Enhancing Solar Still Performance Using Vacuum Pump and Geothermal Energy

Abstract

Improvement in the performance of a solar still is investigated with the integration of a geothermal cooling system and a vacuum pump. Geothermal cooling is simulated to provide a cold, effective underground water temperature, which could reach 15–25 °C below ambient. Cooling is achieved by circulating water underground. As a result of this circulation, the cold fluid from the ground flows into a counter flow shell and tube heat exchanger. A vacuum pump is used to keep the solar still at a certain vacuum pressure. The sizes of the geothermal system and solar still are designed in such a way that the water outlet temperature from the ground and its flow rate are capable of condensing the entire vapor produced by the still. An analytical model was developed and then solved using the Newton–Raphson method for solving non-linear equations. A prototype was built to validate the analytical model. The results were in close agreement. A 305% increase in daily water productivity resulted from the proposed enhancements. After experimental validation, the effects of various parameters such as vacuum pressure, ambient temperature, and wind speed on the yield of geothermal solar still were examined. It was found that the increase in vacuum pressure enhanced performance, whereas the increase in wind speed had a detrimental effect on the yield of the solar still. A higher ambient temperature increased the yield of the solar still. Finally, the design of the heat exchanger for condensing the distilled water using geothermal cooling water was also investigated in terms of the increase in UA (the product of overall heat transfer coefficient and the area of heat exchanger) with inlet cooling geothermal water temperature.