Db

Tray above

Liquid and gasLiquid with bubbles -Tray below m\

FIG. 14-17 Schematic of a tray operating in the froth regime. (Based on H. Z. Kister, Distillation Design, copyright © 1992 by McGraw-Hill; reprinted by permission. )

net area represents the smallest area available for vapor flow in the intertray spacing.

Bubbling area AB (also called active area) The total tower cross-sectional area minus the sum of downcomer top area ADT, down-comer seal area ADB, and any other nonperforated areas on the tray. The bubbling area represents the area available for vapor flow just above the tray floor.

Hole area Ah The total area of the perforations on the tray. The hole area is the smallest area available for vapor passage on a sieve tray.

Slot area AS The total (for all open valves) vertical curtain area through which vapor passes in a horizontal direction as it leaves the valves. It is a function of the narrowest opening of each valve and the number of valves that are open. The slot area is normally the smallest area available for vapor flow on a valve tray.

Open slot area ASO The slot area when all valves are open.

Fractional hole area Af The ratio of hole area to bubbling area (sieve trays) or slot area to bubbling area (valve trays).

Vapor and Liquid Load Definitions

F-factor F This is the square root of the kinetic energy of the gas, defined by Eq. (14-76). The velocity in Eq. (14-76) is usually (not always) based on the tower cross-sectional area AT, the net area AN, or the bubbling area AB. The user should beware of any data for which the area basis is not clearly specified.

C-factor C The C-factor, defined in Eq. (14-77), is the best gas load term for comparing capacities of systems of different physical properties. It has the same units as velocity (m/s or ft/s) and is directly related to droplet entrainment. As with the F-factor, the user should beware of any data for which the area basis is not clearly specified.

Pg Pi Pg

Weir load For trays (as distinct from downcomers), liquid load is normally defined as

volume of liquid

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