Cooling thermal properties

A number of mechanisms have been proposed by which this common irradiated state is obtained. The most widely accepted is the thermal spike theory, which considers the heat generated in the wake of a fast particle passing through a soHd as being sufficient to cause severe stmctural disturbances which are then fro2en in by rapid cooling. Many property changes can be explained by this theory (146). 

Thermal properties that affect the cooling of the polymer. 

Principles of the Processing of Plastics 8.2.6 Thermal Properties Affecting Cooling... 

Thermal Properties. Before considering conventional thermal properties such as conductivity it is appropriate to consi r briefly the effect of temperature on the mechanical properties of plastics. It was stated earlier that the properties of plastics are markedly temperature dependent. This is as a result of their molecular structure. Consider first an amorphous plastic in which the molecular chains have a random configuration. Inside the material, even though it is not possible to view them, we loiow that the molecules are in a state of continual motion. As the material is heated up the molecules receive more energy and there is an increase in their relative movement. This makes the material more flexible. Conversely if the material is cooled down then molecular mobility decreases and the material becomes stiffer. 

The cycle time is controlled by the heating and cooling rates, which in turn depend on the following factors the temperature of the heaters and the cooling medium, the initial temperature of the sheet, the effective heat transfer coefficient, the sheet thickness, and thermal properties of the sheet. 

The PCM sample and a sample with known thermal properties are subject to ambient air. Their temperature history upon cooling down from the same initial temperature to room temperature is recorded (Figure 160). A comparison... 

At first sight, it might appear preferable to use water as a cooling fluid since it has better thermal properties and lower viscosity. In practice, however, water had to be ruled out because of troublesome water electrolysis phenomena which can occur between windings of the solenoids when a voltage is applied accros the magnet. 

The thermal properties of fillers differ significantly from those of thermoplastics. This has a beneficial effect on productivity and processing. Decreased heat capacity and increased heat conductivity reduce cooling time [16]. Changing thermal properties of the composites result in a modification of the skin-core morphology of crystalline polymers and thus in the properties of injection molded parts as well. Large differences in the thermal properties of the components, on the other hand, lead to the development of thermal stresses, which also influence the performance of the composite under external load. 

The thermal properties of rubber are of very great importance, particularly in the processing stages, but there is a remarkable dearth of reliable data. Traditionally, the approach to heating and cooling problems was empirical rather than by careful analysis. The data needed for such analysis was not available, largely because of the undoubted experimental difficulties to be overcome but, even with data, somewhat complicated calculation is required. 

The thermal properties of the polymers reported in Table A.2 and Table A.3 were obtained by using a Perkin-Elmer Differential Scanning Calorimeter Model DSC-7 using a heating rate of 20°C/min. The specific heat was obtained using a heating rate of 10°C/min. For semicrystalline material, the heat of fusion was obtained from the measured specific heat curves. The crystallization temperature was obtained at 20°C/min cooling rate. 

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