Impedance probe to measure local gas volume fraction and bubble velocity in a bubbly liquid

We have developed a dual impedance-based probe that can simultaneously measure the bubble velocity and the gas volume fraction in length scales comparable to the bubble diameter. The accurate determination of the profiles is very important for comparisons with existing theories that describe the rheological behavior of bubbly liquids. The gas volume fraction is determined by the residence time of bubble within the measuring volume of the probe. We have found that the details of the bubble-probe interactions must be taken into account to obtain an accurate measure of the gas volume fraction at a point. We are able to predict the apparent nonlinear behavior of the gas volume fraction measurement at large concentrations. The bubble velocity is obtained from the cross correlation of the signals of two closely spaced identical probes. Performance tests and results are shown for bubble velocity and bubble concentration profiles in a gravity driven shear flow of a bubbly liquid. (C) 2003 American Institute of Physics.