Representative Thermal Property Values

A numerical heat transfer model of thin fibrous materials under high heat flux eonditions (bench-top burner) was developed by Torvi and Dale [37]. The model is applicable to two common, flame resistant fabrics, Nomex IIIA and Kevlar /PBI. A fabric-air gap-test sensor system (Figure 12.4) is used in which heat transfer is assmned to be one-dimensional. The fabric s thermal properties represent the average thermal property values of the fibrous stmcture. Mass transfer, hot gas flow and fabrie stmctural changes are not considered. The fabric s thermal properties are taken as fimetions of temperature only. The authors use energy balance equations and models of heat transfer modes to develop a differential equation (equation 12.26), and initial and boimdary conditions ... 

Figures 4-15-4-20 show some of the results obtained in the cases of Table 4-2. Figure 4-15 shows the effect of thermal expansion [17] for a non-Newtonian fluid (/I = 0.25) with negligible viscous dissipation and constant fluid properties. The various e values represent the average value of Te across the tube. As can be seen, the effect of thermal expansion or compressibility cooling is to depress the point temperatures in the center of the tube.

With these estimates, AG of the reaction above and AHf,29a(ThN) = -88.5 kcal/mol, the enthalpy of formation of Th2N20 is calculated using the thermal properties of Th [12] and of Th02 [11], O2 and N2 [13] as AHf = -303.0 kcal/mol. This value is lower in absolute magnitude than the previously given ones -321.7 [5, 7], -308 [11], and -322 kcal/mol [15]. The free energy of formation as calculated by the authors of this article from the same data by 3rd Law calculations is represented by the equation... 

Board material The FR-4 versus polyimide board material properties did not have a significant impact on trace temperature, which is determined primarily by the thermal conductivity of the dielectric laminate material construction. Table 16.2 lists measured thermal conductivity values for each of the test boards.The column labeled kz presents values through the thickness of the board and represents the resin thermal conductivity.The values in columns kx and ky are in-plane and the difference is attributed to the influence of the glass fiber. 

The crystalline structure of PVA has been discussed in detail by Bunn [14]. On a molecular level, the crystallites of PVA can be described as a layered structure [15, 16]. A double layer of molecules is held together by hydroxyl bonds while weaker van der Waals forces operate between the double layers. A folded chain structure of PVA chains leads to small ordered regions (crystallites) scattered in an unordered, amorphous polymer matrix. Values representative of the crystallinity and thermal properties of PVA have been reported [4]. The crystalline melting range of PVA is between 220 and 240 °C. The glass transition temperature of dry PVA films has been reported at 85 °C. In the presence of water (and other solvents), the glass transition temperature decreases significantly [2]. 

The concentration of maleic acid anhydride (MSA) in the resin influences both reactivity and with it the exothermic nature of curing as well as the crosslinking density of the cured resins that represents a base value for the mechanical-thermal property level,... 

Representative values of k for different materials are given in Table 11.4 together with other thermal properties. 

Polymer thermal properties are highly dependent on density, molecular weight, orientation, and other factors. Thus the values listed in the tables in this article should be considered to be representative but not necessarily absolute. 

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