Gas-Liquid Mass Transfer Characteristics Of Highly Viscous Pesudoplastic System In A Stirred Tank

Most research object involves the Newtonian fluid on the research about basis of gas-liquid contact equipment,For example water-air system is widely used.Non-Newtonian fluid in the chemical industry and biochemical industry are common but the study on mass transfer of non-Newtonian fluid is less.In fermentation industry especially aerobic bacteria in the fermentation process,the oxygen transfer is blocked and the fermentation process is restrained along with the continuous fermentation process and the fermented liquid viscosity increase.In this paper,oxygen mass transfer properties have been done in high viscosity of pseudoplastic system under the background of the industrial production.Meanwhile we use CFD software to carry on the simulation process of the experiment.Providing a reference for follow-up experiments of amplification and industrial productionThe impeller type of InterMIG has mainly been used in the study,the inner part and outer part in same direction and opposite direction have been chosen in the study,respectively named interMIGDD and interMIGUD.The experimental device is a organic glass stirred tank,the diameter is 476 mm.CMC aqueous solution is used as non-Newtonian fluid.The mass fractions of CMC are 0.5%,0.75%,1.0%,1.25%,1.5%,1.75%.0.5%only used to choose the impeller and impeller spacing.Oxygen concentration is measured by the dissolved oxygen electrode in various influence factors.interMIGUD is more advantageous to gas liquid mass transfer in the study of impeller type,and with the increase of specific power consumption this advantage is more obvious,the maximum disparity of mass transfer coefficient can reach 50%.The diameter of the impeller is 290mm.Three kinds of impeller spacing(0.36D,0.5D,0.69D)have been used in the study.The impeller spacing of 0.5D have the best character of mass transfer if the specific power consumption is equal.Compared with 0.36D mass transfer can increased by 25%,compared with 0.69D mass transfer can increase about 11%.Four kinds of rotational speed(350 rpm,400 rpm,450 rpm,500 rpm)have been used in order to study rotational speed effect on mass transfer in the study,The volumetric mass transfer coefficient increases with the increase of rotational speed and the growth is almost the same.The law is regardless of the solution viscosity size.Four kinds of ventilation(5m3·h-1,10m3·h-1,15 m3·h-1,20 m3·h-1)have been used in order to study ventilation effect on mass transfer.The volumetric mass transfer coefficient increases obviously with the increase of ventilation.Three kinds of distributor diameter have been used in order to study distributor diameter effect on mass transfer.The effect of gas-liquid mixing becomes much better with the increase of distributor diameter.Comparing 0.75T and 0.55T,mass transfer coefficient increases up to 12%under the same specific power consumption.Five kinds of mass concentration of CMC aqueous solution have been used in order to study the influence of apparent viscosity on mass transfer,it can draw the conclusion that viscosity has inhibitory effect on oxygen transfer.Simulation results are consistent with experimental results,the increase of stirring speed,ventilation and distributor diameter can effectively promote the mass transfer process,and viscosity has inhibitory effect on mass transfer process.Compared with the experimental results,there are differences in the numerical values of the mass transfer coefficient,the lower viscosity deviation is about 3%,and the deviation is between 10%and 30%when the viscosity increasing.