Simulation Of Vacuum Membrane Distillation Process And Optimization Of Membrane Module

Membrane distillation (MD) is a new type of purification technology developed in 1980's last century, which is a new process of the membrane technology combined with the traditional evaporation process. Based on the equilibrium between the vapor and the liquid, phase change of membrane distillation depends on the latent heat of the evaporation, so does the traditional one. Vacuum membrane distillation (VMD) is one of the four configurations of MD, which has some characteristics such as high water production, good separation coefficients, simple devices and easy to operate and realize. VMD can be widely used in several fields, such as removal of the volatile constitutions and desalination of the sea water and the brackish water. It is meaningful to develop and use the membrane distillation technology to realize the desalination of sea water, energy-saving and emission-reduction and comprehensive utilization of waste water.Based on the primitive research of our seminar, in order to get characteristics such as simple structure, good distribution, and easy installation for the distributor, we designed the pre-distributor of plate type with variable apertures using the CFD technology for the cross flow membrane module. VMD experimental has been carried out using the membrane module with the designed plate pre-distributor. Pure water was employed in the experiment.The mechanism of vacuum membrane distillation process was discussed. The large-scale commercial computational fluid dynamics software FLUENT was applied to numerically simulate the process of VMD. Model for Heat and Mass Transfer in the module was described by user define function (UDF) in the software. By the way, the thermo-physical data of material fluid were adjusted according to different thermo conditions. The process of VMD using cross flow module has been numerically studied with the model. The simulated and experimental results are in good agreement, which means the numerical model is reliable. Basis on this model, the law of how the parameters varied in the module of VMD was studied. Then the displine of the parameters'effect on the total permeate flux, including different operating conditions, variation of flow direction of the feed solution and the distribution of factors around the hollow fiber membrane has been investigated.This paper gets the laws of how each parameters change in the membrane module according to the numerical model. And from a view to the characteristics of the VMD, we present a primary idea of adding heat supply between membrane modules connected in series and changing the flow direction of feed fluid as time went on. Then, we got some points of view on industrial applications of MD and provided references for concrete solutions.In conclusion, this paper systematically discussed the mechanisms of VMD. The plate pre-distributor for the cross flow module was designed and manufactured then some experimental research of the module with pre-distributor is also carried out. Comparing the flux of module between the numerical and experimental results, we find the numerical model is feasible and valuable. For further design of the membrane modules and optimal operating conditions, this paper provided the theoretical basis and the technical references. For integrated application of the energy of VMD process and effective control of membrane fouling, this paper puts forward some constructive proposals.