Thermodynamic Balancing of the Humidification Dehumidification Desalination System by Mass Extraction and Injection

Abstract

Humidification dehumidification (HDH) is a promising technology for small scale seawater desalination and has received widespread attention in recent years. The biggest roadblock to commercialization of this technology is its relatively high energy consumption. In this paper, we propose thermodynamic balancing of the humidifier or the dehumidifier through mass extraction and injection as a potential means of reducing the energy consumption of these systems. Balancing minimizes the entropy generation caused by imbalance in driving temperature and concentration differences. We outline a procedure to model the system, using on-design component variables, such that continuous or discrete extraction and/or injection of air from the humidifier to the dehumidifier or vice versa can be analyzed. We present an extraction profile (mass flow rate ratio versus non-dimensional position) in the dehumidifier and the humidifier for attaining close to complete thermodynamic reversibility in an HDH system with a 100% effective humidifier and dehumidifier. Further, we have examined in detail the effect of having finite-sized systems, of balancing the humidifier versus the dehumidifier, and that of the number of extractions.