Augmenting the productivity of tubular solar still using low-cost energy storage materials

Productivity improvement is one of the high-priority areas in the development of solar stills. The present work describes the use of some low-cost energy storage materials such as sand, gravels, and black granite as potential candidates to improve the productivity of the tubular solar still (TSS). The experimental studies have been carried out at Nagpur (21.1241° N, 79.0023° E) to investigate the effects of these materials on the productivity of the TSS. Three separate TSS experimental setups have been made for each energy storage materials. These include (a) 5 kg of fine sand (0.125-0.25-mm grain size), (b) small gravels (20-30 mm), and (c) black granite (5-mm thickness) placed in the absorber basin of individual TSS setup, separately. The experiments have been performed by varying basin water depth at 0.5 cm, 1 cm, and 2 cm, for each case. The results show that for water depth of 0.5 cm, productivity of TSS-Black granite is enhanced by 10.5% and 34.88% as compared to TSS-Gravel case and TSS-Sand case, respectively. Thermal efficiency and exergy efficiency of TSS-Black granite at 0.5-cm water depth is enhanced by (32.4%, 9.8%) and (92.1%, 21.9%) as compared to TSS-Sand case and TSS-Gravel case, respectively. Furthermore, it has been estimated that the cost of production of freshwater using TSS-Black granite is lowest among all selected combinations.