Mode decomposition and Lagrangian structures of the flow dynamics in orbitally shaken bioreactors

In this study, two mode decomposition techniques were applied and compared to assess the flow dynamics in an orbital shaken bioreactor (OSB) of cylindrical geometry and flat bottom: proper orthogonal decomposition and dynamic mode decomposition. Particle Image Velocimetry (PIV) experiments were carried out for different operating conditions including fluid height, h, and shaker rotational speed, N. A detailed flow analysis is provided for conditions when the fluid and vessel motions are in-phase (Fr = 0.23) and out-of-phase (Fr = 0.47). PIV measurements in vertical and horizontal planes were combined to reconstruct low order models of the full 3D flow and to determine its Finite-Time Lyapunov Exponent (FTLE) within OSBs. The combined results from the mode decomposition and the FTLE fields provide a useful insight into the flow dynamics and Lagrangian coherent structures in OSBs and offer a valuable tool to optimise bioprocess design in terms of mixing and cell suspension. Published by AIP Publishing. https://doi.org/10.1063/1.501630

Mixing Time in Intermediate‐Sized Orbitally Shaken Reactors with Small Orbital Diameters

Orbitally shaken reactors (OSR) are widely used in bioprocess development; however, a scaling law between large reactors, usually shaken in incubators at an orbital diameter of d o = 1.5–5 cm, and microwell plates, shaken in benchtop thermomixers at d o = 3 mm, is still missing. Here, the mixing time was measured in two reactors with the same volume but either cylindrical or square geometry for d o = 3 mm. For such a small d o, the acceleration mode to reach the final speed in the cylinder was found to greatly affect the free surface oscillations and thus the mixing time. The stepwise mode resulted in mixing times approximately six times smaller than in the direct mode. The natural frequency of the reactor, which is independent of d o, was found to be an effective scaling parameter for systems with small d o