Temperature dependence of thermal conductivity

Fig. 6. The temperature dependence of thermal conductivity for CBCF in the as fabricated condition. Reprinted from [14], copyright 1996 Technomic Publishing Company, Inc., with permission.

Dinwiddle et al. [14] proposed a model for the behavior of the CBCF in which the temperature dependence of thermal conductivity (Aj-) may be expressed as... 

Fig. 10. The temperature dependence of thermal conductivity for pyrolytic graphite in three different conditions [66]. The reduction of thermal conductivity with increasing temperature is attributed to increasing Umklapp scattering of phonons.

This competition between electrons and the heat carriers in the lattice (phonons) is the key factor in determining not only whether a material is a good heat conductor or not, but also the temperature dependence of thermal conductivity. In fact, Eq. (4.40) can be written for either thermal conduction via electrons, k, or thermal conduction via phonons, kp, where the mean free path corresponds to either electrons or phonons, respectively. For pure metals, kg/kp 30, so that electronic conduction dominates. This is because the mean free path for electrons is 10 to 100 times higher than that of phonons, which more than compensates for the fact that C <, is only 10% of the total heat capacity at normal temperatures. In disordered metallic mixtures, such as alloys, the disorder limits the mean free path of both the electrons and the phonons, such that the two modes of thermal conductivity are more similar, and kg/kp 3. Similarly, in semiconductors, the density of free electrons is so low that heat transport by phonon conduction dominates. 

Figure 4.25 Temperature dependence of thermal conductivity for a pure metal (Cu) and a non-metal (Ge), illustrating different temperature dependences at low temperature. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission John Wiley Sons, Inc.

Figure 4.34 Temperature dependence of thermal conductivity for selected polymers. Reprinted, by permission, from P. C. Powell and A. J. I. Housz, Engineering with Polymers, p. 288. Copyright 1998 by P. C. Powell and A. J. I. Housz.

T <1K) glasses such as linear specific heat and the 7 18 temperature dependence of thermal conductivity [133,136-138],... 

Intense research has in recent years been devoted to noncrystalline materials. It was discovered also that the majority of semiconducting boron-rich borides display several properties that resemble those of the noncrystalline solids. Among the amorphous properties are the temperature and field dependencies of electrical conductivity at low temperature, the temperature dependence of thermal conductivity at high temperatures, and the temperature dependence of the magnetic susceptibility. In addition, the boron-rich semiconductors display crystalline properties, for example, the temperature dependence of the thermal condnctivity at low temperatures, the lattice absorption spectra and the possibility to change... 

Figure 22.4 shows the temperature dependence of thermal conductivity for AP along with two different compositions of HMXA ITON. The slopes of these plots are probably representative of most explosives. Table 22.2 gives thermal conductivity data for a number of different explosives. 

Figure 6. Temperature dependence of thermal conductivity of arc-melted silicon borides before and after heat-treatment at 1673Kfor 0.5hr.

S.K. Das, N. Putra, P. Thiesen and W. Roetzel, Temperature dependence of thermal conductivity enhancement for nanofluids, Journal of Heat Transfer, 125, 567-574 (2003). 

The temperature dependence of thermal conductivity for liquids, metal alloys, and nonconducting solids is more complicated than those mentioned above. Because of these complexities, the temperature dependence of thermal conductivity for a number of materials, as illustrated in Fig. 1,11, does not show a uniform trend. Typical ranges for the thermal conductivity of these materials are given in Table 1.1, We now proceed to a discussion of the foundations of convective and radiative heat transfer. 

TEMPERATURE DEPENDENCE OF THERMAL CONDUCTIVITY AND THERMAL DIFFUSIVITY FOR SOME POLYMERIC MATERIALS. 

Figure 7.6 Temperature-dependence of thermal conductivities of select MAX phases, (a) k ...

Figure 16.1 Temperature dependence of thermal conductivity, k, dominated by phonon transfer.

It is difficult to calculate thermal conductivity of oriented filled polymers, all the more to ascertain the temperature dependence of thermal conductivity ( ), thermal diffusivity (a), and specific heat (c). The calculation formulae cannot allow for such phenomena as the glass-transition of polymers, the possible lamination of polymer films due to the great discrepancy between the coefficients of linear expansion of the binder and filler, the effect of multiple thermal loading, etc. Therefore, most valuable are the experimental data on thermophysical properties of composite polymers in a wide temperature range (between 10 and 400 K). 

The effect of temperature dependence of thermal conductivity is relatively small actually, thermal conductivity increases about 2-3% per 10°C. 

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