Full-field modeling of heat transfer in asteroid regolith: Radiative thermal conductivity of polydisperse particulates. (arXiv:2002.00144v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ryan_A/0/1/0/all/0/1">Andrew J. Ryan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Munoz_D/0/1/0/all/0/1">Daniel Pino Muñoz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bernacki_M/0/1/0/all/0/1">Marc Bernacki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Delbo_M/0/1/0/all/0/1">Marco Delbo</a>
Characterizing the surface material of an asteroid is important for
understanding its geology and for informing mission decisions, such as the
selection of a sample site. Diurnal surface temperature amplitudes are directly
related to the thermal properties of the materials on the surface. We describe
a numerical model for studying the thermal conductivity of particulate regolith
in vacuum. Heat diffusion and surface-to-surface radiation calculations are
performed using the finite element (FE) method in three-dimensional meshed
geometries of randomly packed spherical particles. We validate the model for
test cases where the total solid and radiative conductivity values of
particulates with monodisperse particle size frequency distributions (SFDs) are
determined at steady-state thermal conditions. Then, we use the model to study
the bulk radiative thermal conductivity of particulates with polydisperse,
cumulative power-law particle SFDs. We show that for each polydisperse
particulate geometry tested, there is a corresponding monodisperse geometry
with some effective particle diameter that has an identical radiative thermal
conductivity. These effective diameters are found to correspond very well to
the Sauter mean particle diameter, which is essentially the
surface-area-weighted mean. Next, we show that the thermal conductivity of the
particle material can have an important effect on the radiative component of
the thermal conductivity of particulates, especially if the particle material
conductivity is very low or the spheres are relatively large, owing to
non-isothermality in each particle. We provide an empirical correlation to
predict the effects of non-isothermality on radiative thermal conductivity in
both monodisperse and polydisperse particulates.
Characterizing the surface material of an asteroid is important for
understanding its geology and for informing mission decisions, such as the
selection of a sample site. Diurnal surface temperature amplitudes are directly
related to the thermal properties of the materials on the surface. We describe
a numerical model for studying the thermal conductivity of particulate regolith
in vacuum. Heat diffusion and surface-to-surface radiation calculations are
performed using the finite element (FE) method in three-dimensional meshed
geometries of randomly packed spherical particles. We validate the model for
test cases where the total solid and radiative conductivity values of
particulates with monodisperse particle size frequency distributions (SFDs) are
determined at steady-state thermal conditions. Then, we use the model to study
the bulk radiative thermal conductivity of particulates with polydisperse,
cumulative power-law particle SFDs. We show that for each polydisperse
particulate geometry tested, there is a corresponding monodisperse geometry
with some effective particle diameter that has an identical radiative thermal
conductivity. These effective diameters are found to correspond very well to
the Sauter mean particle diameter, which is essentially the
surface-area-weighted mean. Next, we show that the thermal conductivity of the
particle material can have an important effect on the radiative component of
the thermal conductivity of particulates, especially if the particle material
conductivity is very low or the spheres are relatively large, owing to
non-isothermality in each particle. We provide an empirical correlation to
predict the effects of non-isothermality on radiative thermal conductivity in
both monodisperse and polydisperse particulates.
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