Extraction based thermodynamic balancing for a humidification dehumidification desalination plant

Abstract

Humidification dehumidification (HDH) desalination is a thermal driven desalination technology. One of the main issues with HDH desalination is the high energy consumption involved. The energy efficiency of thermal desalination systems is given by a non-dimensional number known as the gained output ratio (GOR) which is a ratio of the latent heat of evaporation of the water produced to the net heat input. In Lienhard Research Group at MIT, a particular method of increasing GOR has been invented. This method involves matching the heat capacity ratio (HCR) of the flows exchanging heat and mass to approach unity. Specifically, based on theoretical studies done previously in the group, it had been proposed that mass extraction of air from the humidification device to the dehumidification device changes the HCR favorably. This thesis looks to show the same experimentally. By making adjustments of the HCR in different parts of the process it is possible to increase the GOR substantially. In the current study it has been shown that the GOR is increased from 2.4 to 3.1 for a specific set of boundary conditions. All mass extraction cases found an improved GOR value, confirming that this process reduces the total system irreversibility.