Effects of water thickness and glazing slope on the performance of a double-effect solar still

•The simultaneous reduction in the water thickness of both basins from 2 to 1.2 cm reduced the diurnal yield of the system due to the glazing slope and the influence of the upper water on the temperature of the lower glazing.•The conditions at the top bounding surfaces of both compartments influenced the air temperatures in both cavities, particularly with an increase in air gap.•The optimum glazing slope for temperature and yield improvements was achieved at La+15°.•Increasing the slope from La to La+15° improved the distillate yield by 47.9%.•The evaporative heat transfer coefficients in both basins showed significant improvement with an increase in temperature difference compared to the convective coefficients. This paper presents the effects of water thickness and glazing slope on the performance of a double-effect solar still. The effect of the air gap between the water interface and the glazing was also considered. Energy balance equations were developed for the different components of the system. The development of the equations was made considering the thermal resistances offered by the humid-air media in both chambers of the double-effect still. Numerical computation was conducted for a typical day in Owerri. The results obtained were compared with data from a previous experimental study. The water temperatures in the upper and lower basins increased with a reduction in thickness. However, the yield profile did not follow a similar trend to that of the temperature. This was attributed to the influence of the upper water on the lower-glazing temperature. The temperatures of the still components initially reduced with a deviation from the latitude angle (La) and later increased with an increase in glazing slope. The diurnal yield of the system attained a maximum value of 3.04 kg/m2 at an optimum angle of La+15∘ Increasing the glazing slope from La to La+15∘ improved the distillate yield by 47.9%.