Shear Problems in Fermentation Fluids

Midler and Finn (1966) also studied disruption at relatively high shear rates in a Couette-type device. At shear rates below 1200sec only slight damage was observed. As shown in Fig. 12, data for two runs at the same viscosity of 69c.p. and shear rate of 1970sec , but at different gap widths, fall on the same line. Such consistency supports 2  

When the concept of the mean shear rate predicted by Metzner (1961) was applied, an agitator speed of 700 rpm used in Midler s experiment should have an effea equivalent to only 120 see . However, comparing this with the results in the Couette type device, the equivalent shear rate in those turbulent conditions should be 10-100 times those predicted by Metzner. Therefore, Midler and Finn suggested that maximum rather than average shear stresses must be considered in the presence of high local velocity gradients. 

We (1968) also studied the influence of agitation on disruption of two kinds of mycelial pellets, Lentinus edodes and Aspergillus tdger, in a conventional stirring tank. Since sometimes the growth type of pellet 

For the first of these effects the following experimental correlation was found  

In the second case the rapture of mycelial pellets by agitation follows a monomolecular rate of reacticm as shown in Eq. (12) 

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