The present work aims to study the possibility of enhancing and increasing the productivity of fresh water from the double slope solar still by improving the performance of its condenser. Single basin asymmetrical double sloped solar still was employed during this study. The study was carried out on the roof of Agricultural Engineering Department, Suez Canal University, Ismailia Governorate (Latitude and Longitude angles, respectively, are 30.62ºN and 32.27ºE, and mean altitude above the sea level is 20 m). The solar still consists mainly of a rectangular iron basin (1.80×0.80 m) and 0.10 m deep. The bottom frame was constructed of wood and insulated by 2 cm thick of rock wool. The outer walls of the bottom frame were insulated with 7 cm thick of foam. The condensing zone consists of two inclined surfaces. The first inclined surface (which has the area of 1.46 × 1.05 m2) covered with glass sheet (3 mm thick) to transmit the maximum possible of solar radiation flux incident on it. It was orientated to face the south direction with an inclination angle of 20○. The second inclined surface (which has the area of 1.05×0.83 m2) covered with the same material and the same thickness. It was orientated to face the north direction with an inclination angle of 30○. Two configurations of experiments were performed. Firstly, studying the thermal performance of solar still under local climatic conditions. Secondly, exam lowering the northern glass cover temperature by shading it. This procedure lowered the high temperature of the northern cover, thus the temperature difference between water and northern cover was increased. The solar radiation intensity, wind speed, ambient temperature, amount of fresh water productivity and temperature of other components of the solar still were continuously measured.
The experimental results revealed that, the daily average productivity of fresh water during the first and second configurations was found to be 2.9 and 3.3 l/d, respectively, with an increasing of 13.79%. The maximum values of heat transfer coefficient inside the solar still were 2.2, 7.5 and 33.3 W/m2 K for convective, radiative, and evaporative coefficients, respectively. Because of the evaporative heat transfer coefficient strongly depends on the operating water temperature it was had the highest value. It was also found that, the maximum amount of heat losses that occur in the solar still was the radiation and convection heat transfer from glass to ambient air.