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首页> 外文期刊>International Journal of Heat and Mass Transfer >Evaporation of droplets into a background gas: Kinetic modelling
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Evaporation of droplets into a background gas: Kinetic modelling

机译：液滴蒸发成背景气体：动力学模型

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摘要

A new kinetic model for droplet evaporation into a high pressure background gas, approximated by air, is described. Two regions above the surface of the evaporating droplet are considered. These are the kinetic region, where the analysis is based on the Boltzmann equation, and the hydrodynamic region. It is assumed that the mass fluxes leaving the kinetic region and the corresponding diffusion fluxes in the hydrodynamic region are matched. A modified version of the previously developed method of direct numerical solution of the Boltzmann equation is used. It is assumed that the mass flux leaving the droplet's surface is the maximal one (evaporation coefficient is equal to 1). The model and numerical algorithm allowed us to calculate the value of the net evaporation coefficient, defined as the ratio of the actual mass flux leaving the kinetic region and the maximal possible mass flux. The values of this coefficient for diesel fuel (approximated by n-dodecane) were shown to be much less than 1 for droplet surface temperatures less than 650 K. For these droplets, the kinetic effects predicted by the new model turned out to be negligible when the contribution of air in the kinetic region was ignored. These effects, however, appear to be noticeable, and larger than those predicted by the approximate analysis, if the contribution of air in the kinetic region is taken into account. It is recommended that the kinetic effects are taken into account when accurate analysis of diesel fuel droplet evaporation is essential.
机译：描述了一种新的动力学模型，用于将液滴蒸发成高压本底气体（近似于空气）。考虑了蒸发液滴表面上方的两个区域。这些是动力学区域和流体力学区域，其中分析基于玻耳兹曼方程。假设离开动力学区域的质量通量和流体动力学区域中的相应扩散通量是匹配的。使用以前开发的玻尔兹曼方程直接数值解法的修改版本。假设离开液滴表面的质量通量最大（蒸发系数等于1）。该模型和数值算法允许我们计算净蒸发系数的值，定义为离开动力学区域的实际质量通量与最大可能质量通量之比。对于液滴表面温度低于650 K的情况，该柴油的系数（近似于正十二烷）的值显示为远远小于1。对于这些液滴，新模型预测的动力学效应在以下情况下可以忽略不计空气在动力学区域中的贡献被忽略了。但是，如果考虑到空气在动力学区域中的作用，这些影响似乎很明显，并且比通过近似分析预测的影响要大。当必须精确分析柴油机油滴蒸发时，建议考虑动力学效应。

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