Metallic coatings applied to surfaces in contact have been shown to be effective at reducing thermal contact resistance. Contact resistance is primarily caused by the constriction of heat flo w as it passes through individual contact spots. Most analyses of coated constrictions have been limited to plane contacts of a semi-infinite cylinder, while an actual constriction terminates in a shape like the frustum of a cone. A numerical model has been developed to determine the constriction resistance of such a coated asperity. The gap between the cone and contact surface is considered to either be evacuated or filled with a gas, and the temperature jump phenomenon is included in the gas-gap model. The effects of radiation heat transfer are also included. The results indicate that an optimum coating thickness for minimizing constriction resistance exists in all cases. Most gases are found to reduce the coating effectiveness very slightly, especially compared to the effect of radiation. The effect of radiation on the model is shown to be highly dependent on the joint temperature, substrate and coating thermal conductivities, and constriction ratio. Contrary to current belief, radiation is shown to be important even for temperatures below 300°C when either the substrate conductivity or the constriction ratio is very low.

No abstract