Shear rate in stirred tank and bubble column bioreactors

Stirred tanks and bubble columns are widely used as mixing essels and bioreactors. Average spatial fluid velocity gradients t the level of the eddies or the prevailing shear rate, is an imporant variable in bioreactors but is not easy to characterize. A nowledge of shear rate is essential for at least two main reasons: 1) shear rate influences the average apparent viscosity of nonewtonian fluids and hence affects power absorption, mixing haracteristics and mass transfer phenomena [1]; (2) microoranisms, bioflocs and other suspended solids are susceptible to amage that is dependent on the prevailing shear rate and assoiated shear stress [2,3]. The main equations for estimating average shear rate γ and he maximum shear rateγmax in the impeller zone of stirred tanks re summarized in Table 1 [2,3]. Most authors have correlated