Measurement of Infrared Effective Emissivity by Means of Natural Cooling

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  • 自然冷却を利用した熱赤外実効放射率の測定法

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The total effective emissivity in the thermal infrared radiation region has been measured by different methods; 1) using radiometers, 2) calculating from the data obtained by spectral reflection measurements, 3) measuring the intensities of polarized lights, and 4) measuring the heat losses. The methods 1) and 2) are most popular ones, but they need a reference surface, of which the emissivity must be precisely known, and over which the temperature uniformity must be maintained since it affects the precision of measurement. The method 3) cannot be applied to any surface (successful only for an ideally radiating surface). The method 4) is a fundamental one. But until now it has been unpopular, because it is time-consuming and it needs physical values, such as the specific heat and the radiating area of the surface.<br>However, the present demand for the temperature control of spacecrafts has made the method 4) practically important. For a standardimplementation it requires a special vessel containing high vacuum air (thinner than 10-5 Torr), composed of low temperature walls (cooled by liquid nitrogen or other coolants), in which samples are placed. The apparatus becomes too large for this method to be used popularly.<br>Taking into consideration the present status of affairs, the authors obtained satisfactory values of effective emissivity for practical use, even in a low vacuum and in the standard atomosphere, the surrounding being kept at the normal room temperature.The authors' success may make the method 4) which theoretically has a high precision, more popular in measuring the emissivity.

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