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Performance Enhancement Study on Single Basin Double Slope Solar Still Using Flat Plate Collector

Suresh babu.k, S.Chinnathambi, M.Sridharan
Department of Mechanical Engineering, Saranathan College of Engineering, Panjapur, Tiruchirapalli, India
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The major source of water in the earth is ocean, which is of high salinity.To desalinate the saline water large amount of energy have to employed, a renewable energy like solar energy is utilized it will be a promising source for desalination. The main objective of this research is to utilize the FPC solar water heater effectively for solar still productivity enhancement at an optimal cost.Probably its performance will be one of the best for water production in remote, arid to semi-arid, small communities, where fresh water is unavailable. The experiment is carried out in a typical day in a melded climatic condition at Trichy (10°8050'N, 78°6856' E), Tamilnadu, India. The basin water depth is maintained in 0.02m throughout the study. The performance of the setup is studied theoretically and experimentally. It proves that 77% higher yield when compared to the single basin double slope passive solar still.


FPC, Solar Still, Desalination, Optimal Cost, Efficient etc...


Basic need for all living beings is clean water but manmade products are affecting it adversely through pollution. The global water resource is classified into two: sea water and fresh water (in the form of deep wells and natural aqueducts). Sea water covers the major part of the resource ie. 97.5% and 2.5% of fresh water is available in which human can use only 1% for the purpose of drinking and agriculture due to reachability. By 2025, Due to the scarcity of fresh water, two thirds of the human population in the world will have shortage of drinking water. Supply of the fresh water is decreasing whereas the demand is increasing rapidly. Now our technology has an important role to match the supply of the fresh water with the demand. In the present scenario, people accept the technology created by the scientist when it is ecologically friendly and economically viable. Most of the desalination technologies does not satisfy the above considerations.
In rural areas, nowadays solar distillation has become very popular. Comparing with the other available method, it is very simple and more economical. The method incorporated in solar still is similar to the natural hydrological cycle of evaporation and condensation but the process is carried out in a very small closed system. There is an inclined transparent cover through which the solar energy reaches the basin water. In the inner surface of the transparent cover, water will be condensed before which the water is heated and evaporated. Microbes and contaminates in the water stays on the basis during evaporation and the water is collected in a separate container. Single-basin type solar still has a simple construction and operation. It is also termed as Passive solar still (PSS). Due to the season, region and intensity of solar radiation, it has Low yield of about 2 kg/dm2 (winter) to 5.5 kg/d m2(summer) which is main drawback of PSS[3]. For Productivity enhancement, various designs like weir type, concave type and tube type were also reported. An active mode of operation is developed through considerable research to enhance the yield of solar still[2]. An additional thermal energy like solar collectors or another heat source is supplied to increase the temperature of the water in Active solar still (ASS). Modification in design includes the increase in cost and difficulty in operation. It is reported that solar still integrated with flat plate collector type solar water heater is not done through experimental work in any of the literatures.


The aim of the work is to increase the basin water temperature economically. By utilizing the solar water heater, the basin water temperature is increased. The passive solar distillation system is a slow process for purification of saline/brackish water in solar desalination. To enhance the daily yield many options such as use of various materials for condensing covers, hybrid solar still with parabolic concentrator and evacuated tubeand flat plate collector hadbeen tried by researchers. Due to low maintenance cost and simple design flat plat collector is widely used[1]. When flat plate collector solar water heater is integrated with solar still, extra thermal energy is supplied to the basin water from the storage tank and hence rise in water temperature is more when compared to passive solar still. The objectives of the present studies are
1. Thermal modelling of double slope active solar still under natural circulation mode without considering the heat capacity of condensing cover and thermal insulation. 2. To do experimental study of the flat plate solar water heater integrated with the double slope solar still. India has an abundance of solar energy, many people realized that andadopted solar water heaters. The climatic conditions of the area where the solar water heater [5] is used and the user requirement will decide the FPC solar water heater usage. A survey was taken in solar water heater users in Trichy, Tamilnadu, India over 80% people did not prefer hot water bathing during the summer. In this condition storage tank water will be in higher temperature for a long time, eventually heat losses will be in there. Our present study makes this unusable time of solar water heater for enhancement of productivity in single basin double slope solar still. Eventually the flat plate collector has been made to utilize the solar energy for further heating of the water in natural circulation. By this work the FPC solar water heater and single basin double slope solar still is integrated to work in a hybrid mode. The hybrid system leads to enhancement in productivity with utilization of hot water. The performance of the hybrid active solar still is tested in various methods and also the theoretical and experimental results are validated.
A.Experimental setu p and observations
The schematic diagram of the hybrid single basin double slope solar still is shown in the Figure1. The basin area of single basin double slope solar still is 1m2and 2m2area of flat plate collector is used. The single basin double slope solar still is connected with storage tank of the flat plate collector solar water heater i.e. hot waterfrom the storage tank enters into the solar still under natural circulation. The circulation of water through solar still basin is controlled by a gate valve which is provided in the inlet pipe. A 4mm thick plane glass[14]is used as the condensing cover inclined at an angle 11° to the basin of solar still. The thermocol is used as insulation for the still basin [11].To receive the maximum possible solar radiation, the collector plate is placed in south and inclined at 25° whereas the double slope solar still faces the east-west direction.The solar energy is absorbed by the collector plate and the energy is transferred to the water flowing through the tubes which is then collected in the storage tank. To attain a high absorptivity, black paint is used in the bottom of the solar still surface [3]. For both active and passive mode, the depth of the water should be of 0.02m. At morning 7, experiment should be started. The parameters like solar intensity on the glass cover[9], ambient temperature, distillate yield, temperature of the water and outer condensing cover are measured for continuous 24hours as hourly basis[6].


Energy balance equations for modelling double slope solar still: Tiwari et al. [2] developed the thermal models for flat plate collectors and for various collectors. The following assumptions were taken into consideration for writing energy balance equations for different components of a double slope active solar still:
1. Thermal capacity of insulating material of wall of solar still andglass covers are neglected. 2. The water inside the basinhas no temperature gradient. 3. The condition of the system is under quasi-steady state. 4. The average temperature of water in upper and lower header of flat plate collectoris equal to the average temperature of water column in the basin. 5. The connecting pipe between the flat plate collector andsolar stillare perfectly insulated

Energy balances on east condensing cover:

The energy balance for inner and outer surfaces of east condensing cover are as follows Inner condensing cover
UEW: Internal radiative heat transfer coefficient between east and west condensing cover (W/m2°C) Ubw: Heat transfer coefficient between basin liner and water (W/m2°C) Uba: Heat transfer coefficient between basin liner and ambient air (W/m2°C) Ua: Overall heat transfer coefficient between outer condensing cover and ambient air (W/m2°C)


E : East side
W : West side
C : Collector plate
W : Water
Ci : Inner condensing cover
Co : Outer condensing cover
A : Ambient
b : Basin liner

Greek Letters

αg′: Fraction of solar energy absorbed by glass cover
αb′: Fraction of solar energy absorbed by basin water
εg: Emissivity of glass cover
εW: Emissivity of water
(ατ): Effective absorptance – transmittance product