Methods for studies on bubbly flow characteristics applying an electrode-mesh tomograph

For studies on the characteristics of bubble flow in a rectangular channel (20x100mm) an electrode-mesh tomograph has been applied. The measuring principle is based on local conductivity measurement. The applied sensor scans the local void fraction distribution in 2 parallel planes, separated 1.5mm in flow direction, with a resolution of 6.1x2.2mm and an overall sampling rate of 1200Hz (all 256 points). Algorithms for the calculation of the local instantaneous void fraction distribution and the true gas velocity are presented. Based on these values the approximate shape of bubbles has been reconstructed and the gas volume flow through the sensor evaluated. The superficial gas velocity as well as the local distribution of the gas volume flux was
calculated. Finally, bubble diameter spectra have been obtained and the statistical behavior of the bubble rising velocity in its dependency from bubble diameter in a turbulent flow of high void fraction has been investigated. An extensive sensitivity study illustrating the applicability and accuracy is presented, based on experimental observations as well as theoretical considerations. The evaluated results are compared with high-speed video observations of the flow field as well as data comparing the reconstructed volume flow with measurements by a laminar flow meter. Good agreement can be stated.