Total emissivities and absorptivities of some commercial surfaces at room and liquid-nitrogen temperatures
F. J. Zimmermann
The heat transferred by radiation was measured between surfaces at room temperature and liquid-nitrogen temperature. The surfaces used were various combinations of electroplated gold and silver and polished copper sheet. From the test data, the approximate total emissivities of the room-temperature surfaces and the total absorptivities of the liquid-nitrogen surfaces were computed. The results of these tests indicated that electroplated silver surfaces have lower emissivities and absorptivities than equivalently treated electroplated gold surfaces in this temperature range. The best surface tested was a special, bright, unbuffed silver-plated surface. This surface is known to the trade as ''silver lume.'' The room-temperature emissivity of this surface was approximately 0.017, and the absorptivity at 77.3°K for radiation from a 300°K surface was about 0.0083. These are the lowest values at these temperatures of which we have knowledge. It was found that the electroplated surfaces were best used without buffing or any mechanical working of the surface. It is believed that cold working of the metal surface increases its emissivity and absorptivity by increasing its electrical resistivity. © 1955 The American Institute of Physics.
