Chapt06

# 638 velocity and pressure change through a

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Unformatted text preview: m Eq. (6.125) is the desired solution to the fluid-metering problem. The mass flow is related to Q by m ˙ Q (6.131) and is thus correlated by exactly the same formulas. Figure 6.39 shows the three basic devices recommended for use by the International Organization for Standardization (ISO) [31]: the orifice, nozzle, and venturi tube. Thin-plate orifice. The thin-plate orifice, Fig. 6.39b, can be made with in the range of 0.2 to 0.8, except that the hole diameter d should not be less than 12.5 mm. To measure p1 and p2, three types of tappings are commonly used: | v v 398 | e-Text Main Menu | Textbook Table of Contents | Study Guide 6.10 Fluid Meters 399 Ellipse 2d 3 d Bevel angle: 45° to 60° 0.6 d d Flow D d Flow Edge thickness: 0.005 D to 0.02 D t2 < 13 mm Plate thickness: up to 0.05 D t1 < 0.15 D (b) (a) ISA 1932 nozzle shape Fig. 6.39 International standard shapes for the three primary Bernoulli obstruction-type meters: (a) long radius nozzle; (b) thinplate orifice; (c) venturi nozzle. (From Ref. 31 by permission of the I...
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