%MurNBcriticalflow102552; ]> Memorandum from Raymond L. Murray to Clifford Beck Machine readable transcription Murray, Raymond L. Creation of machine-readable version: Russell S. Koonts Creation of digital images: Russell S. Koonts Conversion to TEI.2-conformant markup: Russell S. Koonts ca. 9 kilobytes NCSU Libraries Raleigh, NC Modern English, MurNBcriticalflow102552

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 10 November, 2000

Nuclear Reactor Digitization Project

Raymond L. Murray Reactor Project Notebook

 Illustrations have been included from the print version. Scanned by Russell Koonts with Photoshop 5.0 software. Memorandum from Raymond L. Murray to Clifford Beck Raymond L. Murray

2 pp. Manuscript copy consulted UA 105.16

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Library of Congress Subject Headings October 25, 1952 English LCSH manuscript 24-bit color: 400 dpi Memorandum from Raymond L. Murray to Clifford Beck Handwritten 2 pp. October 25, 1952 MurNBcriticalflow102552

NCSC-56 Oct 25, 1952 C. K. Beck Critical Flow Orifices copy-file

This note reviews my findings on orifice restriction of gas flow.

Theory: the downstream speed of a gas through an opening is governed by Bernouillis theorem under the conditions of adiabatic flow. The discharge rate reaches a maximum however, when the pressure ration p2/p1 reaches a value rc such that on substitution in the velocity formula yields the velocity of sound. In c.g.s units the maximum flow is

where w is grams/sec, S2 is the aperture area, C is approx. 0.6, a discharge coefficient, p1 the upstream pressure in dynes/cm2 γ is Cp/Cγ = 1/4 for air, M is the molecular weight of air (29), R is the gas contant per mole, 8.3 x 107 erg-deg-1.

Substitution of the above numbers yields

where w1 is the flow in cm3/sec. For example, if w1 is to be 100 cm3/min = 1.67 cm3/sec, then the aperture area should be
the diameter is
or 0.14 mm.

Practice: The material on orifices in <abbr expan="Chemical">Chem.</abbr> <abbr expan="Engineering">Eng.</abbr> Handbook includes comments about the importance of shape of orifices in determining the flow. It would appear that the orifices should be constructed with diameters of the opening of the order of those calculated and tested under pressure conditions comparable to those expected, ie atmospheric on one side, low pressure on the other.

R L Murray.