Thermal Joint Resistance of Conforming Rough Surfaces with Grease-Filled Interstitial Gaps

Thermal joint conductance and resistance models are presented for grease-é lled joints formed by conforming rough surfaces under light contact pressures. One model includes the thermal effect of contacting asperities, whereas the second, simpler model is based on conduction across the gaps only. The models are compared against recently publishedgreaseandphase-changematerial(PCM)dataobtained atonecontactpressure,coppersurfaces having three levels of surface roughness, four values of grease thermal conductivity, and two values of PCM conductivity. The models and the data are found to be in agreement over a wide range of a joint parameter deé ned as the ratio of the effective joint roughness and the thermal conductivity of the gap substance. The models can be used to predict an upper bound on the joint conductance and a lower bound on the specié c joint resistance for surfaces that are turned and milled.