Effect of wall corrugations on scalar transfer to a wavy falling liquid film

Direct numerical simulation is employed to study the effect of small-scale wall corrugations on scalar transfer through the wavy surface of a vertically falling liquid film in interaction with a strongly confined counter-current gas flow. Three wall geometries are considered: (i) a flat wall for ref...

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Bibliographic Details
Published in:Journal of fluid mechanics 2019-01, Vol.859, p.1098-1128
Main Author: Dietze, Georg F.
Format: Article
Language:English
Subjects:
Chemical engineering
Computational fluid dynamics
Computer simulation
Convection
Direct numerical simulation
Dirichlet problem
Falling liquid films
Flooding
Fluid mechanics
Gas flow
Heat
Heat exchange
Heat transfer
JFM Papers
Mass transfer
Mathematical models
Mechanics
Organic chemistry
Physics
Simulation
Solitary waves
Structural engineering
Studies
Surface waves
Wavelength
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Summary:Direct numerical simulation is employed to study the effect of small-scale wall corrugations on scalar transfer through the wavy surface of a vertically falling liquid film in interaction with a strongly confined counter-current gas flow. Three wall geometries are considered: (i) a flat wall for reference; (ii) a sinusoidal corrugation typically found on structured packings in chemical engineering devices; and (iii) a heuristic design consisting of isolated semicircular bumps distanced by the wavelength of the surface waves. We consider the limiting case of a Dirichlet condition for the transported scalar (temperature or mass fraction) at the liquid–gas interface and focus on liquid-side transport. We consider convection-dominated regimes at moderate and large Péclet numbers, representative of heat and mass transfer respectively, and confront forced and noise-driven wave regimes. Our results show that sinusoidal wall corrugations increase transfer by up to 30 per cent in terms of the exchange length required to transfer a fixed amount of the transported quantity. A slightly greater intensification is achieved through the bump-shaped corrugations, which intermittently disrupt the moving-frame vortex forming within the large-amplitude solitary waves, allowing these to replenish with unsaturated liquid. However, when the velocity of the strongly confined gas flow is increased above a certain threshold, the bumps can trigger the flooding of the channel.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2018.851