Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime (Open Access)--颗粒学报PARTICUOLOGY

Wang, K., Wang, P., & Yu, S. (2022). Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime. Particuology, 67, 8-17. https://doi.org/10.1016/j.partic.2021.09.009

Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime (Open Access)

Kaiyuan Wang^{a c}, Pei Wang^a *, Suyuan Yu^b

a Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
b Center for Combustion Energy, Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
c Smoore International Holdings Ltd., Shenzhen 518102, China

10.1016/j.partic.2021.09.009

Volume 67, August 2022, Pages 8-17

Received 13 June 2021, Revised 15 September 2021, Accepted 16 September 2021, Available online 5 October 2021, Version of Record 29 November 2021.

E-mail: wangpei@iapcm.ac.cn

Highlights

• Thermophoretically modified coagulation is presented for the entire size regime.

• Modified kernels are expressed as Brownian kernel times an enhancement factor.

• Enhancement effects are important in the continuum and transition regimes.

• Thermophoretic enhancement effects are ignorable in the free-molecular regime.

• Enhancement factor increases with decreased pressure, increased temperature and increased temperature gradient.

Abstract

In many energy and combustion applications, particles experience large temperature gradients, which can affect the coagulation process due to thermophoresis. This study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size regime. The theoretical derivations are based on the kinetic theory for the free-molecular regime and the harmonic mean method for the transition regime. The coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor. The enhancement factor represents the coagulation rate enhancement induced by thermophoresis and is a function of specific dimensionless numbers. Based on the enhancement factor, the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle conditions. The results show that thermophoretic enhancement effects are ignorable in the free-molecular regime, but need to be considered in the continuum regime and the transition regime. In addition, the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas pressure. The present study can improve understanding of thermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

Graphical abstract

Keywords

Thermophoresis; Brownian coagulation; Enhancement factor; Knudsen number

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