The Application Of Two-phase Flow In The Mcrofiltration Of Titanium Dioxide Suspensions Using Carbon Membrane

The main problem in microfiltration is the sharp decrease of permeate flux as timepassed, which is mainly caused by concentration polarization and pollution of membranes.Although there has been some achievements in reduce of concentration polarization andpollution of membranes, such as turbulences promoters, pulsatile flow,rotary tangential flowand et al. however, all of these methods are hard to realize and impossibly industrialized.Comparing with the methods above the application of gas-liquid in microfiltration has a lot ofadvantages,for example, it can improve the permeate flux greatly,the conduction is notdifficult and the experimental set-up is easy to realize. Nevertheless, there is not anymathematic model or theories that can describe the course of microfiltration perfectly as theresearch on the application of two phase flow has only been carried out recently and thecomplexity of the flow itself.This paper which is based on the background of the application of microfiltration oftitanic dioxide dispersion using carbon membrane has focused on the research of the usage oftwo phase flow in microfiltration and been able to provide some foundational information forindustrialization to reduce the concentration polarization and the pollution of membrane,aswell the decrease of permeate flux in the end. In the experiments the tubular carbonmembranes with mean diameter 1.0um which are prepared by ourselves are used and theexperiments are carried out under the condition of 20C, transmembrane pressure between0.04-0.16mp, liquid superficial velocity between 0.85-1.56m/s and gas velocity between0.29-2.02m/s, concentration of dispersion between 0.1-1.0g/l as well. The results ofexperiments show that, in microfiltration the introduction of gas truly increase the turbulenceof flow of liquid, with the increase of up to 162%. And the slug flow is the most effective.The permeate flux increases rapidly when the gas is introduced, and it also increases as thepressue increases. When the pressure is 0.11mp the greatest permeate flux is achieved as1275L/(m~2·h). it is also shown that gas liquid two phase flow can substantially decrease theblock of membrane pores and the reject of membrane cake. The effect of introduction of gasimproves as the concentration polarization and pollution of membrane escalate. However, thereject of cake decreases rapidly first, then seems to level off, which tells us that theintroduction of gas can not eliminate the reject thoroughly. This paper has discussed the theory of microfiltration with two phase flow, coming to theconclusion that the main reasons which caused the increase of flux are the shear stressτ_gwith gas upwards andτ_l with liquid downwards. The dimensionless model based on thisexperiment is also established, then compare the predicted data with the experimental data,proving the precision and the feasibility of the model.