Vol-2 Issue-2 2017
IJARIIE-ISSN(O)-2395-4396
Computational Fluid Dynamics Analysis Of A
Building Ventilation Solar Chimney
Valmeti.Sudheer1, B.Sridhar Babu2
1
. Professor, CMR Engineering college, Hyderabad-501401
. Associate Professor, CMR Institute of technology, Hyderabad-501401
2
ABSTRACT
Solar energy is one of the most abundant renewable sources of energy. The building ventilation solar
chimney is a passive solar device which are used to improve natural ventilation in buildings and provide comfort. A
detailed thermal analysis and fluid dynamics has been carried out in this paper. To apply this analysis a three
dimensional-CFD model has been built using Ansys 16.0. The parameter of the air width of the chimney is varied
with values 0.1,0.2 and 0.3m and the results were analyzed.
Keyword: - Solar energy, solar chimney, CFD, Thermal analysis, dynamics, fluid flow
1. INTRODUCTION
Nowadays, due to enormous growth of technologies, there is an increment even in the utilization of energy
resources. In order to conserve energy and decrease the unutilized energy several energy conserving techniques are
being promoted.. On basis of energy utilization the final use of energy is usually classified in three main sectors:
industry, transport and buildings. In developed countries as a whole, the buildings sector (which includes residential
and commercial) is thefinal user of the biggest energy amount (35–45%). More than half of that energy is due to
thermal conditioning. In order to reduce this percentage, there is a growing interest in the analysis of the buildings
thermal performance researches are being carried out to increase the energy efficiency and decrease the thermal load
on buildings. Solar energy is one of the most abundant and sustainable renewable energy resources. Daily on the
earth’s surface lot of solar energy is being available but the people are using only 2% of the available solar energy.
The solar energy can be utilized in the buildings to reduce thermal load on buildings. There are two ways of
applying solar radiations into the buildings: active and passive. Amongst the passive ones are the natural convection
system which utilizes solar radiation by generation of convective flows and improves natural ventilation in buildings
and refreshes the inhabited areas. One among the passive systems is solar chimney which improves natural
ventilation in buildings by utilizing solar radiation. One of the most efficient shapes of the solar chimney is a
vertical air channel with a rectangular cross section, where one of the vertical sides is made of glass and the others
are opaque(thermal insulated) surfaces, and one absorber to absorb solar radiation to impregnate the natural
ventilation inside the buildings. The basic principle of solar chimney is that air enters into the room from the
ventilations provided at the top of the room, the solar radiation crosses across the glass and falls on the absorber
plate which absorbs maximum amount of solar radiation and gets heated up. This absorber plate transfers the heat
energy to the air inside the building, the density of the heated air decreases thereby causing a flow of air towards top
of the chimney, this low dense high temperature air passes through the outlet vent and gets evacuated into the
atmosphere. The back of the absorber wall is provided with insulation so that the heat absorbed by the absorber
doesn’t get transferred into the inside room and proper temperature is maintained eventually and cause thermal
comfort. Maria Jose, Ana Maria and Antonio Joseet al.[2] has conducted an numerical simulation(CFD model) and
exergetic analysis of solar chimney and evaluated results with the experimental results which was conducted by K.S.
Ong, C.C. Chowet al.[1], who conducted experimental and mathematical modeling on building ventilated vertical
wall type solar chimney at different solar radiation intensities. Long Shi, Guomin Zhanget al.[3] has developed an
empirical model and found out the performance of solar chimney by varying both room and cavity configurations.
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Gan and Riffatet al.[4] has developed a CFD model and evaluated a particular type of solar chimney combined with
a heat exchanger for heat recovery using simple boundary conditions of constant heat flux. Wei et al.[5], carried out
analysis using CFD techniques. In this parametric analysis of two connected solar chimneys integrated in a twostorey house in China has been done.
2. MODELLING METHODOLOGY
A numerical simulation of the thermal and fluid dynamic behavior of the solar chimney has been done with the Fluid
Dynamic Computational Code FLUENT 16.0, which solves the Navier Stokesequations by the finite volumes
method. The geometry of the solar chimney is shown as below:
Fig. 1: Schematic of Solar Chimney
The materials used are XPS (Extruded Polystyrene) sheets of 20mm thick is used for supporting walls and it is also
used as an insulator provided behind the absorber plate. Aluminum sheet of 2mm thick coated with black paint is
used as absorber. A polycarbonate sheet of 3mm is used as glazing surface. The dimensions of chimney are 1.82m
height, 0.1m air chamber thickness, 1.2m width and 0.45m depth. An air inlet vent of 0.62m x 0.45m is provided.
The air channel width is varied with values 0.1m, 0.2m and 0.3m.
Fig. 2: Dimensions of the Modelled Solar Chimney
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A model is developed in Creo 2.0 with the dimensions and the required geometry. A mesh is developed with a cut
cell method of rectangular cross section with mesh cells ranging between 1,00,000 to 1 million were tested by
applying boundary conditions.
The model is solved by the stationary viscous flow including the energy. For natural air convection, the Boussinesq
approach has been considered and for turbulence motion, the K-epsilon (RNG)model with Enhancement wall
treatment condition is taken and for solar radiation, the DO (Discrete Ordinates) model at the latitude of calicut that
is 11.25° N and longitude of 75.78° E is considered. The ploy carbonate properties are 2315 kg/m3 density, 750 J/kg
K specificheat at constant pressure, 1.15 W/m K thermal conductivity, 1.52refraction index, 0.9 external emission is
considered. The opaque (XPS) walls have the following properties: density 45 kg/m3, specific heat 1500 J/kg K and
thermal conductivity 0.045 W/m K and they are opaque with regard to solar radiation. The inlet velocity of 0.2 m/s
is considered while calculating the velocity of air inside the solar chimney. The analysis has been carried out with
solar radiation intensity of 800 W/m2 with varying chimney air width of 0.1m, 0.2m and 0.3m.
Fig. 3: Cross Sectional view of Modelled Geometry
3. RESULTS AND DISCUSSION
Case 1: Consider the air gap of 0.3 m, the static temperature results show that the maximum temperature of 401 K is
obtained which could be observed at the top section of the absorber. The fluid inside the solar chimney has the
temperature range between 300 K and 391 K.
Fig. 4: Temperature distribution on the Absorber
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Fig. 5: Temperature distribution of Fluid inside Solar Chimney
The maximum velocity obtained is 1.75 m/s which is observed nearly at the air gap near the absorber plate.
Fig. 6: Velocity distribution of Fluid inside Solar Chimney
The average velocity of air at the outlet of the vent is 0.72 m/s. Streamlines of 500 are applied to the fluid flow to
get the direction of streamlines along the flow. In this case 1 as the air gap width of 0.3m, we could observe some
amount of air gets stagnated near the inlet of air gap.
Fig. 7: Streamlines of Fluid Flow inside the Solar Chimney
Case 2: Consider the air gap of 0.2 m, the static temperature results show that the maximum temperature of 409 K is
obtained which could be observed at the top section of the absorber. The fluid inside the solar chimney has the
temperature range between 300 K and 404 K.
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Fig. 8: Temperature distribution of Fluid inside Solar Chimney
The maximum velocity obtained is 1.97 m/s which is observed nearly at the air gap near the absorber plate.
Fig. 9: Velocity distribution of Fluid inside Solar Chimney
The average velocity of air at the outlet of the vent is 0.94 m/s. Streamlines of 500 are applied to the fluid flow to
get the direction of streamlines along the flow. In this case 2 as the air gap width of 0.2m, here we could observe
that no air gets stagnated near the inlet of air gap as in case of case 1.
Fig. 10: Streamlines of Fluid Flow inside Solar Chimney
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Case 3: Consider the air gap of 0.1 m, the static temperature results show that the maximum temperature of 419 K is
obtained which could be observed at the top section of the absorber. The fluid inside the solar chimney has the
temperature range between 300 K and 410 K
Fig. 11: Temperature distribution of Fluid inside Solar Chimney
The maximum velocity obtained is 2.48 m/s which is observed nearly at the air gap near the absorber plate.
Fig. 12: Velocity distribution of Fluid inside Solar Chimney
The average velocity of air at the outlet of the vent is 1.27 m/s. Streamlines of 500 are applied to the fluid flow to
get the direction of streamlines along the flow. In this case 3 as the air gap width of 0.1m, here we could observe
that no air gets stagnated near the inlet of air gap as in case of case 1.
Fig. 13: Streamlines of Fluid flow inside Solar Chimney
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The variation of pressure inside then solar chimney is observed as the minimum value at the air gap near absorber
and maximum at the inlet vent which is same in all three cases.
Fig. 14: The graph plotted between Temperature Vs Air gap
Fig. 15: The graph plotted between velocity and air gaps of 0.1m, 0.2m and 0.3m.
4. CONCLUSION
In this paper a CFD – three dimensional model is generated and thermal and fluid dynamic behaviour inside the
solar chimney for three cases that is air gap of 0.3m, 0.2m and 0.1 were analyzed. It is observed that the outlet
velocity for the case 3 lower air gap of 0.1m is more compared to other two cases. And it is observed that in case 1
that is for air gap of 0.3m, some amount of stagnant air is observed at the entrance of air near the absorber. So, it
can be concluded that as air gap increases there in decrease in velocity of air. No reverse flow of air is observed even
at maximum air gap of 0.3m. The similar variation is observed with respect to temperature distribution inside the
solar chimney that is the temperature of the fluid is more for air gap of 0.1m that is in case 1 compared to other two
cases. By decreasing the air gap from 0.3m to 0.2m nearly13.92% of outlet velocity increase has been observed.
Further decresing it to 0.1m from 0.3m, 44.18% of increase in outlet velocity is observed.
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5. REFERENCES
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