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Long-Term Thermal Resistance of Thin Cellular Plastic Insulations

DAVID W. YARBROUGH, MICHEL P. DROUIN

Abstract


The determination of the long-term thermal resistance (LTTR) of cellular plastic insulations with a low thermal conductivity gas is routinely accomplished using a procedure called “slicing and scaling” to accelerate the gas-exchange process and resulting increase in apparent thermal conductivity with time. This procedure, however, is not useful for insulation products with full-thicknesses of 5 to 15 mm because these products are too thin to slice. An alternate to the slicing and scaling procedure has been developed that extrapolates thermal resistance data for specimen ages less than two years to predict time average values for 15 years or more. Exponential functions that have a horizontal asymptote are used to describe the performance over time and provide LTTR(15). Thermal resistance data and the R/R0 for five sets of thin products have been obtained for periods up to 900 days. The ratio R/R0 for t>0 can be described with confidence and integrated to obtain the time-average value for R/R0 over a specified time period such as 0 to 15 years. The analysis and data that have been obtained will be discussed.


DOI
10.12783/tc33-te21/30340

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