南京工业大学化学工程与工艺专业本科毕业论文(设计)外文资料翻译原文名称 Effects of temporally varying liquid-phase mass diffusivity in multicomponent droplet gasification 原文作者 Huiqiang Zhang, Chung K. Law 原文出版 Combustion an Flame 翻译内容页码 全文 中文名称 在多元液体气化中改变液相大规模扩散的 暂时性影响 学生姓名唐柯楠 专业 化学工程与工艺 班级学号040126指导教师（签字） 对译文的评价 技术学院2008年 6 月Effects of temporally varying liquid-phase mass diffusivityin multicomponent droplet gasificationAbstractThe relative roles of liquid-phase diffusional resistance and volatility differential in multicomponent droplet gasification are revisited, recognizing that liquid-phase mass diffusivities can be substantially increased as the droplet is progressively heated upon initiation of gasification, leading to a corresponding substantial weakening of the diffusional resistance. Calculations performed using realistic and temperature-dependent thermal and mass diffusivities indeed substantiate this influence. In particular, the calculated results agree with the literature experimental data, indicating that the gasification mechanism of multicomponent fuels is intermediate between diffusion and distillation limits. Investigation was also performed on gasification at elevated pressures, recognizing that the liquid boiling point and hence the attainable droplet temperature would increase with increasing pressure, causing further weakening of the liquid-phase diffusional resistance. This possibility was again verified through calculated results, suggesting further departure from diffusion limit toward distillation limit behavior for gasification at high pressures. The study also found that diffusional resistance is stronger for the lighter, gasoline-like fuels as compared to the heavier, diesel-like fuels because the former have overall lower boiling points, lower attainable droplet temperatures, and hence lower mass diffusivities in spite of their lower molecular weights. 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Keywords: Multicomponent droplet; Liquid mass diffusivity; Distillation1. IntroductionIt is well established that the gasification mechanism of a multicomponent droplet is controlled by three competing factors, namely the volatility differentials, the liquid-phase mass diffusivity, and the droplet surface regression rate 17. Consequently, for slow surface regression relative to mass diffusion, as in the case of vaporization in a low-temperature environment, the droplet composition tends to be perpetually uniformized and the fractional gasification rates would be closely controlled by the volatility differentials between the constituents. This leads to a gasification mode that is largely independent of liquid-phase mass diffusion, and as such resembles that of batch distillation 8. This is the formulation adopted in early studies of multicomponent droplet gasification. On the other hand, in the limit of very fast gasification relative to mass diffusion, the composition of the droplet is effectively frozen, so that the fractional gasification rates of the individual constituents are equal to their respective fractions in the original liquid composition. This leads to an onionskin mode of gasification, which is independent of the volatility differentials and as such is similar to the gasification of a solid.Since mass diffusion does occur in the liquid, even for situations of slow diffusion and rapid gasification, the gasification mechanism that has emerged for such mass-diffusion-limited gasification is one that consists of three periods 3,4. Specifically, after initiation of gasification, most of the volatile components in the surface layer are preferentially gasified, leaving this layer with a higher concentration of the less volatile, higher-boiling-point components. The droplet temperature subsequently increases, being largely dependent on the boiling points of the less volatile components. After the concentration layer is established, the supply of species from the droplet interior to the surface is controlled by the slow diffusion and droplet surface regression, resulting in a prolonged period of steady-state gasification, with the diffusion rate balancing the surface regression rate. Finally, toward the end of the droplet lifetime, mass diffusion becomes efficient again, resulting in a brief period during which the more volatile components are rapidly depleted from the droplet interior, with the concomitant increase of the droplet temperature to approach the effective boiling point of the less volatile components. Thus the characteristic of mass-diffusion limited gasification is the attainment of a fairly steady state of gasification resembling the onionskin mode, except for the presence of the thin transition concentration layer at the surface.Experiments were conducted 9 in which