| In the process industry,the occasions involving gas-liquid two-phase mixing are very common.By stirring two-phase fluids in the equipment,the gas undergoes a series of processes such as breakup and coalescence,so as to improve the two-phase mass transfer area to complete the production of industrial products.Therefore,the dispersion characteristics of gas-liquid two-phase are important reference index to obtain high-quality products and improve production efficiency.Due to the complexity of the interaction between gas and liquid,the study of its dispersion characteristics and quantitative description is still an in-depth work.In this paper,the flow field and dispersion characteristics of gas-liquid two-phase in a double-layer stirred tank were studied within the research scope of water and air in the range of high Reynolds number,which provides a theoretical reference for deepening the understanding and application of the gas-liquid two-phase mixing process.Firstly,the agitated experimental study was carried out in the double-layer stirred tank with the combination of PBT and Rushton impeller,and the high-speed camera was used to photograph the macroscopic flow field characteristics and the bubble dispersion process during the experiment.The information of bubbles is obtained through the morphological image processing technology,which provides the experimental data basis for the subsequent numerical simulation of bubble size setting and also provides the image information for the research on the bubble breakup and coalescence behavior.Based on the literature verification and theoretical analysis,the numerical methods and models provided by Fluent were analyzed.Through the comparison ofnumerical simulation method and experimental data in literature,the outlet boundary conditions and drag models that are more suitable for numerical simulation of gas-liquid two-phase at high Reynolds number are explored,and the bubble coalescence model are described.The results show that the gas holdup predicted by Grace model and pressure-outlet boundary is too high,and the simulation results of Tomiyama model and degassing outlet are closer to the experimental values.Based on the results of this study,a gas-liquid two-phase CFD-PBM coupled numerical calculation model was established for the double-layer stirred tank.In order to verify the model,the power values at different speeds and the gas dispersion obtained from the simulation were compared with the experimental values.It is found that the simulation results are in good agreement with the experimental data,which verifies the feasibility of the numerical model established in this paper.Based on the CFD-PBM coupled model,the flow field,gas holdup and bubble size distribution under different speeds and gas inlet rates were simulated.The results show that with the increase of the speed,the degree of turbulence in the agitation tank is increased and the ability of the blade to pump fluid is enhanced.It also effectively expands the gas diffusion range and accelerate the bubble breakup,so the average size of the bubble is reduced.When the gas inlet rate is increased,the influence of the structure of the flow field is not significant,but the position of the circulation vortex is shifted and the overall gas holdup is increased.To a certain extent,the collision of the bubbles has been accelerated and the average size of the bubbles has decreased.It is explained that the differences between the two drag models and the influence mechanism of the speed on the simulation results by comparing the shear stress clouds.The experimental images and simulated vorticity diagram clearly show the shape of cavitation and elaborate its generation and influence. |
