Studies On Multiphase Flow Transport Phenomena In Several Chemical And Metallurgical Reactors

Multiphase flow transport phenomena in several chemical and metallurgical reactors have been studied experimentally and computationally in this dissertation. The Eulerian multiphase modeling approach has been adopted in computation with the commercial software CFX4.4. In calculation, submodels (e.g. micro-inclusion model) have been coded in FORTRAN, and coupled in CFX4.4 through USER FORTRAN interface. Main contents and results of this dissertation are as following: (1) Studies on control of fluid flow and inclusion removal in tundishGas bottom-blowing technique has been introduced to control fluid flow and inclusion removal in tundish.First of all, experiments have been carried out in a water model. The flow pattern, residence time distribution, dead volume fraction etc have been studied with varying gas flow rates and at three different blowing positions. Results show that gas bottom-blowing is in favor of improving flow pattern, increasing average residence time, reducing dead volume fraction. Gas in tundish can form a baffle-like gas column. The best results can be obtained with gas blowing at position B2.Based on the experimental results, Multi-fluid model has been developed to model gas-liquid flow in water model tundish. Gas and water have been considered as laminar and turbulent respectively. Multiphase scalar transport equations have been developed to model the tracer transport in tundish. The effects on improving flow pattern and residence time distribution with different gas blowing positions and gas flow rates have been studied. Results from numerical simulation are consistent with those obtained from experiments.Gas-liquid multi-fluid model, coupled with multiphase scalar transport equations, has been developed and used in modeling gas-liquid-solid system successfully. In modeling, the micro-inclusion model (flotation, collision, coalition, and bubble attachment etc) has been coded in FORTRAN and coupled in CFX4.4 through USER FORTRAN interface. Numerical results show that, small inclusions are difficult to be removed without collision; the removal rate of 50μm inclusion is about 40%; particle collision can improve the removal rate of small inclusion significantly; with gas bottom-blowing,inclusion particle can attach to the bubble, hence removal rate can be improved; baffle-like gas column in bottom-blown tundish, takes on an "rinse effect" on molten steel, which is in favor of inclusion removal.Experimental studies on inclusion removal are also carried out in water model without gas blowing. Polystyrene plastic particles have been used as simulation particles, which have been graded into four groups with a new developed method. Experiments show that the accuracy and repeatability of water model experiment can be improved with this new method. Numerical results on inclusion removal have been validated by the experimental results.(2) Numerical simulation of side-blown Ferro-alloy refining converter Based on former experimental results, a gas-liquid multi-fluid modelhas been developed to model side-blown Ferro-alloy refining process. Gas and liquid have been both considered as turbulent. In numerical simulation, bubble induced turbulence and turbulent dispersion force have both been included with Sato model and Lopez model respectively. Gas-liquid flow pattern has been studied. Tracer, which is modeled by multiphase scalar transport equation, has been used to evaluate the mixing rate and mass transfer ability of the converter with different side-blown modes. Conclusions obtained from numerical simulation are confirmed by the results obtained from It pilot converter by Xinyu Iron&Steel Corp. and the former water model experiment.(3) Numerical simulation of radial flow moving-bed reactorBased on dense particle multi-fluid transport equation and inter-phase drag model, a simplified CFD model has been developed, which is suitable for radial flow moving-bed reactor simulation. The flow pattern and distribution uniformity have been studied in the same reactor with two different porosity of catalyst bed. Results obtained in situ confirm that the developed CFD model coupled with Ergun drag model can be used in calculating fluid flow in radial flow moving-bed reactor.Other works concerned with multiphase flow have also been done during my PhD studies, some of these works have been put in the appendices with abstracts.