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Orifice Plates Sizing for Cases out of the Scope of ASME MFC-14M-2003 (low Re number and low β ratio)

Abstract

Differential-pressure flow measurements using flange orifices plates are most common to measure flows in gas seals support systems. An increasing measured flow or pressure indicates increasing gas seal leakage and possible problems of a gas seal. It is then critical to ensure that orifice plates are designed correctly and provide measurements with precise accuracy. Orifice meters sizing for that purposes is predominantly performed based on empirical and analytical formulas specified in ASME MFC-14M-2003. Recently, for economic and environmental reasons, measured flows are lower and below flows covered in the standard. Gas mass flows are relatively low, and therefore the calculated Reynolds numbers are outside the covered scope. Furthermore, to achieve measurable pressure drop for such gas flow, it is needed to use a small orifice bore for which its ratio to an internal pipe diameter is also out of the scope. Despite this, the industry still uses standard flange orifice plates because of their simplicity, low cost, and availability. This paper aims to check the possibility of calculating such flow cases with the help of CFD analysis. Performed analysis are in 3D domains for steady-state, turbulent and compressible flows. The computational models consist of upstream and downstream pipes of nominal diameters 1" and sharp-edged, bevelled, thin orifice plate. The publication also compares the pressure drop values and discharge coefficients calculated for orifice plates based on normative formulas outside the scope of their applicability to CFD analysis results. The analysed cases include flows for which the Reynolds number is below 1000 through orifice meters of a diameter ratio (β) less than 0.15. Additional measurement uncertainties or correction terms for orifices sized based on normative formulas for such flows can be calculated based on the presented results. The analysis are validated based on cases included in the standard. The conclusion is to assess whether orifice plates sizing considering computed uncertainties is acceptable or whether application of the correction terms is necessary.

Document Details

ReferenceNWC21-244-c
AuthorKonieczny. R
LanguageEnglish
TypePresentation Recording
Date 26th October 2021
OrganisationHPE 8 Sp. z o. o.
RegionGlobal

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