Research Papers: Combustion and Reactive Flows

Effect of Selective Accommodation on Soot Aggregate Shielding in Time-Resolved Laser-Induced Incandescence Experiments

[+] Author and Article Information
K. J. Daun

Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canadakjdaun@mme.uwaterloo.ca

J. Heat Transfer 132(9), 091202 (Jun 28, 2010) (8 pages) doi:10.1115/1.4001614 History: Received July 02, 2009; Revised March 15, 2010; Published June 28, 2010; Online June 28, 2010

Time-resolved laser-induced incandescence is an emerging diagnostic for characterizing primary particle size distributions within soot-laden aerosols. This measurement requires an accurate model of heat conduction between the laser-energized soot and the surrounding gas, which is complicated by the fractal-like structure of soot aggregates since primary particles on the aggregate exterior shield the interior from approaching gas molecules. Previous efforts to characterize aggregate shielding through direct simulation Monte Carlo analysis assume a Maxwell scattering kernel, which poorly represents actual gas/surface interactions. This paper shows how selective thermal accommodation into the translational and rotational modes of the gas molecule influences the aggregate shielding effect using the Cercignani–Lampis–Lord kernel and thermal accommodation coefficients derived from molecular dynamics simulations.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 2

Computational domain of the Markov chain Monte Carlo simulation

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Figure 3

Directional scattering probability in the incidence plane of a molecular beam (19)

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Figure 4

Geometric representation of the CLL (21-23) kernel. Points P, Q, and R, respectively, denote the incident, expected, and actual energy contained in the normal-translational, tangential-translational, and rotational modes of the gas molecule.

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Figure 5

Aggregate shielding factor η versus Np for perfect thermal accommodation

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Figure 6

Aggregate shielding factor η versus Np for neon

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Figure 7

Aggregate shielding factor η versus Np for nitrogen

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Figure 1

Comparison of a TEM image of a soot aggregate with a randomly simulated aggregate generated using the same fractal parameters

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Figure 8

Primary particle shielding parameters for an aggregate with Np=50: (a) Maxwell kernel for neon, (b) CLL kernel for neon, (c) Maxwell kernel for nitrogen, and (d) CLL kernel for nitrogen

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Figure 9

Molecules following the adiabatic-specular scattering channel of the Maxwell kernel are more likely to accommodate with subsequent primary particles compared to those that scatter preferentially in the surface normal direction, as predicted by the CLL kernel




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