Delay zone

Delay zone(s) allowing intervening force the time to respond or time for operators to take evasive action before an adversary reaches a target following detection... 

The potential cause of these differences in melting mechanisms may be found in the pressure development in the delay zone as described by Kacir and Tadmor [59] and the source of the energy needed for melting. For the delay zone, it is generally... 

Kacir, L. and Tadmor, Z., Solids Conveying in Screw Extruders Part III The Delay Zone, Polym. Eng. Sci., 12, 387 (1972)... 

Returning to our pellet, we note the point where it reaches the end of the delay zone when the solid bed has acquired a small upward velocity toward the barrel surface. At some point in the extruder, our pellet will reach the melt film-solid bed interface, experiencing toward the end of this approach a quick (exponential) rise in temperature up to the melting point. After being converted into melt, our fluid particle is quickly swept... 

The Melting Zone As we pointed out earlier, from the axial location where a melt film is formed at the barrel surface (either as a result of barrel heating or as a result of heat generation due to friction), to the axial location where a melt pool appears at the pushing flight, lies the delay zone. The conveying mechanism in this zone is one of viscous drag at the barrel surface, determined by the shear stresses in the melt film and,... 

Solution In this example we know the location of the beginning of the melting zone from experimental data. As Fig. 9.24 indicates, melting starts at turn number 7. Hence, we can proceed with the SBP calculation without evaluating the length of the delay zone. The first step is calculating from Eq. 9.3-33. In the expression for , we have the variables Ut, U, and 6, which we calculate from Eqs. 9.3-35, 9.3-37, and 9.3-38, respectively, with b evaluated from Eq. 9.3-36 ... 

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... 

Delay Zone Length for LDPE. Using Eq. 8.36 and the data in Example 8.2, estimate the number of turns in the delay zone for LDPE. Use the rheological data given in Appendix A for NPE 953 (Table A.l). 

Finally, we note that there is usually a region preeeding the melting zone wherein a melt film exists but in the absenee of a melt pool. This is called the delay zone its length is small, typieally one to two serew turns [11]. Empirieal correlations exist for estimating the extent of the delay zone [3]. 

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