TED-AJ03-533 Measurement of the Thermal Conductivity of Vacuum Insulation Panels

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Vacuum insulation panels have values of thermal conductivity that are extremely low (∿4mW/m-K) compared to the thermal conductivity of most common insulations. Typical test methods such as ASTM C 177,ASTM C 518,ASTM C 745,and ASTM C 1114 are not designed for testing these very low thermal conductivity materials. Specifically, these methods do not take into account the significant conduction through the thin metallized plastic wrap that serves as an air barrier for the panel. Also, the radiation transfer to the environment and within the test apparatus (generally neglected in these methods) become crucial when testing such low thermal conductivity materials.[figure] An apparatus has been built and tested that uses a thin plate heater to test vacuum insulation panels. The test setup (see Fig. A-1) is installed in a vacuum bell jar with a surrounding pressure of 5 to 15 μTorr so that the convection effects are negligible. Typical results are shown in Fig. A-2. The results of three series, with the heater plate at room temperature, 10 C above room temperature and 10 C below room temperature, are plotted. These data are corrected for radiation effects with the surroundings. Several different measurement configurations are studied to determine the effects of the parasitic heat losses. Seemingly insignificant effects are significant with these panels. For example, energy exchange between the heater plates and the C-clamps used to hold the assembly together causes a 15% error in the measured thermal conductivity. Even the ionization gage used to measure pressure causes a 1.5% error. The differences between the aforementioned ASTM standards and this technique are described and the rationale explained. A new ASTM technique for vacuum panels appears to be needed.[figure]
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TED-AJ03-533 Measurement of the Thermal Conductivity of Vacuum Insulation Panels

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