Delay and Melting Zones

There appears to be no reliable mathematical model for predicting the length of the delay zone. Tadmor and Klein (1970), based on limited experimental data, found an empirical correlation between the number of turns (i.e., length of the delay zone) and a dimensionless parameter P, where P is defined later in Eq. 8.64 and represents the ratio of the rate melting to the mass flux of the solid bed in the channel. This relation is 

Pi is the pressure at the base of the hopper, which was calculated in Example 8.1. Thus, P2 is 2.52 X 10 Pa (36.5 psi). The solids conveying zone could in fact extend another turn or two until the surface reaches the melting point. Pm, of 

Based on observations, Tadmor and Klein made the following assumptions  

Melting takes place only at the barrel surface. (In some cases melting has been observed at the root and flights of the screw (Rauwendaal, 1986, p. 271).) 

The solid bed-melt film interface is assumed to be a distinct interface existing at the melting point, Tm, of the polymer. 

---