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Multirelaxation-time lattice Boltzmann model for droplet heating and evaporation under forced convection
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.ORCID-id: 0000-0003-2830-0454
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.ORCID-id: 0000-0003-3336-1462
2015 (Engelska)Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, nr 4, artikel-id 043012Artikel i tidskrift (Refereegranskat) Published
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.

Ort, förlag, år, upplaga, sidor
2015. Vol. 91, nr 4, artikel-id 043012
Nationell ämneskategori
Strömningsmekanik och akustik
Identifikatorer
URN: urn:nbn:se:kth:diva-171704DOI: 10.1103/PhysRevE.91.043012ISI: 000353209300004Scopus ID: 2-s2.0-84929118718OAI: oai:DiVA.org:kth-171704DiVA, id: diva2:844709
Forskningsfinansiär
Vetenskapsrådet, VR2010-3938Vetenskapsrådet, VR2011-5355Swedish National Infrastructure for Computing (SNIC)EU, FP7, Sjunde ramprogrammet, RI-312763
Anmärkning

QC 20150807

Tillgänglig från: 2015-08-07 Skapad: 2015-08-05 Senast uppdaterad: 2017-12-04Bibliografiskt granskad
Ingår i avhandling
1. Phase change, surface tension and turbulence in real fluids
Öppna denna publikation i ny flik eller fönster >>Phase change, surface tension and turbulence in real fluids
2016 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Sprays are extensively used in industry, especially for fuels in internal combustion and gas turbine engines. An optimal fuel/air mixture prior to combustion is desired for these applications, leading to greater efficiency and minimal levels of emissions. The optimization depends on details regarding the different breakups, evaporation and mixing processes. Besides, one should take into consideration that these different steps depend on physical properties of the gas and fuel, such as density, viscosity, heat conductivity and surface tension.

In this thesis the phase change and surface tension of a droplet for different flow conditions are studied by means of numerical simulations.This work is part of a larger effort aiming to developing models for sprays in turbulent flows. We are especially interested in the atomization regime, where the liquid breakup causes the formation of droplet sizes much smaller than the jet diameter. The behavior of these small droplets is important to shed more light on how to achieve the homogeneity of the gas-fuel mixture as well as that it directly contributes to the development of large-eddy simulation (LES) models.

The numerical approach is a challenging process as one must take into account the transport of heat, mass and momentum for a multiphase flow. We choose a lattice Boltzmann method (LBM) due to its convenient mesoscopic natureto simulate interfacial flows. A non-ideal equation of state is used to control the phase change according to local thermodynamic properties. We analyze the droplet and surrounding vapor for a hydrocarbon fuel close to the critical point. Under forced convection, the droplet evaporation rate is seen to depend on the vapor temperatureand Reynolds number, where oscillatory flows can be observed. Marangoni forces are also present and drivethe droplet internal circulation once the temperature difference at the droplet surface becomes significant.In isotropic turbulence, the vapor phase shows increasing fluctuations of the thermodynamic variables oncethe fluid approaches the critical point. The droplet dynamics is also investigated under turbulent conditions, where the presence of coherent structures with strong shear layers affects the mass transfer between the liquid-vapor flow, showing also a correlation with the droplet deformation. Here, the surface tension and droplet size play a major role and are analyzed in detail.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2016. s. xiv, 53
Serie
TRITA-MEK, ISSN 0348-467X ; 2016:02
Nationell ämneskategori
Strömningsmekanik och akustik
Forskningsämne
Teknisk mekanik
Identifikatorer
urn:nbn:se:kth:diva-183487 (URN)978-91-7595-895-8 (ISBN)
Disputation
2016-04-07, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (Engelska)
Opponent
Handledare
Forskningsfinansiär
Vetenskapsrådet, 2010-3938Vetenskapsrådet, 2011-5355
Anmärkning

QC 20160314

Tillgänglig från: 2016-03-14 Skapad: 2016-03-14 Senast uppdaterad: 2016-03-14Bibliografiskt granskad

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Albernaz, DanielDo, Quang MinhAmberg, Gustav
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Fysiokemisk strömningsmekanikLinné Flow Center, FLOW
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Physical Review E. Statistical, Nonlinear, and Soft Matter Physics
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