Thermal conductivity of porous aggregates

Abstract

Context. The thermal conductivity of highly porous dust aggregates is a key parameter for many subjects in planetary science; it is not yet fully understood, however. Aims. We investigate the thermal conductivity of fluffy dust aggregates with filling factors lower than 10 −1 . Methods. We determined the temperature structure and heat flux of the porous dust aggregates calculated through N-body simulations of static compression in the periodic boundary condition. Results. We derive an empirical formula for the thermal conductivity through the solid network k sol as a function of the filling factor of dust aggregates φ. The results reveal that k sol is approximately proportional to φ 2 , and the thermal conductivity through the solid network is significantly lower than previously assumed. In light of these findings, we must reconsider the thermal histories of small planetary bodies.

Thermal conductivity and coordination number of compressed dust aggregates

“…We perform three-dimensional numerical calculations of dust aggregates using the model described by Arakawa et al (2017). Here we briefly summarize our numerical methods.…”

“…For highly porous aggregates, however, Z(φ) is approximately two and behaves as a constant, hence f (φ) would only depend on φ for highly porous aggregates. Arakawa et al (2017) revealed that f (φ) is approximately proportional to the square of φ for highly porous aggregates with filling factors below 10 −1 . In this study, we calculate the dimensionless function of the thermal conductivity f (φ) for both loose (i.e., Z 2) and close (i.e., Z > 2) dust aggregates.…”

“…For highly porous dust aggregates with filling factors in the range from 10 −2 to 10 −1 , Arakawa et al (2017) obtained a relationship between f (φ) and φ as f (φ) φ 2 . Our novel formula of The thermal conductivity of dust aggregates in a vacuum is the sum of k sol and k rad , and the contributions of k sol and k rad are distinguishable by measuring the temperature dependence of the total thermal conductivity (e.g., Sakatani et al, 2016Sakatani et al, , 2017.…”

Scattering, absorption, and thermal emission by large cometary dust particles: Synoptic numerical solution

“…In our computations, the heat conduction coefficient is assumed to be κ = 0.00025 W/m/K, which corresponds to a realistic value for a porous dust aggregate (Krause et al 2011;Arakawa et al 2017;Sakatani et al 2017 coefficient depends on porosity, grain size, and composition. Increasing the heat conduction coefficient flattens the superheating phase functions.…”

Photophoresis in the circumjovian disk and its impact on the orbital configuration of the Galilean satellites

“…(D.4) Therefore, F Ph /F D is independent of a for the case of a < l m , while F Ph /F D is inversely proportional to the square of the particle radius for the case of a > l m This means that the radial drift of cm-sized compact pebbles could not be prevented by photophoresis itself, although the radial drift would be stopped because the pressure maximum formed at the light barrier. We note, however, that the thermal conductivity of dust aggregates is exceedingly lower than that of compact dust particles (e.g., Arakawa et al 2017Arakawa et al , 2019, and the radial drift of aggregated pebbles might be stopped by photophoresis, even if their radius is larger than the mean free path of the gas molecules. Temperature T [K] p = 10 0 dyn cm -2 p = 10 2 dyn cm -2 p = 10 4 dyn cm -2 p = 10 6 dyn cm -2 fitting 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 2 10 3 where c p = 10 7 erg g −1 K −1 is the specific heat (e.g., Ciesla et al 2004).…”