Thermal performance of a single basin solar still with PCM as a storage medium

Transient mathematical models are presented for a single slope-single basin solar still with and without phase change material (PCM) under the basin liner of the still. Analytical expressions for temperatures of the still elements and the PCM have been obtained. The still performance has been investigated by computer simulation. Numerical calculations have been carried out, using stearic acid as a PCM, on typical summer and winter days in Jeddah (lat. 21 degrees 42' N, long. 39 degrees 11' E), Saudi Arabia. Effect of mass of the PCM (m(pcm)) on the daylight P-dl, overnight P-on and daily productivity P-d and efficiency eta(d) of the still for different masses of basin water m(w) has been investigated. It is found that P-dl decreases as m(pcm) increases; but P-on and P-d increase significantly with an increase of m(pcm) due to the increased amount of the heat stored within the PCM. During discharging of the PCM, the convective heat transfer coefficient from the basin liner to basin water is doubled; thus, the evaporative heat transfer coefficient is increased by 27% on using 3.3 cm of stearic acid beneath the basin liner. Therefore, on a summer day, a value of P-d of 9.005 (kg/m(2) day) with a daily efficiency of 85.3% has been obtained compared to 4.998 (kg/m(2) day) when the still is used without the PCM. The PCM is more effective for lower masses of basin water on winter season. (C) 2008 Elsevier Ltd. All rights reserved.