Novel Method of Fast Measurement of Thermal Conductivity in Wide Range of Temperatures

Abstract

Theoretical aspects and practical realization of a new method of fast measurement of thermal conductivity of coating materials (like deposits on wall and tubes of the boilers using fossil fuel, or high-temperature ceramics and adhesive materials) are presented. The method is based on analytical solution of the problem of unsteady heat transfer from the heated probe with coating to the environmental air. Several models of the phenomenon, taking into account convection and thermal radiation components of heat transfer, are described. The records of the probe temperature are processed numerically and compared with calculated values based on analytical solution. The best fit between the curves of recorded and calculated temperatures yields thermal conductivity value used as a parameter of the best fitting. This approach was applied to measurement of thermal properties of Fouling deposition in a coal-firing boiler. It was also demonstrated how extended version of the method allows one to represent the thermal conductivity of coating as a piecewise constant function of temperature, using a single record of the probe cooling curve. With a specially designed software for efficient calculation according to developed mathematical model, the whole experiment in the range 1500 °K–300 °K takes no more than 35–40 min, including processing on a regular PC. Validation of the suggested method was carried out in a special experiment with the substance of known thermal conductivity (Corn oil). The method was applied to Fouling depositions of two kinds of fuel—Columbian bituminous coal and Russian bituminous coal. It was demonstrated that Fouling in these two cases is characterized by significantly different thermal conductivity which also changes markedly with temperature.