mohammad barzgarnezhad

Many researchers have experimentally and theoretically studied fresh water productivity in solar stills. In this regard, water preheating can play a noticeable role in enhancing the productivity of solar stills. In the present study, in order to study the effect of water preheating at the inlet of desalination system, a cascade solar still is built and integrated with two different solar collector in separated modes; an evacuated solar collector and a conventional flat plate solar collector. The mentioned solar still includes an external condenser, fin, and internal and external reflectors. It is worth noting that the embedded fins in the water passage are applied to induce hot spots and increase the evaporation rate and fresh water. The experiments were performed in August 2015 and summer 2017. The results showed that the combined desalination system with conventional flat plate collector and evacuated tube collector enhace productivity %60 and %13, respectively. In addition, efficiency of solar still in combination with conventional flat plate collector and evacuated tube collector was %81.8 and %59.1, respectively. The price of produced fresh water of solar still with conventional collector obtained 0.035 $/lit and for solar still with evacuated tube collector was 0.045 $/lit.

In this paper, a cascade solar desalination unit with external reflector designed and built and experimented in eigth days. In order to increase the production of fresh water, various techniques were applied such as 1) installing a number of finns on the stairs and on the waterway to create hot spots as a new idea, 2) use of internal reflectors at the base of the stairs and 3) use of an external condenser for increasing condensation rate of produced vapor. Then, the under study system was experimented in eight configuration using combination of above techniques and the experimental results were presented as well as the results of economical analysis. The results showed use of the finns led to the most amount of fresh water although the rest of techniques significantly increased the product. It is worth mentioning that use of the finnes led to fresh water with the lowest cost of product in value of 1343.1 Rials/lit. On the other hand, the system with an external condenser had the maximum efficiency and the system with the finns has the third place among the eight study configuration.