Effective Thermophysical Properties of Thermal Interface Materials: Part II — Experiments and Data

Abstract

A new method for determining effective thermal conductivity and Young’s modulus in thermal interface materials is demonstrated. The method denoted as the Bulk Resistance Method (BRM) uses empircal thermal resistance data and analytical modeling to accurately predict thermophysical properties that account for insitu changes in material thickness due to external loading and thermal expansion. The BRM is demonstrated using commercially available sheets of Grafoil GTA. Tests were performed on thermal joints consisting of two Al 2024 machined surfaces with layers of Grafoil GTA in the interface. Test conditions included a vacuum environment, 0.2–6.5 MPa contact pressure, a nominal 50°C mean interface temperature and a continuous loading and unloading cycle. Test results indicated that the BRM consistently predicted thermal conductivity independent of the number of layers tested and that the predicted results were significantly lower than values reported using conventional ASTM test procedures.

Moving Divertor Plates in a Tokamak

“…Table 5 shows ANSYS calculations of the cooling time for hot plates pressed onto a cold copper heat sink, which is either 273°K (room temperature) or 80 ºK (liquid nitrogen temperature). To increase the thermal contact between the divertor and the copper plate, a 0.14 mm layer of high conductivity Grafoil [14] is chosen and 1 MPa pressure is applied between the plate and the copper heat sink to increase the contact area. Both one-sided and double-side cooling options are shown.…”

Thermal contact conductance characterization via computational contact homogenization: A finite deformation theory framework

“…See also Zavarise et al [4] for a critical overview and Jackson et al [5] for an explicit incorporation of length scale effects in asperity deformation models. Specific applications to TIMs have recently been considered in Savija et al [6], Savija et al [7], Prasher and Matayabas [8] and Chung [9].…”

Development of a high-accuracy thermal interface material tester

“…The upper platen is also constructed from 19.05-mm-thick steel. The distance between the opposing faces of the meter bars is measured using an optical micrometer (6).…”

“…This configuration relies on highlyconductive and well-characterized meter bars to both extrapolate the temperature at the surfaces and measure the heat flow through the sample. A number of studies have made use of this general design [3][4][5][6][7] Gwinn et al [4] developed an apparatus for testing TIMs capable of measuring thermal impedances as low as 6.5 × 10-6 m2•K/W with an uncertainty of 10%. The copper meter bars were 38.1 mm square in cross-section and 45 mm long, instrumented with three 1.59 mm RTDs, with the closest RTD located 2 mm from the surface.…”

“…Aluminum alloy 2024 meter bars instrumented with RTDs were used to both extrapolate the temperature at the TIM surfaces and quantify the heat flux. A laser/detector system was used to measure the distance between the meter bars for an accurate in-situ measurement of [6] used empirical data obtained using this apparatus in conjunction with an analytical model to predict the thermophysical properties of commercially available graphite sheets. Additionally, this apparatus was modified to measure the thermal conductivity and contact resistance of adhesives [7].…”