Conducting polymers specific heat

The physical properties of nonnewtonian fluids necessary for the study of forced convection heat transfer are the thermal conductivity, density, specific heat, viscosity, and elasticity. In general these properties must be measured as a function of temperature and, in some instances, of shear rate. In the special case of aqueous polymer solutions it is recommended that all properties except the viscous and elastic properties be taken to be the same as those of water. 

THERMAL CONDUCTIVITY AND SPECIFIC HEAT OF SOME POLYMERS BETWEEN 4.5 AND 1 K. 

TABLE 53.4. Ignition temperature, thermal conductivity, and specific heats of polymers. ... 

As the measurements have shown, thermal properties of filled polymers depend considerably on filler orientation. Thermal conductivity and specific heat of glass plastics with formaldehyde and epoxy binder increase with increasing temperature, whereas thermal diffusivity falls in inverse proportion with temperature. The direction of the heat flux and orientation of the filler are responsible for the conductance and thermal diffusion in a given direction. Specific heat does not practically depend on the heat flux direction, since it characterizes the scalar value, i.e., energy accumulation. 

In the thermal breakdown in polymers, many factors influence the breakdown voltage geometry and size (especially thickness) thermal conductivity and specific heat of the polymer and associated materials ambient temperature rate of voltage increase or its steady value magnitude of tan S and its change with temperature magnitude of e and its change with temperature intrinsic... 

The specific heats of polymers are large - typically 5 times more than those of metals when measured per kg. When measured per m, however, they are about the same because of the large differences in density. The coefficients of thermal expansion of polymers are enormous, 10 to 100 times larger than those of metals. This can lead to problems of thermal stress when polymers and metals are joined. And the thermal conductivities are small, 100 to 1000 times smaller than those of metals. This makes polymers attractive for thermal insulation, particularly when foamed. 

Though short fiber-reinforced mbber composites find application in hose, belt, tires, and automotives [57,98,133,164] recent attention has been focused on the suitability of such composites in high-performance applications. One of the most important recent applications of short fiber-mbber composite is as thermal insulators where the material will protect the metallic casing by undergoing a process called ablation, which is described in a broad sense as the sacrificial removal of material to protect stmcrnres subjected to high rates of heat transfer [190]. Fiber-reinforced polymer composites are potential ablative materials because of their high specific heat, low thermal conductivity, and ability of the fiber to retain the char formed during ablation [191-194]. 

Metals have a sea of delocalized electrons that are not bound to specific nuclei, and these are responsible for both their high electrical and heat conductivities. Organic compounds do not ordinarily have such delocalized electrons, and are poor electrical and heat conductors. In fact, they are used to coat electrical wires as insulators. If polymers can be made to conduct, then they could be of a great deal of utility, as they are light, can be processed at low temperatures and pressures, and the raw material does not depend on metal mining. However, the possibility of a conducting polymer did not arise till very recent times. 

Polymer Thermal linear expansivity (10-= K-i) Specific heat capacity (kJkg-iK-i) Thermal conductivity (W m-i K-i)... 

The coefficient of linear expansion of unfilled polymers is approximately 10 X 10 5 cm/cm K. These values are reduced by the presence of fillers or reinforcements. The thermal conductivity of the polymers is about 5 X 10 4 cal/sec cm K. These values are increased by the incorporation of metal flake fillers. The specific heat is about 0.4 cal/g K, and these values are slightly lower for crystalline polymers than for amorphous polymers. 

The thermophysical properties, such as glass transition, specific heat, melting point, and the crystallization temperature of virgin polymers are by-and-large available in the literature. However, the thermal conductivity or diffusivity, especially in the molten state, is not readily available, and values reported may differ due to experimental difficulties. The density of the polymer, or more generally, the pressure-volume-temperature (PVT) diagram, is also not readily available and the data are not easily convertible to simple analytical form. Thus, simplification or approximations have to be made to obtain a solution to the problem at hand. 

Thermal and thermal storage properties are very important and they determine the limitation of any applications such as molecular electronics, and conducting polymer composites, and so on. The carbon nanotubes have a higher specific heat and a higher thermal conductivity than any other known materials. " " It is known that the heat transport in carbon nanotubes occurs through phonons.The electronic and phonon spectra of carbon nanotubes are quantized owing to their smaller diameter. Low-energy... 

Heat transport in connection with the removal of reversible heat TAS and irreversible Joule heat, may become an additional problem. In contrast to metals, organics and polymers (or at least the conventional, insulating ones) suffer from relatively low specific heat conductivities. Again, graphite pathways and minimized L improve this unfavorable situation to some extent. 

Transient conduction conditions occur in polymer processing. Appendix A derives Eq. (A.14) for one-dimensional transient heat flow, which contains the thermal diffusivity a. This is the combination k/pCp of the thermal conductivity k, density p and specific heat Cp. For most polymer melts a is approximately equal to O.lmm s" (Fig. 5.3). For the melting of low-density polyethylene in an extruder, typical conditions are a barrel temperature of To = 220 °C, an initial polymer temperature Tp = 20 °C, and a melting process complete at T = 120 °C. Consequently, using Eq. (C.19), after a contact time t, the melt front is at a distance from the barrel given by... 

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