Performance test of a solar still for different surface to volume ratio absorber plate with an external condenser

Abstract

Solar distillation is the lowest energy consuming desalination process as it only uses heat from solar radiation. In this study, a solar still is developed to utilize maximum solar irradiation to evaporate water andincrease the rate of condensation by an external condenser. The system is improved by modifying absorber plate with rectangular and triangular channels. This increases surface area of the absorber plate for increasing heat transfer between basin and basin water as well as surface to volume ratio of basin water. To increase condensation of vapor, the effect of an external condenser cooled by feed water is also tested. Feed water flows through the copper tubes of the condenser, cools it and maintains its temperature always below dew point. The condenser also provides extended surface area for condensation when glass surface condensation rate decreases due to excessive film condensation. The water inside tubes of the condenser pick up latent heat of condensation from the vapor condensed on its surface and preheat water. The water is further preheated by solar collector before entering the still. The experiments have been conducted to test the effect of the condenser on overall distillate output against primary glass surface condenseroutput during various temperatures of the glass surface. Different designs of absorber plate are testedfor their effects on rate of evaporation under various hours and weather conditions of several days at Rajshahi, Bangladesh. The maximum average yield obtained is 3.15 L/m2 with triangular channeled absorber plate. The effect of using the external condenser also increased the productivity by 24-30%.