Numerical Simulation And Experimental Study On Bubbling Enhance Process Of Membranes Distillation

In the process of membrane distillation,flux reduction due to the unavoidable problems such as membrane fouling,the phenomenon of temperature polarization and concentration polarization.By means of ultrasonic technology,electromagnetic technology,microwave technology,two-phase flow technology combined with membrane distillation technology,or membrane module optimization,the temperature boundary layer and the concentration boundary layer can be destroyed,which has a positive impact on improving the membrane flux.In this paper Euler multiphase flow model was used to study the flow characteristics of the two-phase flow after bubbling of hollow fiber membrane module and air-gap flat membrane module,including velocity,turbulence intensity,wall shear force and so on.The simulation results show that the speed,turbulence intensity,pressure drop of the membrane modules increase with the increase of the bubbling speed.Therefore,it can be seen from the simulation that the bubbling can change the flow field near the membrane surface,enhance the shear force on the membrane surface,and has a promoting effect on mass transfer process of membrane distillation.Then an experimental platform of bubbling membrane distillation was set up,and the continuous bubbling process and intermittent bubbling process of membrane distillation on hollow fiber membrane modules were studied through experiments.As compared with the changes of flux with the different temperature,flow rate,and bubbling speed during continuous bubbling process,it can be seen that the enhancements is different at a different flow rate and temperature,and the process of mass transfer of membrane distillation was determined by the temperature,flow rate and strength of the bubbling.At the same time,it was found that the flux could be better strengthened when the gas-liquid flow ratio was around 0.5,and the flux enhancement effect reached 31% when the flow rate was 80 L/h and the temperature was 65°C which compared with non-bubbling.By controlling different bubbling time and interval time,the intermittent bubbling experiment was carried out under a certain condition.The results showed that when the bubbling time was the same,the flux increased with the increase of the interval time.When the interval time was the same,the flux increased first and then decreased with the increase of the bubbling time.It also can be founded through experiments that both the intermittent bubbling flux and continuous bubbling flux is greater than the non-bubbling flux,and the intermittent bubbling is more effective than the continuous bubbling process.The bubbling time was controlled at 30 s for intermittent bubbling process,the optimal flux enhancement effect reached 35%.And when the interval time was controlled at 90 s,the optimal flux enhancement effect reached 45%.It is technically feasible to apply the gas-liquid two-phase flow to the membrane distillation process,and the membrane flux was better strengthened in the experimental range.