Numerical Simulation Of A Novel Plate-frame Air GAP Membrane Distillation Process With Heat Recovery

Membrane distillation(MD),which is being developed for desalination,concentration of fruit juice and treatment of hazardous waste water,is a relatively new separation technique in combination with the membrane technology and distillation technology.However,there are still many problems need to be changed in large-scale industrial application.The high heat consumption in MD is one of the limiting factors,which cause a high cost.The hotspot of current research is to develop a new type of membrane distillation device with the ability of heat recovery.Besides,by recycling and using the latent heat of steam,the market competitiveness and application prospect of MD will be improved.In this article,by using computational fluid dynamics(CFD)software,constructed three-dimensional calculation model to research the internal heat and mass transfer progress of the new type of heat recovery of frame and air gap membrane distillation units.Built a new membrane distillation device technology route,then compared experimental measurements and theoretical simulation numerical,from the results we could know that the simulated results fit the experiment data quite well,which showed that the mathematics model had high reliability.And on this basis we investigated and analyzed the change of the flow field distribution of each area in components comprehensively and systematically,in which area contained the front side,hydrophobic membrane and permeate side area.In this way,we could get the change of fluid temperature,flow velocity and pressure in every area of inner-module by different operating conditions,so that we could get the distribution rule of the temperature of boundary layer thickness,coefficient of convection and hyperpolarizing factor of temperature in the components.From the results of steam heat recovery we could know that the condensate of the first layer fiber membrane near the flat membranes absorbed the most heat,which was the highest percentage of total absorb heat.Improving the feed temperature and feed rate were good to the recovery of steam heat,and the recovery efficiency of steam heat would be increased.Increasing the degree of vacuum could increase the membrane flux,but the recovery efficiency of steam heat would be decreased.From the energy efficiency of membrane distillation process and the energy efficiency of components,increasing the feed temperature and feed rate could significantly increase the thermal efficiency of MD and the factors of energy efficiency in components;the thermal efficiency of MD would be increased by increasing the auxiliary vacuum degree.In a word,the total energy efficiency of components firstly decreased and then increased.The research achievement of this thesis has made a valuable exploration on optimizing energy utilization efficiency and devices in MD and the designs of membrane distillation process.