Effect of phase change material on augmentation of

fresh water production of a triangular pyramid solar still

Ravishankar S, M.E., (PhD)

Research Associate

Department of Mechanical Engineering

Hindustan Institute of Technology and Science

Chennai

Hyacinth J Kennady

Professor

Department of Mechanical Engineering

Hindustan Institute of Technology and Science

Chennai

P.K.Nagarajan

Professor

Department of Mechanical Engineering

S.A. Engineering College

Chennai.

Introduction

• A need of pure water is an important phenomenon in day-to-day life. Due to increase in population growth the need of drinking water is shrinking.

• The possible ways of getting pure water is from rivers, lakes, wells, rains etc. This kind of surface water must be purified for human consumption.

• The purification of water involves the removal of un dissolved substances, dissolved substances and harmful microbes.

• The un dissolved substances are removed by sand filtration and the microbes are killed through chlorination and by boiling. Solar desalination does all the three function.

• People living in remote areas or islands, where fresh water supply by means of transport is expensive, face the problem of water shortage every day.

• Solar still presents some specific advantages for their use in these areas due to its easier construction using locally available materials, minimum operation and maintenance requirements and friendliness to the environment.

Factors affecting the efficiency of solar still

• The efficiency of the solar still depends upon the following important parameters :-

1. Tilt angle of cover plate

2. Depth of water

3. Feed water flow rate

4. Cover plate temperature

5. Effect of stills

6. Convective heat transfer from cover plate and side walls

7. Design of structures and shapes

8. Solar tracking

9. Coating

10. External enhancement like heat pipe, coolers.

Literature reviewTitle Author Interference from the study

An experiment with a plastic solar still, Desalination, 142 (2002), pp 221-227

Cappelletti. G.M Efficiency of still is 16 % due to the low temperature in the lower basin. By addition of asphalt coating on the walls increases productivity .Life of the still is less since a plastic material is used. A regular maintenance is required

Effect of water depth on the performance of an inverted absorber double basin solar still, EnergyConversion & Management 40 (1999) 1885–1897

G.N.Tiwari The yield was 11.5 kgm-2day-1 and keeps on decreasing when the depth of water increased.There is no significant increase in the productivity if the number of basin is more than three.

Title Author Interference from the study

A Hybrid Solar Desalination and Water Heating System, Desalination, 164 (2004), 2, pp. 189-195

Voropoulos. K., Mathioulakis, E., Belessiotis, V

Single basin integrated with heater.

Productivity of the still is 2.5 times than the conventional solar still.

An experimental study on a hemispherical solar still, Desalination 286 (2012) 342–348

Arunkumar. T, R. Jayaprakash , D. Denkenberger, Amimul Ahsan , M.S. Okundamiya , Sanjay Kumar, Hiroshi Tanaka ,H.S. Aybar

The average output of 3.5 l/m2/day without cooling and 4.2 l/m2/day with cooling of cover.The temperature of the inlet water can e increased by using PCM storage tanks.

Design and performance of a transportable hemispherical solar still, Renewable Energy 34 (2009) 145–150

Basel I. Ismail Typically produces 2.8 to 5.7 lm-2 day.

Title Author Interference from the study

Thermal performance of a triple basin solar still, Desalination, 174 (2005), pp 23-37

El.Sebaii.A.A Daily productivity equals 12.635 kgm-1day-1 with an average intensity of 651 Wm-2.The total daily productivity of the system is maximum for the least water masses in the lower and middle basins without dry spots over the base of the each effect

Performance of pyramid-shaped solar still: Experimental study, Desalination 291 (2012) 65-68

Yazan Taamneh , Madhar M. Taamneh

Daily yield was increased up to 25% compared to free convection solar still.For a concave wick type the replacement of wick to be carried out.The effect of tilt angle on the system performance has to be studied. This may increase the productivity.

Title Author Interference from the study

Augmentation of saline streams in solar stills integrating with a mini solar pond

Desalination 249 (2009) 143–149

V. Velmurugan , J. Mandlin , B. Stalin , K. Srithar

A mini solar pond was used to store the solar thermal energy. Theheat energy stored by the mini solar pond was used for preheatingsaline water in fin type single basin solar still and stepped solar still.Experiments were carried out with different salinity in the mini solarpond. It was found that the optimum value of salinity in solar pond water was 80 g/kg.

Solar stills integrated with a mini solar pond — analyticalsimulation and experimental validation

Desalination 216 (2007) 232–241

Velmurugan, K. Srithar

Integration of a mini solar pond with a solar still has been developed. Various experiments for the yield of the distilled water from ordinary still, still with sponge, still integrated with a pond, and still with sponge integrated with mini solar pond are being carried out. The average daily production of distilled water has been found to be increased considerably while the sponged solar still is integrated with a mini solar pond

Title Author Interference from the study

Single basin solar still with fin for enhancing productivity.

Energy Conversion and Management 49 (2008) 2602–2608

V. Velmurugan, M. Gopalakrishnan, R. Raghu , K. Srithar

he simple basin solar still was modified by using fins, spongesand wicks for augmenting its productivity. For the yield of the distilled water, various experiments were conducted for the above modifications. Experimental results showed that the average daily production was higher when fins were used in the still. The experimental analysis agreed well with the theoretical. The maximum deviation between theoretical and experimental was around 10%.The productivity increased from 1.88 to 2.8 kg/m2.

Title Author Interference from the study

Integrated performance of stepped and single basin solar stills with mini solar pondDesalination 249 (2009) 902–909

V. Velmurugan , S. Pandiarajan , P. Guruparan , L.Harihara Subramanian ,C. David Prabaharan , K. Srithar

Two types of experiments are carried out. In the first set of experiments, solar pond, stepped solar still and single basin solar still are connected in series to enhance the productivity of the solar stills. For further augmentation of the productivity, pebbles, baffle plates, fins and sponges are used in both the solar stills. A maximum productivity of 80% is obtained, when fins and sponges are used in both the solar stills. In the second set of experiments, a mini solar pond, stepped solar still and wick type solar still are connected in series. Pebbles, baffle plates, fins and sponges are used in the stepped solar still for further productivityaugmentation. The productivity during day and night are calculated. It is found that maximum productivity of 78% occurred, when fins and sponges are used in the stepped solar still. Pebbles store more thermal energy and releases after the sun set. So, more night productivity is obtained, when pebbles are used in the solar stills. Industrial effluent isused as feed. Theoretical analysis gives very good agreement with the experimental results..

Title Author Interference from the study

Single basin double slope solar still with minimum basin depth and energystoring materialsApplied Energy 87 (2010) 514–523

K.Kalidasa Murugavel,S. Sivakumar,J. Riaz Ahamed, Kn.K.S.K. Chockalingam, K. Srithar

A single basin double slope still has been fabricated and tested for different energy storing materials like 1/4 in. quartzite rock, 1/4 in. washed stones and mild steel scraps have been used in the basin with layer of water equivalent to 0.5 cm depth. To improve the production further,3/4 in. quartzite rock, 1 1/4 in. red brick piecesand 1½ in. cement concrete pieces are used in the basin with 0.75 mm depth of water. The still has been theoretically modeled.The transmittance and solar incidence variations are considered. The total radiations on the sloped covers are taken as input. The theoretical performance of the still is compared with actual still.Out of different energy storing materials used,3 /4 in. quartzite rock is the more effective which yields higher production per day.

Title Author Interference from the study

Desalination of effluent using fin type solar stillEnergy 33 (2008) 1719–1727

V. Velmurugan,C.K. Deenadayalan, H. Vinod, K. Srithar

The productivity of the single basin solar still is augmented by integrating fins at the basin plate. Effluent is used as a feed. To enhance the productivity of solar still, it is modified with fin, black rubber, sand, pebble and sponges. Distillation of settled effluent has less productivity than that of low salinity water. Also it is found that productivity increased with increase in solar intensity and decreased with increase in wind velocity. Theoretical analysis closely converges with experimental results. From experimental results, it is observed that the average evaporation rate in the conventional solar still is 1.66 l per 8 h. The evaporation rate increased by about 53% (2.54 l per 8 h) when fins were integrated at the basin plate.

Problem Identification

• Productivity of solar still is lower.• Additional accessories added to increase the

productivity

Methodology• Productivity increases by flowing water over the

glass.• Use of any other heat source such as solar collectors,

electricity, and other conventional sources.• Flat plate collector, storage tank, mini solar pond,

floating perforated plate and baffle suspended absorber are used to increase the inlet temperature of the water.

• The total daily productivity of the system is maximum for the least water masses in the lower and middle basins without dry spots over the base of the each effect.

• The effect of tilt angle on the system performance has to be studied. This may increase the productivity.

• The yield of the still is directly proportional to the plate collector area.

Experimental Investigation and approach

• Experimental investigations are performed to evaluate the performance of solar still under outdoor climatic conditions of Chennai.

• It consists of a metallic container, which is occupied by the saline water up to a certain level and below the exit collecting area where the fresh water flows to the collecting jars kept at three corners of the solar still.

• The solar radiation is transmitted through a 2 mm thick triangular glass cover with a transmissivity of 0.88.

• The bottom plate is black coated which absorbs the heat. with a allowable energy absorbed by the water, a phase transformation takes place in water.

• The evaporated water rises and reaches the inner surface of glass in inclined position.

• Vapor once again undergoes phase change from vapor to liquid.

• The condensed water flows through the channel made of ms sheet which connected to the outlet.

• The contaminated water which contains the impurities is removed by desalination process.

Experimental setup

Experimental Parameters

• The parameters used in the experiment are given in Table .

• The still temperature was recorded using K-type thermocouples and digital temperature indicators.

• The solar radiation intensity was recorded by a precision pyranometer.

Parameter Symbol Value

Transmissivity of glass τc .88

Emissivity of glass εc .98

Density of water ρ 995 kg/m3

Latent heat of vaporization hfg 2376 kJ/kg

Latitude φ 110 North

Results and Discussion

Hourly variation of distillate output on different test days without PCM

Hourly variation of distillate output on different test days with PCM

Variation of temperature difference between glass and water temperature with effect of PCM

Accumulated Yield without PCM

Accumulated Yield with PCM

Variation of solar efficiency and solar radiation without heat storage

• It can be noted that the solar still efficiency increases in the morning time till reaching maximum value around midday and then decreases at slower rate in the afternoon. It is clear that the still efficiency profiles follow similar trends as of those for solar radiation and distillate yield.

• The maximum value of solar still efficiency based on free convection reached approximately 35.2%.

• The difference between the free convection and conventional solar still fresh water production was found to be 40%.

• The increase in the freshwater production is due to the circulation of the air inside the solar still and hence the evaporation rate that has been increased by the wind velocity over the glass surface

Conclusion

• A triangular pyramid solar still with built-in sensible heat thermal energy storage system was fabricated to improve the still productivity.

• Another still with the same characteristics without LHTESS was also constructed for investigation of the internal convective and evaporative heat transfer coefficient.

• Solar still presents some specific advantages for their use in these areas due to its easier construction using locally available materials, minimum operation and maintenance requirements and friendliness to the environment for producing portable water.

• The effect of wind on the solar still shows there is a decrease in productivity during the morning hours. The daily efficiency was found to be 53% with LHTESS and 45% without LHTESS.

• Solar radiation on the test days reveals that the maximum intensity occurred during the mid-day, and the productivity shows that the solar radiation and production rate are directly proportional.

• The temperature difference between water and glass varies from 10-15.5oC during the off-shine period. Experimental results concludes that with PCM the production of fresh water improved to about 4.3 liters/day for a 24 hour operation, its due to the higher specific heat capacity.

References

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[3] Samee Muhammad Ali, Mirza Umar K, Majeed Tariq, Ahmad Nasir. Design and performance of a simple and single basin solar still. Renewable and Sustainable Energy Reviews 2007;11:543–9.

[4] Kalidasa Murugavel K, Chockalingam KnKSK, Srithar K. Progress in improving the effectiveness of the single basin passive solar still. Desalination 2008;220:677–86.

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Thank You