Numerical analysis of a solar still with phase change material under the basin

The present paper is aimed to analyze the effect of energy storage by adding phase change material (PCM) on the bottom of a solar still, via a transient numerical study. A detailed validation was made by comparing the numerical results with experimental and numerical data reported in the literature, obtaining a <1 % relative difference. The simulations were made with the ambient conditions of the two solstices (Jun 21st and Dec 21st) in a city with a desert climate. Four different materials were used to analyze the effect of adding PCM with different phase change temperatures and latent heat. Also, three PCM thicknesses were analyzed for the case with RT70 HC (1, 0.5, and 0.25 cm). A reference case (without PCM) is proposed for the comparison. The hourly and cumulative productivity is presented for each case, and the temperature and water vapor mass fraction contours and velocity vectors for the case with the best performance. Besides, overall efficiency and the Stefan number were calculated as performance indicators. The material RT70 HC is the one with bigger improvement, despite it was not completely melted. Because of this, the mass of PCM was considered a parameter. In the best case, the cumulative productivity increases from 4.53 to 5.42 kg/m², which increases the overall efficiency from 55.78 to 66.70 %. The RT70 HC could store up to 70.42 units of latent heat per unit of sensible heat.