Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........8p&link_type=abstract
Thesis (PH.D.)--ARIZONA STATE UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-04, Section: B, page: 18
Other
3
Scientific paper
A line-heat source apparatus was assembled for the purpose of measuring thermal conductivities of particulate samples under low pressures of a carbon dioxide atmosphere. The primary result of this project is the compilation of the first comprehensive suite of measurements on the dependence of thermal conductivity on particle size. The thermal conductivity increases with increasing particle size and pressure. In particular, the thermal conductivity, kappa was found to be empirically related to particle diameter, Dp, and pressure, P, by the equation kappa = C P^{2/3} D_sp {p}{(0.52-KP)}, where C and K are constants. Preliminary studies of other effects on thermal conductivity were also performed. Measurements on two synthetic and two natural mixtures indicate that the thermal conductivity of a material is essentially equal to that of the largest particles in the sample. The dependence of thermal conductivity on bulk density appears to be linear. There is a 25% reduction in thermal conductivity when the bulk density is reduced by 50% at a pressure of 6 torr. The effect of bulk density increases with increasing atmospheric pressure. At the average pressure of the Martian surface (6 torr), the thermal conductivity varies from 0.011 W/m K, for particles less than 11 μm in diameter, to 0.11 W/m K, for particles 900 μm in diameter. These results differ significantly from the particle size dependence estimated for Mars from previous measurements, except for 200 mu m particles, whose thermal conductivity is 0.053 W/m K. The thermal conductivities of larger particles are lower than the previous estimate, by 40% at 900 muM, and the thermal conductivities of smaller particles are higher than the previous estimate, by 60% at 11 mum. These newer estimates agree with other lines of evidence from martian atmospheric and surficial processes, leading to improved particle size estimates for most of the planet's surface.
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