Experimental estimation of thermal contact conductance across pressed copper–copper contacts at cryogenic-temperatures

Abstract

• Present experimental work presents a valuable database of TCC in cryogenics. • Reports systematic estimates of TCC for copper contacts on which data are scarce. • Effects of broad temperature, pressure, roughness on TCC are covered in vacuum. • Anomalous TCC trend at low temperature is correlated to thermo-physical properties. • Proposes generalized empirical correlations of TCC with temperature and pressure. The accurate estimation of thermal contact conductance (TCC) is a fundamental need towards the optimal design of any cryogen-free conduction-based cooling systems, which routinely utilizes mechanically pressed components of bare copper to form the heat conduction path. There exists a dearth of databases and reliable correlation for TCC between bare copper contacts for such applications. Present work is an experimental study, which has been performed systematically to address the requirement of design engineers for such applications. A novel experimental setup has been made to carry out axial heat transfer experiments between copper contacts under a varying set of temperature and pressure parameters of 50 to 300 K and 0.5 to 8 MPa, respectively. The surface roughness at the contact between copper specimens varied between 0.8 and 10 μ m . The TCC has shown a non-linear variation with temperature in the 50 to 300 K. The temperature-dependent thermophysical properties, nature of asperities deformation, and surface topography characterization were considered in analyzing the results. This effectively helps in dealing with the coupled nature of the TCC problem and thus enhances the accuracy, reliability, and scope of the present study performed at sub-ambient ranges under a varying set of selected parameters. The TCC results have also been compared with theoretical model predictions, and the improvements needed in them are highlighted. Finally, an empirical correlation of the reduced dimensionless TCC with dimensionless temperature and dimensionless pressure has been proposed, which covers a wide deformation range of the asperities, temperature, and surface roughness than existing models in the literature. The proposed correlation consistently explains the non-linear dependence of TCC with temperature and pressure and provides a direct means to the design engineers for the TCC estimation at cryogenic temperatures.