597.5 35 68.14 60.3

5 pm 357 33 43.06 42

Graph 1. Comparison of CFD and experimental results for day1

Also the temperature distribution and flow distribution

are obtained by CFD simulation. The contour plots

obtained for temperature distribution and velocity

distribution in streamlines are shown in fig 5(a), 5(b), 5(c),

5(d).

Fig.5(a) Streamlines for temperature distribution

Fig.5(b) Streamlines for temperature distribution at 9 am of the day

Fig.5(c) Streamlines for velocity distribution



342

Fig.5(d) Streamlines for velocity distribution at time 9am of day

V. CONCLUSION

There is a good agreement between the experimental and

simulated results for outlet air temperatures. Although there

are some small discrepancies due to some experimental

imperfectness matters, we still have a good confidence in

the CFD simulation program that can be used in the future

for more complex solar collector problem.

It is found from the CFD analysis that the flow of air in

the solar flat plate collector is not properly distributed. In

order to overcome this issue we can introduce baffles at the

inlet of collector which improves the efficiency of of solar

flat plate collector.

REFERENCES

[1] D.R.Pangavhane, R.L.Sawhney, “Review of research &

development work on solar dryers for grape drying”, energy conversation and management 43(2002) 45-61

[2] Decho Thueaktphum, Kittitep Fuenkajorn,” A rock fills based solar thermal energy storage for housing”, SienceAsia 36(1010) 237-243

[3] Mohamed Selmi, Mohammed J. Al-Khawaja and Abdulhamid

Marafia, “Validation of CFD simulation for flat plate solar energy collector,” Renewable Energy 33 (2008) 383–387 .

[4] Kumaresan G, Iniyan S and Velraj R, “Experimental and CFD analysis of a solar based cooking unit”, Institute for Energy Studies,

CEG Anna University, Chennai - 600025, India.

[5] Fabio Struckmann, “Analysis of a Flat-plate Solar Collector”, 2008 MVK160 Heat and Mass Transport ,May 08, 2008, Lund, Sweden

[6] . K. Vasudeva Karanth, Manjunath M. S. and N. Yagnesh Sharma, “Numerical Simulation of a Solar Flat Plate Collector using Discrete

Transfer Radiation Model (DTRM) – A CFD Approach”, Proceedings of the World Congress on Engineering 2011 Vol III,WCE 2011, July 6 - 8, 2011, London, U.K.

[7] David Luna, Yves Jannot, Jean-Pierre Nadeau, “An oriented-design simplified model for the efficiency of a flat plate solar air collector”,

Applied thermal engineering 30 (2010) 2808-2814

[8] G. D. Rai, “Solar Energy Utilization”, Khanna Publishers, page no. 156- 199

Ijetae 0413 59

Art & Photos

Transcript of Ijetae 0413 59