Understanding the dynamic behavior and the effect of feeding policies of a direct contact membrane distillation for water desalination

In this study, a dynamic mathematical model for direct contact membrane distillation (MD) is developed and validated. Two model formulations were considered each of which can be cast in lumped or spatial structure. All types of models were verified against experimental transient data for the permeate and brine temperatures. The proposed models provided a perfect prediction of the measured data except at the lowest flow rates. Judicious model modification helped to enhance the model performance. The tuned model is used to analyze the process dynamic in one-dimensional space. It is found that the process possesses an enhanced convective heat transfer mechanism substantiated by the high values for the temperature polarization and Biot number. At very low flow rates, the membrane conduction resistance prevails limiting the heat transfer at the membrane interface and hence the process performance. Preliminary analysis of the special transient operation of the MD process to address challenging operations such as scheduled production strategy and/or intermittent energy sources is outlined.