A comprehensive numerical investigation of the performance of solar stills with various designs

Passive solar distillers are widely used due to their portability and simplicity. Passive solar stills have various designs. However, no study in the literature has compared them according to the laws of thermodynamics. In this paper, five passive solar stills were investigated numerically to evaluate their water productivity and entropy generation. Laminar flow and a 2D computational domain of humid air in still enclosures were simulated using the species transport model. The solar stills included two double-slope solar stills (DSS1 and DSS2), a single-slope still (SSS), a tubular solar still (TuSS), and a triangle solar still (TrSS). All of the stills had an identical water surface length of 102 mm. The effects of the water surface temperature, which ranged from 50degree celsius to 80degree celsius, on convection heat transfer, freshwater production, and entropy generation were investigated. The simulation results showed that the TuSS obtained the highest water production and the smallest total entropy generation. At high operating temperatures, the productivity of the TuSS was nearly two times that of the SSS. Two recirculating zones were observed inside the distillation enclosures, except for the SSS. When the water temperature was greater or lower than 53degree celsius, one recirculating zone and three recirculating zones were created in the SSS, respectively. The change in the number of vortices caused distinct transport characteristics in the SSS. An impinging jet on the water surface in the DSS2 led to the largest entropy generation among the examined stills. Large dead zones on the water surface of the DSS1 caused a reduction in evaporation. Therefore, the TuSS and TrSS designs eliminated the zones due to clearances between the water surface and glass cover.