The power input in stirred bioreactors can be measured through the torque that acts on the impeller shaft during rotation. This manuscript describes how an air bearing can be used to effectively reduce friction losses observed in mechanical seals and improve the accuracy of power input measurements in small-scale vessels.
Kaiser, S. C., Werner, S., Jossen, V., Blaschczok, K., Eibl, D. Power Input Measurements in Stirred Bioreactors at Laboratory Scale. J. Vis. Exp. (135), e56078, doi:10.3791/56078 (2018).