Effect of viscosity (or lack thereof) on the flooding point in a gassed stirred tank.

Flooding is a condition where gas rises vertically upwards from the sparger and through the stirrer region. The flooding point, the impeller speed at which flooding is overcome, is usually considered the minimum operating condition for gas-liquid mixing processes in stirred tanks. Most previous studies on flooding have been performed using low viscosity fluids in the turbulent regime. The present study shows that the flooding point does not change significantly when the viscosity increases (and therefore the Reynolds number decreases) by three orders of magnitude. • The flooding point, N F , can be reliably obtained from shaft torque measurements. • N F is independent of liquid viscosity down to a Reynolds number of approx. 300. • N F estimated using turbulent correlations or data are valid in transitional flow. [ABSTRACT FROM AUTHOR]