HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
HANSER Hanser Publishers, Munich • Hanser Gardner Publications ...
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The use of thermal properties cp and p in design problems is illustrated in the examples<br />
given in Chapter 6.<br />
The expansion coefficient O^ at constant pressure is given by [4]<br />
The linear expansion coefficient Ce11n is approximately<br />
The isothermal compression coefficient yK is defined as [4]<br />
av and yK are related to each other by the expression [4]<br />
2.3 Enthalpy<br />
Equation 2.4 leads to<br />
(2.8)<br />
(2.9)<br />
(2.10)<br />
(2.11)<br />
(2.12)<br />
As shown in Figure 2.4, the measured data on h = h(T) [6] for a polymer melt can be<br />
expressed by the polynomial<br />
(2.13)<br />
The specific enthalpy defined as the total energy supplied to the polymer divided by<br />
throughput of the polymer is a useful parameter for designing extrusion and injection<br />
molding equipment such as screws. It provides the theoretical amount of energy required<br />
to bring the solid polymer to the process temperature.<br />
Values of this parameter for different polymers are given in Figure 2.5 [4].<br />
If, for example, the throughput of an extruder is 100 kg/h of polyamide (PA) and the<br />
processing temperature is 260 0 C, the theoretical power requirement would be 20 kW.<br />
This can be assumed to be a safe design value for the motor horse power, although<br />
theoretically it includes the power supply to the polymer by the heater bands of the<br />
extruder as well.