Effect of humidity level and aspect ratio on convective heat transfer coefficient and water productivity of a solar still: Experimental and theoretical analysis

Abstract

This article proposes a new correlation to estimate the convective heat transfer coefficient inside the evaporation chamber (enclosed space over the basin) of a single slope solar still with a low humidity level. The Rayleigh number, aspect ratio (width to the average height of chamber) and the relative humidity of the chamber are the main variables in proposed correlation. Existing models use only Rayleigh number to characterise the convection and neglect the effect of vapour pressure. Therefore, they fail to accurately predict the convection in higher water temperatures or in unsaturated humidity levels. In this work, the natural convection Nusselt number is generated based on a theoretical approach and the constant values in the correlation are calculated using the multiple linear regression analysis on experimental data obtained in this work. The transient thermal model of solar still using the new correlation predicts daily water yield within 7.6% of experiments under different humidity levels and aspect ratios. Higher performance is obtained in larger aspect ratio and lower humidity inside solar still. The modified solar still with a relative humidity of 62% generated 3.49 kg m−2 d−1 of water during summer in Melbourne, demonstrating an 18% increase in water yield.