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Example for calculating NH with symbols and units
as = 315.5 W/(m 2 • K); DFLT = 59 mm; AL = 600 mm; Th = 150 0 C; cpm = 2 kj/(kg • K)
Stock temperature at the inlet of the screw increment considered:
T1n = 200 0 C
Nn from Equation 5.50:
315.5 -n -59.8 -600 -50 , ft^1TAT,i
NH = = -1.86 kW (heat loss from the melt)
10 6 -cosl7.66°
AT with the values Zc = 3.84 kW, ZFLT = 1.56 kW and th = 41.8 kg/h from the earlier
example from Equation 5.50
Stock temperature at the outlet of the screw increment considered Tout:
Tout=rM+ 152.4 0 C
Melting point of the polymer TM = 110 0 C
Hence, Tout =110 + 152.4 = 262.4 0 C
Average stock temperature T :
As already mentioned, this result can only be an estimate because the effect of the change
of temperature on the viscosity can be calculated only through an iterative procedure as
shown in [9].
5.2.2.5 Melt Pressure
For a screw zone of constant depth the melt or stock pressure can generally be obtained
from the pressure flow by means of Equation 5.29. However, the following empirical
equation [10] has been found to give good results in practice:
where
The sign of Ap corresponds to that of the pressure flow Qp.
(5.51)
(5.52)