Abstract
Thermal contact conductance (TCC) is used to characterise heat transfer across interfaces in contact. It is important in thermal modelling of turbomachinery components and finds many other applications in the aerospace, microelectronic, automotive and metal working industries. In this research, a new method for measuring TCC is described and demonstrated. A test rig is formed from an instrumented split tube with in-line washers and loading applied under controlled conditions. The experimental method and data analysis is described, and the effect on thermal contact conductance of important parameters such as contact pressure, surface roughness, loading history, temperature, thermal conductivity and material strength is investigated. Normalisation of the TCC measured in the experimental program was carried out using appropriate surface and material parameters. The results of this normalisation are used to compare the normalised experimental results with various plastic and elastic models from the literature and it was found that the plastic models provided a better fit to the experimental data. Macroscopic deviations from a nominally flat surface, due to manufacturing inaccuracies or environmental effects, are very common in real engineering surfaces. The surface out-of-flatness was found to lead to a significant decrease in TCC. It is shown how experimental results for a flat surface, combined with a finite element model of the non-flat surface, provide a good estimate of the overall TCC for a non-flat surface. The effect of large scale, repeatable surface deviations on the TCC of an interface formed by the contact of two different profiled surfaces with a ground surface was measured. Simplified periodic finite element models of the contact between the repeatable surfaces and a ground surface were constructed, with the local TCC based on experimental results for the ground flat surface. The models were found to give a reasonable estimate of the measured TCC. The heat flow across a bolted interface was also investigated. Predictions from a correlation in the literature were found to overpredict the TCC when compared to experimental results given by other authors. A finite element model of a typical brake disc assembly was created and analysed. Although the correlation over-predicted the TCC due to assumed material and surface properties, the temperature profiles given by the model were similar to experimental measurements.