The exergetic approach for the analysis of HDH desalination process using a pulverized column

Abstract

In the process of humidification-dehumidification, the cross transfer of heat and mass is due to the affinity between water and air. In the present work, a mathematical model was developed basing on the mass, thermal and exergy balances in order to analyse the performance of a freshwater productivity by desalination of seawater. Firstly, we acquired the thermodynamic properties of the binary system (air-vapour water) through the use of the virial equation of state. To determine the impact of operating variables on the performance of the unit, the concept of degrees of freedom has been introduced. Basing on a rigorous algorithm, the performance of HDH was approached by calculating the productivity of fresh water and exergetic efficiency in relation with the operating variables. The results of the simulation show that the productivity and the gained-output ratio (GOR) increase with the increase of the ratio of the flow rates and the temperature of the inlet air in the humidifier. However, it decreases simultaneously with the outlet water temperature. Besides, the humidifier and dehumidifier exergetic efficiencies increase simultaneously by increasing of the mass flow rates ratio and the temperature of the air at the inlet of the humidifier. Also, we note that the exergetic efficiency of the dehumidifier decreases with outlet water temperature. The simulation results establish that the collector performance diminishes with the liquid mass flow rate. Nevertheless, these results show that the major part of exergy destruction in the unit is localized in the collector with the lowest exergetic efficiency. The largest exergy losses are caused by increasing of the pinch of temperature.