Multi-phase plumes in uniform and stratified crossflow

Abstract

Laboratory experiments of multiphase plumes in uniform and stratified crossflows are presented. In uniform crossflow, multi-phase plumes behave as mixed single-phase plumes up to a critical height, h s, where the entrained fluid separates from the dominant dispersed phase. From the experimental results, an empirical relationship for h s was calibrated giving u ∞ /(B/s ) 1/3 =6.3(us/(B/hs )1/3)-2.4, where u ∞ is the crossflow velocity, B is the total kinematic buoyancy flux of the mixed plume, and u s is the slip velocity. Above h s the separated continuous-phase plume behaves like a momentum jet and the bubble column follows the trajectory of the vector sum of u s and u ∞ In stratified crossflow. the trap height in quiescent water, h T, was compared to h s. For h T « h s, the plumes are stratification-dominated and separation occurs at h T = (2.8-0.27 u s/(B/N)1/4)(B/N 3)1/4, where N is the Brunt- Vaisala buoyancy frequency. For h T, » h s. the plumes are crossflow-dominated, and separation occurs at h s. A simple single-phase model was modified to predict the fate of the separated plume above h s.