Modeling of a solar driven HD (Humidification-Dehumidification) desalination system

The paper presents a computer code developed to simulate the operation of a low-temperature thermally driven desalination system, based on the HD process. The system is a closed air cycle unit and is based on a single-effect humidification/dehumidification technique: heated salt water is introduced into an humidifier to saturate the circulating air and then the water vapor separates in a condensation section, where fresh water production takes place. The modeling procedure allows to investigates the air and water thermodynamic properties across each component. The computer code is able to optimize the heat exchanger surfaces and the air and water mass flow rates, depending on the sea water and the heat source temperature levels. The code was used to analyze an HD desalination unit with fresh water production of about 200 liters per hour, for two different configurations: a direct solar driven scheme, where the salt water entering the HD unit is heated by a solar collector field, and an integrated cooling-desalination system driven by solar energy, where the solar collected heat is used to drive a LiBr absorption machine and then the low-temperature heat rejected by the chiller is exploited to drive the HD process. The simulation code has been integrated into the Trnsys environment to perform a transient simulation of the whole systems. The annual simulations have been carried out on an hourly basis for typical climatic conditions of Abu Dhabi (UAE).