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van As, K. (author), Dellevoet, S. F.L.J. (author), Boterman, J. (author), Kleijn, C.R. (author), Bhattacharya, N. (author), Kenjeres, S. (author)The disease atherosclerosis causes stenosis inside the patient's arteries, which often eventually turns lethal. Our goal is to detect a stenosis in a non-invasive manner, preferably in an early stage. To that end, we study whether and how laser speckle contrast imaging (LSCI) can be deployed. We start out by using computational fluid dynamics...journal article 2022
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Ebrahimi, Amin (author), Sattari, Mohammad (author), Bremer, Scholte J.L. (author), Luckabauer, Martin (author), Römer, Gert-willem R.B.E. (author), Richardson, I.M. (author), Kleijn, C.R. (author), Hermans, M.J.M. (author)The absorptivity of a material is a major uncertainty in numerical simulations of laser welding and additive manufacturing, and its value is often calibrated through trial-and-error exercises. This adversely affects the capability of numerical simulations when predicting the process behaviour and can eventually hinder the exploitation of fully...journal article 2022
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Vesper, J.E. (author), Kenjeres, S. (author), Kleijn, C.R. (author)In the present study, we propose the use of a light, inert carrier gas to support deposition uniformity and rate in continuous physical vapor deposition, in which closely spaced slots or nozzles are required to achieve a sufficiently high deposition rate. Interaction shocks between the emerging rarefied plumes cause undesired nonuniformities...journal article 2022
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van As, K. (author), Simons, Bram A. (author), Kleijn, C.R. (author), Kenjeres, S. (author), Bhattacharya, N. (author)We study how the speckle contrast depends on scatterer velocity, with the goal of further developing laser speckle imaging as a quantitative measurement technique. To that end, we perform interferometric computer simulations on a dilute plug flow. The results of our numerical experiment, that we compare with known analytical expressions to...journal article 2022
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Ebrahimi, Amin (author), Kleijn, C.R. (author), Hermans, M.J.M. (author), Richardson, I.M. (author)Internal flow behaviour and melt-pool surface oscillations during arc welding are complex and not yet fully understood. In the present work, high-fidelity numerical simulations are employed to describe the effects of welding position, sulphur concentration (60-300 ppm) and travel speed (1.25-5 mms-1) on molten metal flow dynamics in fully...journal article 2021
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Ebrahimi, Amin (author), Babu, A. (author), Kleijn, C.R. (author), Hermans, M.J.M. (author), Richardson, I.M. (author)One of the challenges for development, qualification and optimisation of arc welding processes lies in characterising the complex melt-pool behaviour which exhibits highly non-linear responses to variations of process parameters. The present work presents a computational model to describe the melt-pool behaviour in root-pass gas metal arc...journal article 2021
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Ebrahimi, Amin (author), Kleijn, C.R. (author), Richardson, I.M. (author)Development, optimisation and qualification of welding and additive manufacturing procedures to date have largely been undertaken on an experimental trial and error basis, which imposes significant costs. Numerical simulations are acknowledged as a promising alternative to experiments, and can improve the understanding of the complex process...journal article 2021
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Ebrahimi, Amin (author), Kleijn, C.R. (author), Richardson, I.M. (author)Molten metal melt pools are characterised by highly non-linear responses, which are very sensitive to imposed boundary conditions. Temporal and spatial variations in the energy flux distribution are often neglected in numerical simulations of melt pool behaviour. Additionally, thermo-physical properties of materials are commonly changed to...journal article 2021
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Shah, M.S. (author), Kleijn, C.R. (author), Kreutzer, M.T. (author), van Steijn, V. (author)The initial thickness and radius of the film that forms upon close contact of two foam bubbles are known to influence the thinning dynamics and lifetime of the film. Various scalings of lifetime tr, with initial radius Rfilm and thickness ho, have been proposed in literature. In this paper, we present a hydrodynamic thin-film model that...journal article 2021
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Vesper, J.E. (author), Obiji, Chibuikem S. (author), Westerwaal, Ruud (author), Boelsma, Christiaan (author), Kenjeres, S. (author), Kleijn, C.R. (author)In recent years, Physical Vapor Deposition has been advanced to a continuous process which makes it amenable for in-line, high-quality and energy-efficient galvanization. To achieve the high and uniform mass flow required for in-line production, a Vapor Distribution Box is used, in which the zinc is evaporated. The zinc fills the Vapor...journal article 2021
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Vesper, J.E. (author), Broeders, Theo J.M. (author), Batenburg, Joëlle (author), van Odyck, Daniel E.A. (author), Kleijn, C.R. (author)The interaction between rarefied vapor plumes can cause shocks and consequently distinct peaks in mass flux which produce undesirable non-uniformities. To evaluate the impact of shock formation, we study pairs of interacting planar plumes, varying the degree of rarefaction and general geometric parameters, namely, the nozzle-separation...journal article 2021
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Chakkingal, M. (author), Voigt, Roland (author), Kleijn, C.R. (author), Kenjeres, S. (author)We investigate natural convection driven by a horizontal temperature gradient and a vertical concentration gradient in fluid-filled enclosures with obstructions inside it. Within the domain, nine adiabatic and impermeable cylinders are placed, occupying 30% of the domain volume. The Boussinesq approximation is used to account for density...journal article 2020
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Chakkingal, M. (author), de Geus, Julia (author), Kenjeres, S. (author), Ataei Dadavi, I. (author), Tummers, M.J. (author), Kleijn, C.R. (author)We report numerical simulations of assisting and opposing mixed convection in a side-heated, side-cooled cavity packed with relatively large solid spheres. The mixed convection is generated by imposing a movement on the isothermal vertical walls, either in or opposite to the direction of natural convection flow. For a fluid Prandtl number of...journal article 2020
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Chakkingal, M. (author), Schiavo, Sabino (author), Ataei Dadavi, I. (author), Tummers, M.J. (author), Kleijn, C.R. (author), Kenjeres, S. (author)We numerically investigate natural convection in a bottom-heated top-cooled cavity, fully and partially filled with adiabatic spheres (with diameter-to-cavity-size ratio d/L=0.2) arranged in a Simple Cubic Packing (SCP) configuration. We study the influence of packing height and location of porous media. We carry out the simulations using...journal article 2020
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Ataei Dadavi, I. (author), Chakkingal, M. (author), Kenjeres, S. (author), Kleijn, C.R. (author), Tummers, M.J. (author)This paper reports on an experimental study of mixed convection flow and heat transfer in a vented, differentially side-heated cubical cavity filled with a porous medium consisting of relatively large solid low-conductivity spheres. Rayleigh numbers and Reynolds numbers are varied over the ranges 6 × 10<sup>6</sup> < Ra < 7 × 10<sup>7<...journal article 2020
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Chakkingal, M. (author), Kenjeres, S. (author), Ataei Dadavi, I. (author), Tummers, M.J. (author), Kleijn, C.R. (author)We report numerical simulations of natural convection and conjugate heat transfer in a differentially heated cubical cavity packed with relatively large hydrogel beads (d/L=0.2) in a Simple Cubic Packing configuration. We study the influence of a spatially non-uniform, sinusoidally varying, wall temperature on the local flow and heat transfer...journal article 2020
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Ebrahimi, Amin (author), Kleijn, C.R. (author), Richardson, I.M. (author)The high degree of uncertainty and conflicting literature data on the value of the permeability coefficient (also known as the mushy zone constant), which aims to dampen fluid velocities in the mushy zone and suppress them in solid regions, is a critical drawback when using the fixed-grid enthalpy-porosity technique for modelling non-isothermal...journal article 2019
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Ataei Dadavi, I. (author), Chakkingal, M. (author), Kenjeres, S. (author), Kleijn, C.R. (author), Tummers, M.J. (author)This paper reports on an experimental study of natural convection in an enclosure that is heated at the bottom and cooled at the top, filled with a packed bed of relatively large solid spheres. Nusselt numbers were measured for various sphere conductivities, spheres sizes and sphere packings for Rayleigh numbers varying between 10<sup>7</sup>...journal article 2019
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Numerical analysis of natural convection with conjugate heat transfer in coarse-grained porous mediaChakkingal, M. (author), Kenjeres, S. (author), Ataei Dadavi, I. (author), Tummers, M.J. (author), Kleijn, C.R. (author)We report numerical simulations of fluid natural convection with conjugate heat transfer in a bottom-heated, top-cooled cubical cavity packed with relatively large (d/L=0.2) solid spheres in a Body Centred Tetragonal (BCT) configuration. We study largely varying solid-to-fluid thermal conductivity ratios between 0.3 and 198, for a fluid...journal article 2019
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Haringa, C. (author), De Jong, Conrad (author), Hoang, D. (author), Portela, L. (author), Kleijn, C.R. (author), Kreutzer, M.T. (author), van Steijn, V. (author)We show experimentally, and explain theoretically, what velocity is needed to break an elongated droplet entering a microfluidic T-junction. Our experiments on short droplets confirm previous experimental and theoretical work that shows that the critical velocity for breakup scales with the inverse of the length of the droplet raised to the...journal article 2019