Experimental study of a humidification-dehumidification solar technique by natural and forced air circulation

摘要

An experimental investigation of a desalination system based on the HDH (humidification and dehu-midification) of air is studied. The experiments were carried out in the premises of an open roof (six floors) of a Faculty of Engineering, Kafrelsheikh University, Egypt which lies at latitude 31.07°N and longitude 30.57°E.The evaporator (humidifier) unit is based on a cellulose paper as packing materials substratum through which water flows, and has a large area of favor evaporation. Cellulose papers with different wet surface area are used and studied. A modified design of condenser (dehumidifier) is proposed in HDH process to evaluate the performance of the unit. The condenser unit is a liquid-gas heat exchanger, where water vapor is condensed. 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. 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 twice. 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 is 4 kg/min and forced down air circulation the unit productivity is about 23.6 kg/h with water temperature 90 ℃ at humidifier inlet. Results of the proposed design are compared with that for conventional type and the comparison shows that the propped design gives a higher performance. Hence, the modified condenser design increases the condenser effectiveness to be about 0.71 while, for conventional type of 0.49.