Title and Link to Calc:

Compressible Fluid Flow : Two Phase Flashing Flow with Noncondensable, D23 : CFF-RP520-0023

Description:

Determines flow area of a relief valve for two phase flashing flow with a noncondensable gas. Calculates output parameters per D.2.3 of AP RP 520. Calculates omega per equation D.14.

Alternative Descriptors:

Flashing Flow in Relief Valves with a Noncondensable Gas, Sizing of relief valves for two phase flow when noncondensable gas is present

Calc Number:

CFF-RP520-0023

Calc Status:

Beta

Reference:

Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries, API Recommended Practice 520 seventh edition, January 2000, D.2.3, pgs. 74-76

Reference Example(s) Modeled/Generalized:

Calc Origination Date:

03/17/2006

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: Required Effective Discharge Area
Variable Label Description: Required Effective Discharge Area
Variable Calc Name: REDA
Variable Units: SQIN
Variable Calc Upper Limit: 50000
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: 40000
Variable Calc Lower Limit: 0.001
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). Depending on flow regime will print one of the following -- "Critical Flow" or "Subcritical Flow".

Variable Description: Liquid Density at PRV inlet
Variable Label Description: Liquid Density at PRV inlet
Variable Calc Name: LDEN
Variable Units: LBM/CUFT
Variable Calc Upper Limit: 500
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Liquid Specfic Heat at Constant Pressure at the PRV Inlet
Variable Label Description: Liquid Specific Heat at PRV Inlet
Variable Calc Name: LSH
Variable Units: BTU/LBM/R
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Mass Flow Rate through Relief Valve
Variable Label Description: Mass Flow Rate
Variable Calc Name: MFR
Variable Units: LBM/HR
Variable Calc Upper Limit: 100000000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Gas / Vapor Combined Specific Volume at PRV Inlet
Variable Label Description: Gas / Vapor Specific Volume at PRV Inlet
Variable Calc Name: GSV
Variable Units: CUFT/LB
Variable Calc Upper Limit: 1000000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Two Phase Specific Volume at PRV Inlet
Variable Label Description: Two Phase Specific Volume at PRV Inlet
Variable Calc Name: TPSV
Variable Units: CUFT/LB
Variable Calc Upper Limit: 1000000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Gas / Vapor Combined mass fraction (quality) at inlet
Variable Label Description: Gas / Vapor Quality at PRV Inlet
Variable Calc Name: GMF
Variable Units:
Variable Calc Upper Limit: 1
Variable Calc Lower Limit: 0.0001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Saturation Pressure or Vapor Pressure corresponding to Liquid Inlet Temperature
Variable Label Description: Saturation Pressure
Variable Calc Name: SATP
Variable Units: PSIA
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Noncondensable gas partial pressure at PRV inlet
Variable Label Description: Noncondensable gas partial pressure
Variable Calc Name: NCGP
Variable Units: PSIA
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.001
Variable Type: Input
Variable Format: REAL
Variable Notes:

Variable Description: Difference in Liquid and Vapor Specific Volumes
Variable Label Description: Specific Volume Difference:
Variable Calc Name: VLSVD
Variable Units: CUFT/LBM
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.01
Variable Type: Input
Variable Format: REAL
Variable Notes:

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: ISK
Variable Units:
Variable Calc Upper Limit: 3
Variable Calc Lower Limit: 1
Variable Type: Input
Variable Format: REAL
Variable Notes:

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