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The characteristics of thermal contact conductance are increasingly important in a wide range of technologies. As a consequence, the number of experimental and theoretical investigations of contact conductance has increased. This paper reviews and categorizes recent developments in contact conductance heat transfer. Among the topics included are the theoretical/analytical/numerical studies of contact conductance for conforming surfaces and other surface geometries; the thermal conductance in such technological areas as advanced or modern materials, microelectronics, and biomedicine; and selected topics including thermal rectification, gas conductance, cylindrical contacts, periodic and sliding contacts, and conductance measurements. The paper concludes with recommendations for emerging and continuing areas of investigation.

Evaporation and boiling heat transfer coefficients are presented for thin, distilled water films flowing over the outside of horizontal, electrically heated brass tubes. Tests were conducted with a thin-slot water distribution system for 2.54- and 5.08-cm-dia smooth tubes. Both local and average heat transfer data were obtained for nonboiling and boiling conditions corresponding to feedwater temperatures ranging from 49 to 127°C and heat-flux values ranging from 30 to 80 kW/m2. Feed-water flow rates ranged from 0.135 to 0.366 kg/s per meter length per side of the tube. Both nonboiling and boiling correlations of the average heat transfer coefficients were developed and compared.

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The thermal conductivity and thermal contact conductance of several thermoplastic and thermosetting polymers have been studied over a range of interface pressures and temperatures. The temperature range for the thermal conductivity study varied from 10 to 100°C (50 to 212°F). The study showed that ultra high molecular weight (UHMW) polyethylene had the highest thermal conductivity through the range of temperatures and also had the highest thermal conductance values at an interface temperature of 20°C (68°F). The thermal contact conductance study was conducted over a pressure range of 510-2760 kPa (75-400 psi) and a temperature range of 20-40°C (68-104°F). The conductance values for UHMW polyethylene ranged from 1095.3 to 1659.4 W/m 2 K (192.9 to 292.2 Btu/h ft 2 °F), whereas the thermal conductivity remained constant at 0.45 W/m K (0.26 Btu/h ft °F) throughout the range of temperatures. Polycarbonate and Teflon® had the next highest thermal conductance values at the same interface temperature. The thermal contact conductance values for polyethylene, Teflon, and phenolic polymers were measured at an elevated temperature of 40°C (104°F). The thermal contact conductance values for both Teflon and phenolic increased with increasing temperature, whereas the values for UHMW polyethylene decreased due to their unique chain structure at the higher temperature. The polymers were chosen because of their widespread engineering interest applications. Nomenclature A a = apparent area A r = real area E = modulus of elasticity E' = (E^/t^O -v\) + E,(\ -F = flatness H c = hardness H e = elastic hardness (E'/\/2) X m h c = thermal contact conductance h e -dimension elastic conductance h p = dimension plastic conductance k = thermal conductivity m = asperity slope P d = profile slope PIH C = dimensionless plastic contact pressure PIH e = dimensionless elastic contact pressure P r = profile roughness R = roughness W = waviness Subscripts a "=• average p = polymer q -root mean square s -roughness subst = substrate Presented as Paper 95-0421 at the AIAA 33rd Aerospace Sciences