##### From Chemical Engineering License Review, Second Edition

## Permanent Pressure Loss

**Venturi** Permanent pressure loss through venturis depends upon the diameter ratio ? and the discharge cone angle ?. The pressure loss for smaller angles (5 to 7 ) is 10 to 15 percent of the total pressure differential ( *P* _{1} ? *P* _{2}). It is 10 to 30 percent for large angles (> 15 ).

**Subsonic Flow Nozzles** For subsonic flow nozzles, the pressure loss is given by

where ? is the nozzle throat diameter divided by the pipe diameter.

**Concentric Circular Nozzles** In the case of the concentric circular nozzle,

A venturimeter is to be installed in a schedule 40, 6-in line to measure the flow of water. The maximum rate is expected to be 800 gpm at 86 F. A 50-inHg manometer is to be used. Specify the throat diameter of the venturi and calculate the power required to operate it. The discharge cone angle is 5 .

** Solution.** From Eq. (2-14),

*C* = 0.98 for venturis if *N* _{Re} > 10,000 (i.e., fully turbulent flow). Assume fully turbulent flow. Then

where *D* _{ P} is the inside diameter of pipe, ft. Squaring both sides, one obtains

Simplifying and solving for *D* _{ T} gives

Use 2.375 in = 0.1979 ft (a standard size). Check the Reynolds number through the throat of the venturi.

This *N* _{Re} is greater than 10,000 and therefore the flow is in the fully turbulent region. Therefore, the size of...

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