Effect of wind speed on active and passive solar stills

Abstract

The effect of wind speed V on the daily productivity P d of some active and passive solar stills is studied by computer simulation. Numerical calculations have been carried out on typical summer and winter days in Tanta in order to correlate P d with V for different masses of basin water m w for the passive stills and various thicknesses d w or mass flow rates m ̇ w of the flowing brine for the active stills. It is found that for the active and multi-effect passive stills, P d increases with the increase of V up to a typical velocity V t beyond which the increase in P d becomes insignificant. However, for all the investigated single effect passive stills, there is a critical mass (depth) of basin water beyond which P d increases as V increases until V t. For basin water masses less than the critical mass, P d is found to decrease with increasing V until V t. After V t, the change in P d is unimportant in a similar behavior to that obtained for the active and multi-effect passive stills. The critical mass (depth) of basin water for the investigated single effect passive stills is found to be 45 kg (4.5 cm). Moreover, the typical velocity V t is independent on the still shape and the mode of operation (active or passive) but it shows some seasonal dependence. For the investigated stills, V t is found to be 10 and 8 m/s on typical summer and winter days, respectively. Comparisons with the results reported in the previous studies about the effect of wind speed on productivity have been carried out.