Thermal contact conductance and its dependence on load cycling

Heat transfer between contacting surfaces is an important factor in the thermal behaviour of engineering components in turbomachinery and various other areas of technology. Thermal contact conductance (TCC) is a parameter that quantifies this heat flow. Any theoretical prediction of TCC should take into account the effects, if any, introduced by repeated loading and unloading. This study aims to add to the limited volume of work available on this topic in the literature. In particular, the focus of this investigation is machined surfaces that typify the mating surfaces in some turbomachinery applications. Experimental work investigating the effect of loading and unloading history for numerous cycles is presented. An instrumented split tube with in line washers, loaded and unloaded under carefully controlled conditions, was used to measure the TCC of washers made of nickel alloy PE16 and 316 stainless steel. The study also examines the load cycle effect on TCC for a variety of interface surface geometries and pressures that are relevant to turbomachinery applications. The results show that load cycling, beyond the first cycle, has a minimal effect on TCC, in disagreement with other studies in the literature. This observation is seen for variety of surface topographies and maximum contact pressures.