User:Milton Beychok/Sandbox: Difference between revisions

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==Thin-plate orifices==
==Thin-plate orifices==


The flow of real gases through thin-plate, square-edged orifices never becomes fully choked.  The mass flow rate through the orifice continues to increase as the downstream pressure is lowered to a perfect vacuum, though the mass flow rate increases slowly as the downstream pressure is reduced below the critical pressure.<ref name=thin_plate_1>[http://www.engsoft.co.kr/download_e/steam_flow_e.htm Section 3 -- Choked Flow]</ref> Cunningham (1951) first drew attention to the fact that choked flow will not occur across a standard, thin, square-edged orifice.<ref name=thin_plate_2>[http://www.eng-tips.com/viewthread.cfm?qid=51260 Forum post on 1 Apr 03 19:37]</ref>
Experiments carried out by RG Cunningham (1951)<ref>{{cite journal|author=R.G. Cunningham|year=1951|month=|title=Orifice Meters With Supercritical Flow|journal=Trans. ASME |volume=73|issue= |pages=625-630|issn=}}</ref><ref>{{cite book|author=Richard W. Miller|title=Flow Measurement Engineering Handbook|edition=Third Edition|publisher=McGraw Hill|year=1996|isbn=0-07-042366-0}}</ref> demonstrated that the assumption that choked flow could occur for gases flowing through thin, square-edged orifice plates is not correct. The flow continued to increase as the downstream pressure was reduced to as low as 0.2 of the upstream pressure.<ref name=DKB>[http://members.ozemail.com.au/~denniskb/calcs/TECH%20MEMO_Y%20Factor.pdf Flow through Orifice Plates in Compressible Fluid Service at High Pressure Drop]</ref>  
<ref>{{cite book|author=Richard W. Miller|title=Flow Measurement Engineering Handbook|edition=Third Edition|publisher=McGraw Hill|year=1996|isbn=0-07-042366-0}}</ref>


Cunningham’s work included tests using air and steam with the results and conclusions presented as tables, charts and formulas. Limited information was provided for the tests with steam.<ref name=DKB/>


Critical flow can, however, be expected for thick orifice plates (i.e. plates with a thickness of at least 6 times the orifice hole diameter.<ref name=DKB/>
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Revision as of 19:54, 5 January 2009

Thin-plate orifices

Experiments carried out by RG Cunningham (1951)[1][2] demonstrated that the assumption that choked flow could occur for gases flowing through thin, square-edged orifice plates is not correct. The flow continued to increase as the downstream pressure was reduced to as low as 0.2 of the upstream pressure.[3]

Cunningham’s work included tests using air and steam with the results and conclusions presented as tables, charts and formulas. Limited information was provided for the tests with steam.[3]

Critical flow can, however, be expected for thick orifice plates (i.e. plates with a thickness of at least 6 times the orifice hole diameter.[3]

  1. ↑ R.G. Cunningham (1951). "Orifice Meters With Supercritical Flow". Trans. ASME 73: 625-630.
  2. ↑ Richard W. Miller (1996). Flow Measurement Engineering Handbook, Third Edition. McGraw Hill. ISBN 0-07-042366-0. 
  3. ↑ 3.0 3.1 3.2 Flow through Orifice Plates in Compressible Fluid Service at High Pressure Drop
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