Performance study on a passive solar seawater desalination system using multi-effect heat recovery

A novel small-sized solar seawater desalination system with multi-effect heat recovery processes using all-glass evacuated tube absorber as heat collector, in which there is no power pump and the steam and freshwater flow are driven only by pressure drop, was designed and tested. The whole system consists of 7 heat collecting/heat recovery integration units, which were divided into 7 temperature/pressure states. Each unit has a heat collector which consists of a simplified CPC panel, an all-glass evacuated tube absorber, a seawater tank and a bar heat pipe that connects the absorber and seawater tank to transfer heat from the absorber to the seawater tank. Every unit operated under barotropic or atmospheric pressure. Meanwhile, a stepwise heat recovery method was adopted to recycle the sensible heat and latent heat of the steam generated. In order to investigate the effects of operating parameters on system performance, including freshwater yield, solar collecting performance and heat recovery performance, a series of experiments were conducted under different weather condition. It can be found that the all-day freshwater yield of unit area can reach 4.23 kg/m2 on the sunny day and 3.03 kg/m2 on the cloudy day. Meanwhile the collecting efficiency and comprehensive thermal coefficient can reach 0.41 and 1.39 respectively. The experiment results confirm that the designed system has a superior performance in seawater desalination without power consumption.