| 1. |
- Carlson, Andreas, et al.
(författare)
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Dissipation in rapid dynamic wetting
- 2011
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 682, s. 213-240
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a modelling approach for rapid dynamic wetting based on the phase field theory. We show that in order to model this accurately, it is important to allow for a non-equilibrium wetting boundary condition. Using a condition of this type, we obtain a direct match with experimental results reported in the literature for rapid spreading of liquid droplets on dry surfaces. By extracting the dissipation of energy and the rate of change of kinetic energy in the flow simulation, we identify a new wetting regime during the rapid phase of spreading. This is characterized by the main dissipation to be due to a re-organization of molecules at the contact line, in a diffusive or active process. This regime serves as an addition to the other wetting regimes that have previously been reported in the literature.
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| 2. |
- Carlson, Andreas, et al.
(författare)
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Droplet dynamics in a bifurcating channel
- 2010
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322 .- 1879-3533. ; 36:5, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper we present a phenomenological description of droplet dynamics in a bifurcating channel that is based on three-dimensional numerical experiments using the Phase Field theory. Droplet dynamics is investigated in a junction, which has symmetric outflow conditions in its daughter branches. We identify two different flow regimes as the droplets interact with the tip of the bifurcation, splitting and non-splitting. A distinct criterion for the flow regime transition is found based on the initial droplet volume and the Capillary (Ca) number. The Rayleigh Plateau instability is identified as a driving mechanism for the droplet breakup close to the threshold between the splitting and non-splitting regime.
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| 3. |
- Do-Quang, Minh, et al.
(författare)
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Fluid dynamic behavior of dispensing small droplets through a thin liquid film
- 2010
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 9:2-3, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a technology for dispensing droplets through thin liquid layers. The system consists of a free liquid film, which is suspended in a frame and positioned in front of a piezoelectric printhead. A droplet, generated by the printhead, merges with the film, but due to its momentum, passes through and forms a droplet that separates on the other side and continues its flight. The technology allows the dispensing, mixing and ejecting of picolitre liquid samples in a single step. This paper overviews the concept, potential applications, experiments, results and a numerical model. The experimental work includes studying the flight of ink droplets, which ejected from an inkjet print head, fly through a free ink film, suspended in a frame and positioned in front of the printhead. We experimentally observed that the minimum velocity required for the 80 pl droplets to fly through the 75 ± 24 lm thick ink film was of 6.6 m s-1. We also present a numerical simulation of the passage of liquid droplets through a liquid film. The numerical results for different initial speeds of droplets and their shapes are taken into account. We observed that during the droplet-film interaction, the surface energy is partially converted to kinetic energy, and this, together with the impact time, helps the droplets penetrate the film. The model includes the Navier- Stokes equations with continuum-surface-tension force derived from the phase-field/Cahn-Hilliard equation. This system allows us to simulate the motion of a free surface in the presence of surface tension during merging, mixing and ejection of droplets. The influence of dispensing conditions was studied and it was found that the residual velocity of droplets after their passage through the thin liquid film well matches the measured velocity from the experiment.
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| 4. |
- Do-Quang, Minh, et al.
(författare)
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Numerical simulation of the coupling problems of a solid sphere impacting on a liquid free surface
- 2010
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Ingår i: Mathematics and Computers in Simulation. - : Elsevier BV. - 0378-4754 .- 1872-7166. ; 80:8, s. 1664-1673
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a model, using a phase-field method, that is able to simulate the motion of a solid sphere impacting on a liquid surface, including the effects of capillary and hydrodynamic forces. The basic phenomena that were the subject of our research effort are the small scale mechanism such as the wetting property of the solid surface which control the large scale phenomena of the interaction. The coupled problem during the impact will be formulated by the inclusion of the surface energies of the solid surface in the formulation, which gives a reliable prediction of the motion of solid objects in/on/out of a liquid surface and the hydrodynamic behaviours at small scales when the inertia of fluid is less important than its surface tension. Numerical results at different surface wettabilities and impact conditions will be presented and compared with the experiments of Duez el al. [C. Duez, C. Ybert, C. Clanet, L. Bocquet, Nat. Phys. 3 (2007) 180-183] and Lee and Kim [D. Lee. H. Kim, Langmuir 24 (1) (2008) 142]. (C) 2009 IMACS. Published by Elsevier B.V. All rights reserved.
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| 5. |
- Do-Quang, Minh, 1971-, et al.
(författare)
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The impact of ink-jet droplets on a paper-like structure
- 2011
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Ingår i: Fluid Dynamics and Materials Processing. - : Tech Science Press. - 1555-2578 .- 1555-256X. ; 7:4, s. 389-402
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Tidskriftsartikel (refereegranskat)abstract
- Inkjet technology has been recognized as one of the most successful and promising micro-system technologies. The wide application areas of printer heads and the increasing demand of high quality prints are making ink consumption and print see-through important topics in the inkjet technology. In the present study we investigate numerically the impact of ink droplets onto a porous material that mimics the paper structure. The mathematical framework is based on a free energy formulation, coupling the Cahn-Hilliard and Navier Stokes equations, for the modelling of the two-phase flow. The case studied here consists of a multiphase flow of air-liquid along with the interaction between a solid structure and an interface. In order to characterize the multiphase flow characteristics, we investigate the effects of surface tension and surface wettability on the penetration depth and spreading into the paper-like structure.
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| 6. |
- Shiomi, Junichiro, et al.
(författare)
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Low dimensional heat and mass transport in carbon nanotubes
- 2010
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Ingår i: Proceedings of the ASME Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009. - 9780791843895 ; , s. 337-346
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Konferensbidrag (refereegranskat)abstract
- This report covers various issues related to heat and mass transport in carbon nanotubes. Heat and mass transport under quasi-one-dimensional confinement has been investigated using molecular dynamics simulations. It is shown that the quasi-ballistic heat conduction manifests in the length and diameter dependences of carbon nanotube thermal conductance. Such quasi-ballistic nature of carbon nanotube heat conduction also influences the thermal boundary conductance between carbon nanotubes and the surrounding materials. The quasi-one-dimensional structure also influences the mass transport of water through carbon nanotubes. The confinement gives rise to strongly directional dynamic properties of water. Here, it is demonstrated that the confined water can be efficiently transported by using the temperature gradient. Furthermore, the simulations reveal the diameter-dependent anisotropic dielectric properties, which could be used to identify intrusion of water into carbon nanotubes.
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| 7. |
- Strömgren, Tobias, 1978-, et al.
(författare)
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A modelling study of evolving particle-laden turbulent pipe-flow
- 2011
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Ingår i: Flow Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1386-6184 .- 1573-1987. ; 86:3-4, s. 477-495
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Tidskriftsartikel (refereegranskat)abstract
- An Eulerian turbulent two phase flow model using kinetic theory ofgranular flows for the particle phase was developed in order to studyevolving upward turbulent gas particle flows in a pipe. Themodel takes the feedback of the particles into account and its resultsagree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase theunderstanding of the dependence of the development length on particlediameter a simple model for the expected development length wasderived. It shows that the development length becomes shorter forincreasing particle diameters, which agrees with simulations up to aparticle diameter of 100 μm. Thereafter the development lengthbecomes longer again for increasing particle diameters because largerparticles need a longer time to adjust to the velocity of the carrierphase.
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| 8. |
- Strömgren, Tobias, et al.
(författare)
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Deriving fluid-particle correlation closures for Eulerian two-fluid models through use of Langevin equations
- 2011
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Ingår i: European journal of mechanics. B, Fluids. - : Elsevier BV. - 0997-7546 .- 1873-7390. ; 30:3, s. 275-280
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Tidskriftsartikel (refereegranskat)abstract
- The correlation correlation between the fluctuating particle and gas velocity in isotropic turbulence is studied with a set of stochastic differential equations taking into account both particle-particle collisions and the particle feedback on the turbulence. The principal aim of this work is to use the Langevin equations to formulate closures for two-fluid gas-particle flow models. Using Ito calculus we derived solutions for the turbulent kinetic energy of the particle phase and the particle-gas velocity correlations. If particle-particle collisions and particle feedback on the turbulence are neglected the new relations approach the ones derived by Tchen and Hinze but if these effects are included additional terms in the relations appear. In this study we only use a very simple model for the particle-particle collisions. The new relation and the classical relation of Tchen and Hinze for the particle turbulent kinetic energy as well as a relation based on the kinetic theory of granular flows have been implemented in a two-fluid model for turbulent gas-particle flow in a channel in order to make comparison for different particle Stokes numbers. Results show that while the two-fluid model using Hinze's relations only gives good results for small Stokes numbers, the new relation yields significant improvements for a large range of Stokes numbers.
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