A Study of Heat Transfer Through Periodically Contacting Surfaces

Abstract

This thesis describes a theoretical and experimental study of heat transfer through the interface between two solids which make contact and then separate periodically. The cycle of contact and separation is continuous and the quasi-steady state only is considered. The system chosen as the model for study comprised two identical solid bars, arranged with their longitudinal axes in line and able to make periodic contact at their adjacent ends. The remote ends of the bars were maintained at fixed but differing temperatures, so that heat was transferred through the interface when the adjacent ends were in contact and ceased when they were separated. The effects of frequency of contact, thermal contact resistance offered by the interface during the period of contact and the ratio of contact time: periodic time of the cycle on the average thermal resistance of the system were explored theoretically. The results of this study are presented as a set of curves connecting the variables through dimensionless groups. The validity of these results was corroborated by solving the heat diffusion equation by two independent methods, each of which yielded the same result. Experimental work showed that the theoretical data could be used to obtain a first approximation to the average thermal resistance offered by a pair of periodically contacting surfaces, but large variations (probably due to changes in contact geometry between one cycle and the next) could occur. Tests to establish the effect of impact upon the average thermal resistance were inconclusive and an improved experimental technique is required generally for any future work.