Numerical Investigation of Gas Dispersion, Drag-Coefficient Distribution, and Mixing Performance in a Rushton-Turbine Stirred Tank Using a Euler–Euler Model

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Gas dispersion and liquid circulation are critical factors governing the performance of gas–liquid stirred tanks, yet the coupled effects of operating conditions and impeller geometry on hydrodynamic behavior remain insufficiently understood. In this study, a Euler–Euler two-fluid model coupled with the standard k–ε turbulence model is employed to investigate gas dispersion, drag-coefficient distribution, power consumption, and mixing dead zones in a Rushton turbine stirred tank. The numerical model is validated against published experimental data before examining the influences of impeller rotational speed, gas injection velocity, blade height, and blade length. The results reveal that high drag coefficients are concentrated along the impeller discharge path, vortex-core regions and near-wall annular structures, indicating zones of reduced gas–liquid slip and strong interphase momentum exchange. Increasing the stirring speed from 400 to 800 rpm reduces the fluid and liquid dead-zone fractions from 93.31% to 54.27% and from 24.64% to 12.08%, respectively, but increases the power from 8.78 to 77.00 W. By contrast, increasing the gas-injection velocity from 5 to 13 m/s decreases the power draw but expands the fluid dead-zone fraction from 50.94% to 94.54%, indicating a marked deterioration in effective liquid circulation associated with gas accumulation near the impeller. Blade height mainly adjusts local shear and gas-holdup uniformity, whereas blade length is the dominant geometric parameter for dead-zone suppression, although its benefit becomes marginal at the largest length because of the severe power penalty. These findings clarify the coupled effects of gas dispersion, liquid circulation, drag-coefficient distribution, and power demand, and provide guidance for the design and operation of gas–liquid stirred tanks.

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