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The thermal conductivity of many closed-cell foam insulation products changes over time as production gases diffuse out of the cell matrix and atmospheric gases diffuse into the cells. Thin slicing has been shown to be effective in accelerating this process in such a way as to produce meaningful results. One of the challenges for this test method is determining whether a foam product is sufficiently homogenous so that the accelerated prediction accurately reflects the aging of the full-thickness product. A related question is whether or not thin slices extracted from one product thickness can accurately predict the aged thermal conductivity for the same product in a different thickness. Qualification criteria were developed for the prescriptive version of the ASTM C1303 standard test method to ensure that predicted thermal conductivity results would be acceptably accurate. A ruggedness test (a “test the test” process) was initiated to examine multiple test parameters, and to determine whether these qualification criteria were adequate. This test program included the aging of full size insulation specimens for time periods of 5 years for direct comparison to the predicted results. The test program has been completed, and this report discusses the accuracy of the 5-year thermal conductivity prediction for various levels of the homogeneity and alternate product thickness qualification criteria.
accelerated aging, foam insulation, homogeneity
Oak Ridge National Laboratory, Oak Ridge, TN