Thermal design of a humidification-dehumidification desalination cycle consisting of packed-bed humidifier and finned-tube dehumidifier

Abstract

Humidification-dehumidification (HDH) desalination technology is an ideal technology for off-grid and remote locations where fresh water requirement is approximately between 1-100 m3/day. The principal components of the HDH system such as humidifier and dehumidifier have already been utilized in various industrial applications for some time and are readily available in the market. But the actual thermal performance of the HDH system depends on the specific type and size of the components used. In the present study, a detailed heat and mass transfer model has been prepared for a closed-air openwater (CAOW) and water-heated type HDH cycle which uses a counter-flow packed-bed cooling tower for humidification of air and finned-tube heat exchanger for dehumidification purpose. With the help of transport model, the optimum sizes of the humidifier and dehumidifier have been obtained for a desired thermal performance of the cycle, measured in terms of gained output ratio (GOR) and recovery ratio (RR). Additionally, a very basic thermodynamic model for the same HDH cycle is also prepared in order to validate the results of the transport model and results from both the models are found to be in close agreement with each other. Parametric study reveals that for fixed sizes of the humidifier and dehumidifier, there always exists an optimum value of mass flow rate ratio, top brine temperature and feed water temperature at which the GOR of the cycle is maximum. It is also concluded that the thermal performance of the system is greatly influenced by the performance of the dehumidifier as compared to the performance of the humidifier. Finally, the present work will be helpful to design a similar HDH system as per the required GOR and RR.