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Albernaz, D. L., Do-Quang, M., Hermanson, J. C. & Amberg, G. (2017). Droplet deformation and heat transfer in isotropic turbulence. Journal of Fluid Mechanics, 820, 61-85
Open this publication in new window or tab >>Droplet deformation and heat transfer in isotropic turbulence
2017 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 820, p. 61-85Article in journal (Refereed) Published
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.

Keywords
condensation/evaporation, drops, isotropic turbulence
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:sh:diva-32994 (URN)10.1017/jfm.2017.194 (DOI)000400824400006 ()2-s2.0-85018404584 (Scopus ID)
Funder
Swedish Research Council, VR2010-3938Swedish Research Council, VR2011-5355EU, FP7, Seventh Framework Programme, 312763
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2018-07-05Bibliographically approved
Shen, B., Yamada, M., Hidaka, S., Liu, J., Shiomi, J., Amberg, G., . . . Takata, Y. (2017). Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces. Scientific Reports, 7, Article ID 2036.
Open this publication in new window or tab >>Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2036Article in journal (Refereed) Published
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.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:sh:diva-32995 (URN)10.1038/s41598-017-02163-8 (DOI)000401511100043 ()28515431 (PubMedID)2-s2.0-85019418602 (Scopus ID)
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2018-07-05Bibliographically approved
Wang, Y., Do-Quang, M. & Amberg, G. (2017). Impact of viscoelastic droplets. Journal of Non-Newtonian Fluid Mechanics, 243, 38-46
Open this publication in new window or tab >>Impact of viscoelastic droplets
2017 (English)In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 243, p. 38-46Article in journal (Refereed) Published
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.

Keywords
Droplet impact, Viscoelasticity, Contact line, Diffuse interface, Dynamic wetting
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:sh:diva-32996 (URN)10.1016/j.jnnfm.2017.03.003 (DOI)000401379500004 ()2-s2.0-85016417160 (Scopus ID)
Available from: 2017-06-29 Created: 2017-06-29 Last updated: 2018-07-05Bibliographically approved
Nour, Z. M., Amberg, G. & Do-Quang, M. (2017). Kinematics and dynamics of suspended gasifying particle. Acta Mechanica, 228(3), 1135-1151
Open this publication in new window or tab >>Kinematics and dynamics of suspended gasifying particle
2017 (English)In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 228, no 3, p. 1135-1151Article in journal (Refereed) Published
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.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:sh:diva-32451 (URN)10.1007/s00707-016-1748-5 (DOI)000395107300021 ()2-s2.0-84995783715 (Scopus ID)
Available from: 2017-04-28 Created: 2017-04-28 Last updated: 2018-07-05Bibliographically approved
Wang, Y., Amberg, G. & Carlson, A. (2017). Local dissipation limits the dynamics of impacting droplets on smooth and rough substrates. Physical Review Fluids, 2(3), Article ID 033602.
Open this publication in new window or tab >>Local dissipation limits the dynamics of impacting droplets on smooth and rough substrates
2017 (English)In: Physical Review Fluids, ISSN 2469-990X, Vol. 2, no 3, article id 033602Article in journal (Refereed) Published
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).

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:sh:diva-32450 (URN)10.1103/PhysRevFluids.2.033602 (DOI)000399155400001 ()2-s2.0-85020027987 (Scopus ID)
Available from: 2017-04-28 Created: 2017-04-28 Last updated: 2018-04-05Bibliographically approved
Liu, J., Amberg, G. & Do-Quang, M. (2016). Diffuse interface method for a compressible binary fluid. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, 93(1), Article ID 013121.
Open this publication in new window or tab >>Diffuse interface method for a compressible binary fluid
2016 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 93, no 1, article id 013121Article in journal (Refereed) Published
Abstract [en]

Multicomponent, multiphase, compressible flows are very important in real life, as well as in scientific research, while their modeling is in an early stage. In this paper, we propose a diffuse interface model for compressible binary mixtures, based on the balance of mass, momentum, energy, and the second law of thermodynamics. We show both analytically and numerically that this model is able to describe the phase equilibrium for a real binary mixture (CO2 + ethanol is considered in this paper) very well by adjusting the parameter which measures the attraction force between molecules of the two components in the model. We also show that the calculated surface tension of the CO2 + ethanol mixture at different concentrations match measurements in the literature when the mixing capillary coefficient is taken to be the geometric mean of the capillary coefficient of each component. Three different cases of two droplets in a shear flow, with the same or different concentration, are simulated, showing that the higher concentration of CO2 the smaller the surface tension and the easier the drop deforms.

Place, publisher, year, edition, pages
American Physical Society, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:sh:diva-30149 (URN)10.1103/PhysRevE.93.013121 (DOI)000368517500016 ()2-s2.0-84955590690 (Scopus ID)
Available from: 2016-02-18 Created: 2016-06-01 Last updated: 2017-11-30Bibliographically approved
Kekesi, T., Amberg, G. & Wittberg, L. P. (2016). Drop deformation and breakup in flows with shear. Chemical Engineering Science, 140, 319-329
Open this publication in new window or tab >>Drop deformation and breakup in flows with shear
2016 (English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 140, p. 319-329Article in journal (Refereed) Published
Abstract [en]

A Volume of Fluid (VOF) method is applied to study the deformation and breakup of a single liquid drop in shear flows superimposed on uniform flow. The effect of shearing on the breakup mechanism is investigated as a function of the shear rate. Sequential images are compared for the parameter range studied; density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, Reynolds numbers between 20, a constant Weber number of 20, and the non-dimensional shear rate of the flow G = 0-2.1875. It is found that while shear breakup remains similar for all values of shear rate considered, other breakup modes observed for uniform flows are remarkably modified with increasing shear rate. The time required for breakup is significantly decreased in strong shear flows. A simple model predicting the breakup time as a function of the shear rate and the breakup time observed in uniform flows is suggested.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Drop deformation, Drop breakup, Shear flow, Volume of Fluid (VOF)
National Category
Physical Sciences
Identifiers
urn:nbn:se:sh:diva-30135 (URN)10.1016/j.ces.2015.10.019 (DOI)000367117300028 ()2-s2.0-84946594865 (Scopus ID)
Available from: 2016-01-21 Created: 2016-06-01 Last updated: 2017-11-30Bibliographically approved
Wang, Y., Gratadeix, A., Do-Quang, M. & Amberg, G. (2016). Events and conditions in droplet impact: A phase field prediction. International Journal of Multiphase Flow, 87, 54-65
Open this publication in new window or tab >>Events and conditions in droplet impact: A phase field prediction
2016 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 87, p. 54-65Article in journal (Refereed) Published
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.

Keywords
Droplet impact, Phase field method, Simulation, Splashing, Gas entrapment
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:sh:diva-31320 (URN)10.1016/j.ijmultiphaseflow.2016.08.009 (DOI)000386645300006 ()2-s2.0-84987942203 (Scopus ID)
Available from: 2016-12-08 Created: 2016-12-08 Last updated: 2018-07-05Bibliographically approved
Tahir, A. M., Malik, A. & Amberg, G. (2016). Modeling of the primary rearrangement stage of liquid phase sintering. Modelling and Simulation in Materials Science and Engineering, 24(7), Article ID 075009.
Open this publication in new window or tab >>Modeling of the primary rearrangement stage of liquid phase sintering
2016 (English)In: 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) Published
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.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:sh:diva-31123 (URN)10.1088/0965-0393/24/7/075009 (DOI)000385682800004 ()2-s2.0-84991758299 (Scopus ID)
Available from: 2016-11-11 Created: 2016-11-11 Last updated: 2018-07-05Bibliographically approved
Albernaz, D. L., Amberg, G. & Do-Quang, M. (2016). Simulation of a suspended droplet under evaporation with Marangoni effects. International Journal of Heat and Mass Transfer, 91, 853-860
Open this publication in new window or tab >>Simulation of a suspended droplet under evaporation with Marangoni effects
2016 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 91, p. 853-860Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Phase change, Internal circulation, Lattice Boltzmann method, Droplet heating
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:sh:diva-30094 (URN)10.1016/j.ijheatmasstransfer.2016.02.073 (DOI)000374616900082 ()2-s2.0-84960872136 (Scopus ID)
Funder
Swedish Research Council, 2010-3938]Swedish Research Council, 2011-5355]
Available from: 2016-03-14 Created: 2016-06-01 Last updated: 2017-11-30Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3336-1462

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