Optimization of the Performance of a Solar Still Assisted by a Rotating Drum with a Rough Surface

Abstract

Solar still desalination system is a passive technology used to convert saline water into a fresh one. This technology is characterized by its simplicity and low cost, however it has low water yields. In this study, a rough surface rotating drum is integrated within the conventional solar still system to enhance its productivity. A mathematical model is developed to predict the water film thickness created around the rotating drum and to calculate the daily water yield of the still system taking into consideration the roughness effect. In addition, experiments were conducted in order to validate the developed model. Good agreement was obtained between the modeled and experimental results, where the maximum error obtained was less than 10%, validating the ability of the model in capturing the physics behind the operation of a solar still. Also, it was found that upon increasing the roughness ratio from 1 in the case of smooth surface to 2.2 in the case of rough surface, an enhancement of 78% was obtained in terms of the water yield production. On the other hand, an enhancement of 198% was obtained when comparing a no drum system with a system with smooth surface, and 431.1% when comparing a no drum system to a solar still system with a rough drum. A parametric study was conducted to investigate the main factors affecting the system’s performance, where it was found that the increase in roughness ratio and practical radius to length ratio leads to an increase in the productivity of the system. Furthermore, the speed of rotation and the contact angle between the drum and water should be optimized for enhanced performance. A significant increase in the optimal angular speed is observed for contact angles higher than 150ᵒ. Finally, it was found that for the same contact angle, higher the radius to length ratio is, lower the optimal angular speed, which will consequently save energy.