Effective Emissivities of Knudsen Cells Heated by Radiation

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  • MATSUMOTO Kazutoshi
    Research Laboratory of Engineering Materials, Tokyo Institute of Technology
  • SASAMOTO Tadashi
    Research Laboratory of Engineering Materials, Tokyo Institute of Technology
  • SATA Toshiyuki
    Research Laboratory of Engineering Materials, Tokyo Institute of Technology

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  • 放射加熱されているヌッセンセルの実効放射率
  • ホウシャ カネツサレテ イル ヌッセンセル ノ ジッコウ ホウシャリツ

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Abstract

The emissivities of graphite-, thoria- and tungsten-cells being heated by a tungsten cylindrical heater were measured as a function of the orifice diameter in the temperature range of 1000° to 1900°C in order to provide data which are useful at the time when a precise temperature of a Knudsen cell having arbitrary orifice area is determined.<br>In the Knudsen cell constructed by a graphite having a nearly diffuse-reflecting surface and a high emissivity, its effective emissivities were close to unity when the reduced orifice diameter (=the orifice diameter/the cell cross-sectional one), rR, was less than 0.2. With increasing in rR, its emissivities deviated negatively from the calculated values up to rR=0.4, and then in the region of 0.4<rR<1 it increased gradually with increasing in rR due to the back ground radiation from the heater (back ground noise). The results for the thoria-cell were nearly same as that of the graphite-cell except that there was affected considerably by the back ground noise. On the other hand, in the tungsten cell having a more specular surface, its emissivities remained less than unity even if the orifice size was controlled as small as possible.<br>It was concluded that, for a usual Knudsen cell (length=diameter) heated by an outer radiational heat source, only a cell with a diffuse-reflecting surface and a small orifice (rR≤0.1) can be regarded as a black body.

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