1.
Invention Journal of Research Technology in Engineering & Management (IJRTEM)
ISSN: 2455-3689
www.ijrtem.com Volume 1 Issue 2 ǁ March. 2016 ǁ PP 01-05
| Volume 1| Issue 2 | www.ijrtem.com | March 2016| 1 |
CFD Analysis of Single Basin Double Slope Solar Still
C. Uma Maheswari1
, B. Vinodh Reddy2
, A. Navya Sree2
, A, Vishnuvardhan Reddy2
, A. Siva
Prasad Reddy2
, C. Raghu Ram Prasad2
, B. Harish Kumar Varma2
1
Assistant Professor, Department of Mechanical Engineering, Sri Venkateswara College of Engineering and Technology, Chittoor,
Andhra Pradesh, India.
2
Department of Mechanical Engineering, Sri Venkateswara College of Engineering and Technology, Chittoor, Andhra Pradesh,
India.
Abstract : This paper deals with thethermal and CFD analysis of single basin double slope solar still. The modeling of still is done in
solid works software and CFD analysis in ANSYS. CFD analysis for different months of solar irradiance was carried out.
Maximum production rate and temperature distribution in the still was analyzed.
Keywords: Double slope solar still, CFD analysis, solar irradiance, desalination system.
1. Introduction
A lot of technology research work has been carried out on analysis of double slope solar still on their performance.In 2008
KalidasaMurugavel, K., et al.,[1].Developed the Progresses in Improving the Effectiveness of the Single Basin Passive Solar Still and
Thermal analysis was performed. In 2004 Singh, H. N., Tiwari, G. N., [2] did the Monthly Performance of Passive and Active Solar
Stills for Different Indian Climatic Conditions, depending upon the irradiance of the still. In the year 2004Eduardo Rubio, Fernandez,
J. L., Porta-Gandara, M. A.,[3]. Didthe Modellingof Thermal Asymmetries in Double Slope Solar Stills. In year 2000El-Sebaii, A. A.,
et al.[4] ,did the Year-Round Performance of a Modified Single-Basin Solar Still with Mica Plate as a Suspended Absorber, Energy, In
the year 2011[5]. KalidasaMurugavel, K., Srithar, K.[5], did the Performance Study on Basin Type Double Slope Solar Still with
Different Wick Materials and Minimum Mass of Water. The previous works dealt about the modeling and thermal analysis of still.
Main purpose of this work is to perform the CFD analysis of Double slope solar still.
2. Experimental Setup and Procedure
A single basin double slope solar still has been designed.The overall dimensions of the still is 2.3 m x 1 m x0.25 m.The
bottom and sides walls of the solar still is fabricated with mild steel of 5mm thickness. The top of the still is covered with glass plates
of 5mm thickness, inclined at 300
. Solar distillation of water is effected by introducing brackish or salt water in an air tight assembly
whose interiors are painted black. The top of the assembly is covered with an A-tent roof of a material which allows solar radiation to
pass through it, but does not let thermal radiation (emanating from interiors including the water mass) from going out. At the end of
the roof, a V-trough is provided at each of the sides for collecting distilled water. The whole unit is kept in the open in the sun. The
solar radiation passes through the top cover, gets absorbed predominantly by the blackened surface and also to some extent by the
water mass. As a result, the evaporation of water takes place filling the inside air with water vapour and leaving the salts behind. The
inside humidity increases and the condensation takes place on the underside of the top cover, which is sloped gently on both sides to
allow condensed water to trickle down into the U-troughs. A schematic diagram of a single basin double slope solar still is shown in
Figure.1
Fig 1 Single Basin Double Slope Solar Still
This way of distillation replicates the way nature makes rain. Still has a top cover made of a transparent material, i.e., glass,
and the interior surface of its base is blackened to enable absorption of solar energy to the maximum possible extent. The glass cover
allows solar radiation to pass into the still. Here the radiation is mostly absorbed by the blackened basin at the base.

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CFD Analysis Of Single Basin Double Slope Solar Still
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The water begins to heat up and the moisture content of the air, trapped between the water surface and the glass cover,
increases. The base also radiates energy in the infra-red region, which is reflected back into the still by the glass cover, so trapping g
the solar energy inside the still. Heated water vapour evaporates from the basin and condenses on the inside surface of the glass cover.
Condensed water trickles down the inclined glass cover to an interior collection trough, placed at the lower edges of the cover to
collect the distillate.
3. Numerical Analysis
3.1 Modeling
Fig 2 Assembly of Double slope solar still
The above figure 2 shows the model of double slope solar still. The double slope solar still has been modeled in Solidworks.
The still consists of the parts like container, basin, left glass plate, right glass plate and collectors on both the sides of the still are
modelled as per the dimensions.
After completion of the part modelling, open the assembly document in the Solid works. In that assembly go to insert, browse
the existing parts for assembly. By using some mates like coincide, parallel, perpendicular, the parts can assembled as per the
dimensions.
3.2 Meshing
ANSYS ICEM CFD meshing technologies provide physics preferences that help to automate the meshing process. For an
initial design, a mesh (Tetrahedral) can often be generated in batch with an initial solution run to locate regions of interest. Further
refinement can then be made to the mesh to improve the accuracy of the solution. There are physics preferences for structural, fluid,
explicit simulations. By setting physics preferences, the software adapts to more logical defaults in the meshing.
Fig 3 ICEM CFD of Air Domain
Fig 4ICEM CFD of Left glass plate Fig 5 ICEM CFD of Right glass plate

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CFD Analysis Of Single Basin Double Slope Solar Still
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Initially, IGES files of air domain, left glass and right glass of double slope solar still can be imported to Ansys. The domain
is meshed by using ICEMCFD with tetrahedral elements and the global element scale factor 1. In the mesh generation 35362 nodes,
170791 elements are generated. Near the wall of the solar still the elements were created so as to capture the fine boundary layers.
Patch dependent method is used for meshing. After application of smoothing the mesh quality of 0.3 was obtained.
4. Boundary Conditions
Mesh files of solar still are imported to the CFX Pre. In CFX Pre, physics and boundary conditions are applied on the domain
to solve the mass and momentum equation. A two phase domain is created in the frame work for liquid water and air.
Evaporation process is modeled as laminar at quasi steady, accounting for thermal energy heat transfer while considering the effects of
bouncy. A distinct interface between solid and liquid phases exists, hence both phases are continuous. To transfer heat, conservative
interface flux is taken for solid and liquid phases. For drop formation on the condensing cover platesadhesion forces are taken. All
sides are assumed to be thermal, free slip wall boundary condition is specified for both the phase
5. Results and discussions
5.1 Theoretical results:
Fig 6 Overall production of the still
The above figure 6 shows the overall production of the still for different months of the year. The still delivers around 4 L/day
of water in March and November for remaining months the still production varies between 3 to 4 L/day. In March, the solar energy
received and transmitted by the covers are higher and hence the production is also higher. In November the production rate is higher
due to lower atmospheric temperature variation and lower wind velocity. In May and July, the energy received and transmitted by the
covers is minimum.
5.2 Numerical results
5.2.1 Computational Fluid Dynamic Simulations
The performance of solar still depends upon the glass cover angle, depth of water, fabricationmaterials, temperature of water
in the basin and insulation thickness which could be modified for improving the performance. Hence, computational fluid dynamic
simulation approach is adopted to analyze the effect of different temperature distributions for air and water on the rate of evaporation
to obtain the maximum yield. In evaporation water phase change takes pace which is very difficult to model mathematically. The
complicated thermal relationship involved in the phase change of water from liquid to gas phase is accurately solved by using CFD.
CFD CFX 14.0 is used for numerical analysis to determine the temperature distribution and volume fraction.
5.2.2 Temperature distribution:
Fig 7 Air temperature distribution Fig 8 Water temperature distribution
0
3.1605468L/day
3.829245L/day
3.13544L/day
[VALUE]L/day
[VALUE]L/day
[VALUE]L/day
OVERALLPRODUCTIONRATE
L/DAY
MONTH

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CFD Analysis Of Single Basin Double Slope Solar Still
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7&8 shows the results of simulation runs 300
C to 600
C with 10
C rise in intervals. The water in the still starts warming due to
heat supplied from the bottom. Water in the system vaporizes. Temperature difference between water and glass leads to vapour
condensation .due to the temperature source applied at the bottom non uniform temperature distribution is generated inthe domain.
5.2.3 Water Volume Fraction
Fig 9 water volume fraction on right glass plate Fig 10 water volume fraction inside the solar still
Fig 9, 10 shows that the condensed water droplets on the glass as the water heated. The water temperature is higher than the glass
cover temperature. Temperature difference between water vapour and glass leads to vapour condensation on the glass surface. For
drop formation on condensing cover adhesion forces are taken into account. Droplets slip down and get collected in the trace collector
on the left side as shown in figure 10.
It is obvious that gas and liquid phase are completely apart and their interface is distinct. As shown in figures 8, 9 and 10
Liquid is seen at the different positions. When the salivated water is heated water gets evaporated ad converted into water vapour
which is condensed to obtain potable water in liquid state. ANSYS CFX gives the volume fraction of air and water which is divided
by evaporation area to obtain the amount of fresh water produced. It other words the amount of water evaporated is equal to the
amount of water condensed. The same amount of water is collected in the collectors as shown in the diagrams.
6. Comparison of Results
Fig 11 overall production rate for different months
The above figure 11 will represent about the overall production rate of the still by using experimental and numerical results.
The production rate will vary from month to month such that it is maximum in March and November in both the cases and minimum
in the month of September
7. Conclusion
In this work, a single basin double slope solar still was modelled by using solid works and CFD analysis is carried out using
ANSYS. Theoretical models were used to predict the year round performance of the solar still. ASHRAE radiation model and
meteorological data for the local place are used to estimate the irradiances received at the covers in different months. The production
rate variations for different months have been studied as a function of local time. In November and March the variations are steeper.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
january march may july september november
overallproductionrate
month
overall production rate in L/day
experimental numerical

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CFD Analysis Of Single Basin Double Slope Solar Still
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Similarly the time for maximum production rate is also different for different months. This is due to variations in irradiance incidence
on the covers, atmospheric temperature and wind velocity. The overall production is higher in March and November and it is around 4
L/day. The average production of the still is 2.0 L/day/m2. The behavior of phase change and temperature distribution is observed due
to evaporation. The temperature of water obtained by CFX and the production rate is compared with the available data.
8. Nomenclature
Sun declination δ=23.45*sin(360*(n+284)/365) in degrees
Hour angle W=15*(12-LT) in degrees
Hourly direct irradiance Ib=B*sin α*exp(-C/sin α) in watt/m2
Hourly diffuse irradiance Id=D*Ibn in watt/m2
Hourly global irradiance I=Ib+Id in watt/m2
Monthly mean hourly diffuse irradiance Ibd=0.15*Id*(1+cos(β)) in watt/m2
Monthly mean hourly direct irradiance Ibb=(I-Id)*cosθ/sin α in watt/m2
Monthly mean ground reflections Ig-r=I*ρ*0.5*(1-cos(β)) in watt/m2
Global irradiance IB=Ibd+ Ibb+ Ig-r in watt/m2
North cover Qtn=Tn*Agn*In in watt/m2
South cover Qts=Ts*Ags*Is in watt/m2
Evaporation heat transfer Qe,w-g=He,w-g*Aw*(Tw-Tg) in watt
He,w-g=0.0162*hc,w-g*((Pw-Pg)/(Tw-Tg)) in watt/m2
Production of still Mw-c=Qe,wg(t)/hfg in lt/day
References
[1]. KalidasaMurugavel, K., et al., Progresses in Improving the Effectiveness of the Single Basin Passive Solar Still, Desalination, 220 (2008),
1-3, pp. 677–686
[2]. Singh, H. N., Tiwari, G. N., Monthly Performance of Passive and Active Solar Stills for Different Indian Climatic Conditions, Desalination,
168 (2004), 15, pp. 145-150
[3]. Eduardo Rubio, Fernandez, J. L., Porta-Gandara, M. A., Modelling Thermal Asymmetries in Double Slope Solar Stills, Renewable Energy,
29 (2004), 6, pp. 895-906
[4] El-Sebaii, A. A., et al., Year-Round Performance of a Modified Single-Basin Solar Still with Mica Plate as a Suspended Absorber, Energy,
25(2000), 1, pp. 35-49
[5]. KalidasaMurugavel, K., Srithar, K., Performance Study on Basin Type Double Slope Solar Still with Different Wick Materials and
Minimum Mass of Water, Renewable Energy, 36 (2011), 2, pp. 612-620
[6]. KalidasaMurugavel, K., et al., Experimental Analysis on Variation of Transmittance of Different Thickness Window Glasses at Different
Solar Insolation Conditions, 3rd BSME-ASME International Conference on Thermal Engineering, Dhaka, Bangladesh, B. A. 048
(2006),http://bsmeicte2012.iutoicdhaka.edu/proceedings/3rd-bsme-asme-icte-indexret-.html
[7]. ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigeration and Air-Conditioning Engineers, Atlanta, Geo., USA,
1985
[8]. Parishwad, G. V., et al., Estimation of Hourly Solar Radiation for India, Renewable Energy, 12 (1997), pp. 303-313
[9]. KalidasaMurugavel, K., et al., Single Basin Double Slope Solar Still with Minimum Basin Depth and Energy Storing Materials, Applied
Energy, 87 (2010), 2, pp. 514-523