http://bioprocesos.unq.edu.ar/Biopro%20II/Paper%20escalado.pdf

Bioreactor scale-up and oxygen transfer rate in microbial processes: An overview

Mechanically agitated gas-liquid reactors

Correlation of mean drop size and minimum drop size with the turbulence energy dissipation and the flow in an agitated tank

Mixing and fast chemical reaction—I: Test reactions to determine segregation

Multiple-impeller systems with a special emphasis on bioreactors: a critical review.

Based on the finding that the bubbling-controlling condition, the agitation-controlling condition, or the intermediate condition may predominate in an aerated mixing vessel, correlative equations for kLa valid for a wide range of operating conditions are proposed. In addition, the type of mixing of the gas phase in aerated mixing vessels is discussed, and plug-flow type mixing is recommended since the logarithmic mean value of entrance and outlet compositions of gas gives a reasonable gas absorption rate.

Gas absorption in aerated mixing vessels

Aerated mixing vessels are often used in chemical and biological industries. When the rate of gas absorption controls the rate of reactions, kLa is used as the design standard. It was previously reported by the present authors that the overall vessel condition varied from bubbling-controlling condition at relatively high gas rates to agitation-controlling condition at relatively high impeller speeds via intermediate condition. According to this two-region model, kLa for the airwater system in the aerated mixing vessel has been correlated well in a wide range of operational conditions. In this report, the two-region model is applied to Newtonian liquids with various physical properties and to non-Newtonian liquids, and reasonable dimensionless correlative equations are obtained.

Gas absorption in aerated mixing vessels with non-newtonian liquid

The authors ascertained the applicability of the method proposed by Metzner to correlate agitation power for pseudoplastic liquids. For a ribbon impeller that is effective for highly viscous liquids this method is also useful. It was found by the authors that the proportionality constant between average shear rate and impeller speed for pseudoplastic liquids can be estimated by using experimental constants of the power equation for Bingham plastic liquids. Correlated results by using estimated values showed good agreement with data for various impellers. For ribbon and anchor impellers, a correlation curve similar to that for Newtonian liquids was observed throughout the whole region of Reynolds number. For turbines and paddles, however, curves for pseudoplastic liquids deviate from Newtonian in the transition region. These phenomena were explained by the spreading of the discharge flow range as in the case of Bingham plastic liquids.

Power consumption of mixing impellers in pseudoplastic liquids

An experimental equation to estimate power consumption in the mixing of plastic fluids was derived. For ribbon, anchor, turbine and paddle mixers, the following equation was obtained. Np = β(Re")-1 + aNy + 1where Ny (= τy/ρn2d2) is a non-dimensional power number for the yield stress and a is a constant and can be calculated for simple mixers using the following equations. Fnorizontal = 0.58τy, Fvertical = 2.81ryFor turbine and paddle mixers, a drastic transition state was observed between laminar and turbulent regions. In the transition region the periodical generation and disappearance of vortex was observed and the effect was explained by the periodic power consumption of the mixers.

https://www.jstage.jst.go.jp/article/jcej1968/3/2/3_2_237/_pdf

Masabumi Nishikawa

Papers

Gas absorption in aerated mixing vessels

Gas absorption in aerated mixing vessels with non-newtonian liquid

Power consumption of mixing impellers in pseudoplastic liquids

Power consumption of mixing impellers in bingham plastic liquids

Turbulence energy spectra in baffled mixing vessels