RADIANT POWER EXCHANGE IN THERMAL-RADIATION CALORIMETRY

Radiant power exchange for thermal radiation calorimetry was investiga ted both theoretically and experimentally. The geometrical relation in which a disk-shaped copper specimen and a graphite plate are facing e ach other was used as the model configuration. Surfaces of the specime n and the plate were blackened with colloidal graphite to achieve a hi gh surface emissivity. The radiant power density absorbed by the speci men was calculated by taking into account the geometrical configuratio n factors and the total emissivity of the blackened surfaces obtained form spectral reflectivity. A value of 0.56 +/- 0.01 was obtained for the radiant power exchange coefficient from the theoretical results in the temperature range from 220 to 430 degrees C. The coefficient obta ined experimentally by use of a heat capacity measurement was constant with temperature, with a value of 0.54 +/- 0.01 within experimental e rror. No hysteresis in the coefficient was observed for either heating or cooling processes.