Effect of unsteadiness on droplet evaporation

Azimi, Asghar; Arabkhalaj, Arash; Ghassemi, Hassan; Markadeh, Rasoul Shahsavan

doi:10.1016/j.ijthermalsci.2017.06.023

Cited by 18 publications

(6 citation statements)

References 27 publications

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“…They showed that the difference between the QS and fully transient models increased with pressure and ambient temperature. Azimi et al [ 32 ] modelled fully transient evaporation of various hydrocarbons at atmospheric pressure and determined that the QS model overpredicts the evaporation time and the overprediction increases for increased ambient temperature, for heavier fuels and for increased droplet sizes. However, the number of cases was limited to three fuels at two temperatures.…”

Section: Introductionmentioning

confidence: 99%

Deviations from classical droplet evaporation theory

2021

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In this article, we show that significant deviations from the classical quasi-steady models of droplet evaporation can arise solely due to transient effects in the gas phase. The problem of fully transient evaporation of a single droplet in an infinite atmosphere is solved in a generalized, dimensionless framework with explicitly stated assumptions. The differences between the classical quasi-steady and fully transient models are quantified for a wide range of the 10-dimensional input domain and a robust predictive tool to rapidly quantify this difference is reported. In extreme cases, the classical quasi-steady model can overpredict the droplet lifetime by 80%. This overprediction increases when the energy required to bring the droplet into equilibrium with its environment becomes small compared with the energy required to cool the space around the droplet and therefore establish the quasi-steady temperature field. In the general case, it is shown that two transient regimes emerge when a droplet is suddenly immersed into an atmosphere. Initially, the droplet vaporizes faster than classical models predict since the surrounding gas takes time to cool and to saturate with vapour. Towards the end of its life, the droplet vaporizes slower than expected since the region of cold vapour established in the early stages of evaporation remains and insulates the droplet.

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Section: Introductionmentioning

confidence: 99%

Deviations from classical droplet evaporation theory

2021

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“…Experimental data from Ghassemi et al [52] and Nomura et al [59] have only been approached so far either with simplified semi-analytical methods, or specific correlations based on mass-heat transfer dimensionless numbers for the evaporation sub-model [62,63].…”

Section: Description Of the Experimental Casesmentioning

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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“…Recent improvements in calculation capabilities have motivated the formulation of new models that make use of more sophisticated physics to consider the unsteady evaporation of mono-and multicomponent droplets with variable fluid properties (Yang & Wong 2001;Sazhin 2006;Azimi et al 2017;Lupo & Duwig 2018;Fang et al 2019;Pinheiro et al 2019;Ray, Raghavan & Gogos 2019). In spite of such improvements, often numerical predictions do not match with experiments and it is common to utilize correlations or semi-empirical parameters to improve the agreement with measurements (Maqua, Castanet & Lemoine 2008), a practice that hinders the understanding of the underlying physics controlling the vaporization of liquid fuels.…”

Section: Introductionmentioning

confidence: 99%