COMBINED RADIATION AND CONDUCTION HEAT-TRANSFER IN HIGH-TEMPERATURE FIBER THERMAL INSULATION

Three different approaches for describing combined radiation and condu ction heat transfer in fiber thermal insulation al high temperatures a re analyzed and compared. The considered approaches include the radiat ion transfer equation or its approximations, approximation of radiatio n thermal conductivity and the radiation diffusion approximation for r adiation transfer. The first causes difficulties due to the need for e xperimental measurement of optical properties, while calculations base d on the Mie theory may give inexact results. The second rakes into ac count the radiation transfer inaccurately and the experimentally measu red total thermal conductivity may depend on temperature drop, thickne ss of sample, properties of boundaries and time parameters at transien t conditions. It is shown that the most preferable approach is the rad iation diffusion approximation for radiation transfer. The comparison of the radiation thermal conductivity approximation and the radiation diffusion approximation is carried out for the example of modeling the working conditions of the fibrous thermal insulation of the Space Shu ttle when the vehicle enters the Earth's atmosphere. (C) 1997 Elsevier Science Ltd. All rights reserved.