W 2945

Ah VfFh where

uh2 pv

It was recommended (12,56) that the clear liquid height hc in Eq. <6.33) be calculated using Colwell's (68) clear liquid height correlation (Sec. 6.3.3). The denominator of Eq, (6.33) contains the difference between liquid and vapor densities instead of the liquid density in the original Lockett and Banik correlation (56). This modification, incorporated by Colwell and O'Bara (58), has negligible effect at low pressure, but makes the correlation less conservative at high pressure.

Colwell and O'Bara (58) show that the Lockett and Banik correlation tends to give optimistic weep rate predictions near the weep point. They therefore recommended Eq. (6.32) only for hole Froude numbers smaller than 0.2. For larger Froude numbers, they proposed an alternative equation

Ah Frj;

Correlation limitations cited by Lockett and Banik (56) are

■ With large-diameter trays and low liquid loads, a small ratio of W!

Ah corresponds to a large fractional weep. Under these conditions, the correlation is inaccurate,

■ The correlation is unsuitable for trays with very small (< Vs in) holes.

■ The correlation appears to fit most data points to an accuracy of ± 15 to ±30 percent.

The Hsieh and McNulty correlation (63,69)

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