Effect of thermophoresis and its mathematical models on the transport and deposition of aerosol particles in natural convective flow on vertical and horizontal plates
Effect of thermophoresis and its mathematical models on the transport and deposition of aerosol particles in natural convective flow on vertical and horizontal plates
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DOI：
10.1016/j.jaerosci.2014.06.005
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发表时间：
2014-11-01
影响因子：
4.5
通讯作者：
Samanta, Subho
中科院分区：
文献类型：
--
作者：
Guha, Abhijit;Samanta, Subho
分析了由于层流自然对流、布朗扩散和热泳的共同作用，气溶胶粒子在等温水平或垂直平板上的输运和沉积。考虑了四种流动形式：加热水平板上方的流动、冷水平板下的流动、加热垂直板的流动和冷垂直板的流动。考虑了空气中纳米到微米尺寸的颗粒(颗粒直径在1纳米到5微米之间)。结果表明，沉积速度随颗粒直径d(P)的增大而减小(即颗粒施密特数Sc的增大)，随帽上无因次温差Delta(T)的减小而增大(从正值到负值)。对于朝下的冷水平板或冷却垂直板，颗粒的热漂移有助于布朗扩散，从而提高沉积速度。对于向上加热的水平板或加热垂直板，离开表面的热漂移会降低总沉积速度，当颗粒尺寸超过一定值时，沉积速度会急剧下降。结果表明，在某些情况下，热漂移可以使沉积速率提高几个数量级。评估了使用不同的热潜力系数(Kappa)表达式的深远作用。结果表明，用Talbot等人提出的kappa公式计算的沉积速度。(1980)总是高于采用Beresnev和Chernyak(1995)提出的表达式所预测的值。当颗粒直径d(P)较大，而流体与颗粒的热导率比λ(R)较小时，两种热电模型计算的沉积速度相差较大。例如，在类似于1微米的d(P)处，Talbot等人。Talbot等人的模型可能会将沉积速度高估3倍，在d(P)类似于5微米时，Talbot等人。当d(P)和lt；为100 nm时，两种模型之间的差异可以忽略不计。(C)2014爱思唯尔有限公司。保留所有权利。
An analysis is performed to study aerosol particle transport and deposition onto an isothermal horizontal or vertical plate due to the combined effects of laminar natural convection, Brownian diffusion and thermophoresis. Four configurations are considered: flow above a heated horizontal plate, flow beneath a cold horizontal plate, flow due to a heated vertical plate and that due to a cold vertical plate. Nano- to micro-sized particles (particle diameter in the range 1 nm to 5 mu m) in air are considered. It is found that the deposition velocity decreases with an increase in particle diameter d(p) (i.e. an increase in particle Schmidt number Sc), and increases with a decrease in the value of non-dimensional temperature difference Delta(T) over cap (from positive to negative values). For a downward-facing cold horizontal plate or cooled vertical plate, the thermal drift of particles assists Brownian diffusion which enhances deposition velocity. For an upward facing heated horizontal plate or heated vertical plate, the thermal drift away from the surface decreases the overall deposition velocity which decreases drastically above a certain particle size. It is shown that the thermal drift may enhance the deposition rate by several orders of magnitude under certain circumstances. The profound role of using different expressions for the thermophoretic force coefficient (kappa) is assessed. It is found that the deposition velocity calculated using the expression for kappa suggested by Talbot et al. (1980) is always higher than the values predicted by employing the expression proposed by Beresnev and Chernyak (1995). The difference in the calculated deposition velocity for the two thermophoretic models is significant when the particle diameter d(p) is large and the fluid to particle thermal conductivity ratio lambda(r) is small. For example, at d(p) similar to 1 mu m, the Talbot et al. model may overpredict the deposition velocity by a factor 3, and at d(p) similar to 5 mu m, the Talbot et al. model may overpredict the deposition velocity by a factor 10. There is negligible difference between the two models when d(p) < 100 nm. (C) 2014 Elsevier Ltd. All rights reserved.