ISA 75.01.01-2002 (IEC 60534-2Mod)
- Flow Equations for Sizing Control Valves
- standard by The International Society of Automation, 07/03/2002
- Category: ISA
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Scope
ANSI/ISA-75.01.01-2002 includes equations for predicting the flow coefficient of compressible andincompressible fluids through control valves.
The equations for incompressible flow are based on standard hydrodynamic equations for Newtonianincompressible fluids. They are not intended for use when non-Newtonian fluids, fluid mixtures, slurries, orliquid-solid conveyance systems are encountered.
At very low ratios of pressure differential to absolute inlet pressure (D P/ P1), compressible fluids behavesimilarly to incompressible fluids. Under such conditions, the sizing equations for compressible flow can betraced to the standard hydrodynamic equations for Newtonian incompressible fluids. However, increasingvalues of D P/ P1 result in compressibility effects that require that the basic equations be modified byappropriate correction factors. The equations for compressible fluids are for use with gas or vapor and arenot intended for use with multiphase streams such as gas-liquid, vapor-liquid or gas-solid mixtures.
For compressible fluid applications, this part of ANSI/ISA-75.01.01-2002 is valid for all valves. However,manufacturers of some valves with xT ? 0.84 have reported minor inaccuracies (see Annex H). Cautionmust also be exercised when applying the equations for compressible fluids to gaseous mixtures ofcompounds, particularly near phase boundaries.
The accuracy of results computed with the equations in this standard will be governed by the accuracy ofthe constituent coefficients and the process data supplied. Methods of evaluating the coefficients used inthe equations presented herein are given in ANSI/ISA-75.02-1996. The stated accuracy associated withthe coefficients in that document is ?5% when Cv / d 2 < 0.047 N18. Reasonable accuracy can only bemaintained for control valves if C / d 2 < 0.047 N18.
ANSI/ISA-75.01.01-2002 includes equations for predicting the flow coefficient of compressible andincompressible fluids through control valves.
The equations for incompressible flow are based on standard hydrodynamic equations for Newtonianincompressible fluids. They are not intended for use when non-Newtonian fluids, fluid mixtures, slurries, orliquid-solid conveyance systems are encountered.
At very low ratios of pressure differential to absolute inlet pressure (D P/ P1), compressible fluids behavesimilarly to incompressible fluids. Under such conditions, the sizing equations for compressible flow can betraced to the standard hydrodynamic equations for Newtonian incompressible fluids. However, increasingvalues of D P/ P1 result in compressibility effects that require that the basic equations be modified byappropriate correction factors. The equations for compressible fluids are for use with gas or vapor and arenot intended for use with multiphase streams such as gas-liquid, vapor-liquid or gas-solid mixtures.
For compressible fluid applications, this part of ANSI/ISA-75.01.01-2002 is valid for all valves. However,manufacturers of some valves with xT ? 0.84 have reported minor inaccuracies (see Annex H). Cautionmust also be exercised when applying the equations for compressible fluids to gaseous mixtures ofcompounds, particularly near phase boundaries.
The accuracy of results computed with the equations in this standard will be governed by the accuracy ofthe constituent coefficients and the process data supplied. Methods of evaluating the coefficients used inthe equations presented herein are given in ANSI/ISA-75.02-1996. The stated accuracy associated withthe coefficients in that document is ?5% when Cv / d 2 < 0.047 N18. Reasonable accuracy can only bemaintained for control valves if C / d 2 < 0.047 N18.
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