Thermal joint resistance of solid material as a function of pressure and roughness

Abstract

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.

An analytical model was developed for predicting the thermal joint resistance of nonconforming rough surfaces in contact with the presence of air under atmospheric pressure as a TIM. Accordingly four models were developed in the present work. The thermal macrocontact resistance was modeled for the transition case, with the existence of surface roughness and surface out of flatness. The microcontact radius was modeled correlating the microcontact radius to the relative applied pressure, which was used with the !henna! constriction parameter to develop an accurate nondimensional contact conductance and thermal microcontact resistance. The thermal microgap resistance model is derived assuming the TIM is air under atmospheric pressure and taking into account the effect of surface curvature. The microgap resistance has the largest values among the other components, since the TIM which was air has very low !henna! conductivity and a small microgap area. The !henna! macrogap resistance builds up in the region surrounding the macrocontact area which was also IDled with air under atmospheric pressure as TIM. Throughout the above analytical work it was assumed that the surface asperities deform plastically while the bulk material deform elastically as been assumed by almost the majority of the researchers in this field. On the other hand and in order to support the present theoretical models, an experimental investigation was carried out to measure the !henna! joint resistance for the contact of nonconforming rough surfaces with air under atmospheric pressure as a TIM. A laboratory experimental setup was designed and implemented. The examined contacting surfaces were aluminium and brass. Many surface processes were done comprising cutting, chemical cleaning, and ultrasonic cleaning. Also many geometrical and mechanical parameters were measured for the contacting samples that include, surface roughness, surface asperity slope, surface out-<lf-flatness, and material bulk hardness. Collected data are tabulated and the related equations were used to calculate the heat flux, temperature drop, and the thermal joint resistance, as well as their estimated error. The measured results were compared with the theoretical model mentioned above and a good agreement is observed. The differential error estimated for the thermal joint resistance is ranged from (0.00248) to (0.00557) °C/w.