Radiative transfer and thermal performance levels in foam insulation boardstocks

Abstract

The validity of predictive models for the thermal conductivity of foam insulation is established based on the fundamental geometry of the closed-cell foam. The extinction coefficient is experimentally and theoretically determined; the theoretical prediction based on measured geometrical properties differed from the measured values by an average of 6% for ten different foams An approximate method uses measured geometrical values to adjust the measured diffusion coefficients of reference foams. The adjusted coefficients are used as inputs to a computer program which computes the effective thermal conductivity of the foam as a function of time. Values of effective thermal conductivity measured on laboratory and field samples are used as a standard for comparing the results of the physical models and the ageing program. Measured and predicted values differ by 11%, 13%, 1%, 5%, and 1% for the initial thermal conductivity of five foams tested. These errors decrease with time. The ageing program is used to simulate the time-averaged performance as a function of foam density, mean cell diameter, and fractional distribution of solid polymer. The results of the simulation indicate that for a 15 year service life, the optimal density is approximately 3 lb / ft3.