Investigation of flow regime transition in a column flotation cell using CFD
Journal article, 2019

Flotation columns are normally operated at optimal superficial gas velocities to maintain bubbly flow conditions. However, with increasing superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum superficial gas velocity above which loss of bubbly flow occurs. The maximum superficial gas velocity is usually obtained from a gas holdup versus superficial gas velocity plot in which the linear portion of the graph represents bubbly flow while deviation from the linear relationship indicates a change from the bubbly flow to the churn-turbulent regime. However, this method is difficult to use when the transition from bubbly flow to churn-turbulent flow is gradual, as happens in the presence of frothers. We present two alternative methods in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or saddle-shaped profiles with two near-wall peaks and a central minimum, or flat profiles with intermediate features between saddle and parabolic gas holdup profiles. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles that become steeper with increasing superficial gas velocity. The churn-turbulent flow was distinguished by steep parabolic radial gas holdup profiles. Gas holdup versus time graphs were also used to define flow regimes with a constant gas holdup indicating bubbly flow, while wide gas holdup variations indicate churn-turbulent flow.

maximum superficial velocity

churn-turbulent flow

flotation column

transition

bubbly flow

flow regime

Author

I. Mwandawande

Stellenbosch University

G. Akdogan

Stellenbosch University

S. M. Bradshaw

Stellenbosch University

Mohsen Karimi

Chalmers, Chemistry and Chemical Engineering, Chemical Technology, Chemical Process and Reaction Engineering

N. Snyders

Stellenbosch University

Journal of the Southern African Institute of Mining and Metallurgy

2225-6253 (ISSN)

Vol. 119 2 173-186

Subject Categories

Geophysical Engineering

Energy Engineering

Fluid Mechanics and Acoustics

DOI

10.17159/2411-9717/2019/v119n2a10

More information

Latest update

7/2/2021 7