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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

Transient displacement of a viscoplastic material by air in straight and suddenly constricted tubes

Dimakopoulos, Y., Tsamopoulos, J.

2003J. Non-Newtonian Fluid Mech.11243-75

Keywordscleaning, flow displacement, moving boundary problem, viscoplastic fluid

DisciplinesChemical Engineering, Fluid Mechanics

CategoryNumerical simulations

Non-expert summaryThe flushing of a viscous fluid from a pipe or cavity by a less viscous one is widely used in cleaning operations. This paper reports the numerical modelling of the transient displacement of a viscoplastic material from straight or suddenly constricted (square entry) concentric cylindrical tubes of finite length, simulating a gas at higher pressure displacing the geometry initially filled with liquid. A mixed finite element method is coupled with a quasi-elliptic mesh generation scheme in order to follow the very large deformations involved. The gas bubble grows in length and leaves a thin liquid film on the duct wall (so it does not remove all the liquid). The shape of the bubble is computed for various Reynolds and Bingham numbers (ratio of yield stress to viscous stress). The 'tip splitting' instability that can arise in flow of a gas along a tube filled with a viscous Newtonian fluids is suppressed with viscoplastic fluids at higher Bingham numbers. The shape of the bubble as it passes through the constriction is also studied.

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Review article

The fluid mechanics of cleaning and decontamination of surfaces

Landel, J. R., Wilson, D.I.

2021Annual Review of Fluid Mechanics53147-171

Keywordscleaning, decontamination

DisciplinesChemical Engineering, Fluid Mechanics

CategoryReview

Scale1e-9 to 1e-6 m, 1e-6 m, 1e-6 to 1e-3 m, 1e-3 m, 1e-3 to 1 m, 1 to 10 m, 10 to 1000 m, greater than 1 km / less than 1e-3 s, 1e-3 to 1 s, 1 to 60 s, 1 to 60 min, 1 to 24 hours, 1 to 30 days, 1 to 12 months, greater than 1 year

Non-expert summaryBroad review of the fluid mechanics involved in the cleaning and decontamination of surfaces using liquid flows. Three main phases are reviewed: the contacting phase, which requires the liquid cleanser to reach the soil; the action phase, which studies the various physico-chemical effects of the cleanser on the soil; and the removal phase, where the cleanser transports the soil away from the surface through various phenomena.

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Article

Movement of chemical warfare agent simulants through porous media

Jenkins, R.A., Buchanan, M.V., Merriweather, R., Ilgner, R.H., Gayle, T.M., Watson, A.P.

1994Journal of Hazardous Materials37(2)303-325

Keywordschemical warfare agent simulant, decontamination, permeation, porous material, risk

DisciplinesChemical Engineering, Chemistry, Fluid Mechanics

CategoryLaboratory experiments

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

Non-expert summaryExperimental study of the permeation of CWA simulants through different layers of porous building materials: brick, cinder block, wall board, wood. The breakthrough time is measured in a specially designed cell. Anisotropy of the permeation is observed for anisotropic material such as wood. Surface decontamination is tested and shown effective.

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Article

Modelling the cleaning of viscoplastic layers by impinging coherent turbulent water jets

Fernandes, R.R. and Wilson, D.I.

2020Journal of Non-Newtonian Fluid Mechanics282104314

Keywordscleaning, flow displacement, immiscible flow, impinging turbulent jet, viscoplastic fluid

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesLaboratory experiments, Theoretical modelling

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

Non-expert summaryImpinging liquid jets are widely used to clean unwanted soil layers from the walls of structures and vessels. This paper investigates what is observed when a coherent, turbulent, water jet impinges normally on a thin layer of an immiscible viscoplastic material. Removal involves the growth of a cleared area (which is circular for a jet impinging normally) bounded by a berm of displaced material. Previously Glover et al. [2016, J. Food Eng.. 178, 95-109] presented a semi-empirical model relating the rate of removal (location of the berm) to the momentum flow rate in the liquid film. The authors present a first-order model for cleaning thin layers of these materials based on the rate of viscous dissipation in a shallow wedge of material at the cleaning front. This yields a result of the form of the Glover et al. model, with expressions linking the kinetic parameters to measurable quantities including the rheology of the soil. The fully coupled problem is not solved: the wedge angle and residual layer thickness need to be specified and in this work they were obtained by fitting to the data. New and existing experimental results are compared with the model for three soft solids immiscible with water: two petroleum jellies and a soft paraffin, which exhibited Bingham plastic behaviour and creep, for jet Reynolds numbers between 10,000-37,000. The ratio of average film depth and layer thickness was in the range 0.1-1.5.

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Review article

Hydrodynamic systems for assessing surface fouling, soil adherence and cleaning in laboratory installations

Detry, J.G., Deroanne, C. and Sindic, M.

2009Biotechnol. Agron. Soc. Environ.13(3)427-439

Keywordscleaning, decontamination, hydrodynamics

DisciplinesChemical Engineering, Chemistry, Fluid Mechanics

CategoryReview

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

Non-expert summaryThis is a short review presenting and comparing five apparatuses that are used in laboratory scale investigations of cleaning: the parallel plate flow cell, the impinging jet, the radial flow cell, the rotating disk and fluid dynamic gauging. These systems are of particular relevance to the study of surface fouling, surface cleaning or adhesion on solid surfaces in laboratory environment. The key features of their hydrodynamics, as well as their practical advantages and drawbacks, are discussed. Examples of applications fields are also listed. A useful introduction to these devices.

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Article

Mass transfer from a flat surface to an impinging turbulent jet

Rao, V.V., Trass, O.

1964Canadian Journal Chemical Engineering42(3)95-99

Keywordscleaning, decontamination, impinging turbulent jet, mass transfer

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesLaboratory experiments, Theoretical modelling

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

Non-expert summaryThis is a relatively early experimental study of mass transfer of a sparingly soluble material from a flat, solid surface when it is exposed to a normally impinging turbulent jet of water. The nozzle Reynolds numbers ranged from 25,000 to 125,000. The surface was coated with trans-cinnamic acid, and thickness profiles were measure over time to determine the local rate of mass transfer. The mass transfer flux is used to calculate the local Sherwood number (dimensionless mass transfer coefficient). In the wall-jet region these were found to be independent of the nozzle to plate distance, and were correlated as Sh = 1.3*Re^0.84*(x/d)^- 1.27. The authors found reasonable agreement with published heat transfer data . The average Sherwood numbers in the impingement region were found to decrease rapidly beyond a transition zone of 6.5 diameters from the nozzle: mass transfer rates are thus weak beyond this zone.

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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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Article

Hydrodynamic cleaning of a viscous film from the inside of a long tube

Mickaily, E.S. and Middleman, S.

1993AIChE Journal39(5)885-893

Keywordscleaning, decontamination, immiscible flow, thin film

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesLaboratory experiments, Theoretical modelling

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

Non-expert summaryA simple, dynamic model, supported by experiments, is presented for the thinning (removal) of a viscous liquid film from the inside of the smooth interior surface of a long cylindrical tube. The model is based on the motion of the film generated by the shear stress imposed on it by the turbulent flow of air through the tube. The model gives estimates of the mean thickness of the film (an olive oil and a castor oil). The authors extend the investigation to include removal from roughened surfaces, modelling these as regularly spaced triangular cavities.

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Article

Hygienic design: Effect of hydrodynamics on the cleanability of a food processing line

Blel, W., Legentilhomme, P., Legrand, J., Bénézech, T., Le Gentil-Lelièvre, C.

2008AIChE J54(10)2553-2566

Keywordsbacteria, cleaning, hydrodynamics

DisciplinesChemical Engineering, Microbiology

CategoryLaboratory experiments

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

Non-expert summaryAn important part of hygienic design is knowledge of the forces imposed on a surface by the flow of a process liquid, and whether those forces are large enough to remove any contaminants. This is a chiefly experimental study investigating the numbers of adhering Bacillus cereus spores before and after cleaning in place of part of a dairy processing line. Non-intrusive flow characterization, of local wall shear stress and velocity profiles, were measured using electrochemical and ultrasonic Doppler velocimetry techniques. The geometries studied inlcuded gradual asymmetric pipe contractions and pipe expansions and bends. The recirculation zone resulting from the flow detachment after the expansion resulted in a large number of adherent spores downstream of this geometrical change. Welding and gasket regions also retained spores, proving difficult to clean despite high-shear stress forces involved. The flow measurements are compared with some theory so the level of modelling is not high but the data sets present important cases for new investigations, e.g. using CFD methods.

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Article

Convective mass transfer from a submerged drop in a thin falling film

Landel, J.R., Thomas, A.L., McEvoy, H., Dalziel, S.B.

2016J. Fluid Mech.789630-668

Keywordsdecontamination, drop, film flow, interfacial dynamics, mass transfer

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesLaboratory experiments, Theoretical modelling

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

Non-expert summaryThis is an experimental and modelling study of the removal of a passive tracer contained in small, thin, viscous drops attached to a flat inclined substrate using the flow of a thin gravity-driven film. The drop cannot be detached either partially or completely from the surface by the mechanical forces exerted by the cleaning fluid on the drop. Convective mass transfer is established across the interface between the drop and the flowing liquid film and the (dilute) tracer diffuses into the film flow, which takes it away. The Peclet number, comparing the rate of mass transfer in the drop to the rate in the liquid film, is small (< 1) . Two models are presented: a simple empirical model based on film mass transfer coefficients; and a fuller theoretical model solving the quasi-steady two-dimensional advection–diffusion equation in the film, coupled with a time-dependent one-dimensional diffusion equation in the drop. A range of values of the Peclet number (0.01 to 1) is considered in the fuller model. Good agreement is observed between the experimental data and the models.

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Article

Cleaning of a model food soil from horizontal plates by a moving vertical water jet

Wilson, D.I., Köhler, H., Cai, L., Majschak, J-P. and Davidson, J.F.

2014Chemical Engineering Science123450-459

Keywordcleaning

DisciplineChemical Engineering, Fluid Mechanics

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

Non-expert summaryThe paper presents a model to describe the results of an experimental investigation of removal of thin (several microns thick) Xanthan gum layers from flat horizontal plates by a coherent water jet impinging normally on the plate. In the experiments, the impingement point of the jet moved across the plate, replicating the action of a moving or rotating nozzle which causes the point of impact to move across a wall or other surface to be cleaned. Removal was monitored by a fluorescence technique: the Xanthan gum layers contained fluorescent ZnS crystals which allowed the location of the cleaning front to be monitored in situ and in real time. The curved shape, and final width, of the steady state cleaning front was predicted by a first order peeling model based on the momentum flow in the film. The governing equation for the steady state shape is formulated in terms of a general cleaning rate. For these experiments, the parameters of the cleaning model which were obtained from experiments involving static nozzles gave good predictions of the shape of the cleaning front observed with moving nozzles.

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