Normal emissivity of samples surrounded by surfaces at diverse temperatures

The paper deals with the temperature influence of surfaces surrounding a sample on its emitted and reflected radiation during high temperature pyrometry (T > 900 K). Measurements of the true and radiant T have been carried out for stainless steel and titanium samples inside a tubular furnace with a commercial high temperature pyrometer. The band normal emissivity has been computed using a special procedure taking into account reflection of radiation from the furnace walls, whose T was continuously recorded. The total uncertainty of calculated emissivity resulted in few thousands, corresponding to an uncertainty of the sample temperature of about 2 degrees C. The emissivity of the sample, and consequently its true temperature, have been evaluated taking into account both the radiation emitted by surfaces surrounding the sample and the one detected by the pyrometer. All these data, during both heating and cooling, are processed by means of a linear multiple regression, and the best estimate of the emissivity and reflectivity independently was given. Finally true temperature during the usual production practise of metallurgical products can be easily obtained. (C) 2005 Elsevier Ltd. All rights reserved