Emissivity estimation through the solution of an inverse heat-conduction problem

A new transient calorimetric method to measure the total hemispherical emissivity of opaque surfaces as a function of temperature is presented. A disk-shaped specimen for which the emissivity is required to be measured is placed in an evacuated vessel. One of its two surfaces is heated uniformly by means of an electrical resistance. The total hemispherical emissivity of the other—free—surface, which is parallel and very near to a uniformly cooled plate, can then be estimated using only transient temperature measurements at two locations inside the specimen. A model based on the solution of a one-dimensional inverse heat-conduction problem is used. This model allows one to estimate the surface temperature and net radiative heat flux from which the emissivity can be obtained. This property can also be estimated for paints and other surface coatings by covering the free surface with a thin layer of the coating concerned.