Investigation of flow regime transition in a column flotation cell using CFD
Artikel i vetenskaplig tidskrift, 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


bubbly flow

flow regime


I. Mwandawande

Universiteit Stellenbosch

G. Akdogan

Universiteit Stellenbosch

S. M. Bradshaw

Universiteit Stellenbosch

Mohsen Karimi

Chalmers, Kemi och kemiteknik, Kemiteknik

N. Snyders

Universiteit Stellenbosch

Journal of the Southern African Institute of Mining and Metallurgy

2225-6253 (ISSN)

Vol. 119 2 173-186


Geofysisk teknik


Strömningsmekanik och akustik



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