Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

Abstract

The most important scale-up parameters of aerated bioreactors are investigated in 42 and 340 L vessels, with water and various xanthan gum and carboxymethyl cellulose solutions. The study focuses mainly on mass transfer (k L a) measurements under various operating conditions. The relevance of existing correlations is discussed. The traditional viscosity-contribution approach appears unable to predict the changes in k L a during scale-up and an alternative formulation is proposed. The effect of rheology on power consumption and mixing time is in fair agreement with works published on this topic.

Effect of the height‐to‐diameter ratio on the mass transfer and mixing performance of a biotrickling filter

“…This result was somehow expected since the setting of a higher u L results in higher turbulence and mixing of the liquid phase in the BTF. Since t mix is a parameter strongly linked to the mass transfer performance, these results are in good agreement with the effect of u L on k L a when no stirring was provided in the holding tank. The H/D ratio also affected the mixing time of the BTF.…”

Experimental determination of the shear rate in a stirred tank with a non‐newtonian fluid: Carbopol

“…Much of the most important work on stirred tank hydrodynamics has been devoted to the choice of an appropriate impeller or combination of impellers to maximize mixing and mass transfer on a global scale . Because of the difficulties of studying biological media, model fluids have often been chosen as they are cheaper and easier to use.…”

Bis‐arylidene Oxindoles as Anti‐Breast‐Cancer Agents Acting via the Estrogen Receptor

“…Due to the physical differences between scales, the flow patterns in the bioreactors will differ. In bench‐scale bioreactors, perfect mixing of the broth can be assumed, while in a large bioreactor the mixing time for achieving 95% homogeneity (θ 95 ) can be in the range of minutes [40]. This can lead to oxygen starvation in the medium if the degree of mixing is too low [41].…”

“…The same fermentation broth (i.e. same rheological parameters) in bioreactors with equally scaled dimensions and with the same specific power input will give a Reynolds number in the turbulent flow regime in a production‐scale fermenter while in a bench‐scale fermenter it will yield a Reynolds number in the transitional or laminar flow regime [40, 44]. These differences in mixing properties will lead to differences in mass and heat transfer in the processes [45].…”