FullField Modeling of Heat Transfer in Asteroid Regolith: Radiative Thermal Conductivity of Polydisperse Particulates
Abstract
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 surfacetosurface radiation calculations are performed using the finite element (FE) method in threedimensional 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 steadystate 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 areaweighted 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 nonisothermality in each particle. We provide an empirical correlation to predict the effects of nonisothermality on radiative thermal conductivity in both monodisperse and polydisperse particulates.
 Publication:

Journal of Geophysical Research (Planets)
 Pub Date:
 February 2020
 DOI:
 10.1029/2019JE006100
 arXiv:
 arXiv:2002.00144
 Bibcode:
 2020JGRE..12506100R
 Keywords:

 regolith;
 airless bodies;
 numerical modeling;
 thermal conductivity;
 thermal radiation;
 packed pebble bed;
 Astrophysics  Earth and Planetary Astrophysics;
 Physics  Geophysics
 EPrint:
 Accepted by Journal of Geophysical Research: Planets