The impact of thermodynamic balancing on performance of a desiccant-based humidification-dehumidification system to harvest freshwater from atmospheric air

Abstract

The thermodynamic balancing is a powerful tool to minimize the entropy generation in a thermal system. This tool is investigated to thermodynamically balance a novel desiccant-based humidification-dehumidification (HDH) system by extracting the recirculated air. It is carried out for a zero, single, double, triple, quadruple, quintuple, and infinity extractions. The HDH system is incorporated with a number of air dryers to produce freshwater from the humid air. An enthalpy pinch, which is described as the minimum air-to-desiccant enthalpy difference, is used as an index to approach the system thermodynamic balancing. For small values (< 20 kJ kga−1) of enthalpy pinch, the gained output ratio (GOR) is improved substantially as a function of extraction number. While for an enthalpy pinch between 20 and 47.8 kJ kga−1, more than one extraction has no further enhancement in the GOR values. Moreover, for more than 47.8 kJ kga−1 enthalpy pinch, the extraction schemes show no additional improvement in the system performance. The number of air dryers from one to twenty is used to improve condensed water production from 9.5 to 190 kg per hour, respectively.