PERFORMANCE OF DIFFUSION STILLS UNDER EGYPTIAN CLIMATIC CONDITIONS

The performance of diffusion stills used in solar distillation was studied theoretically under the climatic conditions of Alexandria, Egypt. The governing equations for unsteady heat and mass transfer inside vertical and inclined stills were solved numerically for the glass cover, absorber plate and the water layer. The study covered all angles of tilt between horizontal and vertical positions for the twelve months of the year. The effects of the air gap spacing, inlet water flow rate, insulation thickness and wind speed on the daily production were evaluated. The daily still productivity strongly depends on the solar radiation and ambient temperature and varies between 0.5 and 5 Kg/m 2 . An optimum angle of tilt is given for each month of the year. The daily yield increased with increasing the insulation thickness and decreasing the gap spacing or inlet water flow rate. The effect of wind speed was almost negligible up to 5 m/s.