Knowledge Base

Found 9 Results

Article

Experimental investigation of laminar and turbulent displacement of residual oil film

Zhang, Y., Barrouillet, B. and Skadsem, H.J.

2023Scientific Reports1321120

Keywordscleaning, flow displacement, shear flow, thin film

DisciplinesChemical Engineering, Fluid Mechanics, Mechanical Engineering

CategoryLaboratory experiments

Scale1e-6 to 1e-3 m / 1 to 60 s

Non-expert summaryThis paper reports an experimental study of the removal of thin oil films from the wall of a cylindrical tube by a flow of water. The removal of the oil film is measured by monitoring dye concentration in the flushing liquid leaving the system: local extents of removal were not measured. The authors investigated the effect of the flow regime of the displacing fluid (water Reynolds numbers ranged from 1480 to 12690), the duration of the displacing fluid flow, and the estimated wall shear stress imposed on the film. When the volume of fluid is limited, the largest displacement efficiency was observed at Re = 7000-8000 (named the intermediate turbulent regime). The largest Reynolds number flows were most effective for achieving complete cleaning over a long time period.

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Article

Shear flow over a protuberance on a plane wall

Pozrikidis, C.

1997Journal of Engineering Mathematics3129-42

Keywordsdecontamination, flow displacement, shear flow

DisciplinesApplied Mathematics, Fluid Mechanics

CategoryNumerical simulations

Non-expert summaryMany cleaning and decontamination operations employ a flow to detach or move a particle or foreign element (e.g. a piece of dust, baterium or a spore) from a surface. The presence of the element disturbs the flow near the wall. Knowledge of the flow field and the forces imposed on the element is useful for predicting or quantifying removal. This paper considers a simple shear flow of a Newtonian fluid over an axisymmetric protuberance (with uniform shape) on a plane wall. The full 3-D problem is formulated in terms of three scalar Fredholm integral equations of the first kind and is solved using a boundary-element method. The hydrodynamic force and torque exerted on the protuberance, and distribution of shear stresses, are calculated. There is good agreement with previous analytical computations for hemi-spherical and spherical shapes.

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Article

Lift, drag and added mass of a hemispherical bubble sliding and growing on a wall in a viscous linear shear flow

Legendre, D., Colin, C., Coquard, T.

2008Phil. Trans. R. Soc. A3662233-2248

Keywordsflow displacement, shear flow

DisciplinesFluid Mechanics

CategoryNumerical simulations

Non-expert summaryThe Navier-Stokes equations for the three-dimensional flow of a Newtonian fluid around a hemispherical bubble simultaneously sliding along a flat wall and growing are solved. The forces experienced by the bubble (lift, drag and added mass) are calculated for bubble Reynolds numbers greater than or equal to 0.01 and flow Reynolds numbers < 2000. The bubble does not change shape. The scenarios studied are (i) an immobile bubble in a linear shear flow; (ii) a bubble sliding along the wall in an otherwise stagnant fluid; and (iii) a bubble sliding in a linear shear flow. The results are presented in the form of dimensionless coefficients.

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Article

A three-dimensional computer model analysis of three hypothetical biofilm detachment mechanisms

Chambless, J.D., Stewart, P.S.

2007Biotechnology and Bioengineering97(6)1573-1584

Keywordsbacteria, biofilm, cleaning, detachment, flow displacement, shear flow

DisciplinesChemical Engineering, Microbiology

CategoryNumerical simulations

Scale1e-6 m, 1e-6 to 1e-3 m, 1e-3 m / 1e-3 to 1 s, 1 to 60 s, 1 to 60 min

Non-expert summaryThe removal of biofilms by sloughing is a natural phenomenon in biofilm dynamics. Three hypothetical mechanisms of detachment were incorporated into a 3D model of biofilm development. The model integrated processes of substrate utilization, substrate diffusion, growth, cell advection, and detachment in a cellular automata framework. The three detachment mechanisms analyzed represented various physical and biological influences hypothesized to affect biofilm detachment; fluid shear removing protruding material; removal linked to local nutrient availability; and erosion. The detachment mechanisms demonstrated diverse behaviors with respect to the four analysis criteria. The results show that detachment is a critical determinant of biofilm structure and of the dynamics of biofilm accumulation and loss.

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Article

A general description of detachment for multidimensional modelling of biofilms

Xavier, J. de B., Picioreanu, C., van Loosdrecht, M.C.M.

2005Biotechnology and Bioengineering91(6)651-669

Keywordsbacteria, biofilm, cleaning, detachment, erosion, shear flow

DisciplinesChemical Engineering, Microbiology

CategoryNumerical simulations

Scale1e-6 m, 1e-6 to 1e-3 m, 1e-3 m / 1e-3 to 1 s, 1 to 60 s, 1 to 60 min

Non-expert summaryThe structure of many biofilms results in a surface layer which does not detach readily and a growing layer that detaches (sloughs) off more readily. The authors present a general method for describing biomass detachment in a multidimensional biofilm modelling framework. Biomass losses from processes acting on the entire surface of the biofilm, such as erosion, are modelled, and discrete detachment events, i.e. sloughing, are implicitly derived from the simulations. This methodology for biomass detachment was integrated with multidimensional (2D and 3D) particle-based multispecies biofilm models by using the level set method. Application of the method is demonstrated by looking at the trends in biofilm structure and activity over time in two case studies: I - a simple model considering uniform biomass; II - a model discriminating biomass composition in heterotrophic active mass, extracellular polymeric substances (EPS) and inert mass.

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Article

Sliding, pinch-off and detachment of a droplet on a wall in shear flow

Ding, H., Gilani, M.N.H., Spelt, P.D.M.

2010Journal of Fluid Mechanics644217–244

Keywordsdecontamination, drop, hydrodynamics, interfacial dynamics, shear flow

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesNumerical simulations, Theoretical modelling

Non-expert summaryThis modelling study considers what happens after a droplet is set into motion by the action of an impose shear flow. Inertial effects and contact-angle hysteresis are both considered. A number of flow regimes are investigated, including steadily moving drops, partial and entire droplet entrainment. The critical conditions (capillary number) for the onset of entrainment are determined for pinned as well as for moving drops. The approach to breakup is then investigated in detail, including the growth of a ligament on a drop, and the reduction of the radius of a pinching neck. A model based on an energy argument is proposed for the rate of elongation of ligaments. The paper concludes with an investigation of detachment of a hydrophobic droplet from a solid wall.

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Article

Convective mass transport from rectangular cavities in viscous flow

Occhialini, J.M., Higdon, J.J.L.

1992J. Electrochem. Soc.139(10)2845-2855

Keywordscavity flow, cleaning, decontamination, mass transfer, shear flow

DisciplinesChemical Engineering, Fluid Mechanics

CategoryNumerical simulations

Non-expert summaryThe authors conduct a comprehensive numerical study of convective mass transport from 2-D rectangular cavities in low‐Reynolds‐number flows, i.e. the flow set up in a long rectangular trench by the motion of a steady shear flow across the top. They calculate the velocity field in the trench and the associated mass transport (enhancement of diffusion). The flow field is calculated by a high‐order implementation of the boundary‐integral method, while the convective diffusion equation is solved using the spectral‐element method. Results are presented in the form of concentraton contours and local mass fluxes, for cavity aspect ratios from 1:1 to 4:1 and for Péclet numbers from 0 to 100,000. They investigate the effects of inlet flow profile and system boundaries on the system.

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Article

Transport enhancement mechanisms in open cavities

Horner, M., Metcalf, G., Wiggins, S., Ottino, J.M.

2002J. Fluid Mechanics452199-229

Keywordscavity flow, cleaning, hydrodynamics, mass transfer, shear flow

DisciplinesFluid Mechanics

CategoriesLaboratory experiments, Numerical simulations

Scale1e-3 to 1 m / 1 to 60 s, 1 to 60 min, 1 to 24 hours

Non-expert summaryWhen a steady shear flow passes over a long (2-D) cavity it sets up a circulation cell in the cavity, where the flow in the cavity is contained within the cavity (with a boundary called the separatrix) and mass transport into and out of the cavity is predominantly by diffusion. This is particularly true at small scales. The authors investigate numerically and experimentally two methods for enhancing mass transport from these 'cells' - by geometrically modifying the boundary driving the flow, and making the driving flow time-dependent. Both modifications destabilize one of the wall attachment points of the separatrix, allowing fluid exchange between the cavity and channel. The range of Reynolds and Reynolds-Strouhal numbers studied is 7.7 <= Re <= 46.5 and 0.52 <= ReSr <= 12,55 in the spatially dependent mode and 12 <= Re <= 93 and 0.26 <= ReSr <= 5.02 in the time-dependent mode. The transport is described theoretically via lobe dynamics, which characterizes the instability of the separatrix. They find that the resulting mass transfer between the cavity and the outer shear flow, through the distabilized separatrix is enhanced by several orders of magnitude compared to a diffusive mass transfer.

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Article

Local wall shear stress variations predicted by computational fluid dynamics for hygienic design

Jensen, B.B.B., Friis, A., Bénézech, T., Legentilhomme, P., Lelièvre, C.

2005Food Bioproducts Processing83(C1)53-60

Keywordscleaning, decontamination, shear flow, turbulence

DisciplinesChemical Engineering, Fluid Mechanics

CategoryNumerical simulations

Scale1e-3 to 1 m / 1e-3 to 1 s, 1 to 60 s

Non-expert summaryThe prediction of flow behaviour in complex geometries representative of industrial and other practical systems often requires the use of computational fluid dynamics (CFD) simulations. Two important pipe geometries are considered in this paper: a sudden and a gradual expansion or contraction. Steady state simulations using the STAR-CD package were used to predict the distribution of the mean shear stress imposed by a turbulent liquid flow from 1 inch to 2 inch cylindrical geometries (Reynolds number in the 1 inch pipe of 50,000), and the fluctuations in the shear stress. These calculated values are compared with estimates based on electrochemical mass transfer measurements. The data sets provide useful benchmarking results for other studies.

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