Title and Link to Calc:

Compressible Fluid Flow : Two Phase Vapor Relief - Mass Flow Rate Output, D21 : CFF-AP520-1

Description:

Calculates output parameters per D.2.1 of AP RP 520 except that Mass Flow Rate is an output value. This is done by rearranging equation D.7 of the reference. The Relief Valve flow area must be entered as an input. Calculates omega per equation D.1.

Alternative Descriptors:

Two Phase Flow Through a Relief Valve, Two Phase Compressible Flow, Two Phase Flow Through a Nozzle, Two Phase Flow Through a Relief Valve, Non-flashing Sub-cooled Liquid, Two Phase Flow Through a Relief Valve, Non-flashing Sub-cooled Liquid and Non-condensable Gas, Two Phase Flow Through a Relief Valve, Flashing Saturated Liquid & Vapor

Calc Number:

CFF-AP520-1

Calc Status:

Beta

Reference:

Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries, API Recommended Practice 520 seventh edition, January 2000, D.2.1.1, pgs. 69-71

Reference Example(s) Modeled/Generalized:

Calc Origination Date:

03/20/2006

Calc Originator:

RBC

Calc Revision History:

Calc Guidelines:

User should refer to the specified reference above.

Access:

Activating this calc requires entry of the correct access code. Contact eng-calc@eng-calcs.com

Variables:

Variable Description - Description of the variable
Variable Label Description - The description of the variable as it appears in the calc.
Variable Calc Name - The calc internal variable name
Variable Units - The units for the variable
Variable Calc Upper Limit - The highest allowed value in the calc.
Variable Calc Lower Limit - The lowest allowed value in the calc.
Variable Type - Either "Output" or "Input"
Variable Format - Real Number, Text, or Integer
Variable Notes - Other comments about the variable

Variable Description: Mass Flow Rate through the Relief Valve
Variable Label Description: Mass Flow Rate
Variable Calc Name: MFR
Variable Units: LBM/HR
Variable Calc Upper Limit: 50000000
Variable Calc Lower Limit: 0
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Critical Pressure (Sonic Velocity in Throat Condition)
Variable Label Description: Critical Pressure
Variable Calc Name: CP
Variable Units: PSIA
Variable Calc Upper Limit: 50000
Variable Calc Lower Limit: 0
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Critical Pressure Ratio
Variable Label Description: Critical Pressure Ratio
Variable Calc Name: NC
Variable Units:
Variable Calc Upper Limit: 1
Variable Calc Lower Limit: 0
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Omega Parameter
Variable Label Description: Omega
Variable Calc Name: OME
Variable Units:
Variable Calc Upper Limit: 100
Variable Calc Lower Limit: 0.01
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Comments
Variable Label Description: Comments
Variable Calc Name: COM
Variable Units:
Variable Calc Upper Limit:
Variable Calc Lower Limit:
Variable Type: Output
Variable Format: TEXT
Variable Notes: Displays "Input(s) out of range." if an entered input variable(s) are out of range. Displays "Output(s) out of range." if an output variable exceeds its range. The "out of range" variable(s) are displayed in yellow. The limited range values are used in the calculation, not the "out of range" value(s).

Variable Description: Vapor Mass Fraction at the Pressure Relief Inlet
Variable Label Description: Vapor Mass Frac.
Variable Calc Name: VMF
Variable Units:
Variable Calc Upper Limit:
Variable Calc Lower Limit: 1
Variable Type: 0.5
Variable Format: Input
Variable Notes: REAL

Variable Description: Vapor Specific Volume at Pressure Relief Valve Inlet
Variable Label Description: Vapor S. Vol.
Variable Calc Name: VSV
Variable Units:
Variable Calc Upper Limit: CUFT/LBM
Variable Calc Lower Limit: 15000
Variable Type: 0.6365
Variable Format: Input
Variable Notes: REAL

Variable Description: Required Effective Discharge Area
Variable Label Description: Required Effective Discharge Area
Variable Calc Name: REDA
Variable Units: SQIN
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Two Phase Specific Volume at Pressure Relief Valve Inlet
Variable Label Description: Two Ph. S. Vol
Variable Calc Name: TPSV
Variable Units:
Variable Calc Upper Limit: CUFT/LB
Variable Calc Lower Limit: 1000000
Variable Type: 0.2462
Variable Format: Input
Variable Notes: REAL

Variable Description: Specific Volume Difference at Pressure Relief Valve Inlet
Variable Label Description: S. Vol. Diff.
Variable Calc Name: VLSVD
Variable Units:
Variable Calc Upper Limit: CUFT/LB
Variable Calc Lower Limit: 1000000
Variable Type: 0.1549
Variable Format: Input
Variable Notes: REAL

Variable Description: Latent Heat of Vaporization at the saturation pressure
Variable Label Description: Heat of Vaporization
Variable Calc Name: LHV
Variable Units: BTU/LBM
Variable Calc Upper Limit: 100000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Pressure at the pressure relief valve inlet
Variable Label Description: Pressure at PRV Inlet
Variable Calc Name: PIP
Variable Units: PSIA
Variable Calc Upper Limit: 100000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Temperature at the pressure relief valve inlet
Variable Label Description: Temperature at PRV Inlet
Variable Calc Name: PIT
Variable Units: R
Variable Calc Upper Limit: 100000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Downstream Back Pressure
Variable Label Description: Downstream Back Pressure
Variable Calc Name: DBP
Variable Units: PSIA
Variable Calc Upper Limit: 100000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Valve Discharge Coefficient
Variable Label Description: Valve Discharge Coefficient
Variable Calc Name: VDC
Variable Units:
Variable Calc Upper Limit: 3
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Back Pressure Correction Factor
Variable Label Description: Back Pressure Correction Factor
Variable Calc Name: BPC
Variable Units:
Variable Calc Upper Limit: 3
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Rupture Disk Correction Factor
Variable Label Description: Rupture Disk Correction Factor
Variable Calc Name: RDC
Variable Units:
Variable Calc Upper Limit: 3
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Ratio of Specific Heats
Variable Label Description: Specific Heat Ratio
Variable Calc Name: SHR
Variable Units:
Variable Calc Upper Limit: 3
Variable Calc Lower Limit: 1
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Liquid Specific Heat at the PRV Inlet
Variable Label Description: Liquid Specific Heat
Variable Calc Name: LSH
Variable Units:
Variable Calc Upper Limit: 15000
Variable Calc Lower Limit: 0.01
Variable Type: Input
Variable Format: REAL
Variable Notes:

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