EXPERIMENTAL INVESTIGATION OF BUBBLY FLOW REGIME TRANSITIONS IN A HORIZONTAL 7-ROD BUNDLE USING FIBER OPTIC PROBE

Abstract

Two-phase air-water bubbly flow regime transitions in the sub-channels of a horizontal 7-rod bundle were experimentally investigated using a two-sensor fiber optic probe to provide accurate physical descriptions of the local void fraction, interfacial velocity, bubble chord length, and interfacial area concentration. The air-water tests were performed using 90 different combinations of gas and liquid superficial velocities, which ranged between j_G,atm of 0.2 to 4.0 m/s and j_L of 0.3 to 1.5 m/s, respectively. The 7-rod bundle test section geometry was 2972 mm long with a hydraulic diameter of 7.63 mm, and the probe was installed at an axial distance equivalent to 271 hydraulic diameters from the bundle inlet. Probe measurements were performed along an azimuthal angle of 60° at a radial location of 21.32 mm. The probe results demonstrated that larger bubbles tended to move slower than smaller bubbles, which coincided with qualitative two-phase flow visualizations for elongated bubble, dispersed and slug regime transitions. A new two-phase bubbly flow regime map is proposed for 7-rod bundle based on the fiber optic probe measurements.