Coefficient orifice

Knowledge-based systems typically use quaHtative methods rather than quantitative ones. For example, consider a simple tank system. The equation describing the flow rate of Hquid out of the tank is given below, where C is the orifice coefficient, d is the diameter of the orifice, and h is the height of Hquid in the tank. Based solely on the form of the equation, a human reasoner can infer that the flow rate F increases monotonically with the height b of Hquid in the tank. 

To reflect this type of reasoning, a KBS captures quaHtative relationships between variables. By contrast, a conventional program that implements the flow equation calculates the value of the flow rate for numerical values of the input variables, ie, orifice diameter, orifice coefficient, and Hquid height. 

FIG. 6-19 Orifice coefficient vs. Fronde number. (Couttesy E. I. duVont de Nemours [Pg.648]

The orifice coefficient has a value of about 0.62 at large Reynolds numbers (Re = D V p/ > 20,000), although values ranging from 0.60 to 0.70 are frequently used. At lower Reynolds numbers, the orifice coefficient varies with both Re and with the area or diameter ratio. See Sec. 10 for more details. 

The orifice coefficient deviates from its value for sharp-edged orifices when the orifice wall thickness exceeds about 75 percent of the orifice diameter. Some pressure recovery occurs within the orifice and the orifice coefficient increases. Pressure drop across segmental ori-fiees is roughly 10 percent greater than that for concentric circular orifices of the same open area. 

Co Orifice coefficient Dimensionless Dimensionless dispersed phase ... 

Figure 8-128. Orifice coefficient for perforated trays. Used by permission, Hughmark, G. A., and O Connell, H. E., The Americsn Institute of Chemical Engineers, Chem. Eng. Prog., V. 53, (1957), p. 127M, all rights reserved.

Orifice coefficient. Figure 8-129, read at 0.41 tray/hole gives Cq orifice coefficient = 0.75 Hole velocity = 347/8.66 = 40.06 fps Dry Tray pressure drop... 

Ch = specific heat of trapped fluid, Btn/lb/°F Co = subsonic flow constant for gas or vapor, function of k = cp/cv, Table 7-11 c = orifice coefficients for liquids... 

It is evident that the orifice coefficient incorporates the effects of both friction loss and velocity changes and must therefore depend upon the Reynolds number and beta ratio. This is reflected in Fig. 10-8, in which the orifice (discharge) coefficient is shown as a function of the orifice Reynolds number (NR d) and... 

The orifice coefficient shown in Fig. 10-8 is valid to within about 2-5% (depending upon the Reynolds number) for all pressure tap locations except pipe and vena contracta taps. More accurate values can be calculated from Eq. (10-10), with the parameter expressions given in Table 10-1 for the specific orifice and pressure tap arrangement. 

Square-edge orifice coefficients, calculation of, 11 659 Square planar... 

K = an orifice coefficient, which can be as low as 0.3 for a smooth hole in a thick plate and 0.6 to 0.95 for various valve tray caps... 

V = velocity of the fluid through the orifice plate, ft/s D, = density of the fluid, whether vapor or liquid, lb/ft3 a = an orifice coefficient... 

You should look up the orifice coefficient K in your Cameron or Crane handbook—but it is typically a number like 0.6 to 0.8. 

The orifice coefficient K takes into account both frictional pressure losses, and conversion of pressure to velocity. The frictional losses represent an irreversible process. The conversion of pressure to velocity represent a reversible process. 

K0 = an orifice coefficient for a hole in metal plate, typically 0.4 to 0.6... 

High Viscosity and Surface Tension Bravo (Paper presented at the AIChE Spring National Meeting, Houston, Tex., 1995) studied a system that had 425-cP viscosity, 350 mN/m surface tension, and a high foaming tendency. He found that efficiencies were liquid-phase-controlled and could be estimated from theoretical HTU models. Capacity was less than predicted by conventional methods which do not account for the high viscosity. Design equations for orifice distributors extended well to the system once the orifice coefficient was calculated as a function of the low Reynolds number and the surface tension head was taken into account. 

The velocity based on the hole area is v . The pressure Pi is the pressure upstream of the orifice, typically about 1 pipe diameter upstream, the pressure P2 is the pressure at the vena contracta, where the flow passes through a minimum area which is less than the orifice area, and the pressure P3 is the pressure downstream of the vena contracta after pressure recovery associated with deceleration of the fluid. The velocity of approach factor 1 — (AJA)2 accounts for the kinetic energy approaching the orifice, and the orifice coefficient or discharge coefficient C accounts for the vena contracta. The location of the vena contracta varies with AJA, but is about 0.7 pipe diameter for AJA < 0.25. The factor 1 — AJA accounts for pressure recovery. Pressure recovery is complete by about 4 to 8 pipe diameters downstream of the orifice. The permanent pressure drop is Pi — P3. When the orifice is at the end of pipe, discharging directly into a large chamber, there is negligible pressure recovery, the permanent pressure drop is Pi — P2, and the last equality in Eq. (6-111) does not apply. Instead, P2 = P3. Equation (6-111) may also be used for flow across a perforated plate with open area A and total area A. The location of the vena contracta and complete recovery would scale not with the vessel or pipe diameter in which the plate is installed, but with the hole diameter and pitch between holes. 

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