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ASME MFC-7-2016 pdf download

ASME MFC-7-2016 pdf download.Measurement of Gas Flow by Means of Critical Flow Venturis and Critical Flow Nozzles.
1 SCOPE AND FIELD OF APPLICATION This Standard applies only to the steady flow of single-phase gases through critical flow venturis (CFV) of shapes specified herein [also sometimes referred to as critical flow nozzles (CFN), sonic nozzles, or critical flow venturi nozzles]. This Standard applies to CFVs with diverging sections on the downstream side of the throat. When a CFN (no diverging section) is discussed, it is explicitly noted. This Standard specifies the method of use (installation and operating conditions) of CFVs. This Standard also gives information necessary for calculating the mass flow of the gas and its associated uncertainty. This Standard applies only to CFVs and CFNs in which the flow is critical. Critical flow exists when the mass flow through the CFV is the maximum possible for the existing upstream conditions. At critical flow or choked conditions, the average gas velocity at the CFV throat closely approximates the local sonic velocity. This Standard specifically applies to cases in which (a) it can be assumed that there is a large volume upstream of the CFV or upstream of a set of CFVs mounted in a parallel flow arrangement (in a common plenum), thereby achieving higher flow; or (b) the pipeline upstream of the CFV is of circular cross section with throat to pipe diameter ratio equal to or less than 0.25 2 REFERENCES The following publications are referenced in this Standard. The latest editionofASME publications should be used. ASME MFC-3M, Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi ASME PTC 19.5, Flow Measurement Publisher: The American Society of Mechanical Engineers (ASME), Two Park Avenue, New York, NY 10016-5990 (www.asme.org) ISO 9300:2005, Measurement of gas flow by means of critical flow Venturi nozzles ISO/IEC Guide 98-3:2008, Uncertainty of measurement—Part 3: Guide to the expression of uncertainty in measurement Publisher: International Organization for Standardization (ISO) Central Secretariat, Chemin de Blandonnet 8, Case Postale 401, 1214 Vernier, Geneva, Switzerland (www.iso.org) NIST Standard Reference Database 23, NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP): Version 9.1 Publisher: National Institute of Standards and Technology (NIST), 100 Bureau Drive, Stop 1070, Gaithersburg, MD 20899 (www.nist.gov) 3 SYMBOLS AND DEFINITIONS 3.1 Symbols and Nomenclature See Table 3.1-1. 3.2 Definitions 3.2.1 Temperature Measurement measured gas temperature: temperature of the gas after being irreversibly brought to rest against the temperature probe.
(c) The material should be dimensionally stable and should have known and repeatable thermal expansion characteristics (if it is to be used at a temperature other than that at which the throat diameter has been measured), so throat diameter corrections and uncertainty estimates can be made. A period of time is generally required to achieve steady-state temperature conditions, and the flow reported by the CFV will change gradually as equilibrium is approached. The amount that the flow changes as steady state is approached depends on flow conditions, CFV geometry, ambient temperature conditions, gas type, and response time of the instrumentation. Generally, the time necessary to achieve steady state should be determined experimentally. 6.1.3 Surface Finish. The throat and toroidal inlet up to the conical divergent section of the CFV should be smoothly finished. Where it can be measured, the arithmetic average roughness height should not exceed 15 ? 10 −6 d. If the roughness cannot be measured the CFV should be flow calibrated. The throat and toroidal inlet up to the conical divergent section should be free from dirt, films, and other contamination. The form of the conical divergent portion of the CFV should be controlled such that any steps, discontinuities, irregularities, and lack of concentricity do not exceed 1% of the local diameter. If there is a diameter discontinuity in the divergent portion of the CFV, then the diameter should increase (not decrease) in the direction of flow. The arithmetic average roughness of the conical divergent section should not exceed 10 −4 d. 6.2 Standard CFV Geometries Two different designs are possible for standard CFVs: a toroidal throat design and a cylindrical throat design. The toroidal throat design is the most widely used and is the primary focus of this Standard. However, for completeness, guidance is also given for the cylindrical throat design. NOTE: Critical nozzles (i.e., CFNs with no divergent section) are not a recommended design (although they are allowed) due to poor pressure recovery and the greater possibility of flow performance being affected by downstream disturbances (i.e., flow pulsations). However, the same flow equations and discharge coefficients apply to CFNs as to CFVs.

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