Two-phase Flow Enhancement And CFD Simulation Of Membrane Distillation Process For Seawater Desalination

Fresh water resources shortage has become a global problem,seawater desalination technology is recognized to be one of the most effective way to solve the freshwater shortage,but current seawater desalination technology has the disadvantages of high energy consumption,high operation cost and low purity.Developing new water desalination technology to replace the current method of thermal and membrane desalination technology,has become the research focus in the study of related scientific researchers around the world.Membrane distillation is a new type of me mbrane separation technology,its volatile components after vaporizating from the feed liquid side,under the impetus of the steam partial pressure difference between two sides of membrane,pass through the hydrophobic microporous membrane,the water vapor is condensed to realize the separation of the mixture.Because of its high product purity,low operating temperature and pressure,MD has a broad development prospects in the field of desalination.The disadvantages of MD's low permeate flux limits its industrial app lication.Therefore,preparation high performance membrane material,optimization of operating conditions,strengthening the process,to explore the mechanism and improve the permeation flux of membrane distillation process is of great significance.Take self-made carbon-based tubular membrane as the separating membrane,through air gap membrane distillation for sodium chloride solution experiments,examined the influence of operating conditions on the permeate flux and retention rate.The results show that the permeation flux increase with the rising of feed inlet temperature and feed flow rate,decrease with the rising of feed concentration and inlet temperature of cooling water.The retention rate increases with the increase of the liquid concentration,and the variation of other operating conditions has no significant influence on the retention rate.On this basis,gas-liquid twophase flow technology was applied to membrane distillation process enhancement experimental study,examined the influence of various operating parameters on permeate flux and flux improvement efficiency,and compared with previous experimental data,the results show that permeation flux can be improved effectively with nitrogen and water vapor piping in the membrane pipe,and the enhancement effect of piping in water vapor is better,permeation flux increase with the increase of nitrogen flux and then decrease slowly,increase continually with the increase of water vapor flux.On the basis of experiment,using FLUEN T software for air gap membrane distillation and its two-phase flow enhancement process in numerical simulation of the fluid in the process of membrane module as the research object,the physical and mathematical model is established,the permeation flux of the simulation value and experiment value compared to verify the reliability of the model,In addition,also investigated under different conditions,the speed of membrane and membrane wall material liquid,temperature and shear stress distribution,the results show that the material along the flow direction of fluid flow and temperature boundary layer gradually formed and de veloped,and the nearer the material liquid export material liquid velocity in the center of the pipe,the lower the temperature,the greater the boundary layer thickness.Membrane module within the temperature drop are mainly concentrated in the air gap a nd cold inside the wall,N itrogen gas bubbled into can improve material liquid superficial velocity,increasing the material liquid of disturbance,inner surface shear stress,increase the membrane to weaken the influence of the temperature polarization,improve the efficiency of the heat and mass transfer in the process of membrane distillation.