Power consumption in shaking flasks on rotary shaking machines: I. Power consumption measurement in unbaffled flasks at low liquid viscosity

In this first article of a series a new method is introduced that enables t he accurate determination of the power consumption in a shaking flask. The method is based on torque measurements in the drive and appropriate compens ation of the friction losses. The results for unbaffled shaking flasks at l ow viscosities are presented after varying shaking frequency, flask size, f illing volume, shaking diameter, and surface quality (hydrophilic and hydro phobic) of the inner flask walls. The order of magnitude of the values of p ower consumption in shaking flasks is equal to, or even higher than, the va lues typical for agitated tank bioreactors. A physically based model equati on for shaking flasks is derived that introduces a modified power number an d a resulting constant as the only fitting parameter. With this equation, t he measured results are correlated with sufficient accuracy. For the first time, comprehensive data for the power consumption in unbaffled shaking fla sks at low viscosity is available, giving a detailed picture of the influen ces of the different variables. (C) 2000 John Wiley & Sons, Inc.