Effects of Shape and Surface Physical and Chemical Heterogeneities on Condensation/Evaporation of Aerosol Particles

形状和表面物理化学异质性对气溶胶颗粒凝聚/蒸发的影响

• 批准号: 9904139
• 负责人: Sudarshan Loyalka
• 金额: $ 21万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9904139&HistoricalAwards=false
• 关键词: Effects; Shape; Surface; Physical; Chemical

ABSTRACTCTS-9904139S. LoyalkaU. of Missouri @ ColumbiaA comprehensive three-year theoretical study is proposed to investigate the role of variable surface conditions in the condensation/evaporation and reaction of vapors and gases on arbitrarily shaped, heterogeneous aerosol particles that may or may not be wetted. We will consider one or more particles of arbitrary shape and size situated in an infinite expanse of a gas-vapor mixture in which diffusing vapor molecules are present in small amounts. The particle surface conditions will be allowed to be compositionally and/or chemically heterogeneous to correspond to various natural and anthropogenic particles. Also to be considered and particles that are wetted, e.g. Hygroscopic particles that ultimately acquire shapes dictated by surface tension effects. For the continuum and jump regimes, we will use a Green's function technique to convert the Laplace equation together with its boundary conditions into a boundary integral equation. This allows the reduction of the 3-D Laplace equation to a 2-D integral equation and thus easier handling of the surface morphology and adsorption properties. The integral equation will then be discretized, and a generalized computer program will be developed to obtain local and global condensation (or evaporation) rates. For the transition regime, in which some particle dimension is comparable to the vapor molecular mean free path, we will obtain solutions of the linear Boltzmann equation. We will explore applications of boundary fitted coordinate techniques as well as multigrid methods in conjunction with our previous work on spherical particles. The shapes of complex wetted agglomerates will be obtained by solving the Young-Laplace equation with the associated free boundary conditions that involve the wetting angles at the contact points. We will use differential geometry to characterize arbitrary surfaces, and a combination of finite differencing and Newton's method to solve for the shapes of liquid surfaces. This research will result in the development of general and versatile mathematical and numerical frameworks for the determination of local and global condensation rates. Specifically, new understanding of the dependence of rate expressions for the growth of wetted particles, chain-like agglomerates, and bio-aerosols on surface heterogeneities will become available. These rate expressions will find use in computer codes for the modeling of various natural and engineered processes (e.g., programs for assessing or predicting air quality, global warming trends, optimal catalyst surfaces, etc.). Fine particles are a high priority issue in the area of air quality risk assessment as well as with respect to global warming issues. The present research will permit more realistic estimations of these risks and will aid in improving particle synthesis and manufacturing techniques.

abstractcts - 9904139。LoyalkaU。提出了一项为期三年的综合理论研究，以调查可变表面条件在蒸汽和气体在任意形状的非均质气溶胶颗粒上的冷凝/蒸发和反应中的作用，这些颗粒可能被润湿也可能不被润湿。我们将考虑一个或多个任意形状和大小的粒子，它们位于无限广阔的气体-蒸汽混合物中，其中扩散的蒸汽分子少量存在。允许颗粒表面条件在组成和/或化学上不均匀，以对应各种自然和人为颗粒。同样要考虑的还有湿润的颗粒，例如最终获得由表面张力效应决定形状的吸湿颗粒。对于连续体和跳跃状态，我们将使用格林函数技术将拉普拉斯方程及其边界条件转换为边界积分方程。这允许将3-D拉普拉斯方程简化为2-D积分方程，从而更容易处理表面形貌和吸附特性。然后将积分方程离散化，并开发一个通用的计算机程序来获得局部和全局冷凝（或蒸发）速率。对于某些粒子维度与蒸汽分子平均自由程相当的过渡态，我们将得到线性玻尔兹曼方程的解。我们将探索边界拟合坐标技术的应用，以及结合我们之前在球形粒子上的工作的多网格方法。通过求解Young-Laplace方程和涉及接触点润湿角的相关自由边界条件，可以得到复杂润湿团块的形状。我们将使用微分几何来描述任意表面，并结合有限差分法和牛顿法来求解液体表面的形状。这项研究将导致一般和通用的数学和数值框架的发展，以确定局部和全球凝结率。具体来说，对湿润颗粒、链状团聚体和生物气溶胶生长速率表达式对表面非均质性的依赖性的新理解将成为可能。这些速率表达式将在计算机代码中用于各种自然和工程过程的建模（例如，用于评估或预测空气质量、全球变暖趋势、最佳催化剂表面等的程序）。细颗粒物在空气质量风险评估领域以及全球变暖问题中都是一个高度优先的问题。目前的研究将允许对这些风险进行更现实的估计，并将有助于改进颗粒合成和制造技术。