Numerical Investigation on the Performance of Two Elliptical Solar Stills

Freshwater distillation using renewable energy is vital for remote and inaccessible areas, and islands. In these regions, freshwater and availability of high-grade energy are limited. Hence solar energy is feasible to evaporate water in seawater. In this study, solar stills with elliptical shell were investigated to determine water production and sustainability in terms of entropy production. The elliptical shell is oriented vertically or horizontally. Two-dimensional numerical simulation with laminar fluid flow and species transport model were conducted to the solar stills, and their performance compared with a circular shell solar still. Results showed that the circular still yielded the highest production. But the configuration exhibited larger entropy generation than that of horizontal elliptical shell. The vertical shell indicated the smallest hourly yield and the biggest exergy destruction. This is because the small cross-sectional area of the vertical shell contributed to high temperature and vapor mass fraction inside the distillation chamber. Therefore, the performance of the vertical elliptical solar distiller is minimum. Water production and entropy production of circular, horizontal, vertical elliptical shells are respectively 0.81, 0.78, 0.77 kg/(hr.m2) and 0.61, 0.57, 0.62 W/(m3.K). Diffusive entropy generation earned the largest portion followed by thermal entropy generation and frictional entropy generation. The largest local volumetric entropy generation was observed at the peak of the shell and two sides of the water surface.