In this study, the effects of adding a condensing cavity in a passive single-basin solar still are investigated experimentally under the climate condition of Mashhad. The condensing cavity acts as an interior cooler. It is cooled by the natural convection heat transfer with the surroundings and accordingly; it keeps the evaporating chamber at a lower pressure. Hence, the condensing cavity increases the rate of evaporation. As a result, this still can increase the productivity of freshwater. The results show that the ratio of vapor condensation on the inner surface of the condensing cavity is about 43% of the vapor condensation on the inner surface of the glass cover, which is 30% of the total freshwater during one day of experiment. This modified solar still represents a simple system, and it can be easily manufactured at a low cost.

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