ABSTRACT
A round robin was initiated in February of 2000 to compare different methods of determining the effective thermal resistance of vacuum panels. The outcome of this round robin will 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. 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 eight participating laboratories measured the center-of-panel resistance of each of the six panels as described in the ASTM standard C1484-00 and reported those results along with pertinent information about the transducer(s) size and location. Several laboratories also determined the whole-panel effective thermal resistance, using two assumed sets of boundary conditions. Considering the exploratory nature ofthis round-robin, and the complexity of the measurements, the results showed surprisingly good agreement.
