A Numerical Procedure for Calculating Combined Conduction and Radiation Heat Flux Through Fibrous Insulation

Abstract

This article presents a numerical procedure for calculating heat flux through fibrous insulation. It deals primarily with the radiation component, and the interaction between the radiation and conduction. The program determines the temperature profile by an iterative method, and uses it to evaluate the conductivity of the air and the extinction coefficient of the fibrous material at locations through the material. The temperature dependence of the extinction coefficient accounts for the nongray nature of fibrous materials. The algorithm allows for the edge effect. The article deals primarily with steady state heat flow, and includes an example of nonsteady heat flow. A method to estimate the contribution of the fiber structure is included. The thermal properties of insulation are derived from the results of R-value tests in vacuum and in air at different mean temperatures.