Adaptive Correction of Dynamic Temperature Measurements to Improve Estimation of Thermophysical Properties

The influence of sensor dynamics on the estimation of thermophysical properties of materials in transient heat conduction experiments is investigated. The temperature measured by the sensor (subminiature sheathed thermocouple) is corrected by identifying, in the same experiment, as well as the thermophysical properties of the material, also the unknown coefficients appearing in the dynamic model of the sensor itself. This approach provides an auto-adaptive temperature correction which can be used to improve the accuracy of the estimated thermophys- ical properties and to give quantitative information on the behaviour of the sensor in a dynamic regime. Different kinds of sensor-material coupling are investigated and compared: ideal thermal contact; presence of a thin air gap with or without the application of a heat sink compound at the measurement junction. Several results are presented, both from numerical simulations and true experiments at atmospheric pressure. Moreover, first results concerning the dynamic behaviour of the thermocouple inserted in a porous insulating material below atmospheric pressure are also presented. Among the different dynamic models utilised for characterising the transient thermal behaviour of the sensor, the first-order differential system with constant coefficients is relatively simple to implement, efficient, stable, and recommended.