Knowledge Base

Found 7 Results

Article

Numerical investigation of ice pigging isothermal flow in water-supply pipelines cleaning

Hu, J. and Tao, T.

2022Chemical Engineering Research & Design182428-437

Keywordscleaning, detachment, flow displacement, heat transfer, hydrodynamics, multiphase flow

DisciplinesChemical Engineering, Fluid Mechanics

CategoryNumerical simulations

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

Non-expert summaryIce-pigging is a cleaning method in which a dense slurry (to be removed) is pushed along a channel (often a pipe, but more complex geometries can also be cleaned by this method) by an upstream solid-liquid thick ice slurry. The authors use the commercial CFD code FLUENT to evaluate a numerical model of this multiphase (solid-liquid) material undergoing pipe flow. In this coupled Eulerian-Eulerian description the two phases are treated separately as continuous phases coupled by pressure and interphase forces. They validate their model against experimental data from literature and report the predicted ice volume fraction, wall shear stress and melting rate. The results show strong inhomogeneity in the solid content (ice volume fraction).

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Article

Pressure-driven miscible two-fluid channel flow with density gradients

Sahu, K.C., Ding, H., Valluri, P., Matar, O.K.

2009Physics of Fluids21043603

Keywordscleaning, flow displacement, hydrodynamics, miscible liquids, multiphase flow

DisciplinesChemical Engineering, Fluid Mechanics

CategoryNumerical simulations

Non-expert summaryThe displacement of one liquid by another in a channel of constant height occurs in flushing and cleaning operations. The authors study the effect of buoyancy (arising from different fluid densities) on a pressure-driven flow of two miscible fluids in inclined channels using direct numerical simulations DNS). The flow dynamics are governed by the continuity and Navier–Stokes equations, without the Boussinesq approximation for buoyancy, coupled to a convective-diffusion equation for mass transfer between the two liquids. The effect of concentration on viscosity and density is modelled. The effect of varying the density ratio, Froude number, and channel inclination on the flow dynamics is examined, for moderate Reynolds numbers. These detailed simulations give insights into mixing and cleaning behaviour.

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Article

Linear stability analysis and numerical simulation of miscible two-layer channel flow

Sahu, K.C., Ding, H., Valluri, P., Matar, O.K.

2009Physics of Fluids21042104

Keywordscleaning, flow displacement, interfacial dynamics, linear stability analysis, miscible liquids, multiphase flow

DisciplinesChemical Engineering, Fluid Mechanics

CategoriesNumerical simulations, Theoretical modelling

Non-expert summaryWhen one liquid is pumped into a channel containing a second liquid, the behaviour depends on the properties of the two fluids and pressure driving force. This paper considers the stability of a flow of two miscible fluids in a horizontal channel. The flow dynamics are governed by the continuity and Navier–Stokes equations, with mass transfer between the two. An analysis of the flow in the linear regime delineates the presence of convective and absolute instabilities, and shows that vertical gradients of viscosity perturbations (caused by mixing) are the main destabilizing influence of the interface (in agreement with previous work). Previous work in the area is reviewed as well. Transient numerical simulations demonstrate the development of complex dynamics in the nonlinear regime, characterized by roll-up phenomena and intense convective mixing.

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Article

Transient displacement of Newtonian and viscoplastic liquids by air in complex tubes

Dimakopoulos, Y., Tsamopoulos, J.

2007J. Non-Newtonian Fluid Mechanics142(1-3)162-182

Keywordscleaning, flow displacement, hydrodynamics, multiphase flow, viscoplastic fluid

DisciplinesApplied Mathematics, Fluid Mechanics

CategoriesNumerical simulations, Theoretical modelling

Non-expert summaryThe use of pressurised air to displace a viscoplastic liquid from a complex duct geometry is simulated using detailed numerical modelling. The transient displacement of Newtonian and viscoplastic liquids by air in cylindrical tubes of finite length with a concentric expansion followed by a contraction in their cross section is considered. The change in diameter is not sudden. Various expansion and contraction ratios are studied. Papanastasiou's formula is employed to regularize the discontinuous Bingham model. Results are presented for a range of fluid and geometrical parameters, and some cases are compared to analytical results.

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Article

Washing wedges: capillary instability in a gradient of confinement

Keiser, L., Herbaut, R., Bico, J., Reyssat, E.

2016Journal of Fluid Mechanics790619-633

Keywordscapillary instability, linear stability analysis, multiphase flow

DisciplinesApplied Mathematics, Fluid Mechanics

CategoryLaboratory experiments

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

Non-expert summaryExperimental exploration of the exchange of two immiscible fluids in a wedge. Due to antagonist principal curvature, the more wetting fluid exchange with the less wetting fluid in the wedge, through a capillary instability. The instability develops in the form of fingers pinching into droplets. The less wetting fluid is thus displaced out of the wedge. Measurements are performed for varying geometry and viscosity. Discussion but no conclusion of the physical mechanisms are proposed in light of the more well known viscous fingering instability.

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Review article

Liquid jet impingement

Lienhard, J.H.

1995Annual Review of Heat Transfer6199-270

Keywordscleaning, heat transfer, multiphase flow

DisciplinesFluid Mechanics, Mechanical Engineering

CategoryReview

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 review of heat transfer and flow phenomena during unsubmerged liquid jet impingement on solid surfaces, such as when a water jet passes through air and impinges on a wall. Both axisymmetric and planar jets are considered. The focus is on convective transport without phase change. Results for the stagnation zone are given first, followed by those for the regions downstream. Correlations are presented for flow and heat transfer phenomena. The heat fluxes that can be generated in these systems can be large, so there is a considerable body of work on topic. Splattering - the formation of breakaway droplets from the liquid film - that accompanies turbulent jet impingement is described. Other aspects of liquid jet impingement cooling are discussed briefly.

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Article

Numerical simulation of pressure-driven displacement of a viscoplastic material by a Newtonian fluid using the lattice Boltzmann method

Swain, P.A.P., Karapetsas, G., Matar, O.K., Sahu, K.C.

2015Eur J. Mech. B Fluids49197-207

Keywordscleaning, flow displacement, interfacial dynamics, multiphase flow

DisciplinesApplied Mathematics, Chemical Engineering, Fluid Mechanics

CategoryNumerical simulations

Scale1e-6 to 1e-3 m, 1e-3 m, 1e-3 to 1 m, 1 to 10 m

Non-expert summaryThe Lattice-Boltzman numerical method is used to solve the Navier-Stokes equations describing the displacement of a viscoplastic fluid from a cylindrical pipe by the injection of a Newtonian liquid. The equations are written in dimensionless form so no particular time or length scale is specified. Gravity and surface tension effects are included. The average velocity of the Newtonian liquid is such that its flow is laminar. The numerical code is able to resolve several features of the process: the growth of a 'finger' of Newtonian liquid as it pushes the viscoplastic fluid out and the development of waves at the liquid-fluid interface. The impact of key dimensionless groups, particularly the Bingham number (ratio of critical or yield stress to stress induced by the flow) and Reynolds number.

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