Development and testing of the new design for a single-stage solar still

Abstract

The global water demand is increasing alongside the growing world population. Adequate access to clean drinking water is essential for the well-being of all living organisms, and the scarcity of this resource is a significant worldwide issue. In addressing this challenge solar desalination systems, particularly solar stills, have proven to be effective solutions, generating fresh drinking water from saline or contaminated water. A solar still is a device used to produce fresh water from contaminated water using heat from the sun. Solar stills mainly consist of a water basin, a glass cover positioned at an angle facing the sun, a collecting tray, a collecting tank and a feeding tank. The basic operation of the device is that the contaminated water inside the water basin is heated and evaporated using the heat from the sun. This water vapor then is condensed on the inner surfaces of the solar still cover and from there potable water is accumulated. This study comprises a design, fabrication and testing of a new design of a double slope single-stage solar still (D5S). The system was constructed at the Mechanical Engineering workshop at Cape Peninsula University of Technology (CPUT), Bellville Campus. The tests were conducted on the roof of the Mechanical Engineering workshop over twelve days during October and November 2023 (spring season in South Africa). Out of the four seasons, spring is the second warmest after summer, thus, testing during this season was deemed feasible, given that sun irradiation is one of the most important elements influencing the productivity of solar stills. The D5S was incorporated with a 16-tube evacuated tube solar collector. The solar still was tested during the day (7 am to 7 pm) and night (7 pm to 7 am). The system consisted of a saline tank that was elevated and positioned to allow a gravitational flow of seawater to the basin. A water circulation pump was used to hasten the flow from the basin to the solar collector and back to the basin where the evaporation and condensation processes took place, thus, leading to the production of the distillate. During the experiment test, the highest production obtained per day was 513ml, being the total production for day and night achieved on a day when the maximum outdoor temperature was 30oC. The minimum distillate produced was 140ml on a day that had a maximum temperature of 22oC that was one of the coldest days during the testing period. The total distillate produced by the solar still system during the testing cycle was 3821 ml. The knowledge produced from this research will assist the industries dealing with water distribution and management in enhancing the water resources. The knowledge will also serve as the guide in cases where such systems are taken for commercialization. The knowledge from this study can be useful in remote areas that are faced with the water crisis and all sectors that are water depended for their operations and for remote areas.