Performance characteristics of the diffusion driven desalination process

A diffusion driven desalination (DDD) process has recently been reported where warm water is evaporated into a low humidity air stream, and the vapor is condensed out to produce distilled water. Although the process has a low fresh water to feed water conversion efficiency, it has been demonstrated that this process can potentially produce low cost distilled water when driven by low grade waste heat. A detailed heat and mass transfer analysis has been developed to model the dynamic performance of the DDD process. This analysis is used to parametrically explore the performance of the DDD process over a wide range of operating conditions. The optimum operating condition for the DDD process with a high temperature of 50°C and sink temperature of 25°C has an air mass flux of 1.5 kg/m2-s, air to feed water mass flow ratio of 1 in the diffusion tower, and a fresh water to air mass flow ratio of 2 in the condenser. Operating at these conditions yields a fresh water production efficiency (mfw/mL) of 0.035 and electric energy consumption rate of 0.0022 kW-h/kgfw. A brief economic analysis is presented to demonstrate the added value provided by using a DDD facility to produce fresh water using waste heat from a thermoelectric power plant.