THERMAL-CONDUCTIVITY OF THE CARBON FELTS, STRONGLY ANISOTROPIC INSULANTS - MODELING OF HEAT-CONDUCTION BY SOLID-PHASE

Uses of carbon felts for high temperature insulation are reviewed. Eff ects of raw material and fabrication method on the felt properties are discussed. The connection between the thermal conductivity lambda and the other felt properties are analysed. Evidence is given for the exi stence of three hierarchized anisotropy levels of lambda: crystal latt ice, fiber and felt. The two directional felt conductivities - the lon gitudinal lambda(T), and the transversal lambda(T) ones - are modelled using a definite geometry of the felt texture and a previously introd uced expression for the constriction resistance of a fiber/fiber conta ct. lambda(T) depends on both components of fiber conductivity: axial lambda(A) (assumed to be equal to the longitudinal) and radial lambda( R). The geometrical parameters considered are: felt porosity, fiber to rtuosity, aspect ratio (fiber width to heigth), fiber mean size, conta ct spot size a and relative frequency of direct interlayer crossing, U . The experimental validation is currently only approximate, since mea surements of lambda(R), a and U are not accurate enough yet.