Solar Desalination by Indirect Heating

A solar unit to produce desalinated water and hot water from saline feed water was designed and tested. The unit consists of a solar collector (5 evacuated tubes) that heats a thermal fluid circulating in a closed loop due to thermo siphoning effect. The hot thermal fluid passes through a water bath giving its thermal energy and causes some of the water in the bath to evaporate. The vapor generated condenses on an inclined glass plate and withdrawn as desalinated water. The effect of the ambient temperature, the solar irradiation, and the other weather conditions on the productivity of the unit (liters of desalinated water produced/hr) was investigated. The results showed that the unit was capable of producing 0.15 L of desalinated water/hr. The experiments showed that the unit productivity was improved by cooling the glass cover on which the water vapor condenses. Two types of thermal fluids were used namely; jojoba oil and water. Water as a thermal fluid gave better productivity. The effect of feed water salinity on the unit productivity was tested by feeding water of salinity ranging between 0.5 g/L (tap water) to 25 g/L. The productivity decreased as the feed water salinity was increased.