Characterization of Rough Engineering Surfaces for Use in Thermal Contact Conductance Modeling

Most surface properties used in the calculation of contact conductance are not intrinsic to the surface, but vary with the sampling frequency of the instrument used to characterize the surface. This paper offers a methodology for characterizing a surface based on intrinsic surface characterization properties (the self-affine fractal dimension and topothesy), intrinsic material properties, and applied load. A surface characterization model is developed to predict the wavelengths on a surface that are of significance in the prediction of thermal contact conductance. The surface characterization model is combined with surface deformation and constriction resistance models to predict contact conductance across nominally flat, metallic surfaces. The long-wavelength cutoff in the surface characterization is set by the dimensions of the contact area. A theoretical correlation for the short-wavelength cutoff as a function of surface and material properties and load is developed, and then improved by a least-squares fit to experimental data. The integrated model developed predicts contact conductance in three modules: defining the unique asperity geometries important in the deformation modeling; calculating the mode of deformation of asperities; and taking into account the actual geometry of asperities in the constriction resistance model. The predicted contact conductance compares well to experimental data over a range of surface roughnesses, pressures, and substrate materials. * Submitted for publication in AIAA Journal of Thermophysics and Heat Transfer, January 2005, and in revised form, August 2005 ‡ To whom correspondence should be addressed: 765-494-5621, 765-494-0539 (FAX), [email protected]