Detecting non-uniform foam density using electrical resistance tomography

Measurement of the density distribution in foams is required for the monitoring and control of foam structure and breakdown. In flowing foam systems, rapid measurement is required for process control. This density distribution is difficult to measure non-intrusively, due to the high gas fraction, the foam opacity and the relative fragility of the system. Electrical resistance tomography (ERT) is shown to be a suitable method for the visualisation of regions of different density in foams. Close correspondence was found between local foam density, observed as regions of different bubble sizes, and electrical conductivity. The results show that ERT can identify non-uniform density regions within a foam and thereby affords a new technique for process control in a foaming system. (C) 1999 Elsevier Science Ltd. All rights reserved.