Liquid backmixing in bubble columns and the axial dispersion coefficient

Liquid backmixing in bubble columns is commonly described using the 1-D axial dispersion model, wherein all the contributing mechanisms leading to liquid macromixing are lumped into a single axial dispersion coefficient. No relationship has been reported that allows the quantification of various fluid-dynamic contributions to the axial dispersion coefficient in bubble columns. In this study, a Taylor-type analysis was performed to arrive at an expression for the axial dispersion coefficient in terms of the two dominant fluid-dynamic factors, convective recirculation and eddy diffusion. Experimental measurements of the relevant fluid-dynamic parameters are used to study the effects of operating conditions on the axial dispersion coefficient and its contributing factors.