Investigation of flow regime transition in a column flotation cell using CFD
Date
2019-02
Journal Title
Journal ISSN
Volume Title
Publisher
Southern African Institute of Mining and Metallurgy
Abstract
ENGLISH ABSTRACT: 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.
Description
CITATION: Mwandawande, I. et al. 2019. Investigation of flow regime transition in a column flotation cell using CFD. Journal of the Southern African Institute of Mining and Metallurgy, 119(2):173-186. doi:10.17159/2411-9717/2019/v119n2a10
The original publication is available at https://www.saimm.co.za/publications/journal-papers
The original publication is available at https://www.saimm.co.za/publications/journal-papers
Keywords
Flotation, Maximum superficial -- Velocity, Flow regime, Bubbly flow, Transition, Churn-turbulent flow
Citation
Mwandawande, I. et al. 2019. Investigation of flow regime transition in a column flotation cell using CFD. Journal of the Southern African Institute of Mining and Metallurgy, 119(2):173-186. doi:10.17159/2411-9717/2019/v119n2a10