Open slot area

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

Typical open-slot areas for moving valve trays are 14 to 15 percent of tfie bubbling area. Here the higher hole areas can be afforded due to the high turndown of the valves. 

Multipass Balancing There are two balancing philosophies equal bubbling areas and equal flow path lengths. Equal bubbling areas means that all active area panels on Fig. 14-21 d are of the same area, and each panel has the same hole (or open-slot) area. In a four-pass tray, one-quarter of the gas flows through each panel. To equalize the L/G ratio on each panel, the liquid needs to be split equally to each panel. Since the center weirs are longer than the side weirs, more liquid tends to flow toward the center weir. To equalize, side weirs are often swept back (Fig. 14-22b) while center weirs often contain picket fences (Fig. 14-22c). 

Open slot area, ASo (valve trays) the slot area when all the valve units are fully open. 

Cf = throughflow rate = unit capacity = open-area factor F, = slotted-area factor... 

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. 

A. = bubble-cop slot area, perforation sieve-troy Oreo, or volve-opening... 

A, = minimum cross-sectional area for downcoming liquid flow in finite-stage tower, ft2 Ar cross-sectional area of flow reactor, ft2 A, = bubble-cap slot area, perforation sieve-tray area, or valve-opening valve-tray area, ft2 A, = total cross-sectional area of tower, ft2 b = width of slot at base, ft B = nB/N0 in Eqs. (48), (49), (52), and (54) c = height of slot, ft C = Ncl/N0 in Eqs. (48) to (53)... 

A, = bubble-cap slot area, perforation sieve-tray area, or valve-opening valve-tray area,... 

Caps may be 2-8 in. in diameter or larger, but there is a performance advantage for the smaller 3 or 4 in. caps. The vapor slots are typically 0.25-0.50 in. wide, with total slot area perhaps 10% of the tower cross-sectional area. The vapor risers (Fig. 4) prevent liquid from flowing down through the openings in the tray. 

For nonfoaming systems, Ff = 1.0 for many absorbers, Fp may be 0.75 or even less. The quantity A is taken to be the area open to the vapor as it penetrates into the liquid on a tray. It is the total cap slot area for bubble cap trays and the perforated area for sieve trays. 

Figure 13.3 appears to be applicable to valve trays also. This is shown in Fig. 13.4 where entrainment flooding data of Fractionation Research, Inc. (FRI) -, for a 4-ft-diameter column with 24-in. tray spacing are compared to the correlation in Fig. 13.3. As seen, the correlation is conservative for these tests. For valve trays, the slot area A is taken as the full valve opening through which vapor enters the frothy liquid on the tray at a 90° angle with the axis of the column.

Transverse stopes are normally mined in three blasts, as illustrated in Figure 9. In primary stopes, the first two blasts widen the slot area to the full stope thiekness in 10 to 14 m lifts. For the stope final blast, the remaining blastholes are loaded full column, to a maximum charge per delay of 175 kg, and fired into the open slot. Typieally, the firsttwo slot blasts represent approximately 5% and 20%, respectively, of the total stope volume. The remaining 75% is broken in the third and final blast. 

A, = Active area, the area on the tray actively involved in gas/liquid contact, typically the column cross section less two downcomers, sq. ft Ah = Total slot, perforated, or open valve area on plate, sq. ft A = Net area for vapor flow, typically the column cross section less one downcomer (used for calculating U), sq. ft... 

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