Heat and Mass Transfer Analysis for Membrane Distillation
Membrane Distillation (MD) has recently emerged as promising technology for desalination as it is less sensitive to feed concentration which increase distilled water yield of desalination process. However, one major drawback of MD is the high energy consumption despite the continuous effort to optimize the processes through various configurations. In this thesis, we evaluate a configuration to reduce energy consumption of membrane distillation while maintaining state-of-the-art mass flux rate through membranes. Localizing heat generation at the liquid-membrane interface reduces ambient exposure of heated mass resulting in reduction of ambient thermal losses. Additionally, operating on stagnant feed eliminates energy required for circulating fluid. Furthermore, we took advantage of the stagnation to accurately measure instantaneous mass flux rate through membrane. Experimental mass flux rate matched analytical predictions developed by imposing porous medium effects on natural evaporation of free surface. Our locally heated membrane distillation (LHMD) demonstrates a good eciency with up to 75% reduction of energy compared to direct contact membrane distillation. In addition, we explored the performance of silver based membranes. Compared to conventional polymer based membranes, silver membranes have higher thermal stability. Also, pore sizes can be controlled more precisely for silver membranes. Our results indicate that silver membranes have similar performances to polymer based membranes. Combining LHMD along with thermally stable membranes has a potential beyond desalination. Controlling constant interface temperature is easier in similar configuration, which opens avenues for high temperature fluid mixture separation.
Marconnet, Purdue University.
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