Specific heat and thermal conductivity

If we assume (from heat release data, see helow) t/min = 10 ° for PMMA and Mmin = 6 X 10 ° for PS and from the measured ci we obtain a density of states P = 4.0 x 10 (7.5 X 10 ) 1/Jg for PMMA (PS) in reasonable agreement with the values obtained in earlier specific heat measurements [17] and also from acoustic measurements for PMMA [24]. Recent optical hole burning experiments on PMMA and PS [15] indicate that the density of states of TS for PS is about two times larger than for PMMA in reasonable agreement with our specific heat measurements. 

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Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

The hydrogen content, heat of combustion, specific heat, and thermal conductivity data herein were abstracted from Bureau of Standards MisceUaneous Pubhcation 97, Thermal Propei tie.s of Petroleum Products. These data are widely used, although other correlations have appeared, notably that by Linden and Othmer Chem. Eng. 54[4, 5], April and May, 1947). 

Figure 10-47. Flow inside tubes for gas and vapors. Physical property factor depends on viscosity, specific heat, and thermal conductivity. (Used by permission Ning Hsing Chen, Chemical Engineering, V. 66, No. 1, 1959. McGraw-Hill, Inc. All rights reserved.)...

The performance of soluble oils is made possible not only by their high specific heat and thermal conductivity but by their low viscosity, which permits good penetration into the very fine clearances around the cutting zone. Consequently, these fluids are used mainly where cooling is the primary requirement. Lubricating properties can be improved by polar additives, which are agents that enhance the oiliness or anti-friction characteristics. Further improvements can be effected by EP (extreme-pressure) additives, which are usually compounds of sulfur or chlorine. 

Zhang Yinping, Jiang Yi, 1998. A simple method, the T-history method, of determining the heat of fiision, specific heat and thermal conductivity of phase-change materials, Meas. Sci. Technol., 10, 201-205. 

The transport of heat in metallic materials depends on both electronic transport and lattice vibrations, phonon transport. A decrease in thermal conductivity at the transition temperature is identified with the reduced number of charge carriers as the superconducting electrons do not carry thermal energy. The specific heat and thermal conductivity data are important to determine the contribution of charge carriers to the superconductivity. The interpretation of the linear dependence of the specific heat data on temperature in terms of defects of the material suggests care in interpreting the thermal conductivity results to be described. 

Using Equations 5.53-5.56 a three-dimensional non-isothermal simulation of a typical IP process has been performed using a finite element control volume technique [31,34-36], The density specific heat and thermal conductivity of the resin and reinforcement used in the simulations are given in Table 5.1. 

No term is included in this equation which might account for the relative quantities of the two phases present, except in the viscosity and density terms. Obviously the specific-heat and thermal conductivity terms must also depend on the relative quantities of the two phases present, as well... 

The specific heat and thermal conductivity.—A. Campetti33 found the thermal... 

A natural application of the Green s function approach is to the case where the density, specific heat, and thermal conductivity remain essen-... 

This leads to a powerful method when the densities, specific heat, and thermal conductivity can be assumed to have constant average values throughout the entire solid-liquid region. In this case, the moving boundary can be considered to be a source surface. As an example, consider the freezing of a semi-infinite region occupied by liquid with arbitrary initial and surface temperature and conditions. In this case Eq. (159) becomes... 

Taking the heat transfer coefficient, h, as a function of the fluid velocity, density, viscosity, specific heat and thermal conductivity, u, p, p, Cp and k, respectively, and of the inside and outside diameters of the annulus, di and do respectively, then ... 

There is no difference in chemical and physical properties between para- and ortho-hydrogen except at low temperatures as regards specific heat and thermal conductivity. The transformation into para-H2 at low temperatures only takes place after adsorption on charcoal. The reverse reaction occurs at room tempera-... 

It is also unfortunately true that our detailed knowledge of specific heats and thermal conductivities both for multicomponent systems and at the temperatures in question is hardly quantitative. 

The combustion mechanism addressed involves inert heat conduction in the solid, surface gasification by an Arrhenius process and a gas-phase deflagration having a high nondimensional activation energy. With the density, specific heat, and thermal conductivity of the solid assumed constant, the equation for energy conservation in the solid becomes... 

The specific heat and thermal conductivity of extruded cordierite substrates are relatively insensitive to wall porosity and substrate temperature. Their average values are [22] ... 

Thermal Properties.—The thermal qualities of refractories, specific heat, conductivity and expansion are determined according to the established physical methods. It is evident that these properties are of considerable practical importance. The data available, however, on these subjects are quite meager, especially if it is considered that the structure of the manufactured product, irrespective of its chemical nature, is of paramount importance. Furthermore, these properties are subject to change with temperature and comparatively few constants are at hand to illustrate the character of these relations. It is known that the specific heat and thermal conductivity increase with temperature but the fundamental laws governing these changes have not been established. Furthermore, it must be realized that the structure of all these materials is certain to undergo physical changes which affect the thermal qualities. 

Molten lithium metal is a potential candidate for the coolant to be circulated through the blanket. Lithium is a light metal with a low melting point (186 degrees Celsius). In the liquid state, it has a high specific heat and thermal conductivity. These properties make it an excellent heat transfer material and thus, a good choice as a means of removing heat from the reactor. When lithium is used in the blanket for heat transfer it also serves as the primary absorber of the 14,100 keV neutrons from the D + T reaction. 

When an FEA model is run, several elements must be present. These include the CAD data, material properties, loads acting on the part, and the boundary conditions used. Table 4.3 shows the typical input to conduct an analysis through one of the software programs. The minimum input for structural analysis is the modulus of elasticity, Poisson ratio, and density. For thermal predictions, the minimum inputs are coefficient of thermal expansion, specific heat, and thermal conductivity. For modal analysis, the minimum inputs are modulus of elasticity, Poisson ratio, and density. 

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