Experimental study of a solar desalination unit with humidification-dehumidification by using natural and forced air circulation. (Dept. M.)

Abstract

An experimental investigation of a desalination system based on the humidification- and dehumidification (HDH) of air is studied, at the weather conditions of Kafrelsheikh city, Egypt. The evaporator (humidifier) unit is based on a cellulose paper as packing materials substratum through which water flows and has a large area to favor evaporation. Cellulose papers with different wet surface area are studied. In this study a modified design of condenser (dehumidifier) is used in HDH process to improve the performance evaluation of the unit. The condenser unit is a liquid-air heat exchanger, where water vapor is condensed, and the enthalpy of condensation is recovered to preheat the water. The working principle of the set-up is based on the idea of open-water and closed air cycles. An evacuated solar water heater is integrated with the desalination unit to evaluate the continuity production of distillate. The air is circulated either by natural or forced circulation. The effect of three types of forced circulating air (up, down and up-down) on the unit performance is considered. Also, the influence of inlet water temperature and inlet water mass flow rate to the humidifier on the performance HDH unit is studied. In addition, the optimal ratio of cold water at condenser inlet to hot water at evaporator inlet (C/H) is obtained. The results show that the maximum productivity is obtained when (C/H) is 2. Also, it is found that forced down air circulation gives higher performance than that obtained for forced up, forced up-down and natural air circulation. At C/H =2, inlet water mass flow rate to the humidifier 4 kg/min and forced down air circulation the unit productivity is about 23.6 kg/h with water temperature 90 °C at humidifier inlet.