Radiant power exchange in thermal radiation calorimetry

Radiant power exchange for thermal radiation calorimetry was investigated both theoretically and experimentally. The geometrical relation in which a disk-shaped copper specimen and a graphite plate are facing each other was used as the model configuration. Surfaces of the specimen and the plate were blackened with colloidal graphite to achieve a high surface emissivity. The radiant power density absorbed by the specimen was calculated by taking into account the geometrical configuration 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 obtained experimentally by use of a heat capacity measurement was constant with temperature, with a value of 0.54 +/- 0.01 within experimental error. No hysteresis in the coefficient was observed for either heating or cooling processes.