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A Structural Model of Heat Transfer through Rigid Polyurethane Foam

Anthony Cunningham
ICI Polyurethanes Group, Everslaan, 45, B-3078 Kortenberg, Belgium

Abstrakt

The low thermal conductivity of polyurethane (PUR) rigid foam is considered commercially to be one of its most important solid-state properties. Such foam can be easily fabricated on the large-scale with initial λ-values in the range 0.016-0.019 W/mK (10°C).
Although it is well known that these low initial λ-values primarily result from the production of a closed cell material incorporating a low λ-value gas, structural parameters can also play an important secondary role. For instance, both average cell-size and cellular anisotropy strongly influence the measured λ-value. In this paper a structural model of heat transfer by way of conduction and radiation is proposed with specific emphasis on the anisotropy of heat transfer via thermal conduction.
Together with a new method for the accurate determination of anisotropic cell size, this model is used in conjunction with experimentally determined, initial foam, λ-values to develop an improved structural understanding of heat transfer through commercial rigid polyurethane foam (PUR). In conclusion, an estimate of the minimum λ-value theoretically obtainable, without any change of blowing agent, is given.

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