Vapor Cross Section

The cross-sectional area for longitudinal flow of vapor will be the largest of the following:
1. An area equal to 10% of the vessel cross section.
2. The area which results when the vertical height above the maximum liquid level (Dimension “D” minus Dimension “H” in Figure 300-6) is equal to 12 inches.
3. The area determined by applying Equation 300-1. (Derate or use a higher value of velocity for less critical service as discussed in Section 331.)

Note that in this case the vapor moves horizontally and the liquid droplets settle out at right angles to the vapor flow. This would seem to be an advantage. However, it is partially offset by turbulence and entrance/exit effects. If the vapor flow area is to be determined by Equation 300-1, some designers use 125% of the allowable Gc; others use Gc directly. The latter practice is recommended.

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