Thinner Walls, Slower Flow: CFD Design of a Cavity-Receiver Heat Plate for a Solar Fresh Water Generator Serving Coastal Communities

Abstract

Coastal communities in Indonesia face a persistent shortage of potable water, since abrasion renders groundwater brackish and piped supply networks do not reach many settlements. A solar-driven fresh water generator offers a decentralised remedy, and the thermal performance of such a device is governed principally by the design of its heat receiver. This study determines the cavity-receiver heat plate configuration that maximises the overall heat transfer coefficient in a small parabolic dish system, using computational fluid dynamics simulation in ANSYS Fluent to compare two designs differing in wall thickness and working-fluid velocity. Model 1 combined a wall thickness of 1 mm with a flow velocity of 0.05 m/s; Model 2 combined 2 mm with 0.15 m/s. Water was adopted as the working fluid, with temperature-dependent specific heat, density, and dynamic viscosity represented by polynomial functions. Simulation showed that Model 1 produced a uniform temperature distribution across the inner plate surface and attained the higher outlet temperature, whereas Model 2 concentrated heat at a single region and remained below 40 °C. Model 1 also exhibited the lower internal pressure and a pronounced pressure drop across the plate outlet, conditions associated with more effective absorption of concentrated radiation. The study concludes that the thinner wall reduces conductive resistance while the lower velocity lengthens residence time, and that these two effects act in the same direction. The recommended configuration is therefore a 1 mm inverted cavity operating at 0.05 m/s, which the simulation indicates can raise the working fluid to 54 °C.