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A study of the flow structures generated by oscillating flows in a helical baffled tube

Lookup NU author(s): Dr Jonathan McDonough, Dr Anh Phan, Professor Adam Harvey

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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


Abstract

Oscillatory baffled reactors (OBRs) are able to generate plug flow at laminar net flow conditions, providing appropriate oscillation conditions are selected. Mesoscale OBRs containing helical baffles exhibit wider “operating windows” (i.e. a broader oscillation intensity range) for plug flow than other baffle designs. It has been hypothesised that additional swirling in the flow provides another mechanism to limit axial dispersion. These swirling flows have previously been qualitatively identified, but in this study these flows were investigated both numerically and experimentally using CFD and PIV for the first time. The flow structures obtained via simulation (laminar solver) were visualised using isosurfaces of the Q-criterion and 3D streamlines. The characteristic feature of the flow is a helically shaped vortex that forms behind the baffle. Streamlines move both radially (wrapping around the vortex structure) and tangentially. Using the swirl number and analogous ‘radial’ number, a transition between vortex-dominated and swirl-dominated mixing was observed providing evidence that the hypothesis is valid. It was found that when the oscillation intensity is increased, the tangential motion of the flow increases faster than the increase in radial flow because the vortex sizes are bounded by the column diameter.


Publication metadata

Author(s): McDonough JR, Ahmed SMR, Phan AN, Harvey AP

Publication type: Article

Publication status: Published

Journal: Chemical Engineering Science

Year: 2017

Volume: 171

Pages: 160-178

Print publication date: 02/11/2017

Online publication date: 22/05/2017

Acceptance date: 17/05/2017

Date deposited: 27/06/2017

ISSN (print): 0009-2509

ISSN (electronic): 1873-4405

Publisher: Elsevier

URL: http://doi.org/10.1016/j.ces.2017.05.032

DOI: 10.1016/j.ces.2017.05.032


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