Computational and experimental investigation of flow and fluid mixing in the roller bottle bioreactor

The fully three-dimensional velocity field in a roller bottle bioreactor is simulated for two systems (creeping flow and inertial flow conditions) usi ng a control volume-finite element method, and validated experimentally usi ng particle imaging velocimetry. The velocity fields and flow patterns are described in detail using velocity contour plots and tracer particle pathli ne computations. Bulk fluid mixing in the roller bottle is then examined us ing a computational fluid tracer program and flow visualization experiments . It is shown that the velocity fields and flow patterns are substantially different for each of these flow cases. For creeping flow conditions the fl ow streamlines consist of symmetric, closed three-dimensional loops; and fo r inertial flow conditions, streamlines consist of asymmetric toroidal surf aces. Fluid tracers remain trapped on these streamlines and are unable to c ontact other regions of the flow domain. As a result, fluid mixing is great ly hindered, especially in the axial direction. The lack of efficient axial mixing is verified computationally and experimentally. Such mixing limitat ions, however, are readily overcome by introducing a small-amplitude vertic al rocking motion that disrupts both symmetry and recirculation, leading to much faster and complete axial mixing. The frequency of such motion is sho wn to have a significant effect on mixing rate, which is a critical paramet er in the overall performance of roller bottles. (C) 2000 John Wiley & Sons , Inc.