In our previous studies the volume-averaged strain rates, of 2-22s-1, were obtained in an oscillatory baffled column (OBC) based on velocity measurements over a half baffled cell for oscillatory Reynolds numbers of 1000-4030. These values are very low compared with those in a traditional stirred tank vessel (at least >100s-1) for similar operational conditions and the same power consumption. It was also observed that the volume-averaged strain rates in the OBC fluctuated with the phase of oscillation over any cycle, with high values coinciding with eddy generation, and low values with eddy cessation. The objective of this study is to show that such fluctuations can be attenuated by employing innovative flexible baffles, whose inside edges move with the fluid oscillation. In this paper experimental measurements of velocity vector maps and strain rate distributions using Digital Particle Image Velocimetry (DPIV) are presented for both conventional and flexible baffles in an OBC. Mixing characterisation, in terms of axial dispersion coefficients, are compared for both baffle designs. The results show that the flexible baffles can reduce the fluctuations and magnitudes of the volume-averaged strain rates in the OBC without compromising the mixing performance. Low and uniform strain rate distributions in time and space are essential biochemical, biomedical and pharmaceutical applications where shear sensitive cultures are involved. © 2001 Society of Chemical Industry.
- Digital particle image velocimetry
- Flexible baffles
- Oscillatory baffled column
- Velocity vector maps
- Volume-averaged strain rate