Experimental investigation and performance evaluation of an oval tubular solar still with phase change material

The problem of freshwater scarcity is a major issue for people all over the world. Solar still is one of the most simplest and affordable ways to produce freshwater using solar energy which is available with no cost and eco-friendly. Recently, tubular solar stills (TSS) have gained popularity as one of the best solutions for acquiring pure water, especially in arid and coastal areas. The main objective of this paper is to enhance the productivity and efficiency of TSS by introducing a new form/shape, the oval tubular solar still (OTSS), integrated with cover cooling and phase change material (PCM). The OTSS is made of a transparent oval tube that is permeable to sunlight from all directions to maximize solar irradiance, and it is integrated with a black basin to improve absorption and water evaporation. It has an appropriate level of flexibility, durability, and low cost. Experiments were conducted out in the climatic conditions of Cairo, Egypt. This paper investigated different basin water depths and different water cover cooling flow rates to obtain their optimal values. Moreover, the effects of using PCM as a thermal management solution were studied in detail. In the case of no cooling, it is observed that the production rate decreases with increasing the water depth in the basin and the maximum production rate reached up to 5.21 L/m2/day at the optimal water depth of 0.5 cm. However, with cooling, the maximum production rate of 6.34 L/m2/day was achieved at the optimum water-cooling flow rate of 2 L/h. Using the PCM the maximum production rate of 6.78 L/m2/day was able to be achieved. The efficiency and productivity of the OTSS were enhanced by 41.26 % and 32.42 %, respectively, when using PCM. Furthermore, the daily thermal exergy efficiency of the OTSS was 3.46 %, 3.85 %, and 4.14 % for the cases no cooling, with cooling and with PCM, respectively. Economically, the cost per liter of desalinated water production was $0.020, $0.017, and $0.017 for the three cases, respectively.