Thermal Conductivity of Carbon Fibers

The thermal conductivity measurements of some glass fiber and carbon fiber reinforced plastics have been determined [144]. 

Pilling et al [145] determined the transverse thermal conductivities of Morganite HMS and HTS carbon fibers in a DX2IO/BF34OO matrix at 180 K, 225 K and 270 K and were found to be 2.0, 3.1 and 5.7 Wm K respectively. 

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Figure 2 Thermal conductivity of carbon fibers and various materials.

The thermal conductivity of carbon fibers shows the same general features as its electrical counterpart although there are much fewer data presently available. As shown in Figure 15 and Table V, the thermal conductivity of the best mesopitch based UHM carbon fibers (P-100, P-120 and P-140) is higher than those of copper and silver [3] [38] [61]. 

Keith, J. M. King, J. A. Miller, M. G. Tomson, A. M. Thermal conductivity of carbon fiber/ liquid crystal polymer composites. J. Appl Polym. Sci. 2006, 102, 5456-5462. 

Kim Y A, Kamio S, Tajiri T, Hayashi T, Song S M, Endo M, Terrones M and Dresselhaus M S (2007), Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes , Appl Phys Lett, 90, 093125(1)-093125(3). 

Electrical and thermal conductivities of carbon fibers cover wide ranges. For the most graphitic, ultrahlgh-modulus fibers, the electrical conductivity on a weight-specific basis Is within a factor of three of equalling steel. The absolute thermal conductivity (room temperature or below) exceeds that of copper (46]. 

Table 8.10. Thermal Conductivity of Carbon Fibers and Selected Metals...

During the 1980s, the development of PAN-based carbon fibers was driven by use in composites for military aircraft. Due to reduction in weight and improvement of performance, the carbon fibers used into sporting goods, medical devices, industrial applications, and infrastructure. Electrical and thermal conductivity of carbon fibers are also important in many applications. By increasing modulus electrical resistivity (pQ.cm) and thermal conductivity (W/mK) decrease and increase, respectively [201]. 

There is little available data to analyze the predictive at ty of these modek to evaluate the through-the-plane conductivity of composites in which tte fibers are randomly oriented within a plane. In Delmonte s text there is limited data on the thermal conductivity of carbon fiber reinforced polyamide 66 composites, measured through the thickness of the plane of orientation of the fibers [26]. This data is summarized in Table 3. The fiber aspect ratios were taken from Fig. 8, based on the assumption that sufficient 3-D mixing occurred in the compounding and injection molding machines to reduce the fibers to an aspect ratio compatible with the maximum fraction associated with a random isotropic condition. The Hatta and Taya model does quite well in predicting the thermal conductivity across the plane of fiber orientation for these composites. 

Table 3. Through-the plane thermal conductivity of carbon fiber reinforced polyamide 66 composites...

At RT, thermal conductivities of carbon fiber composites with high tensile fibers differ from those of high modulus fibers and are much higher than the thermal conductivity of the epoxy matrix. Below 7 K, they become similar within 25% and lower than the thermal conductivity of the epoxy matrix (37,47). The similarity is owing to the fact that at low temperatures only long phonon wavelengths are activated they cannot resolve different graphite microstructures of different carbon fiber types which are dominant at RT (36,43). In most cases, the specific heat of composites is lower than that of the polymeric matrix. 

Dinwiddie, R.B., Nelson, G.E., and Weaver, C.E., The effect of sub-minute high temperature heat treatments on the thermal conductivity of carbon-bonded carbon fiber (CBCF) insulation. In Proc. Thermal Conductivity 23, ed. K.E. Wilkes, R.B. Dinwiddie and R.S. Graves, Technomic Pub. Co., Inc., Lancaster, PA, 1996, pp. 466 477. 

Because direct calculation of thermal conductivity is difficulty 1], experimental measurements on composites with nanotubes aligned in the matrix could be a first step for addressing the thermal conductivity of carbon nanotubes. High on-axis thermal conductivities for CCVD high-temperature treated carbon fibers have been obtained, but have not reached the in-plane thermal conductivity of graphite (ref. [3], Fig. 5.11, p. 115). We expect that the radial thermal conductivity in MWNTs will be very low, perhaps even lower than the c-axis thermal conductivity of graphite. 

Aerospace and Technologies Corporation use carbon fiber to improve the weight and size of other more bulky heat transfer devices, while maintaining suitable thermal conductivity. Insulated carbon fiber can also be shaped and bent to fit the area involved while meeting the heat transfer requirements. 

Figure 16.2 Thermal conductivity versus carbon fiber volume percentage for aluminum reinforced with various kinds of carbon fiber (BP Amoco Thomel P-55, P-75, P-100, P-120 and P-140 in order of increasing modulus) in a cross plied configuration. Source Reprinted with permission from Thaw C, Minet R, Zemany J, Zweben C, SAMPE J, 23(6), 40-43, 1987. Copyright 1987, The Society for the Advancement of Material and Process Engineering (SAMPE).

Compared with glass fiber-reinforced plastics, the carbon fiber composites generally feature greatly improved tensile and flexural strengths and moduli. Thermal expansion of the carbon formulations is lower, and mold shrinkage ranges from about one-half to one-fifth that exhibited by the nonreinforced resin. Thermal conductivity of carbon composites is abont twice that of equivalent glass-reinforced formulations. 

Zamel et al. presented a study on the estimation of effective thermal conductivity of carbon paper GDL stmctures based on the aforementioned DNS formalism (Eq. 9.12). The 3D carbon paper GDL microstractures were reconstracted using the stochastic method by Schulz et al. They investigated the influence of fiber orientation, anisotropy, compression and binder fraction. Figure 9.27 shows the representative effective thermal conductivity prediction along with experimental data available in the literatirre." " ... 

Fig. 8. Comparison of electrical and thermal conductivity of PAN- and pitch-based carbon fiber to metals, where P = pitch, T = Thornel, and...

Fig. 18. The temperature dependence of the thermal conductivity of hybrid carbon fiber monoliths measured in the to fibers direction at two densities.

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