Optimal size of spherical rock salt balls as low-cost thermal storage materials for performance augmentation of hemispherical solar distillers: Experimental investigation and thermo-economic analysis

Passive solar distiller is one of the vital solutions to alleviate freshwater shortage problems. However, the production from solar distillers is limited due to their low efficiency. In this work, an experimental investigation is carried out to ameliorate the freshwater product of a hemispheric solar distillatory. Spherical rock salt balls are embedded in the basin saline water to improve the absorption rates for efficacious heat transfer of salty water and also act as a low-cost sensible energy storage material to promote the basin saltwater temperature in the inadequacy of solar irradiation periods. To determine the optimum size of the spherical salt balls that maximizes the best freshwater production of hemispherical distillers, four diversified sizes of salt balls (0.50, 1.0, 1.50, and 2.0 cm) are investigated and compared with the reference hemispheric solar distillatory (RHSD) under the same hot conditions of ElOued, Algeria. The findings indicated that the freshwater product of hemispheric solar distillers for using the spherical rock salt balls reached 6.77, 6.25, 5.92, and 5.67 kg/day.m² for spherical rock salt balls sizes of 2.0, 1.50, 1.0, and 0.50 cm, respectively, compared to 4.65 kg/day.m² yielded by the RHSD. The enhancement in the freshwater production for the usage of spherical rock salt balls reached 45.6%, 34.4%, 27.3%, and 21.9%, respectively. Moreover, under these conditions, the amelioration in the daily energy efficiency for utilizing the spherical rock balls is estimated to be 43.91%, 33.22%, 26.10, and 21.13%, respectively, compared to the RHSD. Additionally, the hemispheric distillers using the spherical salt balls show respectively a 28.83%, 23.47%, 19.73%, and 16.84% reduction in the freshwater production cost in comparison with that of RHSD. Conclusively, it is inferred that spherical salt balls with a size of 2.0 cm achieved the maximum thermo-economic performance of the hemispheric solar distillatory.