Investigation of Thermal Accommodation Coefficients in Time-Resolved Laser-Induced Incandescence

Abstract

Accurate particle sizing through time-resolved laser-induced incandescence (TR-LII) requires knowledge of the thermal accommodation coefficient, but the underlying physics of this parameter is poorly understood. If the particle size is known a priori, however, TR-LII data can instead be used to infer the thermal accommodation coefficient. Thermal accommodation coefficients measured between soot and different monatomic and polyatomic gases show that the accommodation coefficient increases with molecular mass for monatomic gases and is lower for polyatomic gases. This latter result indicates that surface energy is accommodated preferentially into translational modes over internal modes for these gases.

Thermal accommodation coefficients between polyatomic gas molecules and soot in laser-induced incandescence experiments

“…Daun et al [7] endeavored to address this shortcoming by measuring a between laser-energized soot particles of known morphology and different gas species. They observed two main trends in the data: first, that a increases with gas molecular mass; and second, that a decreases with increasing structural complexity for gas molecules having similar masses.…”

“…(1) is the maximum energy that can be transferred to the translational and internal energy modes of gas molecule, which would occur if the gas molecule equilibrated with a thermal reservoir at T s . The thermal accommodation coefficient used to carry out TiRe-LII particle sizing is usually found by performing LII experiments on aerosols containing particles with sizes characterized through thermophoretic sampling and electron microscopy [3][4][5][6][7] or light scattering [8]. Unfortunately, most of these experiments reveal very little about the gas-surface scattering physics that underlies soot particle cooling in the free-molecular regime, largely because a systematic comparison of accommodation coefficients obtained from different studies is precluded by the high degrees of variability and experimental uncertainty in the thermophysical properties and morphology of soot particles.…”

Derivation of a temperature-dependent accommodation coefficient for use in modeling laser-induced incandescence of soot

“…For lack of better information, current LII models use temperature-independent values for α T , despite expectations that this parameter should be dependent on surface temperature and gas temperature [5,6]. Some LII models use values of 0.07 [7], 0.18 [8], 0.25 [9], 0.37 [10,11], and 1.0 [12] inferred from measured LII decay rates by fitting model predictions of signal decay rates to measured values and allowing α T to be one of the adjustable parameters. LII models, however, have significant uncertainties beyond the accommodation coefficient, and the conditions for the measurements are difficult to control, making this approach indirect and unreliable.…”

Modeling of subcontinuum thermal transport across semiconductor-gas interfaces

“…These parameters are therefore expected to be the primary determinants of interfacial thermal resistance at a gas-solid boundary. There has been significant effort dedicated to quantifying the accommodation of gas molecules on a solid surface both experimentally 11,55,67 and from MD simulations. 56,57 While each transport property has its own accommodation to a surface, the Maxwell model for gas-surface interaction has been widely used to describe transport phenomena that do not include high speed nonisothermal conditions.…”