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  • 1.
    Albernaz, Daniel
    et al.
    KTH.
    Do, Quang Minh
    KTH.
    Amberg, Gustav
    KTH.
    Multirelaxation-time lattice Boltzmann model for droplet heating and evaporation under forced convection2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 4, article id 043012Article in journal (Refereed)
    Abstract [en]

    We investigate the evaporation of a droplet surrounded by superheated vapor with relative motion between phases. The evaporating droplet is a challenging process, as one must take into account the transport of mass, momentum, and heat. Here a lattice Boltzmann method is employed where phase change is controlled by a nonideal equation of state. First, numerical simulations are compared to the D-2 law for a vaporizing static droplet and good agreement is observed. Results are then presented for a droplet in a Lagrangian frame under a superheated vapor flow. Evaporation is described in terms of the temperature difference between liquid-vapor and the inertial forces. The internal liquid circulation driven by surface-shear stresses due to convection enhances the evaporation rate. Numerical simulations demonstrate that for higher Reynolds numbers, the dynamics of vaporization flux can be significantly affected, which may cause an oscillatory behavior on the droplet evaporation. The droplet-wake interaction and local mass flux are discussed in detail.

  • 2.
    Albernaz, Daniel L.
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Do-Quang, Minh
    KTH.
    Simulation of a suspended droplet under evaporation with Marangoni effects2016In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 91, p. 853-860Article in journal (Refereed)
    Abstract [en]

    We investigate the Marangoni effects in a hexane droplet under evaporation and close to its critical point. A lattice Boltzmann model is used to perform 3D numerical simulations. In a first case, the droplet is placed in its own vapor and a temperature gradient is imposed. The droplet locomotion through the domain is observed, where the temperature differences across the surface is proportional to the droplet velocity and the Marangoni effect is confirmed. The droplet is then set under a forced convection condition. The results show that the Marangoni stresses play a major role in maintaining the internal circulation when the superheated vapor temperature is increased. Surprisingly, surface tension variations along the interface due to temperature change may affect heat transfer and internal circulation even for low Weber number. Other results and considerations regarding the droplet surface are also discussed.

  • 3.
    Albernaz, Daniel L.
    et al.
    Royal Inst Technol, Dept Mech, Linne Flow Ctr, S-10044 Stockholm, Sweden..
    Do-Quang, M.
    Royal Inst Technol, Dept Mech, Linne Flow Ctr, S-10044 Stockholm, Sweden..
    Hermanson, J. C.
    University of Washington, Seattle, USA.
    Amberg, Gustav
    KTH.
    Droplet deformation and heat transfer in isotropic turbulence2017In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 820, p. 61-85Article in journal (Refereed)
    Abstract [en]

    The heat and mass transfer of deformable droplets in turbulent flows is crucial. to a wide range of applications, such as cloud dynamics and internal combustion engines. This study investigates a single droplet undergoing phase change in isotropic turbulence using numerical simulations with a hybrid lattice Boltzmann scheme. Phase separation is controlled by a non-ideal equation of state and density contrast is taken into consideration. Droplet deformation is caused by pressure and shear stress at the droplet interface. The statistics of thermodynamic variables are quantified and averaged over both the liquid and vapour phases. The occurrence of evaporation and condensation is correlated to temperature fluctuations, surface tension variation and turbulence intensity. The temporal spectra of droplet deformations are analysed and related to the droplet surface area. Different modes of oscillation are clearly identified from the deformation power spectrum for low Taylor Reynolds number Re, whereas nonlinearities are produced with the increase of Re A, as intermediate frequencies are seen to overlap. As an outcome, a continuous spectrum is observed, which shows a decrease in the power spectrum that scales as similar to f(-3) Correlations between the droplet Weber number, deformation parameter, fluctuations of the droplet volume and thermodynamic variables are also developed.

  • 4.
    Albernaz, Daniel L.
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Lattice Boltzmann Method for the evaporation of a suspended droplet2013In: Interfacial phenomena and heat transfer, ISSN 2167-857X, Vol. 1, no 3, p. 245-258Article in journal (Refereed)
    Abstract [en]

    In this paper we consider a thermal multiphase lattice Boltzmann method (LBM) to investigate the heating and vaporization of a suspended droplet. An important benefit from the LBM is that phase separation is generated spontaneously and jump conditions for heat and mass transfer are not imposed. We use double distribution functions in order to solve for momentum and energy equations. The force is incorporated via the exact difference method (EDM) scheme where different equations of state (EOS) are used, including the Peng-Robinson EOS. The equilibrium and boundary conditions are carefully studied. Results are presented for a hexane droplet set to evaporate in a superheated gas, for static condition and under gravitational effects. For the static droplet, the numerical simulations show that capillary pressure and the cooling effect at the interface play a major role. When the droplet is convected due to the gravitational field, the relative motion between the droplet and surrounding gas enhances the heat transfer. Evolution of density and temperature fields are illustrated in details.

  • 5.
    Amberg, Gustav
    KTH.
    Solidification microstructure, dendrites and convection2004In: Phase Change With Convection: Modelling And Validation / [ed] Kowalewski, TA., Gobin, D., Wien: Springer, 2004, p. 1-53Conference paper (Refereed)
  • 6.
    Carlson, Andreas
    et al.
    KTH.
    Bellani, Gabriele
    KTH.
    Amberg, Gustav
    KTH.
    Contact line dissipation in short-time dynamic wetting2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 4, article id 44004Article in journal (Refereed)
    Abstract [en]

    Dynamic wetting of a solid surface is a process that is ubiquitous in Nature, and also of increasing technological importance. The underlying dissipative mechanisms are, however, still unclear. We present here short-time dynamic wetting experiments and numerical simulations, based on a phase field approach, of a droplet on a dry solid surface, where direct comparison of the two allows us to evaluate the different contributions from the numerics. We find that an important part of the dissipation may arise from a friction related to the motion of the contact line itself, and that this may be dominating both inertia and viscous friction in the flow adjacent to the contact line. A contact line friction factor appears in the theoretical formulation that can be distinguished and quantified, also in room temperature where other sources of dissipation are present. Water and glycerin-water mixtures on various surfaces have been investigated where we show the dependency of the friction factor on the nature of the surface, and the viscosity of the liquid.

  • 7.
    Carlson, Andreas
    et al.
    KTH.
    Bellani, Gabriele
    KTH.
    Amberg, Gustav
    KTH.
    Universality in dynamic wetting dominated by contact-line friction2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, no 4, article id 045302Article in journal (Refereed)
    Abstract [en]

    We report experiments on the rapid contact-line motion present in the early stages of capillary-driven spreading of drops on dry solid substrates. The spreading data fail to follow a conventional viscous or inertial scaling. By integrating experiments and simulations, we quantify a contact-line friction mu(f) which is seen to limit the speed of the rapid dynamic wetting. A scaling based on this contact-line friction is shown to yield a universal curve for the evolution of the contact-line radius as a function of time, for a range of fluid viscosities, drop sizes, and surface wettabilities.

  • 8.
    Carlson, Andreas
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Droplet dynamics in a bifurcating channel2010In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 36, no 5, p. 397-405Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Do-Quang, Minh
    et al.
    KTH, Mekanik.
    Amberg, Gustav
    KTH, Mekanik.
    Modeling of Time-Dependent 3D Weld Pool Flow Due to a Moving Arc2003In: Modeling, Simulation and Optimization of Complex Processes: Proceedings of the International Conference on High Performance Scientific Computing, March 10-14, 2003, Hanoi, Vietnam / [ed] Hans Georg Bock, Ekaterina Kostina, Hoang Xuan Phu, Rolf Rannacher, Berlin: Springer, 2003, p. 127-138Conference paper (Other academic)
  • 10.
    Do-Quang, Minh
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Modelling of time-dependent 3D weld pool flow2003In: Mathematical modelling of weld Phenomena 7 / [ed] Cerjak, H; Bhadeshia, H. K. D. H.; Kozeschnik, E., Graz: Graz Techn. Univ. , 2003, p. 91-112Conference paper (Refereed)
    Abstract [en]

    The fluid flows in molten pools during arc welding are important factors. These in turn influence in overall heat and mass transfer, which determine the mechanical properties and quality of the weld fusion zone. Here, modelling results are presented concerning the time dependent weld pool flow and temperature in gas tungsten arc welding (GTA) of the difference type of stainless steels. It is proved that the temperature fields are strongly affected by the convection at the weld pool’s surfaces. With the stainless steel type 304 (low sulfur content 0.0005 weight % and high sulfur content 0.0139 weight %), the actual chaotic time dependent melt flow is obtained with a fully time dependent model. In those cases, the fluid flow in the weld pool is highly complex and it influenced the weld pool`s depth and width. For the 645 SMO steel, which has an extremely low sulfur content and low conductivity, the chaotic fluid flows did not appear. The calculated geometry of the weld fusion zone and heat affected zone were in good agreement with the experimental results, both with or without chaotic fluid flows.

  • 11.
    Do-Quang, Minh
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Brethouwer, Gert
    KTH.
    Johansson, Arne V.
    KTH.
    Simulation of finite-size fibers in turbulent channel flows2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 1, article id 013006Article in journal (Refereed)
    Abstract [en]

    The dynamical behavior of almost neutrally buoyant finite-size rigid fibers or rods in turbulent channel flow is studied by direct numerical simulations. The time evolution of the fiber orientation and translational and rotational motions in a statistically steady channel flow is obtained for three different fiber lengths. The turbulent flow is modeled by an entropy lattice Boltzmann method, and the interaction between fibers and carrier fluid is modeled through an external boundary force method. Direct contact and lubrication force models for fiber-fiber interactions and fiber-wall interaction are taken into account to allow for a full four-way interaction. The density ratio is chosen to mimic cellulose fibers in water. It is shown that the finite size leads to fiber-turbulence interactions that are significantly different from earlier reported results for point like particles (e.g., elongated ellipsoids smaller than the Kolmogorov scale). An effect that becomes increasingly accentuated with fiber length is an accumulation in high-speed regions near the wall, resulting in a mean fiber velocity that is higher than the mean fluid velocity. The simulation results indicate that the finite-size fibers tend to stay in the high-speed streaks due to collisions with the wall. In the central region of the channel, long fibers tend to align in the spanwise direction. Closer to the wall the long fibers instead tend to toward to a rotation in the shear plane, while very close to the wall they become predominantly aligned in the streamwise direction.

  • 12.
    Do-Quang, Minh
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Carlberg, Torbjörn
    Mid Sweden University.
    Three-dimensional modelling of radial segregation due to weak convection2004In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 269, no 2-4, p. 454-463Article in journal (Refereed)
    Abstract [en]

    A comprehensive three-dimensional, time-dependent model of heat, momentum and solute transfer during solidification is carried out to illustrate the influence of weak convection, caused by surface tension forces, on radial dopant segregation occurring in crystal growth under micro-gravity conditions. 3D adaptive finite element method is used in order to simulate the motion and deformation of the solidification interface. The geometry studied is a Bridgman configuration with a partly coated surface. The small slots in the coating gives a free surface in a controlled way, and is varied in order to alter the Marangoni flow. In this study, A comparison is made between the numerical results and the experimental results. A good agreement has been observed for the effective distribution coefficient keff and for the radial segregation [Delta]c’. The radial dopant segregation is affected by weak convection.

  • 13.
    Do-Quang, Minh
    et al.
    KTH.
    Carlson, A
    KTH.
    Amberg, Gustav
    KTH.
    The impact of ink-jet droplets on a paper-like structure2011In: Fluid Dynamics & Materials Processing, ISSN 1555-256X, E-ISSN 1555-2578, Vol. 7, no 4, p. 389-402Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Do-Quang, Minh
    et al.
    KTH.
    Geyl, Laurent
    KTH.
    Stemme, Göran
    KTH.
    van der Wijngaart, Wouter
    KTH.
    Amberg, Gustav
    KTH.
    Fluid dynamic behavior of dispensing small droplets through a thin liquid film2010In: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 9, no 2-3, p. 303-311Article in journal (Refereed)
    Abstract [en]

    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.

  • 15.
    Do-Quang, Minh
    et al.
    KTH.
    Stemme, Göran
    KTH.
    van der Wijngaart, Wouter
    KTH.
    Amberg, Gustav
    KTH.
    Numerical Simulation of the Passage of Small Liquid Droplets Through a Thin Liquid Film2008In: Proceedings Of The 6Th International Conference On Nanochannels, Microchannels, And Minichannels, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2008, p. 857-861Conference paper (Refereed)
    Abstract [en]

    We simulate numerically a novel method for dispensing, mixing and ejecting of picolitre liquid samples in a single step. The system consists of a free liquid film, suspended in a frame and positioned in front of a droplet dispenser. On impact, a picolitre droplet 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. Through this process the liquid in the droplet and that in the film is mixed in a controlled way. We model the flow using the Navier Stokes together with the Cahn-Hilliard equations. 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 passage through the thin liquid film matches the measured velocity from the experiment well.

  • 16.
    Gullman-Strand, Johan
    et al.
    KTH.
    Törnblom, Olle
    KTH.
    Lindgren, Björn
    KTH.
    Amberg, Gustav
    KTH.
    Johansson, Arne V.
    KTH.
    Numerical and experimental study of separated flow in a plane asymmetric diffuser2004In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 25, no 3, p. 451-460Article in journal (Refereed)
    Abstract [en]

    Computations of the turbulent flow through plane asymmetric diffusers for opening angles from 8degrees to 10degrees have been carried out with the explicit algebraic Reynolds stress model (EARSM) of Wallin and Johansson [J. Fluid Mech. 403 (2000) 89]. It is based on a two-equation platform in the form of a low-Re K - omega formulation, see e.g. Wilcox [Turbulence Modeling for CFD, DCW Industries Inc., 1993]. The flow has also been studied experimentally for the 8.5degrees opening angle using PIV and LDV. The models under-predict the size and magnitude of the recirculation zone. This is, at least partially, attributed to an over-estimation of the wall normal turbulence component in a region close to the diffuser inlet and to the use of damping functions in the near-wall region. By analyzing the balance between the production and dissipation of the turbulence kinetic energy we find that the predicted dissipation is too large. Hence, we can identify a need for improvement of the modeling the transport equation for the turbulence length-scale related quantity.

  • 17.
    Gustafsson, Anders
    et al.
    Södertörn University College, School of Business Studies.
    Wenngren, Johanna
    Södertörn University College, School of Business Studies.
    Möjligheter med Supply Chain Management i produktionen av Active Pharmaceutical Ingredient: en utvärdering och empirisk fallstudie av Demand Driven Supply inom AstraZeneca AB2008Independent thesis Basic level (degree of Bachelor), 10 points / 15 hpStudent thesis
    Abstract [sv]

    De stora läkemedelsbolagen har sedan mitten på 1990-talet fått en ökad press på att optimera sina försörjningskedjor på grund av att patent på olika mediciner gått ut. När patentet gått ut kan generiska konkurrenter börja sälja liknande mediciner, de kan sälja dem till lägre pris eftersom de inte har forsknings och utvecklingskostnader att täcka. AstraZeneca tog i slutet av 1990-talet beslutet att implementera en ny strategi för deras försörjningskedja i deras produktion. Detta gjordes för att sänka deras produktionskostnader för att kunna konkurrera mot generiska konkurrenter. En konsultfirma togs in och Demand Driven Supply (DDS) implementerades. Syftet med denna uppsats är att definiera Demand Driven Supply och att utvärdera om denna implementering gett de resultat som eftersträvades. Vi presenterar en teoretisk referensram som behövs för att få en förståelse över de metoder och verktyg som behövs för att optimera varuförsörjningskedjan och därigenom kunna sänka kostnaderna. Dessa teorier står till grund för den implementering som skedde hos AstraZeneca. Den huvudsakliga anledningen till att DDS implementerades var att AstraZeneca ville gå mot sugande produktionsstyrning för att därmed korta ledtiden, sänka kostnader och sänka kapitalbindningen och höja marginalerna på sin försäljning för att få kapital till att återinvestera i företaget.

  • 18.
    Hansen, Kjetil Falkenberg
    et al.
    KTH Royal Institute of Technology.
    Dimitrov, Smilen
    KTH Royal Institute of Technology.
    Using the Reactable as experimental interface for instrument design prototypingIn: Organised Sound, ISSN 1355-7718, E-ISSN 1469-8153Article in journal (Other academic)
    Abstract [en]

    This paper describes an experiment of using an existing hardware platform, the Reactable, to help designing the interaction between three different sound models and instrument interfaces. The aim was to test if prototyping could be facilitated by interacting with models of control actions derivedfrom performance gestures on an intermediate interface. The Reactable isa tangible table-top electronic musical instrument, and the software models include a DJ scratch interface, a virtual turntable, a physics-based sound model representing a bow-and-string interaction, and a physics-based friction sound model for sonification of the user gestures. The interaction was evaluated by two experts: one Reactable musician and one DJ. Their task was to practice expressive, musical performances. Data from the performers were collected through questionnaires and video recordings. The advantages of usinga single, versatile, hardware setup as a designer tool for various interface tasks are discussed. It is suggested how this hardware can be described as an alternative mapping layer.

  • 19.
    Hansen, Kjetil Falkenberg
    et al.
    KTH Royal Institute of Technology.
    Fabiani, Marco
    Bresin, Roberto
    Analysis of the acoustics and playing strategies of turntable scratching2011In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 97, no 2, p. 303-314Article in journal (Refereed)
  • 20.
    Johansson, Anders
    et al.
    Kungliga tekniska högskolan.
    Bohlin, Karl
    Kungliga tekniska högskolan.
    Alvarsson, Jesper
    Södertörn University, School of Social Sciences, Psychology.
    Annoyance and Partial Masking of Wind Turbine Noise from Ambient Sources2019In: Acta Acoustica united with Acustica, ISSN 1610-1928, E-ISSN 1861-9959, Vol. 105, no 6, p. 1035-1041Article in journal (Refereed)
    Abstract [en]

    This paper investigates noise annoyance from wind turbines of different sizes and in different acoustic surroundings. A listening test was conducted where wind turbine noises were rated alone and together with background sounds from a deciduous forest, a busy city and road traffic. A magnitude production procedure was implemented which showed high correlation between repeated measurements and the results were analysed using A-weighted sound levels, signal-to-noise ratios and time varying loudness and partial loudness. Ratings for wind turbine sound heard alone showed no coherent statistically significant differences between wind turbine types, neither for A-weighted sound levels nor loudness. The masking test indicate that road traffic noise is a superior masker compared to forest sound. However, these effects where only statistically significant at low sound levels, below the range 35–45 dB(A), where noise guidelines for wind turbine noise usually are stipulated.

  • 21.
    Kékesi, Timea
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Prahl Wittberg, Lisa
    KTH.
    Drop deformation and breakup2014In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 66, p. 1-10Article in journal (Refereed)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to investigate the deformation and breakup of an initially spherical drop in the bag- and shear breakup regimes, induced by steady disturbances. The onset of breakup is sought by studying steady-shape deformations while increasing the Weber number until breakup occurs. A parameter study is carried out applying different material properties and a wide range of drop Reynolds numbers in the steady wake regime. Density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, and Reynolds numbers between 20 and 200 are investigated for a constant Weber number of 20. The critical Weber number is found to be 12, in agreement with observations of earlier studies. For Weber number of 20 varying density, viscosity ratios and Reynolds numbers, interesting mixed breakup modes are discovered. Moreover, a new regime map including all modes observed is presented. A criterion for the transition between bag-and shear breakup is defined relating the competing inertial and shear forces appearing in the flow. Furthermore, results on breakup times and the time history of the drag coefficient are presented; the latter is concluded to be a potential parameter to indicate the occurrence of breakup. (C) 2014 Elsevier Ltd. All rights reserved.

  • 22.
    Laurila, T.
    et al.
    Aalto University School of Science, Aalto, Finland.
    Carlson, Andreas
    KTH.
    Do-Quang, Minh
    KTH.
    Ala-Nissila, T.
    Aalto University School of Science, Aalto, Finland / own University, Providence, United States.
    Amberg, Gustav
    KTH.
    Thermohydrodynamics of boiling in a van der Waals fluid2012In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, no 2, article id 026320Article in journal (Refereed)
    Abstract [en]

    We present a modeling approach that enables numerical simulations of a boiling Van der Waals fluid based on the diffuse interface description. A boundary condition is implemented that allows in and out flux of mass at constant external pressure. In addition, a boundary condition for controlled wetting properties of the boiling surface is also proposed. We present isothermal verification cases for each element of our modeling approach. By using these two boundary conditions we are able to numerically access a system that contains the essential physics of the boiling process at microscopic scales. Evolution of bubbles under film boiling and nucleate boiling conditions are observed by varying boiling surface wettability. We observe flow patters around the three-phase contact line where the phase change is greatest. For a hydrophilic boiling surface, a complex flow pattern consistent with vapor recoil theory is observed.

  • 23.
    Lee, Y.
    et al.
    University of Tokyo, Bunkyo-ku, Tokyo, Japan.
    Matsushima, N.
    University of Tokyo, Bunkyo-ku, Tokyo, Japan.
    Yada, S.
    KTH.
    Nita, S.
    University of Tokyo, Bunkyo-ku, Tokyo, Japan.
    Kodama, T.
    University of Tokyo, Bunkyo-ku, Tokyo, Japan.
    Amberg, Gustav
    Södertörn University. KTH.
    Shiomi, J.
    University of Tokyo, Bunkyo-ku, Tokyo, Japan.
    Revealing How Topography of Surface Microstructures Alters Capillary Spreading2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, no 1, article id 7787Article in journal (Refereed)
    Abstract [en]

    Wetting phenomena, i.e. the spreading of a liquid over a dry solid surface, are important for understanding how plants and insects imbibe water and moisture and for miniaturization in chemistry and biotechnology, among other examples. They pose fundamental challenges and possibilities, especially in dynamic situations. The surface chemistry and micro-scale roughness may determine the macroscopic spreading flow. The question here is how dynamic wetting depends on the topography of the substrate, i.e. the actual geometry of the roughness elements. To this end, we have formulated a toy model that accounts for the roughness shape, which is tested against a series of spreading experiments made on asymmetric sawtooth surface structures. The spreading speed in different directions relative to the surface pattern is found to be well described by the toy model. The toy model also shows the mechanism by which the shape of the roughness together with the line friction determines the observed slowing down of the spreading.

  • 24.
    Liu, Jiewei
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Do-Quang, Minh
    KTH.
    Numerical simulation of particle formation in the rapid expansion of supercritical solution process2014In: Journal of Supercritical Fluids, ISSN 0896-8446, E-ISSN 1872-8162, Vol. 95, p. 572-587Article in journal (Refereed)
    Abstract [en]

    In this paper, we numerically study particle formation in the rapid expansion of supercritical solution (RESS) process in a two dimensional, axisymmetric geometry, for a benzoic acid + CO2 system. The fluid is described by the classical Navier-Stokes equation, with the thermodynamic pressure being replaced by a generalized pressure tensor. Homogenous particle nucleation, transport, condensation and coagulation are described by a general dynamic equation, which is solved using the method of moments. The results show that the maximal nucleation rate and number density occurs near the nozzle exit, and particle precipitation inside the nozzle might not be ignored. Particles grow mainly across the shocks. Fluid in the shear layer of the jet shows a relatively low temperature, high nucleation rate, and carries particles with small sizes. On the plate, particles within the jet have smaller average size and higher geometric mean, while particles outside the jet shows a larger average size and a lower geometric mean. Increasing the preexpansion temperature will increase both the average particle size and standard deviation. The preexpansion pressure does not show a monotonic dependency with the average particle size. Increasing the distance between the plate and the nozzle exit might decrease the particle size. For all the cases in this paper, the average particle size on the plate is on the order of tens of nanometers.

  • 25.
    Liu, Jiewei
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Numerical Simulation of Rapid Expansion of Supercritical Carbon Dioxide2015In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 61, no 1, p. 317-332Article in journal (Refereed)
    Abstract [en]

    Axisymmetric rapid expansion of supercritical carbon dioxide is investigated in this article. The extended generalized Bender equation of state is used to give a good description of the fluids over a wide range of pressure and temperature conditions. The locations of Mach disks are analyzed and compared with an experimental correlation for the case where there is no plate positioned in front of the nozzle exit. It is found that the disagreement between our numerical results and the experimental formula is very small when the pressure ratio is small, and increases as the pressure ratio increases. It is also found that with different equations of state, the predicted positions of Mach disks do not differ a lot, but the temperature profiles in the chamber differ a lot. The case where there is a plate positioned in front of the nozzle exit is also studied in this article. A universal similarity solution is obtained.

  • 26.
    Lövgren, Kristin
    Södertörn University College, School of Business Studies.
    Slakthusområdet: ett lågteknologiskt industriellt kluster2008Independent thesis Advanced level (degree of Magister), 10 points / 15 hpStudent thesis
  • 27.
    Malik, Amer
    et al.
    KTH.
    Ogden, Sam
    Uppsala University.
    Amberg, Gustav
    KTH.
    Hjort, Klas
    Uppsala University /VTT Technical Research Center Finland, Espoo, Finland.
    Modeling and analysis of a phase change material thermohydraulic membrane microactuator2013In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 22, no 1, p. 186-194Article in journal (Refereed)
    Abstract [en]

    Presented in this work, is a Finite Element Method (FEM)-based model for phase change material actuators, modeling the active material as a fluid as opposed to a solid. This enables the model to better conform to localized loads, as well as offering the opportunity to follow material movement in enclosed volumes. Modeling, simulation and analysis of an electrothermally activated paraffin microactuator has been conducted. The paraffin microactuator used for the analysis in the current study exploits the large volumetric expansion of paraffin upon melting, which combined with its low compressibility in the liquid state allows for high hydraulic pressures to be generated. The purpose of the study is to supply a geometry independent model of such a microactuator through the implementation of a fluid model rather than a solid model, which has been utilized in previous studies. Numerical simulations are conducted at different frequencies of the heating source and for different geometries of the microactuator. The results are compared with the empirical data obtained on a close to identical paraffin microactuator, which clearly show the advantages of a fluid model instead of a solid state approximation.

  • 28.
    Nilsson, Mats E.
    et al.
    Stockholms universitet, Psykologiska institutionen.
    Alvarsson, Jesper
    Stockholms universitet, Psykologiska institutionen.
    Rådsten-Ekman, Maria
    Stockholms universitet, Psykologiska institutionen.
    Bolin, Karl
    KTH.
    Auditory masking of wanted and unwanted sounds in a city park2010In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 58, no 5, p. 524-531Article in journal (Refereed)
    Abstract [en]

    Auditory masking of unwanted sounds by wanted sounds has been suggested as a tool for outdoor acoustic design. Anecdotal evidence exists for successful applications, for instance the use of fountain sounds for masking road traffic noise in urban parks. However, basic research on auditory masking of environmental sounds is lacking. Therefore, we conducted two listening experiments, using binaural recordings from a city park in Stockholm exposed to traffic noise from a main road and sound from a large fountain located in the center of the park. In the first experiment, 17 listeners assessed the loudness of the road traffic noise and fountain sounds from recordings at various distances from the road, with or without the fountain turned on. In the second experiment, 16 listeners assessed the loudness of systematic combinations of a singular fountain sound and a singular road traffic noise. The results of the first experiment showed that the fountain sound reduced the loudness of road traffic noise close to the fountain, and that the fountain sound was equally loud or louder than the road traffic noise in a region 20-30 m around the fountain. This suggests that the fountain added to the quality of the city park soundscape by reducing the loudness of the (presumably unwanted) traffic noise. On the other hand, results from the second experiment showed that road traffic noise was harder to mask than fountain sound, and that the partial loudness of both sources was considerably less than expected from a model of energetic masking. This indicates that auditory processes, possibly related to target-masker confusion, may reduce the overall masking effect of environmental sounds.

  • 29.
    Nour, Z. Moradi
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Do-Quang, M.
    KTH.
    Kinematics and dynamics of suspended gasifying particle2017In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 228, no 3, p. 1135-1151Article in journal (Refereed)
    Abstract [en]

    The effect of gasification on the dynamics and kinematics of immersed spherical and non-spherical solid particles have been investigated using the three-dimensional lattice Boltzmann method. The gasification was performed by applying mass injection on particle surface for three cases: flow passing by a fixed sphere, rotating ellipsoid in simple shear flow, and a settling single sphere in a rectangular domain. In addition, we have compared the accuracy of employing two different fluid-solid interaction methods for the particle boundary. The validity of the gasification model was studied by comparing computed the mass flux from the simulation and the calculated value on the surface of the particle. The result was used to select a suitable boundary method in the simulations combined with gasification. Moreover, the reduction effect of the ejected mass flux on the drag coefficient of the fixed sphere have been validated against previous studies. In the case of rotating ellipsoid in simple shear flow with mass injection, a decrease on the rate of rotation was observed. The terminal (maximum) velocity of the settling sphere was increased by increasing the ratio of radial flux from the particle boundary.

  • 30.
    Pihl, Joakim
    et al.
    Södertörn University College, School of Business Studies.
    Stenman, Joakim
    Södertörn University College, School of Business Studies.
    Just-In-Time-aspekter: Scania2008Independent thesis Basic level (degree of Bachelor), 10 points / 15 hpStudent thesis
    Abstract [sv]

    Denna uppsats har för avsikt att utreda begreppet Just-In-Time (JIT) och dess komponenter för att sedan försöka finna dessa i den svenska lastbilstillverkaren Scanias produktionssystem. Litteratur har bidragit med en definition av JIT som sedan har jämförts med hur Scania arbetar inom produktionen. Empiri har erhållits genom intervjuer med berörd personal samt observationer på plats i Oskarshamn och i Södertälje.

    För japanerna är inte Just-In-Time-tänket en ny företeelse utan det är något de har arbetat efter en längre tid. Denna uppsats har valt att utgå från Jeffrey K. Likers (2004) definition i The Toyota Way. Liker delar upp filosofin i fyra stycken sektioner. Uppsatsen fokuserar på två av dessa som behandlar arbetsprocessen och ständiga förbättringar. Scanias produktionssystem bygger till stor del på Toyotas. Denna uppsats kommer att påvisa likheter och skillnader mellan teorins JIT och Scanias produktionssystem (SPS).

  • 31.
    Schenk, Linda
    KTH, Filosofi.
    Comparison of Data Used for Setting Occupational Exposure Limits2010In: International journal of occupational and environmental health, ISSN 1077-3525, E-ISSN 2049-3967, Vol. 16, no 3, p. 249-262Article in journal (Refereed)
    Abstract [en]

    It has previously been shown that occupational exposure limits (OELs) for the same substance can vary significantly between different standard-setters. The work presented in this paper identifies the steps in the process towards establishing an OEL and how variations in those processes could account for these differences. This study selects for further scrutiny substances for which the level of OELs vary by a factor of 100, focussing on 45 documents concerning 14 substances from eight standard-setters. Several of the OELs studied were more than 20 years old and based on outdated knowledge. Furthermore, different standard-setters sometimes based their OELs on different sets of data, and data availability alone could not explain all differences in the selection of data sets used by standard-setters. While the interpretation of key studies did not differ significantly in standard-setters' documentations, the evaluations of the key studies' quality did. Also, differences concerning the critical effect coincided with differences in the level of OELs for half of the substances.

  • 32.
    Shen, Biao
    et al.
    Kyushu University, Fukuoka, Japan.
    Yamada, Masayuki
    Kyushu University, Fukuoka, Japan.
    Hidaka, Sumitomo
    Kyushu University, Fukuoka, Japan.
    Liu, Jiewei
    KTH.
    Shiomi, Junichiro
    University of Tokyo, Tokyo, Japan.
    Amberg, Gustav
    KTH.
    Do-Quang, Minh
    KTH.
    Kohno, Masamichi
    Kyushu University, Fukuoka, Japan.
    Takahashi, Koji
    Kyushu University, Fukuoka, Japan.
    Takata, Yasuyuki
    Kyushu University, Fukuoka, Japan.
    Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2036Article in journal (Refereed)
    Abstract [en]

    For phase-change cooling schemes for electronics, quick activation of nucleate boiling helps safeguard the electronics components from thermal shocks associated with undesired surface superheating at boiling incipience, which is of great importance to the long-term system stability and reliability. Previous experimental studies show that bubble nucleation can occur surprisingly early on mixed-wettability surfaces. In this paper, we report unambiguous evidence that such unusual bubble generation at extremely low temperatures-even below the boiling point-is induced by a significant presence of incondensable gas retained by the hydrophobic surface, which exhibits exceptional stability even surviving extensive boiling deaeration. By means of high-speed imaging, it is revealed that the consequently gassy boiling leads to unique bubble behaviour that stands in sharp contrast with that of pure vapour bubbles. Such findings agree qualitatively well with numerical simulations based on a diffuse-interface method. Moreover, the simulations further demonstrate strong thermocapillary flows accompanying growing bubbles with considerable gas contents, which is associated with heat transfer enhancement on the biphilic surface in the low-superheat region.

  • 33.
    Shiomi, Junichiro
    et al.
    University of Tokyo, Tokyo, Japan.
    Lin, Yuan
    KTH.
    Carlborg, Carl Fredrik
    KTH.
    Amberg, Gustav
    KTH.
    Maruyama, Shigeo
    University of Tokyo, Tokyo, Japan.
    Low dimensional heat and mass transport in carbon nanotubes2010In: Proceedings of the ASME Micro/Nanoscale Heat and Mass Transfer International Conference 2009, MNHMT2009, 2010, p. 337-346Conference paper (Refereed)
    Abstract [en]

    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.

  • 34.
    Strömgren, Tobias
    et al.
    KTH.
    Brethouwer, Geert
    KTH.
    Amberg, Gustav
    KTH.
    Johansson, Arne V.
    KTH, Mekanik.
    A modelling study of evolving particle-laden turbulent pipe-flow2009In: Turbulence, Heat And Mass Transfer 6, Begell House , 2009, p. 713-716Conference paper (Refereed)
    Abstract [en]

    An Eulerian turbulent two phase flow model in cylindrical coordinates was developed in order to study evolving turbulent gas particle flows in a downward pipe flow. The model takes the feedback of the particles into account. Simulations shows good agreement with experiments and showed that the pipe length required for particle laden turbulent pipe flow to become fully developed is four times longer than for unladen flows, even for rather low mass loadings. The accumulation of particles in the near wall region showed a nonmonotonic behaviour and was found to be strongest for St=0.5.

  • 35.
    Strömgren, Tobias
    et al.
    KTH.
    Brethouwer, Geert
    KTH.
    Amberg, Gustav
    KTH.
    Johansson, Arne V.
    KTH.
    A modelling study of evolving particle-laden turbulent pipe-flow2011In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 86, no 3-4, p. 477-495Article in journal (Refereed)
    Abstract [en]

    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.

  • 36.
    Strömgren, Tobias
    et al.
    KTH.
    Brethouwer, Geert
    KTH.
    Amberg, Gustav
    KTH.
    Johansson, Arne V.
    KTH.
    Deriving fluid-particle correlation closures for Eulerian two-fluid models through use of Langevin equations2011In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 30, no 3, p. 275-280Article in journal (Refereed)
    Abstract [en]

    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.

  • 37.
    Strömgren, Tobias
    et al.
    KTH.
    Brethouwer, Geert
    KTH.
    Amberg, Gustav
    KTH.
    Johansson, Arne V.
    KTH.
    Modelling of turbulent gas-particle flows with focus on two-way coupling effects on turbophoresis2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 224, p. 36-45Article in journal (Refereed)
    Abstract [en]

    An Eulerian model was developed for turbulent gas-particle flow that takes into account the influence of particles on the gas-phase turbulence. For the description of the particle-phase stress the kinetic theory of granular flow and the simpler Hinze model were adopted. A K-ω model was used as the gas phase turbulence model. The difference between one- and two-way coupling was investigated for different particle volume fractions and particle diameters. It was found that particles with a much higher density than the fluid substantially affect the gas-phase in turbulent channel flow for particle volume fractions as low as 10 -4. The models with the particle-phase stress described by the kinetic theory of granular flow and the simpler Hinze model produce similar results for particles with small response times but deviate for larger response times. The study shows that two-way coupling and the turbophoretic effect must be taken into account in models even at relatively low particle volume fractions.

  • 38.
    Tahir, Abdul Malik
    et al.
    KTH.
    Malik, Amer
    KTH.
    Amberg, Gustav
    Modeling of the primary rearrangement stage of liquid phase sintering2016In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 24, no 7, article id 075009Article in journal (Refereed)
    Abstract [en]

    The dimensional variations during the rearrangement stage of liquid phase sintering could have a detrimental effect on the dimensional tolerances of the sintered product. A numerical approach to model the liquid phase penetration into interparticle boundaries and the accompanied dimensional variations during the primary rearrangement stage of liquid phase sintering is presented. The coupled system of the Cahn-Hilliard and the Navier-Stokes equations is used to model the penetration of the liquid phase, whereas the rearrangement of the solid particles due to capillary forces is modeled using the equilibrium equation for a linear elastic material. The simulations are performed using realistic physical properties of the phases involved and the effect of green density, wettability and amount of liquid phase is also incorporated in the model. In the first step, the kinetics of the liquid phase penetration and the rearrangement of solid particles connected by a liquid bridge is modeled. The predicted and the calculated (analytical) results are compared in order to validate the numerical model. The numerical model is then extended to simulate the dimensional changes during primary rearrangement stage and a qualitative match with the published experimental data is achieved.

  • 39.
    Villanueva, Walter
    et al.
    KTH.
    Amberg, Gustav
    KTH.
    Phase-field Simulations Of Free Boundary Microflow2006In: Proceedings of Second International Conference on Transport Phenomena in Micro and Nanodevices, 2006Conference paper (Refereed)
  • 40.
    Villanueva, Walter
    et al.
    Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Boettinger, W. J.
    National Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Warren, J. A.
    Institute of Standards & Technology (NIST), Gaithersburg, USA.
    Amberg, Gustav
    KTH.
    Effect of phase change and solute diffusion on spreading on a dissolving substrate2009In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 57, no 20, p. 6022-6036Article in journal (Refereed)
    Abstract [en]

    Dissolutive wetting is investigated numerically using a diffuse-interface model that incorporates fluid flow, solute diffusion and phase change. A range of materials parameters are investigated: (1) permitting recovery of the hydrodynamic limit by suppressing the dissolution of the substrate and (2) evaluating the role of diffusion. The time history of droplet size, droplet concentration and angles between the interfaces are given. For cases in which convection dominates, the dynamics of spreading agrees with a known hydrodynamic model for spreading of inert fluids. A phase change increases wetting speed, due to a condensation that takes place near the triple junction. There is also a strong dependence of the wetting kinetics on the solute diffusivities. Details of composition changes during spreading are also discussed, such as the composition path of the bulk liquid probed at different locations in the drop. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

  • 41. Wang, Jiayu
    et al.
    Do-Quang, Minh
    KTH.
    Cannon, James J.
    University of Tokyo, Tokyo, Japan.
    Yue, Feng
    University of Tokyo, Tokyo, Japan.
    Suzuki, Yuji
    University of Tokyo, Tokyo, Japan.
    Amberg, Gustav
    KTH.
    Shiomi, Junichiro
    KTH.
    Surface structure determines dynamic wetting2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 8474Article in journal (Refereed)
    Abstract [en]

    Liquid wetting of a surface is omnipresent in nature and the advance of micro-fabrication and assembly techniques in recent years offers increasing ability to control this phenomenon. Here, we identify how surface roughness influences the initial dynamic spreading of a partially wetting droplet by studying the spreading on a solid substrate patterned with microstructures just a few micrometers in size. We reveal that the roughness influence can be quantified in terms of a line friction coefficient for the energy dissipation rate at the contact line, and that this can be described in a simple formula in terms of the geometrical parameters of the roughness and the line-friction coefficient of the planar surface. We further identify a criterion to predict if the spreading will be controlled by this surface roughness or by liquid inertia. Our results point to the possibility of selectively controlling the wetting behavior by engineering the surface structure.

  • 42.
    Wang, Yuli
    et al.
    KTH / University of Oslo, Oslo, Norway.
    Amberg, Gustav
    Södertörn University. KTH.
    Carlson, Andreas
    University of Oslo, Oslo, Norway.
    Local dissipation limits the dynamics of impacting droplets on smooth and rough substrates2017In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 2, no 3, article id 033602Article in journal (Refereed)
    Abstract [en]

    A droplet that impacts onto a solid substrate deforms in a complex dynamics. To extract the principal mechanisms that dominate this dynamics, we deploy numerical simulations based on the phase field method. Direct comparison with experiments suggests that a dissipation local to the contact line limits the droplet spreading dynamics and its scaled maximum spreading radius beta(max). By assuming linear response through a drag force at the contact line, our simulations rationalize experimental observations for droplet impact on both smooth and rough substrates, measured through a single contact line friction parameter mu(f). Moreover, our analysis shows that dissipation at the contact line can limit the dynamics and we describe beta(max) by the scaling law beta(max) similar to (Re mu(l)/mu(f))(1/2) that is a function of the droplet viscosity (mu(l)) and its Reynolds number (Re).

  • 43.
    Wang, Yuli
    et al.
    KTH / Jiangsu University, Zhenjiang, Peoples R China.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Impact of viscoelastic droplets2017In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 243, p. 38-46Article in journal (Refereed)
    Abstract [en]

    We conduct numerical experiments on viscoelastic droplets hitting a flat solid surface. The results present time-resolved non-Newtonian stresses acting in the droplet. Comparing with the simulation of the impact of a Newtonian droplet, the effects of viscoelasticity on droplet behaviors such as splashing, the maximum spreading diameter and deformation are analyzed. With detailed information on the contact line region, we demonstrate how the contact line behaves according to the transition of the fluid property from elasticity dominated to shear-thinning dominated when a droplet expands and contracts on the substrate. The propose of this work is to discuss whether and how the elasticity in an impinging droplet takes effect.

  • 44.
    Wang, Yuli
    et al.
    KTH.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Viscoelastic droplet dynamics in a y-shaped capillary channel2016In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 3, article id 033103Article in journal (Refereed)
    Abstract [en]

    Non-Newtonian droplet dynamics commonly exist in microfluidic systems. We report simulations of viscoelastic (VE) droplets traveling in a two dimensional capillary bifurcation channel. A numerical system combining phase field method, VE rheology, and Stokes flow equations is built. As a generic microfluidic two-phase problem, we study how a non-Newtonian droplet that approaches a channel bifurcation will behave. We identify conditions for when a droplet will either split into two or be directed into one of the branches. In particular, we study the importance of the non-Newtonian properties. Our results reveal two different non-Newtonian mechanisms that can enhance splitting and non-splitting of droplets with respect to Newtonian droplets, depending on the size of droplet and capillary number.

  • 45.
    Wang, Yuli
    et al.
    KTH / Jiangsu University, Zhenjiang, Peoples R China.
    Gratadeix, Anthony
    ENSTA ParisTech, Marechaux, France.
    Do-Quang, Minh
    KTH.
    Amberg, Gustav
    KTH.
    Events and conditions in droplet impact: A phase field prediction2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 87, p. 54-65Article in journal (Refereed)
    Abstract [en]

    The phenomenon of droplet impact on a smooth, flat, partially wetted surface is studied by phase field simulation. A map of the different impact regimes is constructed for Reynolds numbers ranging from Re = 9 to Re = 9 x 10(4), and Ohnesorge numbers ranging from Oh = 3.3 x 10(-4) to Oh = 1.05. The results are compared with previous experiments from several aspects such as gas bubble entrapment, spreading radius and liquid sheet splashing, etc. The simulation proposes event predictions that are consistent with previous experiments. Our results and discussions give an overview of important characteristics during droplet impact, and provide insights on the droplet spreading after impact.

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