4.1.3 Hydraulic Tray Pressure Drop
The weight of liquid on a tray is created by the weir height plus the crest height. We have defined the crest height (in inches of clear
liquid) in Chap. 3, as Crest height 0.4 (GPM/inch outlet weir length)0.67 The actual height of fluid overflowing the weir is quite a bit greater than we calculate with this formula. The reason is that the fluid overflowing the weir is not clear liquid, but aerated liquid—that is,
foam. The fluid on the tray deck, below the top of the weir, is also foam. This reduces the effective weight of the liquid on the tray due to aeration. To summarize, the weight of liquid on the tray, called the hydraulic tray pressure drop, is
Phyd AF WH 0.4 (GPM/inch outlet weir length)0.67 where Phyd hydraulic equipment tray pressure drop, in inches of clear liquid WH weir height, in AF aeration factor GPM gallons (U.S.) per minute The aeration factor AF is the relative density of the foam, to the density of the clear liquid. It is a combination of complex factors, but is typically 0.5.
The weight of liquid on a tray is created by the weir height plus the crest height. We have defined the crest height (in inches of clear
liquid) in Chap. 3, as Crest height 0.4 (GPM/inch outlet weir length)0.67 The actual height of fluid overflowing the weir is quite a bit greater than we calculate with this formula. The reason is that the fluid overflowing the weir is not clear liquid, but aerated liquid—that is,
foam. The fluid on the tray deck, below the top of the weir, is also foam. This reduces the effective weight of the liquid on the tray due to aeration. To summarize, the weight of liquid on the tray, called the hydraulic tray pressure drop, is
Phyd AF WH 0.4 (GPM/inch outlet weir length)0.67 where Phyd hydraulic equipment tray pressure drop, in inches of clear liquid WH weir height, in AF aeration factor GPM gallons (U.S.) per minute The aeration factor AF is the relative density of the foam, to the density of the clear liquid. It is a combination of complex factors, but is typically 0.5.
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