Performance evaluation of a solar and vacuum assisted multi-stage humidification-dehumidification desalination system

Abstract

This study compares the freshwater productivity of a three-stage vacuum humidification-dehumidification (VHDH) desalination system to a single-stage VHDH system. Experimental study on a multi-stage humidification in sub-atmospheric pressure condition confirmed its superiority over previous multi-stage humidification-dehumidification processes. The variation of the desalination rate was measured experimentally using the three-stage vacuum humidification and heating modes. The results showed that the maximum desalination rate of the unit was 1.8 kg.h−1 per 1 m2 of solar water heater area with minimum specific power consumption (SPC) of 0.1 kW h.kg−1 when the maximum solar intensity was 1106 W.m-2 in July 2020. This investigation indicated that the system had high freshwater productivity and low SPC compared to a single-stage VHDH system. The system performance was improved when the operation was further optimized using the response surface methodology (RSM). The optimal values of saline water to air mass flow rate ratio (sw/a) and humidifier pressure (PH) of 1.77 and 33 kPa led to the maximum freshwater productivity. In all operating conditions, through converting the single-stage humidification to two-stage and three-stage humidification processes, the humidity ratio was enhanced by about 51 % and 19 %, respectively. The optimal freshwater productivity could be realized only when multi-stage vacuum humidification was utilized at isothermal heating mode in all stages and the cost was $0.002 per liter.