Characterisation of flexible baffles in an oscillatory baffled column

In our previous studies the volume-averaged strain rates, of 2-22 s(-1), we re obtained in an oscillatory baffled column (OBC) based on velocity measur ements over a half baffled cell for oscillatory Reynolds numbers of 1000-40 30. These values are very low compared with those in a traditional stirred tank vessel (at least > 100 s(-1)) for similar operational conditions and t he same power consumption. It was also observed that the volume-averaged st rain rates in the OBC fluctuated with the phase of oscillation over any cyc le, with high values coinciding with eddy generation, and low values with e ddy cessation. The objective of this study is to show that such fluctuation s can be attenuated by employing innovative flexible baffles, whose inside edges move with the fluid oscillation. In this paper experimental measureme nts of velocity vector maps and strain rate distributions using Digital Par ticle Image Velocimetry (DPIV) are presented for both conventional and flex ible baffles in an OBC. Mixing characterisation, in terms of axial dispersi on coefficients, are compared for both baffle designs. The results show tha t the flexible baffles can reduce the fluctuations and magnitudes of the vo lume-averaged strain rates in the OBC without compromising the mixing perfo rmance. Low and uniform strain rate distributions in time and space are ess ential biochemical, biomedical and pharmaceutical applications where shear sensitive cultures are involved. (C) 2001 Society of Chemical Industry.