Thermally softened polymers heat transfer

EXPERIMENTAL AND EMPIRICAL STUDIES OF CONVECTIVE HEAT TRANSFER FOR LAMINAR FLOW OF MOLTEN OR THERMALLY SOFTENED POLYMERS... 

The earliest experimental studies of heat transfer to flowing molten or thermally softened polymers were the papers of Beyer and Dahl [31] and Schott and Kaghan [32]. These dealt mainly with determining the radial point at which temperature approximated the mass average fluid temperature. Later Bird [33] measured a few experimental points that did not check well with theory. Gee and Lyon [19] also indirectly checked their theory by showing that calculated and experimental average flow rates of a thermally softened polymer undergoing heat transfer compared favorably. 

The remaining investigations [36, 37, 41-45] made measurements in tube flow under more controlled conditions. The earliest of these efforts [36] found that temperatures could be measured quite precisely at a given circumference (deviation of only 0.5 C or less). This result for (Gz < 5) and subsequent corroboration in later studies [37, 41-45] showed that natural or free convection was not a problem in heat transfer to flowing molten or thermally softened polymers. In addition, evidence was found for both cooling by expansion and viscous dissipation. 

Heat-Transfer Data for Thermally Softened Polymer Systems... 

HEAT-TRANSFER DATA FOR THERMALLY SOFTENED POLYMER SYSTEMS... 

The temperature profile data for heat transfer to and from molten and thermally softened polymers give considerable insight into the intimate behavior of such systems. However, it is equally important to be able to treat the overall heat-transfer situation as well. These data can then be used for engineering evaluations and design purposes. 

Fig. 4-44 Effect of viscous dissipation on heat transfer to a thermally softened polymer [44]. B is modified Brinkman number.

Summarizing these microscopic examinations, transfer of heat resistant polymers onto the countersurface generally increases with temperature and much transferred materisl is produced when thermal softening of the polymer s-urface becomes severe. However, the amount of transferred material did not always increase with thermal softening of polymer frictional surface in the cases of PI and PAI. Although thermal softening of PI frictional surface at 200 C was clearly observed in electron microscopy, electron microscopic examination of the frictional track rubbed at 200 C indicated a relatively small amount of transferred material. On the other hand, transfer at 150 0 was considerably less than that at 100 and 200 0 in the case of PAI. 

Use the heat-transfer data for molten and thermally softened flowing polymer systems (i.e., Figs. 4-26-4-50) to fit the relation... 

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