Large flight clearance

Due to the high cost of replacing the feed casing and the lack of direct evidence that the ledge and large flight clearance were the root cause of the reduced rate, an alternative experiment needed to be developed that simulated the process. Without these data plant personnel were unwilling to replace expensive components and incur downtime based on indirect evidence. 

The bracketed term on the right-hand side of Eq. 7.404 can be used to as a correction term in Eqs. 7.381 through 7.400 to incorporate the effect of the power dissipated in the flight clearance. Obviously, for polymers with a relatively large value of the power law index, the correction can be significant. 

We can use the expressions above to determine the minimum X value that will yield a Go less than 0.01, meaning that less than 1% of the fluid will not pass through the clearance at all. This is achieved when the dimensionless time X > 4.6. For certain values of L, H, W, r, cp, and w, we can then determine how large the flight clearance 8 has to be to make A, > 4.6 or Go < 0.01. The passage distribution function for A, = 4.6 is shown in Fig. 8.86(b). 

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