Effect of wind speed on active and passive solar stills

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)over dot(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. (C) 2003 Elsevier Ltd. All rights reserved.