Abstract
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.
Highlights
There have been significant advances in the theory of inertial suspensions, in particular those that describe the rheology of bubble suspensions
In addition to the measurement of the gas volume fraction, the presented system is capable of measuring the bubble velocity by cross correlating the signals of two identical probes placed at a small distance
At low concentration the superficial gas velocity measurements are slightly higher than the values measured directly with the impedance probe, but for more concentrated mixtures the measured bubble velocity is always larger than that calculated from the flow rate
Summary
There have been significant advances in the theory of inertial suspensions, in particular those that describe the rheology of bubble suspensions. The extent of the validity of these theories could only be assessed if comparisons with detailed experimental measurements are performed. There exist several other techniques to measure volume fraction in a multiphase flow which include light attenuation, transmission of gamma rays, neutron radiography, etc. All of these techniques are limited to obtain line or volume average measurements. In addition to the measurement of the gas volume fraction, the presented system is capable of measuring the bubble velocity by cross correlating the signals of two identical probes placed at a small distance. Detailed sets of experimental results and their comparisons with theoretical predictions can be found in Refs. Detailed sets of experimental results and their comparisons with theoretical predictions can be found in Refs. 10 and 11
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