Thermal contact conductance of spherical, rough metals.

摘要

Predicting thermal contact conductance of metals is a fundamental problem in the field of contact heat transfer. Most theoretical models are intended only for nearly optically flat surfaces, which are prohibitively expensive or not technologically achievable for many engineering applications. Empirical correlations for contact conductance of nominally flat (though typically arbitrarily nonflat) surfaces demonstrate limited success.;The few previous investigations addressing nonflat surfaces have modeled arbitrarily nonflat surfaces as spherical to make analysis tractable. One theoretical model is available for spherical, smooth metals, that is, the limiting case opposite that of flat, rough surfaces. However, it suffers from the same limited utility as do theories for flat, rough surfaces. The handful of theories for spherical, rough metals require computationally intensive numerical solution. Only one of these models has been experimentally verified for the common case in which both significant roughness and flatness deviation are present and their effects on contact conductance are of the same order. However, the model requires tedious measurement of the contact pressure distribution.;The present model for thermal contact conductance of spherical, rough metals is a synthesis and refinement of previous contact models and experimental results for rough, spherical metals and a thermal contact conductance model for surfaces with non-uniform contact pressure distributions. It is presented in an algebraic/graphical format (and implemented in a FORTRAN 90 program) that is readily utilized by the practicing engineer.;The present model is compared to a very large database of experimental conductance results for a number of metals and alloys and to another often cited model for thermal contact conductance of flat, rough metals. Although both models agree well with experimental data for flat, un-oxidized surfaces, neither model accounts for the reduction in contact conductance due to surface oxidation. The previous model is substantially over-predictive (non-conservative) for nonflat surfaces. The present model is quite robust in that it is in good agreement with most experimental results for not only flat, rough and spherical, rough metals, but also for most nominally flat (though typically arbitrarily nonflat), rough metals typically dealt with in engineering applications.