New analysis for determination of hemispherical total emissivity by feedback-controlled pulse-heating technique

Abstract

A new analysis for the determination of hemispherical total emissivity has been developed on electrically conductive materials under a brief steady-state established by a feedback-controlled pulse-heating technique. The new analysis is based on an equation describing a more realistic situation of the thermal balance of the sample during the “apparently” static period. The dependency of sample temperature on time and space during the apparently static period is necessary in carrying out the new analysis, and is semiempirically estimated using experimental results for the electrical resistivity of the sample as a function of time. The new analysis was applied to the determination of the emissivity of molybdenum at temperatures beyond 1500 K. Contrary to the general expectation, the emissivity derived by the new analysis, which takes conductive heat loss into account, is systematically larger than that derived by the previous analysis, which neglects the heat loss. The deviation between the new and previous analyses is explained in terms of five factors. The dominant factor is associated with the decrease in the average temperature of the sample during the apparent temperature plateau and cannot be neglected even at the beginning of the apparently static period. The emissivity determined on molybdenum by the new analysis is in good agreement with the literature data obtained by two different methods.