Flow generated by radial flow impellers: PIV measurements and CFD simulations

Particle image velocimetry (PIV) and computational fluid dynamics (CFD) have been used to investigate the single phase and gas-liquid flow generated by a Scaba SRGT turbine. The key details of the trailing vortices, the turbulent flow around the impeller blades and the accumulation of gas have been studied by using PIV measurements and CFD simulations. Both the experimental and numerical results show that the flow and the trailing vortices are not altered significantly upon gassing. The simulated results are generally in good agreement with the experimental findings. The CFD simulations also show that only small low-pressure regions exist behind the blades of the Scaba turbine compared with the very large lowpressure zones formed by the Rushton turbine. These results enable better understanding of the improved performance of the Scaba turbine for gas-liquid dispersions compared with the Rushton turbine

Gas-liquid flow generated by a pitched blade turbine : PIV measurements and CFD simulations

Axial flow impellers, like pitched blade impellers, are being increasingly used for gas-liquid systems in stirred vessels. In this work we have used particle image velocimetry (PIV) and computational fluid dynamics (CFD) models to investigate gas-liquid flow generated by a down-flow pitched blade turbine. PIV measurements were carried out in a fully baffled stirred vessel (of 0.19 m diameter) with a dished bottom. Angle resolved measurements of the flow field with and without gas dispersion were carried out. An attempt was made to capture key details of the trailing vortex, the accumulation of gas and the flow around the impeller blades. A two-fluid model along with the standard k-e turbulence model was used to simulate dispersed gas-liquid flow in stirred vessel. The computational snapshot approach was used to simulate impeller rotation and was implemented in the commercial CFD code, FLUENT4.5 (of Fluent. Inc., USA). The model predictions were verified by comparison with the PIV measurements and other available experimental data. The computational model and results discussed in this work are useful for better understanding and simulating of gas-liquid flow generated by axial impellers in stirred vessels

CFD simulation of gas-liquid stirred vessel: VC, S33, and L33 flow regimes

A comprehensive computational model based on the Eulerian-Eulerian approach was developed to simulate gas-liquid flows in a stirred vessel. A separate submodel was developed to quantitatively understand the influence of turbulence and presence of neighboring bubbles on drag acting on bubbles. This submodel was used to identify an appropriate correlation for estimating the interphase drag force. The standard k-ε turbulence model was used to simulate turbulent gas-liquid flows in a stirred vessel. A computational snapshot approach was used to simulate motion of the standard Rushton turbine in a fully baffled vessel. The computational model was mapped onto FLUENT4.5, a commercial CFD solver. The model predictions were compared with the previously published experimental data of Bombac and co-workers. The model was used to simulate three distinct flow regimes in gas-liquid stirred vessels: vortex clinging (VC), alternating small cavities (S33), and alternating large cavities (L33). The predicted results show reasonably good agreement with the experimental data for all three regimes. The computational model and results discussed in this work would be useful for understanding and simulating gas holdup distribution and flow regimes in stirred vessels