自由分子体系中气溶胶团块的沉降和光致悬浮

IF 3.9 3区 环境科学与生态学 Q2 ENGINEERING, CHEMICAL
A.A. Cheremisin , A.V. Kushnarenko
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引用次数: 0

摘要

通过数值实验研究了分形气溶胶团在稀薄气体介质中,在黑暗和类似阳光的外部光照下的沉积情况,同时考虑了取向效应,这取决于在很大范围内变化的分形维度。力及其力矩(包括摩擦力和光致伸缩力)的计算是在自由分子气体动力学机制近似和先前开发的蒙特卡洛算法的基础上进行的。在没有光照的情况下,当粒子温度等于气体环境温度时,多粒子集群的沉降速度是分形维数的一个明显函数,与单个球形粒子的沉降速度相当接近。沉降速度近似值取决于分形维度。光照使沉降模式发生了巨大变化,星团沉降速度的变化范围大幅扩大,这是重力光导效应的一种表现,因此一些星团甚至开始悬浮。悬浮集群的比例基本上取决于分形维度。在海拔 30 千米的地方,在类似于太阳光的辐照和相当于大气压的压力下,烟尘状团聚体的悬浮比例约为 7%,这与实验数据非常吻合。在光致发光现象的背景下,获得了一个原理性结果:在太阳光照射下,由相同的主粒子组成的气溶胶烟尘状聚集体在与平流层高度相应的压力下可能发生重力光致发光悬浮。这一结果表明,重力光电效应可能对地球平流层和中间层的烟尘气溶胶迁移和定位产生重大影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Sedimentation and photophoretic levitation of aerosol clusters in the free molecular regime
Sedimentation of fractal aerosol clusters in rarefied gas medium in the dark and under external illumination similar to sunlight is studied in a numerical experiment taking into account orientation effects, depending on fractal dimension varying within a broad range. The calculation of forces and their moments, including friction forces and photophoretic forces, was carried out on the basis of approximation of free molecular gas kinetic regime and previously developed Monte-Carlo algorithms. Calculation involved 10 000 clusters, each of them containing 160 primary spherical particles and efficiently absorbing sunlight and IR radiation, similarly to the particles of soot aggregates.
The velocity of multi-particle cluster settling in the absence of illumination, when particle temperatures are equal to the temperature of the gaseous environment, is a distinct function of fractal dimension and is rather close to the velocity of settling of single spherical particles. The settling velocity approximation depending on fractal dimension has been obtained.
Illumination brings dramatic changes into sedimentation pattern. The range of cluster sedimentation rate variations broadens substantially, which is a manifestation of gravito-photophoretic effect, so that some clusters even start to levitate. The proportion of levitating clusters is essentially dependent on fractal dimension. For soot-like clusters under irradiation similar to sunlight and pressure equal to atmospheric at the altitude of 30 km, the proportion of levitating aggregates is approximately 7%, which is in good agreement with the experimental data. In the dark and under irradiation, the aggregates rotate, and their trajectories are shaped as spirals.
In the context of photophoretic phenomena, a result of principle has been obtained: under irradiation with sunlight, gravito-photophoretic levitation of aerosol soot-like aggregates composed of identical primary particles is possible at a pressure corresponding to the stratospheric altitudes. This result points to the possibility of substantial influence of gravito-photophoretic effect on transport and localization of soot aerosol in the Earth’s stratosphere and mesosphere.
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来源期刊
Journal of Aerosol Science
Journal of Aerosol Science 环境科学-工程:化工
CiteScore
8.80
自引率
8.90%
发文量
127
审稿时长
35 days
期刊介绍: Founded in 1970, the Journal of Aerosol Science considers itself the prime vehicle for the publication of original work as well as reviews related to fundamental and applied aerosol research, as well as aerosol instrumentation. Its content is directed at scientists working in engineering disciplines, as well as physics, chemistry, and environmental sciences. The editors welcome submissions of papers describing recent experimental, numerical, and theoretical research related to the following topics: 1. Fundamental Aerosol Science. 2. Applied Aerosol Science. 3. Instrumentation & Measurement Methods.
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