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A round robin was initiated in February of 2000 to compare different methods of determining the effective thermal resistance of vacuum insulation panels. The outcome of this round robin was designed to provide support for the ASTM material specification and the development of a future ASTM test method. Four issues were identified and addressed: (1) calorimetric vs. center-of-panel/barrier conductivity approaches, (2) comparison of available finite difference/element models, (3) appropriate boundary conditions for all measurements/models, and (4) comparison of center-of-panel measurements to provide a preliminary precision estimate. Six conventional vacuum panels were constructed. All six shared the same dimensional configuration, the same core material, the same getter insert, and the same manufacturing techniques and equipment. Two different barrier materials (three panels from each) were used because barrier thermal conductivity is recognized as a key factor in the determination of effective thermal resistance for vacuum panels, and because the different methods used in this round robin comparison should be sensitive to the barrier thermal properties. The getters were included in these panels to help them remain stable throughout the duration of the round robin.
Each of the nine participating laboratories measured the center-of-panel thermal resistivity of each of the six panels as described in the ASTM standard C1484-00 and reported those results along with pertinent information about their transducer(s) size and location. Several laboratories also calculated the whole-panel effective thermal resistance, using specified sets of boundary conditions.
Vacuum insulation, evacuated insulation, insulation panels, thermal resistance, effective thermal resistance, round robin
Research Engineer, Oak Ridge National Laboratory, Oak Ridge, TN
Chief Executive Officer, LaserComp Inc., Saugus, MA