LAUSR

This paper provides experimental evidence supporting the idea that the transition to turbulent flow is governed by the ratio of the specific power input (SPI) and the term G/λ, where G is the viscoelastic modulus of the liquid and λ is the relaxation time, in a vessel containing a fluid agitated by sparged gas (air) at low superficial gas velocities. This finding provides a method for judging the flow regime within a vessel a priori using a nondimensional quantity and can be used as a scale for decision-making in cases where real-time visual analysis is not possible. While the work reported below is motivated by anaerobic digestion of wastewater sludge, the results are obtained using model liquids and should, therefore, have wide application in chemical process engineering, such as CFD simulation of mixing in viscoelastic fluids and mixing in fermentation processes.