Open balance point

The pressure drop remains essentially constant as long as the liquid flow on tray remains steady during the period point A to point B on the diagram (the open balance point) [201]. At point B all valves are completely open off their seats, but are on the verge of closing and may be oscillating from open to closed. At point B the vapor velocity through the holes, opened balance point is ... 

Vpt, B = vapor velocity through holes, open balance point, ft/sec... 

Coefficients for the Closed and Open Balance Point Equations Equations 8-311 and 8-312... 

F igure 14-36 illustrates the pressure drop of a typical moving valve tray as a function of gas velocity. At low velocities, all valves are closed. Gas rises through the crevices between the valves and the tray deck, with increasing pressure drop as the gas velocity rises. Once point A, the closed balance point (CBP), is reached, some valves begin to open. Upon further increase in gas velocity, more valves open until point B, the open balance point (OBP), is reached. Between points A and B, gas flow area increases with gas velocity, keeping pressure drop constant. Further increases in gas v ocity increase pressure drop similar to that in a sieve tray. 

For all valves fully open (above the open balance point)... 

Between the closed and open balance points, the dry pressure drop is constant (Fig. 6.216), and equals the pressure drop at either the closed or open balance points. Therefore, Eq. (6.44a) can be used, with uh in Eq. (6.42) set equal to the velocity at the closed balance point, u-uk cBp- Alternatively, Eq, (6.446) can be used with uh in Eq. (6.42) set equal to the velocity at the open balance point, uvh Qbp-Note that between the open and closed balance points the hole velocity at the relevant balance point, and not the actual gas velocity of gas through the holes, is used as uh in Eq. (6.42). 

OBP At open balance point of a valve tray (Sec. 6.3.2) point At a point on the tray S Superficial... 

Valve trays. Figure 6.216 illustrates the dry pressure drop of a t31>ical valve tray as a function of vapor velocity. At low vapor velodties, all valves are dosed (i.e., seated on the tray deck). Vapor rises through the crevices between the valves and the tray deck, and fiiction losses through these crevices constitute the dry pressure drop. Once the closed balance point (CBP) is reached, there is sufficient force in Uie rising vapor to open some valves, A further increase in vapor velodty opens more valves. Since vapor flow area increases as valves open, pressure drop remains constant until all valves open. This occurs at the open balance point (OBP). Further increases of vapor velodty cause the dry pressure drop to escalate in a similar manner to a sieve tray. When two weights of valves are used in alternate rows on the tray, a similar behavior applies to each valve type. The result is the pressure drop-vapor velocity relationship in Fig. 6.19c,... 

Bolles s (1976) design procedure uses the sieve tray design procedure as a basis and modifies it as necessary. One major difference between valve and sieve trays is in their pressure drop characteristics. The dry tray pressure drop in a valve tray is shown in Figure 10-23 fBolles. 19761. As the gas velocity increases, Ap first increases and then levels off at a plateau level. In the first range of increasing Ap, all valves are closed. At the closed balance point, some of the valves open. Additional valves open in the plateau region until all valves are open at the open balance point. With all valves open, Ap increases as the gas velocity increases further. The head loss in inches of liquid for both closed and open valves can be e q)ressed in terms of the kinetic energy. 

Figure 8-148. Typical operating valve tray pressure drop profile. Valves start to open at A, the closed balance point. Used by permission, Klein, G. F. Chem. Eng. V. 89, No. 9 (1982) p. 81 all rights reserved.

In order to determine whether the valves are fully open, fully closed or in between, and in order to apply the pressure drop equation between the open and closed balance points, the vapor hole velocities aft each balance point must be evaluated. The balance-point hole velocities are evaluated from a balance between the vapor force pushing the valve open and the gravity force tending to close it. This force balance gives (71,80)... 

The plant and buildings of the BWR 90 are laid out and designed to satisfy aspects of safety, maintenance and communication in a balanced way. The layout is strongly influenced by safety requirements, in particular the physical separation of safety-related equipment. With respect to building layout and arrangement ABB Atom has traditionally favoured a coordinated and compact building complex the number of doors and transport openings, release points, transport routes etc. can be kept low and supervision becomes easier. 

Figure 4.49 Application of open two-point edge nozzles in a 16-cavity mould for the production of aerosol caps [16] - theologically balanced mould...

For the gravity discharge case, the height of the fluid at maximum vacuum, which is the point at which air would begin to backflow into the tank, is determined by Eq. (26-54). Equation (26-55) calculates the corresponding vacuum in the tank s headspace at this hquid height. Since the drain nozzle is open to the atmosphere, this solution is a static force balance that is satisfied when the sum of the internal pressure and the remaining fluid head is equal to the atmospheric pressure. 

This means that thermostatic balanced pressure steam traps which open when their element senses a temperature somewhat below that of saturated steam at the pressure existing within the steam space are very effective when used as automatic air vents. They are connected to a steam space at any location where air will collect. Usually this means at any remote point from the steam entry, along the path the steam takes as it fills the steam space. 

Last but not least, one should check the inertness of the auxiliary electrodes in single-pellet arrangements, both under open and closed circuit conditions and, also, via the closure of the carbon balance, the appearance of coke deposition. This is especially important in systems with a variety of products (e.g. selective oxidations), where the exact value of selectivity towards specific products is of key interest. This in turn points out the importance of the use of a good analytical system and of its careful calibration. 

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