Predicting the evaporation rate of stationary droplets with the VOF methodology for a wide range of ambient temperature conditions

Strotos, George; Malgarinos, Ilias; Νikolopoulos, Nikos; Gavaises, Manolis

doi:10.1016/j.ijthermalsci.2016.06.022

Cited by 55 publications

(42 citation statements)

References 65 publications

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“…The species properties depend on the local temperature [64,65] and mass averaging rules are used for the gaseous mixture assuming incompressible ideal gas. For the complete presentation of the equations solved, the reader is referred to Strotos et al [54]. The simulations were performed with the commercial CFD tool ANSYS FLUENT v14.…”

Section: Numerical Model and Methodologymentioning

confidence: 99%

“…The model has been successfully validated in [33,54,63,67,68] for cases including the motion of a free falling droplet, droplet breakup, droplet evaporation and droplet impact onto a solid substrate.…”

Section: Numerical Model and Methodologymentioning

confidence: 99%

“…Similarly, in multicomponent studies the first ones were those of [48,49], followed by [50] who included variable thermophysical properties and [52,53] which conducted parametric studies. The aforementioned studies were restricted to the modelling of isolated spherical droplets and a detailed presentation of the works referring to droplet evaporation, was given in Strotos et al [54].…”

Section: Introductionmentioning

confidence: 99%

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Aerodynamic breakup of an n -decane droplet in a high temperature gas environment

Strotos

Malgarinos

Νikolopoulos

et al. 2016

Fuel

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The aerodynamic droplet breakup under the influence of heating and evaporation is studied numerically by solving the Navier-Stokes, energy and transport of species conservation equations; the VOF methodology is utilized in order to capture the liquid-air interphase. The conditions examined refer to an n-decane droplet with Weber numbers in the range 15-90 and gas phase temperatures in the range 600-1000K at atmospheric pressure. To assess the effect of heating, the same cases are also examined under isothermal conditions and assuming constant physical properties of the liquid and surrounding air. Under non-isothermal conditions, the surface tension coefficient decreases due to the droplet heat-up and promotes breakup. This is more evident for the cases of lower Weber number and higher gas phase 2 temperature. The present results are also compared against previously published ones for a more volatile n-heptane droplet and reveal that fuels with a lower volatility are more prone to breakup. A 0-D model accounting for the temporal variation of the heat/mass transfer numbers is proposed, able to predict with sufficient accuracy the thermal behavior of the deformed droplet.

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Section: Numerical Model and Methodologymentioning

confidence: 99%

Section: Numerical Model and Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Aerodynamic breakup of an n -decane droplet in a high temperature gas environment

Strotos

Malgarinos

Νikolopoulos

et al. 2016

Fuel

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“…For the latter cases, the bubble density obeys a polytropic gas equation of state ( ), where the constant parameter κ is set according to a reference state for gas pressure and density. The thermal VOF model has been extensively used in a number of studies from the authors' group in deforming droplet simulations such as in [10][11][12] and in [13][14][15], but also in cases with polytropic bubble dynamics as in [16,17]. The model equations have been presented in detail in the aforementioned works and thus they are not repeated here.…”

Section: Mathematical Modelsmentioning

confidence: 99%

Numerical investigation of the role of heat transfer in bubble dynamics

Fostiropoulos¹,

Malgarinos²,

Strotos³

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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Bubble dynamics is generally described by the well-known Rayleigh-Plesset (R-P) equation in which the bubble pressure (or equivalently the bubble density) is predefined by assuming a polytropic gas equation of state with common assumptions to include either isothermal or adiabatic bubble behaviour. The present study examines the applicability of this assumption by assuming that the bubble density obeys the ideal gas equation of state, while the heat exchange with the surrounding liquid is estimated as part of the numerical solution. The numerical model employed includes the solution of the Navier-Stokes equations along with the energy equation, while the liquidgas interface is tracked using the Volume of Fluid (VOF) methodology; phase-change mechanism is assumed to be insignificant compared to bubble heat transfer mechanism. To assess the effect of heat transfer and gas equation of state on bubble behaviour, simulations are also performed for the same initial conditions by using a polytropic equation of state for the bubble phase without solving the energy equation. The accuracy of computations is enhanced by using a dynamic local grid refinement technique which reduces the computational cost and allows for the accurate representation of the interface for the whole duration of the phenomenon in which the bubble size changes significantly. A parametric study performed for various initial bubble sizes and ambient conditions reveals the cases for which the bubble behaviour resembles that of an isothermal or the adiabatic one. Additional to the CFD simulations, a 0-D model is proposed to predict the bubble dynamics. This combines the solution of a modified R-P equation assuming ideal gas bubble content along with an equation for the bubble temperature based on the 1 st law of thermodynamics; a correction factor is used to represent accurately the heat transfer between the two phases. KeywordsBubble dynamics, heat transfer, CFD-VOF model, 0-D model. IntroductionThe need for the inclusion of thermal effects in bubble dynamics was first addressed in [1] among others; it was shown that the polytropic gas assumption may provide inaccurate predictions of the bubble behaviour when thermal processes are taken into consideration. Since then, the effect of heat and mass transfer on bubble dynamics were examined in a large number of studies, either by CFD numerical models that are capable of solving the complex equations that characterize the physical processes of the bubble motion, or by reduced order models which include various assumptions but are computationally more efficient. In the framework of the CFD studies, the effect of heat transfer by solving the equation of gas-vapour bubble including variation of liquid temperature and assuming liquid incompressibility was examined in [2]. The main assumption in this study, was that the temperature distribution inside the bubble to be uniform, which allowed the authors to integrate analytically the continuity and momentum equations inside the bubble. In [3], the motion ...

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“…The rapid size reduction of the droplet makes surface tension to be more and more dominant, further amplifying the problem. Even if some works concerning droplets vaporization with VOF methodology are available in literature [34,35,36], the problem of parasitic currents is often not even mentioned. These works are based on commercial CFD codes (mainly Ansys FLUENT R and COMSOL R ), making very difficult to reproduce the results with open-source codes since the adopted numerical algorithms are not provided in detail.…”

Section: Introductionmentioning

confidence: 99%

DropletSMOKE++: A comprehensive multiphase CFD framework for the evaporation of multidimensional fuel droplets

Saufi¹,

Frassoldati²,

Faravelli³

et al. 2019

International Journal of Heat and Mass Transfer

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This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi-empirical evaporation sub-models.The strong surface tension forces often prevent to model small droplets evaporation, because of the presence of parasitic currents. In this work we by-pass the problem, eliminating surface tension and introducing a centripetal force toward the center of the droplet. This expedient represents a major novelty of this work, which allows to numerically hang a droplet on a fiber in normal gravity conditions without modeling surface tension. Parasitic currents are completely suppressed, allowing to accurately model the evaporation process whatever the droplet size. DropletSMOKE++ shows an excellent agreement with the experimental data in a wide range of operating conditions, for various fuels and initial droplet diameters, both in natural and forced convection. The comparison with the same cases modeled in microgravity conditions highlights the impact of an external fluid flow on the evaporation mechanism, especially at high pressures.Non-ideal thermodynamics for phase-equilibrium is included to correctly capture evaporation rates at high pressures, otherwise not well predicted by an ideal gas assumption. Finally, the presence of flow circulation in the liquid phase is discussed, as well as its influence on the internal temperature field. DropletSMOKE++ will be released as an open-source code, open to contributions from the sci-

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Predicting the evaporation rate of stationary droplets with the VOF methodology for a wide range of ambient temperature conditions

Cited by 55 publications

References 65 publications

Aerodynamic breakup of an n -decane droplet in a high temperature gas environment

Aerodynamic breakup of an n -decane droplet in a high temperature gas environment

Numerical investigation of the role of heat transfer in bubble dynamics

DropletSMOKE++: A comprehensive multiphase CFD framework for the evaporation of multidimensional fuel droplets

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