Contribution à l’analyse du fonctionnement d’un système de dessalement dans une colonne pulvérisée ‘Calcul énergétique et exergétique' .

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 mass, thermal and exergy balances in order to analyze the performance of a freshwater productivity by desalination of brackish (eg.seawater). To carry out this technique, we firstly acquired all the thermodynamic properties of the binary system (air-water mixture) using the virial of state of equation (SOE). In order to determine the impact of operating variables on the performance of the unit, we have introduced the concept of degrees of freedom. We have emitting many assumptions, its value is ND=12. We have established the different balances (mass, energy and exergy) for each element in the unit. Moreover, the separation efficiency was approached by calculating the productivity of fresh water in relation with the operating variables, basing on a sufficiently rigorous algorithm. From the operating conditions, the results of the simulation show that the productivity and the GOR increase with the increase in the ratio of the flow rates (

̇ ̇ )and the temperature of the inlet air in the humidifier. However, they decrease simultaneously with the outlet water temperature (T4). Basing on our results, we noted that the humidifier exergetic efficiency increases by increasing simultaneously the flow rates ratio (

̇ ̇ )and the inlet air temperature (T5). Moreover, the exergetic efficiency of the dehumidifier increases with the flow rates ratio (

̇ ̇ )and decreases with the outlet water temperature (T4). At this stage, we conclude that the dehumidifier is relatively an important source of irreversibility that must be reduced to its minimum, hence the interest of working at low values of T4. The solar collector performance was approached analyzing the impact of the amounts ̇ and Tred on the exergetic efficiency. We note that this last increases with Tred and diminishes with ̇ . Nevertheless, the simulation results show that it has the lowest exergetic efficiency and the largest exergy losses are caused by increasing of the pinch of temperature (Tsun-T3). Its values are very low, , explaining that the major part of exergy destruction in the unit is localized in the collector