Research Of Simulation About Mass Transfer In Gas-Liquid Multiple Impellers Stirred Tank

The gas-liquid stirred reactor is widely used in all kinds of area in chemical engineering, and gas-liquid mass transfer, which is the key factor of controlling in many process of technology, is closely related to the output and quality. And in recent years, more and more gas-liquid reactors equipped with multiple impellers as the devopling of large-scale reactor, because the multiple impellers used is positive for the distribution of the power input as certurn demand around all the vessel. Also, all kinds of combinations with different function can be used according to specific demands to make a circulation of the liquid that is beneficial to the actual process. With the developing of the computer technology and CFD(Computation Fluid Dynamics), it is an efficiency way of the scientific and reasonable scaling-up of the gas-liquid reactor to calculate the interaction between gas and liquid with computers, which can make prediction to the practice process without actual experiment.CFD numerical simulation is used in this essay. With the help of CFX software, simulation of a gas-liquid reactor equipped with three impellers combination (HEDT below and two WHu above) was run. In the simulation, water is used as the liquid and air is the gas. Different kinds of simulation schemes combine with different mass transfer models are investigated as the key focus. The relationship is investigated between the power consumption per unit mass, the overall gas volume fraction and volumetric mass transfer coefficient, and all of the three parameters are calculated through simulation and compared with the experiment. Try to find the factors that make influence to mass transfer and the best simulation methods, and then the methods are compared and evaluated.For power consumption per unit mass, the average of relative error of different simulation methods compared to experiment is around 2.5%. For the overall gas volume fraction, there is a certain deviation which the relative error is around 14%, and it is around 12% to the volumetric mass transfer coefficient. The relative error of the simulation is within the acceptable range. The simulation can provide a reference to the industrial scale-up.In the gas-liquid reactor, the domain with large power input and intense gas-liquid interaction has a promotion in both a and kL. So the volumetric mass transfer coefficient is big in this kind of domain.In this research, four simulation schemes combine with four mass transfer models are studied, and four of the combinations that perform the best are concluded. There are both advantages and disadvantages in there methods, and each of them is adopted to a certurn situation. The method of using standard k- s model at low resolution couple with eddy model has a good accuracy and the lowest calculated amount, but there are some problems with the local distribution. The one using standard k-? model at high resolution couple with slip velocity model is the best method of calculating the volumetric mass transfer coefficient but it performs poor in calculating other parameters. The method of using RNG k-? model couple with the slip velocity model has the best accuracy among all the element, but the accuracy of it is not that good which is far more better than the other methods and has a large amout of calculating. So when it is needed to take all the factors into consideration, maybe this method is not that good. And using k-? EARSM model couple with eddy cell model acts well in the situation when the gas superficial is high, but it is not applicable to other situations.