Evaporation of droplets into a background gas: Kinetic modelling
Evaporation of droplets into a background gas: Kinetic modelling
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DOI：
10.1016/j.ijheatmasstransfer.2006.11.043
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发表时间：
2007-07
影响因子：
5.2
通讯作者：
S. Sazhin;I. N. Shishkova;A. Kryukov;V. Levashov;M. Heikal
中科院分区：
文献类型：
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作者：
S. Sazhin;I. N. Shishkova;A. Kryukov;V. Levashov;M. Heikal
描述了一种新的液滴蒸发成高压背景气体的动力学模型。考虑了蒸发液滴表面以上的两个区域。它们是基于玻尔兹曼方程进行分析的动力学区域和流体动力学区域。假定离开动态区的质量通量与流体动态区中相应的扩散通量相匹配。采用了先前发展的直接数值求解Boltzmann方程方法的改进版本。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，其定义为离开动态区的实际质量通量与最大可能质量通量的比率。当液滴表面温度低于650K时，柴油的这一系数(用正十二烷近似)远小于1。对于这些液滴，当忽略动态区空气的贡献时，新模型预测的动力学效应可以忽略不计。然而，如果考虑到动态区空气的贡献，这些影响似乎是明显的，而且比近似分析所预测的要大。建议在对柴油液滴蒸发进行准确分析时考虑动力学影响。
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 650K. 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.