Study On Gas-liquid Mass Transfer Characteristics Of Non-newtonian Fluids In Multiple Axial Impeller Stirred Reactor

The gas-liquid stirred reactors are widely used in the chemical industry.Currently,Newtonian fluids are mostly used when studying the flow and mass transfer phenomena of fluids in stirred reactors.Few studies have been done in which the liquid phase is a high-viscosity non-Newtonian fluid with pseudoplasticity.The differences in the laws of transfer properties between non-Newtonian and Newtonian systems have not been sufficiently studied.In addition,the study of the transfer characteristics of non-Newtonian systems will provide theoretical guidance for increasing the transfer efficiency of mass transfer in industry.Previous studies on non-Newtonian systems mostly focus on the properties of macroscopic gas-liquid dispersion.However,there are few studies on the mass transfer characteristics of the system under different impeller types.Therefore,a combination of experimental and numerical simulations is used in this paper.The gas-liquid mass transfer and mixing characteristics in different stirred reactors is studied.The results of the power consumption,gas-liquid dispersion and mass transfer of different stirred reactors in non-Newtonian systems provide theoretical support for chemical industry.Firstly,the relative power and mass transfer characteristics were studied experimentally in a gas-liquid stirred reactor with CMC aqueous solution system by using four InterMIG triple-impeller combinations with different structures and two gas distributors with different annular diameters.The relative power demand and volumetric mass transfer coefficient of the stirred reactors under different aeration and power consumption were obtained.The correlations of the gassed power numbers and the volumetric mass transfer coefficients of the four combined impellers are also obtained.Then,the velocity fields of the four combined impellers are qualitatively and quantitatively compared by numerical simulation methods.The results show that there is a better effect of mass transfer for the InterMIG_UD triple-impeller combination and the gas distributor with a diameter of 0.65T under the same power consumption.The optimized combined impeller and gas distributor are determined by the above experiments and simulations.The characteristics of gas-liquid dispersion and mass transfer under the optimized combined impeller are analyzed.First of all,the effects of the agitation speed,gas flow rate and the apparent viscosity on gas-liquid dispersion and mass transfer are obtained by experiments.The correlation equations for the mass transfer coefficient（k _La）and gas holdup of the aqueous CMC system are also obtained.Then,the local gas holdup and the gas-liquid interface area distribution of the stirred reactor under different agitation speeds and gas flow rates were analyzed by using the numerical simulation method.The results are correlated with the mass transfer characteristics of the stirred reactors as well.The results show that the k _La increases with the increase of the agitation speed and the gas flow rate,and decreases with the increase of apparent viscosity.Among agitation speed,gas flow rate and apparent viscosity,the apparent viscosity had the greatest influence on mass transfer with the influence index of-0.527,and the gas flow rate had the least influence on mass transfer with the influence index of 0.215.The results of this work can support reference for the design and scale-up of the gas-liquid stirred reactors of non-Newtonian fluid.