Analysis of a novel humidification-dehumidification desalination system

This paper reports on mathematical modeling and experimental demonstration of a compact humidification-dehumidification (HDH) system. The HDH system studied here consists of a humidifier where the air is humidified and a dehumidifier where externally heated moist air condenses. The latent heat of condensation is recovered via a common-conducting heat transfer wall shared between the humidifier and the dehumidifier. For the present study, a bubble-column dehumidifier is investigated, while falling film air-water counter-flow configuration is considered as a humidifier. Condensed produce water is collected at the dehumidifier, and brine is rejected at the water outlet of the humidifier. In this paper, a modified heat exchanger analysis is reported that accounts for a volumetrically uniform heat source due to condensation in the dehumidifier. The analysis also accounts for co-current air-water vapor flow from an evaporating stream of water. Heat and mass transfer in the wet evaporating channel is analogous to that in a cooling tower. The model is able to predict the variation of the temperature difference between the humidifier and the bubble column condenser as a function of the vertical distance of the shared wall. Gained-output-ratio (system energy efficiency) is quantified using the model developed and compared against simple prototype HDH experiments in an open-air open-water configuration. Finally, the utility of the mathematical analysis and deduced results are discussed.