Advanced design techniques in passive and active tubular solar stills: a review.

Clean water production using green energy supply plays a significant role in the globe's health and economic development. In recent years, so much importance is given on developing the advanced designs of solar stills to improvise the productivity of conventional solar stills. Tubular solar stills (TSSs) are one of the emerging areas to improve clean water productivity. This paper's main aim is detailed review of passive and active tubular solar still design specifications and highlighting the specific merit of each design. The common tube materials in passive and active TSS are glass, stainless Steel 304, vinyl chloride, flexi glass, poly carbonate, and poly ethylene with variation in thickness from 0.07 to 2.5 mm. Diameter of the tube varied from 50 to 280 mm in both the cases. Also, the monetary analysis of TSS is discussed, and the average price of water for passive and active tubular solar still is $0.022 and $0.027 per liter of water. Future perspectives also included in the conclusion section for the possible design and material improvements one can do to enhance the performance of the TSS for the benefit of researches. The excellent cover material for TSS is polythene film when compared to the vinyl chloride sheet. TSS with PCM, wick materials, and corrugated absorber enhance productivity during night time. Multi-effect tubular stills performed 28.70% better in comparison to single-effect stills, and TSSs with horizontal axis are 19.12% more productive than vertical axis tubular stills.