Improved Technique for Measuring Total Hemispherical Emissivities of Metals at Low Temperatures.

概要

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A transient calorimetric technique for measuring total hemispherical emissivities εTH of metals at low temperatures has been improved to be more accurate and to make time-interval of measurement shorter.The accuracy of this technique mainly depends upon the heat loss through thermocouple leads Qt. To reduce Qt, an iron-constantan thermocouple of diameter about 20μm which suspends a specimen and measures its temperature, is used, and temperature distributions of the thermocouple leads are controlled by a guard heater attached to the other sides of the thermocouple leads.Qt evaluated by heat conduction analysis taking account of radiative heat transfer from the leads is less than 8% of the total power loss of copper thin wire, and 2% for copper thin plate.The total hemispherical emissivity εTH of an annealed copper thin wire which was mechanically polished was in good agreement with the extrapolated lines from the data reported by us [22-24] at high temperatures. The annealing process reduces the εTH of copper. This result may be explained from conditions of surface layer: damaged surface by mechanical polishing, recrystallization and growth of crystal grain due to annealing. Reduction of the εTH of annealed copper may improve the performance of vacuum insulation.
日本熱物性学会の論文