Methods of Monochromatic One- and Two-Color Radiation Thermometry of Melts in Metallurgy. Part 1

Abstract

Radiation thermometry is the most suitable for continuous measurement of melts temperature. It is necessary for measuring control of their states during melting, as well as for energy-saving management of melting. For maximizing the probability of measuring control and increasing energy efficiency of melting, the task of melts temperature measurement uncertainty decreasing is relevant. If we use rational approach, the diversity of known monochromatic one- and two-color methods of radiation thermometry can be used to solve this task. These methods have been divided on two groups, depending on utilization of information about spectral emissivity of the object in their measurement models. The current work is devoted to the 1 group of radiation thermometry methods – those in which the correction for spectral emissivity of the object is not utilized. It is shown that the equality of the conditional and thermodynamic temperatures takes place for the thermodynamically equilibrium radiation of the absolutely black body, the spectral emissivity of which is identically equal to unity. Accordingly, the methods of one- and two-color radiation thermometry of the melts without correction for their emissivity are based on the assumption that the melts emit as the absolutely black body. It has been established that the empirical ways of temperature estimation of incandescent objects, including melts, by visual observation of their energy brightness and color historically appeared firstly. At the beginning of the last century, the 2 classical methods of monochromatic radiation thermometry in the visible wavelength range were originated from mentioned empirical ways. The other 6 conditional temperatures, which appeared later as a result of the development of the theoretical base of radiation thermometry have been joined in “non-classical” subgroup. Measurements models of conditional temperatures are considered. The 3 relationships between the values of the spectral emissivity of a “non-black” object at two wavelengths are presented, which provide the exclusion of systematic methodological errors of some two-color thermometry methods. The dependence of the spectral emissivity on the wavelength, which causes these relationships, is given. In practice, for “non-black” objects with essentially unstable emissivity, including melts, adequate conditions for the applicability of the considered methods (under which methodological error of them is excluded by definition) are implemented with the help of radiation normalization technologies. Operation principle of the 5 technologies is described and the list of their disadvantages is given. Considering the complexity and significant cost of these technologies, as well as the low methodological accuracy of temperature measurement by the considered methods of radiation thermometry without them, more metrologically advanced thermometry methods combined with the methods of measuring spectral emissivity are necessary for contactless temperature control of melts in metallurgy.