Measurement of physical characteristics of bubbles in gas-liquid plumes: Part II. Local properties of turbulent air-water plumes in vertically injected jets |
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Authors: | A H Castillejos J K Brimacombe |
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Affiliation: | (1) The Centre for Metallurgical Process Engineering, The University of British Columbia, V6T 1W5 Vancouver, BC, Canada |
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Abstract: | The structural development of air-water bubble plumes during upward injection into a ladle-shaped vessel has been measured
under different conditions of air flow rate, orifice diameter, and bath depth. The measured radial profiles of gas fraction
at different axial positions in the plume were found to exhibit good similarity, and the distribution of the phases in the
plume was correlated to the modified Froude number. Different regions of flow behavior in the plume were identified by changes
in bubble frequency, bubble velocity, and bubble pierced length which occur as bubbles rise in the plume. Measurement of bubble
velocity indicates that close to the nozzle the motion of the gas phase is strongly affected by the injection velocity; at
injection velocities below 41 m/s, the velocity of the bubbles along the centerline exhibits an increase with height, while
above, the tendency reverses. High-speed film observations suggest that this effect is related to the nature of gas discharge,i.e., whether the gas discharge produces single bubbles or short jets. In this region of developing flow, measurement of bubble
frequency and pierced length indicates that break-up of the discharging bubbles occurs until a nearly constant bubble-size
distribution is established in a region of fully developed flow. In this largest zone of the plume the bubbles influence the
flow only through buoyancy, and the spectra of bubble pierced length and diameter can be fitted to a log-normal distribution.
Close to the bath surface, a third zone of bubble motion behavior is characterized by a faster decrease in bubble velocity
as liquid flows radially outward from the plume. |
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