Thermal conductivity of composite

Fig. 7. Thermal conductivity of composites obtained using various densification processes.

Stelmakh O.I., Vovchenko L.L., Matzui L.Yu. Electrical and thermal conductivity of composite materials graphite- metal. Funct. Mater. 2004 11 546-550. 

The thermal conductivity k is a transport property whose value for a variety of gases, liquids, and solids is tabulated in Sec. 2. Section 2 also provides methods Tor predicting and correlating vapor and liquid thermal conductivities. The thermi conductivity is a function of temperature, but the use of constant or averaged values is frequently sufficient. Room temperature values for air, water, concrete, and copper are 0.026, 0.61, 1.4, and 400 W/(m K). Methods for estimating contact resistances and the thermal conductivities of composites and insulation are summarized by Gebhart, Heat Conduction and Mass Diffiision, McGraw-Hill, 1993, p. 399. 

H.J. Ott, Thermal conductivity of composite materials. Plastic and Rubber Processing and Application, 1, 9-24 (1981). 

The incorporation of fillers can induce modifications in the thermal properties of the polymers. Factors that affect the thermal conductivity of composites are the dispersion and orientation of the filler particles, the filler aspect ratio, and the relative ratio of thermal conductivity of the filler and the matrix. The thermal conductivity was found to be increased when the Ti02 volume fraction increases. The measured values of thermal conductivity have been compared to different theoretical models. 

Agarwal et al. [35] analysed the variation of thermal conductivity and thermal diffusivity of banana fibre-reinforced polyester composites caused by the addition of glass fibre. They observed that the thermal conductivity of composites increased when compared with the matrix. However, the thermal conductivity of the composites with increased percentage of glass fibre decreases in comparison to composite of pure banana fibre. 

Effect of fiber loading The thermal conductivity and thermal diffusivity of OPF-reinforced PF composites was less than that of pure resin. The thermal conductivity ( ) and thermal diffusivity (x) of xmtreated OPF-PF composite of 40% fiber loading was 0.29 W/mK and 0.16 mmVs, respectively where as the thermal conductivity and thermal diffusivity of pure PF were 0.348 W/m K and 0.167 mmVs, respectively [74]. The effective thermal conductivity of composite can also be predicted from individual thermal conductivities of fibers and matrix by employing different models [75]. The incorporation of OPF in PF matrix resulted in decrease of glass transition temperature [20]. This was due to higher void formation at higher fiber content as voids facilitate the chain mobility at lower temperatures resulting decrease in T value. 

Determination of thermal conductivity of composite wall apparatus... 

Hassehnan Diedricus P.H., and Johnson Lloyd F. Effective thermal conductivity of composites with interfacial thermal barrier resistance. /. Compos. Mater. 21 no. 6 (1987) 508-515. 

The axial thermal conductivities of composites reinforced with glass, aramid, boron, and a number of the carbon fibers are relatively low. In fact. E-glass and aramid PMCs are often used as thermal insulators. As Table 5.5 shows, most PMCs have low thermal conductivities in the transverse direction, as a result of the low thermal conductivities of the matrix and the fibers in the radial direction. Through-thickness conductivities of laminates tend to be similar to the transverse thermal conductivities of unidirectional composites. 

Fig. 3. The predicted effect of maximum packing fraction on the relative thermal conductivity of composites filled with spherical particles in which kf/k 1000, according to the Nielsen model...

Nielli s nKKfel was not devdoped to predict the bdmvior of fiber reinforced composites, except for the ca% of isotropic, very short fiber reinforced composites [33. It cannot adequately i edict the thermal conductivity of composites measured through the [dane when the fibers are randomly dispersed within the plane. 

Agari Y, Ueda A, Nagai S (1991) Thermal conductivities of composites in several types of dispersion systems. J Appl Polym Sd 42 1665-1669... 

Fig.7 Thermal conductivity of composites vs. filler content. Based on [40]...

Tanaka et al [43] have studied the effect of nanotubes thickness on the equivalent thermal conductivity of composites which has been evaluated by element free Galerkin method using different length of nanotube. The result of this study is shown in figures 9 10 ... 

In the previously available data, the effect of the interfacial thermal resistance on the effective thermal conductivity of composites has been studied, but this one does not discuss the relationship between chemical structure and the overall effective thermal conductivity. 

To conclude and as discussed above, the effect of the interface on the overall conductivity of composites plays an important role. The interface thickness has a small effect on the thermal conductivity of composite for short nanotubes, whereas interface has a significant effect for long nanotubes. 

Table 3 Effect of thickness and temperature on thermal conductivity of composites...

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