A new electrode-mesh tomograph for advanced studies on bubbly flow characteristics

For studies on the characteristics of bubble flow in a rectangular channel (20 x 100 mm) a new electrode-mesh tomograph have been applied. The measuring principle is based on local conductivity measurement and a signal concerning. The applied sensor scans the local void fraction distribution in 2 parallel planes, separated 1.5 mm in flow direction, with a resolution of 3.0 x 2.2 mm and a overall sampling rate of 1200 Hz (all 256 points). Algorithm 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 have 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 can be calculated. 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. (author)