Closed balance point

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.

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 closed (below the closed 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). 

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)... 

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,... 

A constant in the weeping rate equation, Eq. (6.36), dimensionless. Closed balance point for valve trays (Sec. 6.3.2). 

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. 

The closed balance point can be determined by noting that the pressure must support the weight of the valve, Wyaivg, in pounds. Pressure is where is the valve area in square feet. The pressure... 

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 ... 

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

Fig. 9.1. Multipurpose tensimeter. Since the standard taper joint is positioned close to the manometer, the joint is close to the balance point of the apparatus. The tensimeter is best supported by clamping at the taper joint and by resting the bottom of the tensimeter on a piece of foam in a small dish which in turn is supported by a ring clamp. The brace between the left arm of the manometer and the joint is held in place with epoxy cement and adds stability to the apparatus. The tensimeter is Tilled with mercury in the same manner as a U-manometer (see Fig. 7.1 caption). To minimize the votume of mercury, capillary tubing is used for the bottom and part of the teft leg.

In the stable region the barrier appears to be constant except close to the balanced point. We expect that the pic-tme changes in this respect when one also consider direct interactions between different patches of the film. 

Figure 9.3 shows the most clear-cut image of the macroemulsion inversion as a function of temperature equal volumes of oil and water are emulsified at various temperatures. Five hours after preparation, the macroemulsions sediment completely. Below the balanced temperature (HLB temperature), a stable O/W macroemulsion is formed, whereas above the balanced temperature a stable W/O emulsion is formed. Close to the balanced point (60-68 °C), a three-phase equilibrium is observed and neither O/W or W/O emulsions are stable. 

This has the same type denominator as the Bahner formula and when the other numbers are compared, it is found that the Bohr equation is essentially the same as the Balmer equation. There is only a slight difference due to the fact that the nucleus in the Bohr model is fixed at die center of the atom while the real spectra include the fact that the electron and proton both orbit around the center-of-mass (the see-saw balance point) of the two particles. That is really very close to the position of the proton because it is much more massive than the electron. When this correction is made to the Bohr formula, the agreement with the experimental spectra is essentially exact. 

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