Liquid phase hydrodynamics in an aerated tank stirred by a down-and an up-pumping pitched blade turbine have been investigated using Particle Image Velocimetry. The effect of agitator configuration and the gas phase on the mean velocity fields and turbulent quantities in the vessel have been investigated. The global mean gas holdup has also been evaluated for the two pumping conditions. For the gas flow rate used, the presence of gas only slightly alters the liquid flow patterns produced by both the down-and up-pumping configurations and causes a general decrease in the mean liquid velocities. The turbulent kinetic energy in the impeller discharge region was not affected by the presence of gas, but in the bulk of the tank, aeration caused a decrease in this value. Global gas holdup was found to be ~36% greater for the up-pumping impeller and a large amount of gas was found to be entrained by the primary circulation loop.

This paper presents an experimental study of pressure drop of single-phase flow and liquid-liquid dispersion through a Sulzer SMX mixer in the turbulent flow regime. Emulsification experiments are performed with various numbers of mixing elements from 2 to 20 and different flow rates ranging from 204 to 600 L/h. Pressure drop in single phase flow when Re is greater than 800 is modeled using a correlation based on the Blasius approach. The pressure drop is quantified at high Reynolds numbers for a liquid-liquid system. The droplet size distribution evolves along the mixer, and 10 mixing elements are required to reach break-up coalescence equilibrium in the case of emulsification experiments. Finally, assuming Kolmogorov's theory of isotropic turbulence, a new correlation is established to predict the Sauter mean diameter in this mixing device as a function of the Reynolds and Weber numbers as well as the number of mixing elements.

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The aim of this paper is to investigate the influence of physico-chemical parameters on liquid-liquid dispersion at high dispersed phase concentration in Sulzer SMV TM mixer. Four different oil-in-water systems involving two different surfactants are used in order to evaluate the effect of interfacial tension, densities and viscosities ratio on mean droplets size diameters. Moreover the influence of the dispersed phase concentration on the pressure drop as well as on the droplet size distribution is investigated. Two different droplets size distribution analysis techniques are used in order to compare the resulting Sauter mean diameters. The comparison between residence time in the mixer and surfactants adsorption kinetics leads to take into account the evolution of the interfacial tension between both phases at short times. Finally experimental results are correlated as a function of dimensionless Reynolds and Weber numbers.

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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-ε 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.

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 low-pressure 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.

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