Investigation of the impact of probes and internals on power and flow in stirred tank reactors

Abstract

This study characterises the power requirements and flow patterns in several commercial stirred tank bioreactors with working volumes ranging from 60 mL to 1 L, and investigates the isolated impact of internals, i.e. baffles and probes, on the power number, P0. Results show that the presence of probes leads to a rise of the turbulent power number, P0, equivalent to the presence of baffles, and as the number of internals increases the variation of P0 gets smaller until it plateaus for large probe quantity and high-volume blockage. Internals have a greater impact on flow with radial flow impellers, causing a significant increase in P0 in comparison to axial flow impellers. An experimental and computational flow dynamics study is also conducted to investigate the interaction between the probe wake and the impeller trailing vortices, and an estimate is provided of the form drag from the pressure distribution acting on the probe, with a good agreement to the corresponding power number increase. A comparison between P0 data obtained from conventional-cylindrical and novel-streamlined probe configurations shows that optimising probe geometry and location with respect to the incoming flow can be an effective approach for reducing power requirements, local values energy dissipation rate and stress levelsinside the tank. This study provides valuable insights into the impact of internal components and flow type on power input per unit volume, P/V, in small-scale bioreactors and supports the development of more robust scaling procedures for the biopharma industry.