Question

To ensure turbulent conditions and minimum mixing time during
agitation with a turbine impeller, the Reynolds number must be at least 10⁴
1. A stirred laboratory-scale bioreactor equipped with a 5-cm turbine impeller
is operated at 800 rpm. If the density of broth being stirred is close to that of water, what is
the upper limit for viscosity of the suspension if adequate mixing is to be maintained?
2.The mixing system is scaled up so the tank and impeller are 15 times the
diameter of the laboratory equipment. The stirrer in the large vessel is operated so that the
stirrer tip speed (tip speed = πNiDi) is the same as in the laboratory apparatus. How does scale-up affect the maximum viscosity allowable for maintenance of turbulent mixing conditions?

Answer 1

For turbulent condition Reynold no. should be morethen 104 ( according to question)

So, in first case dynamic viscosity condition is calculated using Reynold No.

Dynamic Similarity conditions are applied for 2nd case.