Size- and Structure-lnsensitivity of the Thermophoretic Transport of Aggregated “Soot” Particles in Gases

Abstract There is now convincing theoretical and experimental evidence, assembled and discussed here, for the remarkable insensitivity of the orientation-averaged thermophoretic properties of aggregated particles to aggregate size and structure (morphology), as well as the nature of gas/surface scattering. Indeed, theoretical consideration of straight chains, and uniformly “packed” quasi-spherical agglomerates, as well as recent experimental data on soot aggregate transport in/from laminar flames at atmospheric pressure, indicates that the orientation-averaged thermophoretic diffusivity, (αTD)n, of an aggregate containing N primary particles is usually within about 8% of the (αTD)i,-value for a single “primary” sphere in the free-molecule regime and within about 21 % in the continuum limit. Among other things, this implies that, especially in the free-molecule regime, thermophoretically-dominated transport rates can be adequately predicted without a detailed knowledge of the size and morphology (-distribu...

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