Shear rate and direct numerical calculation of the Metzner-Otto constant for a pitched blade turbine

Gas Dispersion in Non-Newtonian Fluids with Mechanically Agitated Systems: A Review

Gas dispersion in non-Newtonian fluids is encountered in a broad range of chemical, biochemical, and food industries. Mechanically agitated vessels are commonly employed in these processes because they promote high degree of contact between the phases. However, mixing non-Newtonian fluids is a challenging task that requires comprehensive knowledge of the mixing flow to accurately design stirred vessels. Therefore, this review presents the developments accomplished by researchers in this field. The present work describes mixing and mass transfer variables, namely volumetric mass transfer coefficient, power consumption, gas holdup, bubble diameter, and cavern size. It presents empirical correlations for the mixing variables and discusses the effects of operating and design parameters on the mixing and mass transfer process. Furthermore, this paper demonstrates the advantages of employing computational fluid dynamics tools to shed light on the hydrodynamics of this complex flow. The literature review shows that knowledge gaps remain for gas dispersion in yield stress fluids and non-Newtonian fluids with viscoelastic effects. In addition, comprehensive studies accounting for the scale-up of these mixing processes still need to be accomplished. Hence, further investigation of the flow patterns under different process and design conditions are valuable to have an appropriate insight into this complex system.

A General Review of the Current Development of Mechanically Agitated Vessels

The mixing process in a mechanically agitated vessel is a widespread phenomenon which plays an important role among industrial processes. In that process, one of the crucial parameters, the mixing efficiency, depends on a large number of geometrical factors, as well as process parameters and complex interactions between the phases which are still not well understood. In the last decade, large progress has been made in optimisation, construction and numerical and experimental analysis of mechanically agitated vessels. In this review, the current state in this field has been presented. It shows that advanced computational fluid dynamic techniques for multiphase flow analysis with reactions and modern experimental techniques can be used with success to analyse in detail mixing features in liquid-liquid, gas-liquid, solid-liquid and in more than two-phase flows. The objective is to show the most important research recently carried out.

Flow characteristics of the Rushton and pitched blade turbines in turbulent and laminar mixing

The velocity field and concentration distribution of three radial and axial impellers were studied in miscible liquid blending in a stirred tank reactor. To obtain a better insight into the applicability of each impeller system, the influence of velocity profiles on the generated concentration profiles was studied in detail for each impeller. Particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) methods were used as the measurement techniques. In the turbulent regime, the Rushton turbine provided a homogeneous concentration field throughout the reactor by generating high radial and axial velocities in the bottom and upper zones of the tank. Operation comparisons of the up and down-pumping pitched blade turbines illustrated that the up-pumping turbine had a better performance in overall because of producing high turbulence in the upper half of the reactor. In this region, the radial concentration profile approached the final homogenized value in a shorter time. In the laminar regime, all three impellers acted in a similar way and produced a radial flow throughout the reactor.