Heat Transfer Through Fiberglass Insulation

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Abstract
Heat transfer by radiation and conduction through a fiberglass insulation placed between two opaque, isothermal walls has been theoretically predicted. Glass fibers absorb, emit, and anisotropically scatter spectrally as a function of their size and orientation. Accordingly, measured spectral optical constants of glass as well as the fiber sizes and orientations were used to calculate their bulk scattering and absorption coefficients and phase functions appearing in the radiative transport equation. The coupling of radiation and conduction required an iterative solution of the energy equation and the discrete ordinate approximation to the equation of radiative transfer. It was found that radiation and conduction are each responsible for about one-half of the total heat transfer and this coupling induces, in general, a nonlinear temperature profile. Of the radiation, about one-half occurs at less than 8 µm because of the nongray optical properties of glass. The theoretical prediction of the total heat flux is in excellent agreement with available laboratory measurements.

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