Exergy analysis of the solar multi-effect humidification–dehumidification desalination process

An exergy analysis method is presented of the solar multi-effect humidification–dehumidification desalination (HDD) process. Pinch technology is used in the humidification process to determine the maximum possible saturated air temperature and the temperature of water rejected from the unit, and then the dehumidification process to determine the temperature of water leaving from the heat exchanger. The formulae to calculate the exergy of water and saturated air are given. The solar plane collector is used. From exergy analysis, the solar collector has the lowest exergy efficiency; the HDD process has a lower exergy efficiency, and the water rejected has also a large exergy loss. The energy and exergy recovery rate of the desalination process is also lower. The solar multi-effect HDD process has much room for improvement. Three ways to enhance fresh water output per square meter area of solar collector are suggested. The first is to enhance the energy and exergy efficiency, that is, to take measures for larger amounts of energy and exergy. The second is to improve the flow of the solar multi-effect HDD process in order to gain a high energy recovery rate and the gain output ratio. The last is to reuse the rejected water to obtain fresh water.