Measurement of the thermal contact resistance of aluminum honeycombs

An experimental investigation of thermal contact resistance of the aluminum honeycomb (made of Al3104-H19 and Al3003-H16) sandwiched by two aluminum blocks was conducted with the honeycomb specimens aligned in either axial or lateral orientations. Honeycombs adopted in this study include two different cell diameters (dc), 6.3 and 12.7 mm, as well as two different axial heights (Hz), 7.8 and 14.8 mm. For the axial tests, honeycomb sandwich specimens were jointed by four or eight pieces of bolts with an applied torque ranged from 1 to 6 N m. The interfacial contact pressures of axial honeycombs under different bolt-joined conditions were measured by the pressure-measuring films. For the lateral tests, the honeycomb was simply inserted between two aluminum blocks without using bolts to fasten. Results show that due to the anisotropic nature in heat conduction and the close contact provided by bolted joints, the total thermal conductance of axial honeycomb is greater than that of honeycomb in the lateral orientation under the condition with the same specimen height. An increase of either the cell diameter or specimen height of honeycombs leads to a decrease of the axial total conductance. Moreover, the axial total conductance was substantially enhanced by a double of the number of bolts used in the assembly of honeycomb specimens. However, the influence of bolt torque on the axial total conductance was observed only for the honeycomb with dc= 6.3 mm and Hz= 7:8 mm. Due to the difference in specimen joint conditions, the thermal contact resistance between the solid aluminum surface and a lateral honeycomb is larger than that with an axial honeycomb. Under the conditions tested in this study, the thermal contact resistance of honeycombs in the axial direction appears to be one order of magnitude smaller than the total resistance. Nevertheless, the contribution of the lateral contact resistance of honeycombs to the total resistance was quite significant, especially for the specimen with a small height. It was found that the contact pressure of bolt-joined honeycombs in the interface increases evidently with an increase of either the bolt torque or the number of bolts. The empirical correlations between contact pressure and applied torque were also obtained for different joint conditions.