date: 2012 April 25 (Wed) 15:00-16:00
room: Hokkaido University, Science Bldg. #8, Cosmo-studio
speaker: Naoya Sakatani (ISAS/JAXA)
organizer: Jun Kimura
title: Thermal conductivity measurement of powder materials under vacuum environment
abstract: Solid planetary surface, such as Moon and asteroids, is covered with regolith, and its thermal conductivity is key information for thermal state of these bodies, thermal evolution, and furthermore, thermal designs of future landing probe vehicles. Thermal conductivity of powder material as regolith has extremely low (order of 0.001 W/mK) and depends on several parameters such as particle size, porosity, temperature, etc.
Crustal heat flow of the bodies is fundamental information for understanding the present thermal state. In Apollo heat flow experiments, although the thermal conductivity of lunar surface regolith was measured, it is indicated that the measured thermal conductivity is different from original one due to change of regolith conditions during inserting of heat flow probes. For correction of the measured thermal conductivity and for in-situ heat flow measurements in future, it is required to investigate the parameter dependencies of the thermal conductivity. In addition, the regolith layer behaves as strong heat-insulating layer as a result of its low thermal conductivity. Therefore, its presence on small bodies, such as planetesimals, will affect their thermal evolutions. However, due to uncertainty of regolith condition under micro-gravity environment, modeling the thermal conductivity of the regolith and restricting its range are necessary. On the basis of these science backgrounds, we are conducting thermal conductivity measurement for powder materials under vacuum condition with the parameters being controlled and aim at understanding the heat transfer mechanism and modeling the thermal conductivity.
Until now, we have investigated the effects of particle size, temperature, and compressional stress on the thermal conductivity using glass beads as a model material. In this presentation, these experimental results will be presented and suggested heat transfer mechanisms will be discussed.
keywords: Thermal Conductivity, Powder Materials, Regolith, Heat Flow Measurements, Thermal Evolution