Role of Interfacial Gaseous Heat Transfer in the Transverse Thermal Conductivity of a Uniaxial Carbon Fiber‐Reinforced Aluminoborosilicate Glass

Abstract

The transverse thermal conductivity of an aluminoborosilicate glass uniaxially reinforced with carbon fibers was found to be lower under near-vacuum than in nitrogen, whereas no such difference was found for the longitudinal thermal conductivity. This effect was attributed to the existence of an interfacial gap resulting from the thermal expansion mismatch between the matrix and fibers. The presence of this gap permits the gaseous environment access to the fiber-matrix interface and thereby contributes to the interfacial heat transfer. Its presence does not affect the longitudinal thermal conductivity, however, because the gap is aligned parallel to the fibers and, therefore, the direction of heat flow. Analysis of the experimental data indicates that, in nitrogen at atmospheric pressure, the gaseous conductance constitutes about one-third of the total interfacial conductance.

Effective Thermal Conductivity of Continuous Matrix-spherical Dispersed Phase Composite with Single-point Interfacial Thermal Contact: Continuum Regime Gas Conduction in the Gap

“…This effect is consistent with the expected closure of the gap when the temperature nears the one at which the composite was made, at which temperature the fiber and matrix were in full contact. Similar effects were observed for a 10 mm-diameter uniaxial carbon fiber-reinforced aluminoborosilicate glass investigated by Donaldson et al [13], which exhibited a value for the transverse thermal conductivity in nitrogen, some 20% higher than in near vacuum, with no such effect evident for a heat flow parallel to the fiber direction. Furthermore, as expected from gap closure with increasing temperature, the transverse thermal conductivity exhibited a more positive temperature dependence than either the glass matrix itself or the composite parallel to the fiber direction.…”

Effective Thermal Conductivity of Continuous Matrix-spherical Dispersed Phase Composite with Single-point Interfacial Thermal Contact: Free Molecular Gas Conduction in the Gap

“…It is therefore critical that a data base of the thermal conductivity of such composites be established for a range of conditions, including a variety of gas phases and range of pressures. Support for this recommendation is provided by the earlier experimental data of Bhatt et al [10] and Donaldson et al [11].…”

“…Interfacial separation was experimentally observed to play a significant role in composite thermal conductivity [10][11][12]. For a number of uniaxially fiber-reinforced brittle matrix composites, the thermal conductivity transverse to the fiber direction was found to be a function of the surrounding atmosphere, the lowest and highest values being found in a vacuum and helium, respectively, with intermediate values in an argon atmosphere.…”

Comment on “Inverse Problem for Composites with Imperfect Interface: Determination of Interfacial Thermal Resistance, Thermal Conductivity of Constituents, and Microstructural Parameters”

“…Similar interfacial gaps explain the observations of Bhatt et al 14 -16 for the dependence of the transverse thermal conductivity of SiC-fiberreinforced Si 3 N 4 -matrix composites on temperature and ambient atmosphere. The same theory applies to the thermal conduction behavior of carbon-fiber-reinforced aluminoborosilicate-glassmatrix composites that were investigated by Donaldson et al 17 Low-thermal-conductivity coatings on dispersed phases can also be regarded as thermal barriers. For such composites, the interfacial thermal resistance between the coating and the matrix and the dispersed phase may also need to be considered, as demonstrated by the study of Lu et al 18 However, none of these types of interfacial thermal barriers existed for the composites investigated by Russell et al: 2 the whiskers and matrix are considered to be in perfect thermal contact.Indirect proof for the existence of an interfacial thermal barrier for composites with direct mechanical contact between the phases may rely on the theoretical prediction that the thermal conductivity for such composites should be dependent on the dimensions of the dispersed phase.…”