Experimental and theoretical analysis of single sloped basin type solar still consisting of multiple low thermal inertia floating porous absorbers

This paper presents the experimental and theoretical work, conducted in central India at Rewa (M.P.) (24°32″N, 81°18″E) to analyse the performance of modified basin type solar still, incorporating multiple low thermal inertia porous absorbers, floated adjacent to each other on the basin water with the help of thermocol insulation. The porous absorbers were made up of ordinary blackened jute cloth. Multiple floating absorbers of smaller width ensured that the absorber surface was always wet due to capillary action and there were no dry spots. Due to low thermal inertia of the porous absorber, quicker start-up times, as well as higher operating temperatures were achieved resulting in higher distillate yield. Also, the increase in the evaporation surface area further aided the performance. In order to evaluate the improvement obtained by the modification, the performance of the modified still was compared with a conventional basin type solar still of same size, under similar operating conditions on both clear and partially clear days. The results indicate that on clear days, about 68% more distillate output was obtained by the modified still, whereas it was nearly 35% more on cloudy days. Since the basin water beneath the floating insulation remained warm enough during the off shine hours, reasonable amount of nocturnal distillate output was also obtained from the modified still. A twin reflector booster was constructed by placing two plane mirrors mutually perpendicular to each other. On applying the twin reflector booster with the modified still an increase in the yield by 79% was obtained over the modified still without booster. The basin water depth does not have any significant effect on the performance of the modified still; therefore the modification can be effectively applied on deep basin stills also. Results obtained from the thermal model have fair agreement with the experimental values. The effect of wind transfer coefficient, base heat loss coefficient and the floating insulation heat transfer coefficient has also been theoretically analysed.

► Better output is obtained due to quicker start-up and higher operating temperatures.
► Base and side heat losses are much less. Water depth has insignificant effect.
► Output gain of 68% on clear day and 35% on partially clear day is obtained.
► Twin reflector booster gives 79% gain over modified still without booster.
► Thermal model gives effect of heat transfer coefficients and performance accurately.