Thermal conductivity, dependence

The glass-transition temperature, T, of dry polyester is approximately 70°C and is slightly reduced ia water. The glass-transitioa temperatures of copolyesters are affected by both the amouat and chemical nature of the comonomer (32,47). Other thermal properties, including heat capacity and thermal conductivity, depend on the state of the polymer and are summarized ia Table 2. 

Thermal Conductivity. The refractory thermal conductivity depends on the chemical and mineral composition of the material and increases with decreasing porosity. The thermal conductivities of some common refractories are shown in Figure 2. 

Frequently, the transport coefficients, such as diffusion coefficient or thermal conductivity, depend on the dependent variable, concentration, or temperature, respectively. Then the differential equation might look like... 

Y. B. Zel dovich and A. S. Kompaneets, On the theory of propagation of heat with thermal conductivity depending on temperature, in Collection of Papers Dedicated to the 70th Birthday of A.F. Yoffe, Izd. Akad. Nauk SSSR, Moscow (1947), pp. 61-71. 

The thermophysical properties of a foam heat capacity and thermal conductivity, depend on the total liquid content and its distribution in the foam. The bubbles shape and distribution of liquid between borders, films and vertexes also affect thermal conductivity. By definition the bulk heat capacity CV (at p - const) equals... 

The most important property for insulation is thermal conductivity. The following transport types participate in the transmission of heat heat conduction in PS, heat conduction in the filling gas (air), radiation heat transfer and heat convection by convection flows in the closed cells. The thermal conductivity of the air in the cells contributes the most to the total heat transport. The radiation fraction depends on the diameter of the cells formed. The thermal conductivity depends on the density of the foamed PS material. Thermal conductivity decreases with increasing bulk density, reaches a minimum and then rises again (Figure 9.15). The following processes are responsible for this characteristic. 

For binary and multicomponent mixtures, the thermal conductivity depends on the concentrations as well as on temperature, and the formulas of the accurate kinetic theory are quite complicated [5]. Empirical expressions for X are therefore more useful for both binary [9] and ternary [6], [26] mixtures, although few data exist for ternary mixtures. Tabulations of available experimental and theoretical results for thermal conductivities may be found in [5], [6], [13], and [18]-[21], for example. The thermal diffusivity, defined as 2p/Cp, often arises in combustion problems its pressure and temperature dependences in gases are XjpCp T7p ( < a < 2), and its typical values in combustion lie between 10 cm /s and 1 cm s at atmospheric pressure. 

L. S. Kowalczyk. Trans. Am. Soc, Mech. Engrs. 77, 1021-35 (1955). Thermal conductivity dependence on temperature and pressure. 

Gomes, C.J., M. Madrid, and C.H. Amon. Thin Film In-Plane Thermal Conductivity Dependence on Molecular Dynamics Surface Boundary Conditions, in Proceedings of the 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE 2004-62264. 2004. Anaheim, CA. 

The heat flux due to thermal conduction depends on the temperature gradient and the area according to Fourier s first law (Equation 2.3.1-6a) ... 

When there are two axes of heat transfer, x and y, with the two values of the thermal conductivity dependent on the axis, the differential equation of heat conduction ... 

The thermal conductivity depends on the mean free path of the phonons, which is the distance between collisions of the phonons in the stmcmre. A short mean free path correlates with a low thermal conductivity. Defects in a stmcmre drastically shorten the mean free path and reduce thermal conductivity significantly. An inherent problem with ceramic materials is that they are usually formed by sintering. This process naturally leads to the formation of many internal defects such as grain boundaries, pores and voids. Because of this, the thermal conductivity of sintered bodies is usually much lower than the intrinsic thermal conductivity. Fired-clay ceramics have very high porosity and a very low thermal conductivity. At... 

In addition to the type of filler, thermal conductivity depends on many other factors including the amount of filler used, whether it is by weight or by volume, its form and size, the surface treatment of the filler particles, the completeness of cure, and the test conditions used for measurement. Test methods are described in MIL-STD-883, Method 1012.1 and in ASTM C518. ... 

Thermal-transfer adhesives that are electrically insulating also exhibit wide ranges of thermal conductivities, depending on the filler type and amount. The thermal conductivities of epoxies filled with boron nitride or diamond are approximately 4 W/m K and 12 W/m K, respectively, while those of the more common aluminum-oxide-filled adhesives range from 1 to 2 W/m K. 

As mentioned in Chapter 1, thermal conductivity depends on microstructure. Anything that changes the local atomic arrangement or induces elastic strains in the lattice will decrease 1. 

Fig. 3.1 (a) Constant pressure heat capacity dependence upon pressure and temperature, (b) Thermal conductivity dependence upon pressure and temperature, (c) Dynamic viscosity dependence upon pressure and temperature. 

The thermal conductivity dependence of the resulting nanofluids on O2/CH4 ratios in plasma... 

Note in the table that copper-clad Invar has both variable Tg, and variable thermal conductivity depending on the volume mix of copper and Invar in the substrate. Copper has a high TCE, and Invar has a low TCE, and so the TCE increases with the thickness of the copper layers. In addition to heat transfer considerations, board material decisions must also be based on the expected stress and humidity in the application. 

In the case of amorphous polymers, the phonon mean free path is an extremely small constant (a few angstroms) due to phonon scattering from numerous defects, leading to a very low thermal conductivity of polymers (Agari et al. 1997). The thermal conductivity depends on the degree of crystallinity because vibration and movement/rotation of macromolecular chains transfer heat energy. 

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