Optical void measurement method for stratified wavy two phase flows

We developed a measurement method to determine the phase distribution in a stratified wavy two-phase flow of water and air. It is based on an optical observation of the flow, followed by an image processing and evaluation process. Two-dimensional images were taken of a three-dimensional channel flow. Through averaging in the channel depth and integration over time, a two-dimensional distribution of the liquid and the gaseous phase of the channel flow is obtained. The flow was observed in a rectangular channel with a cross section of 90 × 110 mm2 consisting of a horizontal and a inclined part. The volume flow of air varied between 125 and 180 l/s, and the water flow varied between 25 and 45 l/min. A validation, performed by comparing the measurement results with those obtained by a local electric resistivity probe, showed a good agreement. Deviations between both measurement results are supposed to be based on the different detection of the disperse phase which is underestimated by the resistivity probe and overestimated by the optical method.