Dual Purpose Public Walkways as Passive Solar Collectors for Freshwater Yield Improvement in Basin Solar Distillers

This paper aims to examine the possibility of refurbishing pavements of public parks into passive solar collectors to preheat the feedwater and boost productivity of single-basin solar stills. It is aimed at converting an unused urban surface into an affordable thermal surface to produce freshwater. An implicit finite-difference scheme was created based on transient, heat transfer in three domains: the walkway slab, shallow sub-surface water duct, and a solar still (basin liner, thin water layer and glass cover) and balances the energy of all domains using transient, time-dependent conditions under realistic solar, ambient and wind. The model has the surface radiative and convective losses, conduction through the walkway and advective heating of flowing feedwater prior to entering the still. Findings indicate that addition of walkway boosts the annual output of distillate by about 32% relative to when a standalone still is used, and amount of radiative loss on collector surface is approximately 5.8 times higher than amount of convective loss, and much depends on orientation of wind. The parametric analysis indicates that increased rates of water mass flow can significantly increase the yield, thinner water ducts can increase the heat transfer and evaporation, but the thickness and depth of walkways do not have a significant effect within the bounds of their structures. These results show that standard city infrastructure can be used as an example of a zero-cost thermal preheater, which provides a feasible, scalable path to enhance freshwater generation in solar desalination systems without extra land or specific collectors.