Sensors for thermal conductivity at high temperatures
This thesis describes research undertaken to improve a technique for the measurement of the thermal conductivity of molten materials. The research follows on from the work of previous researchers who designed and tested an instrument for the measurements of the thermal conductivity of molten metals up to 750 K. The previously used transient hot-wire technique, which consisted of the experimental measurement of the voltage response of a sensor and a subsequent inverse Unite element analysis, has been significantly upgraded. The experimental part of the technique has been improved by the introduction of a new design of the sensor for the measurement of the thermal conductivity. Both the new and the original designs have been used to investigate the same material samples in order to demonstrate the robustness and repeatability of the experimental technique. Additionally, the finite element analysis employed has also undergone various major improvements and resulted in a new finite element model which not only represents the true geometry of the experimental device but also employs a more accurate solution of the transient, conductive heat transfer. The significant upgrade of the technique and the availability of two different sensor designs have helped to uncover systematic errors which could not have been previously identified and may have resulted in deviations of the measured thermal conductivity. Five original sensors and five sensors with the new design have been used to investigate the thermal conductivity of molten indium, tin and lead at various temperatures up to 750 K. The results have been compared to previously published data and the discrepancies have been discussed and explained. Each metal has been measured using at least two sensors and the consistency of the measured data has also been verified by using two different samples of pure tin. Besides the pure metals, the thermal conductivity of several metal alloys currently used in industry has been investigated within the same temperature range. The overall uncertainty of the measurements of the thermal conductivity is estimated to be ±3 %.