Measurement Of The Mass And Heat Transfer Coefficients And Simulation Of Flow Property In Magnetically Stabilized Bed

Combining the characteristics of the fluidized bed with those of the fixed bed, the magnetically stabilized bed reactors have experienced widely industrial applications. Up to now, it lacks of fundamental data for the design and scale up of these kinds of reactors. Ttherefore, the characteristics of gas-liquid mass transfer, liquid-solid mass transfer, liquid-solid heat transfer and the local hydrodynamics have been studied in this dissertation. The gas-liquid mass transfer characteristic in the gas-liquid concurrent and countercurrent three-phase magnetically stabilized bed have been studied in this paper. Effects of operation conditions and physical parameters (such as magnetic field intensity, superficial liquid velocity, superficial gas velocity, particles size and liquid viscosity) on the gas-liquid mass transfer have been obtained. It shows that under the effect of external magnetic field, the volumetric mass transfer coefficients of gas-liquid mass transfer in the gas-liquid concurrent and countercurrent three-phase magnetically stabilized bed are larger than that of normal three-phase fluidized beds. The gas-liquid mass transfer coefficient k a increases with the increase of magnetic field intensity, superficial gas velocity, superficial liquid velocity and particle size, showing an approximately linear increase with superficial gas velocity. In the lower viscosity range, the increase of liquid viscosity makes for the process of gas-liquid mass transfer. Two correlation equations of gas-liquid mass transfer coefficients have been obtained for the gas-liquid concurrent and countercurrent three-phase magnetically stabilized bed respectively, which show good agreement with the experiments. The electrochemical method is used to determine the liquid-solid mass transfer coefficients in gas-liquid countercurrent three-phase magnetically stabilized bed. It shows that by comparison with normal countercurrent three-phase fluidized bed, the liquid-solid mass transfer coefficient Ks in countercurrent three-phase magnetically stabilized bed is larger. The liquid-solid mass transfer coefficient Ks increases with the increase of magnetic field intensity, superficial gas velocity and superficial liquid velocity, but decreases with the increase of liquid viscosity and liquid surface tension. The local liquid-solid mass transfer coefficient Ks almost remains constant, and the axial distribution is uniformity, but the radial distribution is different, except for a little of large near the wall, the liquid-solid mass transfer coefficient Ks is uniformity too in other places. A correlation equation of the liquid-solid mass transfer coefficient has been established, which can predict the liquid-solid mass transfer coefficient well in the range of experiments operation conditions. Measurement of electrical metal thermo-foil heater surface temperature is used to study the liquid-solid heat transfer characteristic in liquid-solid two-phase, gas-liquid concurrent three-phase and gas-liquid countercurrent three-phase magnetically stabilized bed. It concludes that the liquid-solid heat transfer coefficient in magnetically stabilized bed is smaller than that of conventional fluidized bed, and the heat transfer coefficients increases with the increase of superficial liquid velocity, but decreases with the increase of magnetic field intensity and liquid viscosity. And the local radial distribution of heat transfer coefficient is uniformity. The increase of superficial gas velocity and decrease of liquid surface tension also result in increasing of heat transfer coefficient in gas-liquid concurrent and countercurrent three-phase magnetically stabilized. Three correlation expressions of heat transfer coefficient have been gained for the liquid-solid two-phase, gas-liquid concurrent three-phase and gas-liquid countercurrent three-phase magnetically stabilized bed, respectively. The Eulerian-Eulerian method combining with kinetic theory of granular flow is used for numerical simulation of the hydrodynamics characteristics in the liquid-solid and gas-solid two-phase magnetically stabilized bed. It shows a good agreement between the simulation results and the experiments, and the average relative error for the bed expansion ratio of simulated value and the experimental data is 2.21%, and the average relative error for the local solid holdup is 1.44%. Therefore, this model can be used to estimate the evolvement of the flow structure, which is fundamental to design of industrial reactors.