Coefficient of discharge

FIG. 10-19 Coefficient of discharge for square-edged circular orifices for Nrs > 30,000 with the upstream tap located between one and two pipe diameters from the orifice plate [Spitzglass, Trans. Am. Soc. Mech. Eng., 44, 919 (1922).]... 

FIG. 10-20 Coefficient of discharge for square-edged circular orifices with comer taps. [Tuve and Sprenkle, Instruments, 6, 201 (J.933),]... 

Accuracy Square-edged orifices and venturi tubes have been so extensively studied and standardized that reproducibihties within 1 to 2 percent can be expected between standard meters when new and clean. This is therefore the order of reliabihty to be had, if one assumes (1) accurate measurement of meter differenfial, (2) selection of the coefficient of discharge from recommended published literature, (3) accurate knowledge of fluid density, (4) accurate measurement of critical meter dimensions, (5) smooth upstream face of orifice, and (6) proper location of the meter with respect to other flow-disturbing elements in the system. Care must also be taken to avoid even sh t corrosion or fouliug during use. 

The coefficient of discharge method (Kj = 0.62) was specified to calculate the capacity of the rupture disc device. However, the validity of this method is limited to a disc mounted close to the pressure vessel and the discharging to atmosphere. The ASME Code provides guidance for the limited use of this method ... 

C capacity, coefficient of discharge, concentration d diameter (throat)... 

Coefficient of discharge A coefficient describing the actual discharge of a fluid jet compared to the theoretical discharge. 

Kj = valve coefficient of discharge (from valve manufacturer) Farris and Consolidated spring-operated,... 

K(j = valve coefficient of discharge = 0.92 for pilot-operated Pi = flowing pressure, psia MW = molecular weight of gas = 23.2 Z = compressibility factor = 0.9334 C - gas constant based on ratio of specific heats Cp/C ... 

Note Kd = effective coefficient of discharge for valve = 0.973 for equations above and Equations 7-25, 26, 27... 

Kti = coefficient of discharge (obtainable from the valve manufacturer). Kj is equal to 0.975 for sizing relief valves. 

The coefficient of discharge, Ko, is the actual flow divided by the theoretical flow and must be determined by tests for each type or style and size of rupture disk as well as pressure-relieving valve. For rupture disks, the minimum net flow area is the calculated net area after a complete burst of the disk, making allowance for any structural members that could reduce the net flow area of the disk. For sizing, the net flow area must not exceed the nominal pipe size area of the rupture disk assembly [1]. 

Kd = actual Hotv/theoretical flow = coefficient of discharge... 

K,j = coefficient of discharge, K = 0.62 for rupture disks, except some coefficients are different. For example, the Zook graphite standard ASME disks when tested mono-style, Figures 7-9B and 7-13A have a KD of 0.888, and when inverted, Figure 7-13B have a KD of 0.779. Consult manufacturer for special disks. 

K,h = steam superheat correction factor from Table 7-7 Kn = Napier steam correction factor for set pressures between 1500 and 2900 psig from Table 7-6 K = Kj = coefficient of discharge ... 

It is shown in Chapter 6 that the minimum flow area A2 tends to be somewhat smaller than the area Ao of the aperture because the gas leaves with a small radial inwards velocity component. Furthermore, there will be some reduction of discharge rate because of the frictional effects which have been neglected. Grouping these factors together by means of a coefficient of discharge Co, where Co < 1, gives ... 

Using a coefficient of discharge Co to take account of the frictional losses in the meter and of the parameters C, i, and ot2 ... 

Sulphuric acid of density 1300 kg/m3 is flowing through a pipe of 50 mm, internal diameter. A thin-lipped orifice, 10 mm in diameter is fitted in the pipe and the differential pressure shown on a mercury manometer is 0.1 m. Assuming that the leads to the manometer are filled with the acid, calculate (a) the mass flow rate of acid and (b) the approximate drop in pressure caused by the orifice in kN/m2. The coefficient of discharge of the orifice may be taken as 0.61, the density of mercury as 13.550 kg/m3 and the density of the water as OHIO kg/m ... 

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