Experimental study of contacting surfaces microgeometry and gas gap impact on thermal contact conductance of metallic joints

Thermal contact resistance is an important phenomenon in heat transfer and impacts many fields of technology. The interrelated influences of many factors-such as geometry and microgeometry of con-tacting surfaces, their mechanical and thermal properties, apparent contact pressure, type and properties of interstitial fluid-make prediction of this resistance problematic and necessitate both theoretical and experimental research. The paper reports an experimental study of thermal contact conductance (the re-ciprocal of thermal contact resistance) of joints created by flat, conforming metallic surfaces in static contact. The measurements were performed for samples made of mild steel and stainless steel with rela-tively low roughness (Sigma = 0.5 -2.14 mu m) and large slope of asperities ( m = 0.4 - 1.3), resulting in values of Sigma ef /mef = 1.25 -1.96 mu m that are distinctly lower than reported in the majority of experimental re-search on thermal contact conductance. The apparent contact pressure was changed from 1.5 to 11 MPa and for some cases up to 19 MPa. Analysis of the results obtained showed that the correlations available in the literature, for greater values of roughness and smaller asperity slope, mostly overestimated the predicted thermal contact conductance. The elasticity indices values for samples used in this study indi-cated plastic deformation of asperities, but it was concluded that the smoothest surfaces of both kinds of steel underwent elastic deformation. A new experimental correlation for contact of mild steel surfaces (Sigma = 0.5 -2.14 mu m, Sigma ef/mef = 1.25 -1.96) was proposed. The results of this study indicate the need for further investigation of thermal contact conductance, especially for this range of surface microgeometry parameters, which is not dealt with in the correlations available in the literature. There is also a need to study the impact of asperity curvature on contact conductance. The results of this study proved the important role that air gaps play in the transfer of heat across a joint. The gap conductance values were predicted correctly for low mechanical loads and rough surfaces.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

Thermal contact resistance is an important phenomenon in heat transfer and impacts many fields of technology. This paper presents an experimental study on the thermal contact conductance of joints created by static contact of metallic surfaces. The study revealed that existing correlations in the literature often overestimate the predicted thermal contact conductance and further investigation is needed, especially for a certain range of surface microgeometry parameters.