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Unformatted text preview: and contractions. The original, or classical, venturi was invented by a U.S. engineer, Clemens
Herschel, in 1898. It consisted of a 21° conical contraction, a straight throat of diameter d
and length d, then a 7 to 15° conical expansion. The discharge coefficient is near unity, and
the nonrecoverable loss is very small. Herschel venturis are seldom used now.
The modern venturi nozzle, Fig. 6.39c, consists of an ISA 1932 nozzle entrance and
a conical expansion of half-angle no greater than 15°. It is intended to be operated in
a narrow Reynolds-number range of 1.5 105 to 2 106. Its discharge coefficient,
shown in Fig. 6.42, is given by the ISO correlation formula
Cd 0.9858 0.196 4.5 (6.136) It is independent of ReD within the given range. The Herschel venturi discharge varies
with ReD but not with , as shown in Fig. 6.41. Both have very low net losses.
The choice of meter depends upon the loss and the cost and can be illustrated by
the following table:
Type of meter Net head loss Cost Orifice
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08