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

Abstract

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.

Prediction of Gas Holdup in an Aerated Coaxial Mixer Containing Yield Stress Fluids for Mixing Process System Development

“…One important application of multiphase mixing systems takes place in bioreactors, where an adequate gas distribution is required to avoid the formation of oxygen-deficient regions [6,7]. Several of these bioreactors comprise non-Newtonian fluids in which the agitation mechanism needs to overcome the mixing challenges arising from the rheological nature of these fluids [8][9][10]. In view of that, this work aims to characterize the gas dispersion in pseudoplastic fluids possessing yield stress in terms of the gas holdup and investigate the effect of different process conditions on the mixing performance.…”

Degassing of Aluminum Alloy Melts by High Shear Melt Conditioning Technology: An Overview

“…They increase with rotor speed and decrease with the gas flow rate. Three main regimes associated with the gas-liquid mixing can be defined in mechanically agitated systems [33]: Flooded, Loaded, and Dispersion. A fourth regime, denoted as Recirculation, can be also considered as an evolution or extension of the dispersion regime [34][35][36][37].…”

Power Consumption Characterization of Energy-Efficient Aerated Coaxial Mixers Containing Yield-Stress Biopolymer Solutions

“…Under the counter-rotation operation, in turn, the power consumption of the close-clearance impeller increases since its rotation is in the opposite direction of the predominant fluid flow. , Besides the individual effect of the main process variables, there is a significant influence of variable interaction on the power mixing characteristics. In fact, the operating variables’ effects on the mixing performance normally depend on the rheological properties and impeller configurations. , For that reason, different empirical correlations have been fitted and utilized for power uptake estimation according to the fluid and impeller types, as reviewed by Barros et al…”

“…In fact, the operating variables' effects on the mixing performance normally depend on the rheological properties and impeller configurations. 23,24 For that reason, different empirical correlations have been fitted and utilized for power uptake estimation according to the fluid and impeller types, as reviewed by Barros et al 25 Furthermore, the power consumption is characterized by the power curve featured by the power number versus the Reynolds number, which accounts for viscous, inertial, and resistance effects on the mixing process. The power curve allows for accurate prediction of the power demand of a stirred vessel once the Reynolds number is known.…”