Experimental Study On Desalination Of Basin Type Solar Stills

In recent years, the problems of freshwater and energy became serious in China. More and more areas are facing freshwater shortage, especially in the remote areas, land-far islands and sailing vessels, where electricity is also in short. Solar desalination technology is an effective way to provide fresh water with less or even no electricity consumption. This paper studied experimentally characteristics of an inclined type still and a floating type solar still and provided a group of empirical correlations to predicate distillate production rate.Inclined falling film evaporation was studied through heating electrically under various operating conditions, including heat flux density, feed water flow rate, tilt angle and cooling water flow rate. The distillate production rate increased linearly with the increase of heat flux density. If the feed water flow rate was in the range of5.5～10.0kg·h-1·m-1, the distillate production rate increased linearly as the feed water flow rate decreased; and if it was0.7～5.5kg·h-1·m-1, the feed water flow rate had a less effect on the distillate production rate. If the tilt angle varied from15to60°, the still’s distillate production rate had an increasing trend with the increase of angle. The distillate production rate would improve when cooling water flowed through the upper of condensing surface.Outdoor experimental study of a floating type solar still was conducted under different weathers and no stormy wave conditions. The results showed that solar irradiation and depth of basin water were the most important factors to the distillate productivity. The distillate productivity was significantly improved by36～65%in similar weather conditions by arranging a suspended absorber plate in the still.A solar simulation lamp, an electric fan and a motor stirrer were used in indoor conditions to simulate the floating type solar still in a sea with stormy waves. Trough the arrangements of the perforated thin aluminum sheet, wrapped in black cloth, the black sponge and nothing in the still successively, the still’s distillate production rate was investigated under different radiation density conditions. The study indicated that the distillate production rate which increased linearly with the increase of radiation density was improved by17～36%and25～66%in the first and the second case respectively. Besides, in the case, using black sponge as a suspended absorber plate in the still, the water depth, length of pipes, strength of wind and waves all affected the distillate production rate. With the increase in water depth, the distillate production rate increased to the maximum value first and then decreased. The distillate production rate increased with the increase in length of pipes, strength of wind and decreased with the increase in strength of waves.This paper brought forward a group of empirical correlations to predict distillate production rate of a basin type solar still by modifying a model of heat and mass transfer, combining boundary layer analysis methods and a natural convection heat transfer correlation in limited spaces. The predication results indicated the maximum deviation is10.5%under various operating conditions.