Diffusion-driven desalination using waste heat in air streams.

Recently a diffusion-driven desalination (DDD) process has been described as a method for distilling mineralized water. Extensive studies have already examined the performance of the process using waste heat in water streams. This work focuses on the performance of the diffusion tower (evaporator) using waste heat in air streams. Both experimental and parametric investigations are included. It is observed that the evaporation process is very inefficient when heated air and ambient water are input to the diffusion tower. In contrast, efficient evaporation is achieved when both heated air and heated water are input to the diffusion tower. An industrial application is considered where a waste heat air stream at 82°C is available and a recuperative heat exchanger is used to heat the feed water. It is found that the optimum operating conditions include an air mass flux of 1.5 kg m-2 s-1, an air to feed water mass flow ratio of 10 in the diffusion tower and a fresh water to air mass flow ratio of 2 in the direct contact condenser. At these operating conditions, a fresh water production efficiency of 0.22 and a specific energy consumption of 0.0012 kW h kg-1 can be achieved. The analytical model used to analyze the performance of the DDD process agrees well with the experimental measurements. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]