Title and Link to Calc:

Incompressible Fluid Flow : Subcooled Liquid Relief - Mass Flow Rate Output, D22 : IFF-RP520-0021-1

Description:

Determines volumetric flow rate of a pressure relief valve of known flow area for a subcooled liquid. Calculates output parameters per D.2.2 of AP RP 520 - Sizing for Subcooled Liquid at the Pressure Relief Valve Inlet. Calculates omega per equation D.8. Mass Flow Rate is ouput. This calc is a back calculation of the method specified in the reference.

Alternative Descriptors:

Subcooled Liquid in Relief Valves, Flashing subcooled liquid in relief valves, Liquid flow in relief valves, Sizing of relief valves for liquid flow, Sizing of relief valves for subcooled flashing liquid flow

Calc Number:

IFF-RP520-0021-1

Calc Status:

Beta

Reference:

Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries, API Recommended Practice 520 seventh edition, January 2000, D.2.2 pgs. 72-74

Reference Example(s) Modeled/Generalized:

Generalizes example D.2.2.2 of the above reference

Calc Origination Date:

03/17/2006

Calc Originator:

RBC

Calc Revision History:

Calc Guidelines:

User should refer to the specified reference above. The method in the reference calculates the required relief area based on the user inputting the desired relieving rate in GPM. This calc back calculates the mass flow rate from relief area, and other parameters, by rearranging equation D.12 of the reference.

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: Volumetric Flow Rate through relief valve
Variable Label Description: Volumetric Flow Rate
Variable Calc Name: VFR
Variable Units: GPM
Variable Calc Upper Limit: 500000
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: Saturated Omega Parameter
Variable Label Description: Omega Saturated
Variable Calc Name: OME
Variable Units:
Variable Calc Upper Limit: 40
Variable Calc Lower Limit: 5
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Saturation Pressure Ratio , Ratio of vapor pressure corresponding to inlet temperature to inlet pressure
Variable Label Description: Saturation Pressure Ratio
Variable Calc Name: SPR
Variable Units:
Variable Calc Upper Limit: 1
Variable Calc Lower Limit: 0.00001
Variable Type: Output
Variable Format: REAL
Variable Notes:

Variable Description: Ratio of vapor pressure to inlet pressure where flashing transits (from/to) throat (from/to) upstream of throat
Variable Label Description: Transition Saturation Pressure Ratio
Variable Calc Name: NST
Variable Units:
Variable Calc Upper Limit: 1
Variable Calc Lower Limit: 0.00001
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 -- "Low Subcooling Critical Flow", "Low Subcooling Subritical Flow", "High Subcooling Critical Flow", "High Subcooling 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: Relief Valve Discharge Flow Area
Variable Label Description: Relief Valve 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: Temperature at the Pressure Relief Valve Inlet in Rankine
Variable Label Description: Temp. at PRV Inlet
Variable Calc Name: PIT
Variable Units: R
Variable Calc Upper Limit: 10000
Variable Calc Lower Limit: 0.01
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: 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: 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:

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