Parametric study of a vertical solar still under desert climatic conditions

Solar distillation of brackish water is a practical alternative which offers life to those regions where the lack of fresh water hinders development. In arid zones of Algeria, there is an abundance of the sun’s energy where the shortage of fresh water is more critical; these arid zones have the highest solar radiation intensities for a long period during the year, particularly in Adrar. Shallow horizontal-basin solar stills are simple to construct, reliable and cost effective. Other types of solar distillation can produce more water than shallow horizontal-basin solar stills, but they are more complicated. For this simple model we chose to construct a vertical solar still, low in cost, easily made and installed. The prototype, with a vertical flat absorber surface of 0.817 m2 made from black sponged cloth, has a total glass cover area of 0.8769 m2. The vertical still was constructed and tested in the summer from May to July, 2003, and in the autumn from September to November on the platform of the solar station at Adrar (latitude: 27°53NN), (longitude: 0°17NW), 364 m above sea level. In this paper a vertical solar still was built and tested to study parametric values affecting the performance of the still under desert climatic conditions: effects of saline water input and output temperature to the still, ambient temperature, cover glass temperature, solar radiation and orientation of the still and productivity of still. A 4-month study showed that the productivity of the vertical still strongly depended on solar radiation, ambient temperature and solar orientation. The daily still productivity varied from 0.5 to 2.3 kg/m2 on the sponged cloth area.

A prototype of a vertical solar still was built and tested in the desert climate of Adrar, Algeria. A preliminary test was carried out to investigate the effect of different parameters on its performance. The latent heat of condensation of water vapour in our prototype raised the temperature of the glass cover but was lost to the environment. This results in a low temperature difference between the glass cover and film water on spongy cloth. Since the rate of evaporation of water from the tray depends on this temperature difference, and on the presence of saturated water in the space between the glass cover and the water film surface, the yield of distillate water from the still was consequently reduced and a low thermal efficiency of the still was obtained. The still’s orientation should be in the direction at which the highest average incident solar radiation is obtained. Further study of the effect of inclination is recommended, as well as looking into the feed water system and water distributor, which are not satisfactory at present.