Correlation between conductivity and liquid hold-up for a multi-segment industrial foam probe for fermentation

Abstract

In this paper we describe the use of a multi-segment conductivity probe for measuring conductivity as a function of height and time in a foam phase. Relationships between the conductivity ratio (ratio of conductivity in a foam to conductivity in the bulk liquid) and the liquid hold-up in the foam have been described previously by a number of researchers. If conductivity measurements from the multi-segment probe could be interpreted in terms of liquid hold-up in the foam this would provide valuable information about the physical nature of foam in, for example, a fermentation process, in which foams are known to have a number of adverse effects. Conductivity ratios have been determined for two multi-segment probes (one measures over a rectangular section of foam central to a cylindrical vessel, whilst the other measures over a disk like slice of foam). Liquid hold-up was measured using a specially designed column, which allows selected sections of foam (corresponding to segments on the foam probe) to be collected and weighed for determination of liquid content. A range of solutions and process parameters were used to generate foams with a range of structures and liquid hold-ups. At low values of liquid hold-up (<0.04), the conductivity ratios could be predicted well by Lemlich’s equation, which assumes that all the liquid is in the Plateau borders irrespective of process conditions (although there was a concentration dependence for the two BSA concentrations considered). At higher values of liquid hold-up, data were generally better predicted by an equation, which is an interpolation between Lemlich’s equation (valid in the dry limit) and Maxwell’s equation (valid for higher liquid hold-ups). These results should be useful in allowing prediction of dynamic changes in liquid hold-up as a function of foam height from conductivity ratios determined using a mutli-segment conductivity probe similar to the fermenter probe described here, in fermentation processes.