Numerical Simulation And Flux Enhancement Research Of Vacuum Membrane Distillation

Membrane distillation employs thermal permeation-evaporation method, inwhich the no-selective permeable membrane is used. It has several advantages：It canwork in a normal pressure and low temperature with cheap equipment and easyoperation; Solar, geothermal, hot springs, factory waste heat can be used as energy forMD; The water from MD is so clean because of the selectivity of membrane, that MDcan become a effective mean to prepare ultrapure water with a large scale and lowcost. MD is the only membrane process which can separate crystallized productsdirectly from solution. Moreover, the membrane module is easily designed asrecovery form of latent heat to form the large-scale manufacturing system with theflexibility of small module. The research of MD has important meaning on Seawaterdesalination, high concentrated brine processing, material concentration, wastewaterrecycling.In this paper, according to the uniform distribution of fluid after getting intomembrane module from distributor, the Fluent is used to set the cross flow hollowfiber membrane model, writing the user-defined function to achieve the reducedpressure membrane distillation couple process of heat and mass transfer. And thegood consistency between the calculating membrane flux and laboratory measuringdata shows the model reflects the reduced pressure membrane distillation. On thisbasis, the temperature and flow distribution, heat transfer effect and temperaturepolarization effect were analyzed to optimize the processing conditions.Besides the systematic analysis of characteristics of shell fluid, the mean velocityof the vapor in tube was calculated according to the water flux to set up the vaporflow diffusion model in tube. Also the corresponding pressure distributions and theflow speed conditions of tube vapor under different processing conditions werecompared with each other, to propose the suitable method to reinforce the masstransfer and vapor diffusion.According to the vibration of fiber observed under the high flow speed condition,the effect of fiber vibration on the flow field and temperature field near the fibersurface was analyzed. The analysis of this effect and the influence of speed and temperature filed toward the boundary layer convection heat transfer coefficient wereused to propose the theory of improving membrane flux through strengthening theconvection heat transfer.