Research On Gas Dispersion, Mass-transfer And Mixing Characteristics Of Co-axial Mixers In Shear-thinning Fluids

Gas-liquid mixing equipment has been widely used in many process for its high adaptability and simple operation, such as biochemical, petrochemical, pharmaceutical engineering, food industry and so on, whose purpose is to achieve good gas-liquid dispersion by effective contact collision and expanding the gas-liquid interfacial area, which will enhanced efficiency of the mass transfer and heat transfer. However, researches on gas-liquid mixing have weakness in some research fields:firstly, the studied object is Newtonian system mainly. Exactly, in the actual mixing production, the shear-thinning plays a critical role. Secondly, nowadays, the research focused on single or multiple impellers mostly, no research on the gas-liquid mixing of co-axial mixers exists. Therefore, this paper aims to study the gas dispersion, mass-transfer and mixing characteristics of co-axial mixers in shear-thinning fluids made up of xanthan gum by experiment and simulation.First of all, the gas-liquid dispersion of single and co-axial mixer with different rotating modes is researched. Then, the influence of different impellers(inner:Rushton, 6BDT,6PBDT,outer:Gate,DHR), different operating conditions(superficial gas velocity of stirring speed), viscosity (0.1%XG,0.15%XG,0.2%XG,0.3%XG) on the gas dispersion, mass-transfer and mixing characteristics were also researched. Besides, in order to achieve more detail information, CFD method was adopted.Experimental results show that, the co-axial mixers under the counter rotating mode have better performance on gas-liquid dispersion according to the pumping capacity and global gas holdup. So the following researches is done on the basis of the counter rotating mode only. And as far as pumping capacity and global gas holdup are concerned,6BDT+GT is recommended, while on mass transfer,6PBDT+GT and RT+DHR are better. In addition, pumping capacity and mass transfer will decrease with increasing viscosity, while global gas holdup and mixing time are opposite. And global gas holdup, mass transfer will increase with the increasing stirring speed. The fitting of formula is also done to explore the different effect degree of every parameter by different impeller types.During the numerical simulation, the drag model and bubble coalescence model are corrected, and the flow pattern and other local parameters were obtained, the global parameters show favorable agreement with the experiment results.