New experimental insights into two-phase air–water bubbly and intermittent flow in large duct and cross-flow configurations

This study focuses on the characterization of two-phase air–water cross-flow in a tube bundle with square pitch configuration, and of the upward flow in the free duct region upstream of the bundle. Two measurement techniques were used: a wire mesh sensor and a dual optical probe. The research focuses on analyzing void fraction, gas velocity, gas–liquid interface/bubble shape and size, and two-phase flow regime transitions. Bubbly flow and intermittent flow regimes were investigated, by varying the gas flow rate for a fixed liquid flow rate. The intermittent flow showed a periodic generation of large gas structures in the central region of section. The frequency of these structures was obtained and found not to vary significantly between the free duct region downstream of the tube bundle, the region within the tube bundle and the region downstream of the bundle. Gas velocities could be measured as a function of the size of the gas structures. The profiles of void fraction and gas velocity at different positions within the tube bundle were measured and analyzed.