HydDown Documentation

HydDown is an open source Python package for calculating hydrogen (or other pure gas phase species) pressure vessel filling and discharge incorporating heat transfer effects.

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User Guide

• Introduction
  • Citing HydDown
  • Background
  • Getting the software
  • Requirements
  • Testing
  • Units of measure
  • Credit
  • License
• Usage
  • Basic usage
  • Demos
  • Calculation methods
  • Script
  • Module import
  • Input file examples
  • Input fields and hierarchy
• Theory
  • Thermodynamics
  • Flow devices
  • Heat transfer
  • Vessel geometry
  • Rupture evaluation
  • Model implementation
  • Multicomponent mixtures
• Validation
  • Hydrogen discharge (Type I)
  • Hydrogen filling (Type I)
  • Nitrogen discharge (Type I)
  • Multi-component discharge (Type I)
  • 1-D transient heat transfer
  • Validation against GasTeF experiments (Type IV)
  • Validation against Type III cylinder discharge experiments
  • Validation against Type III cylinder filling experiments
  • Validation of fire heat load
• Example use cases
  • LPG vessel subject to fire heat load
  • Rupture estimation
  • Composite cylinder subject to blowdown
• Installation
  • Requirements
  • Installation via pip
  • Installation from Source
  • Dependencies
  • Optional Dependencies
• Quick Start
  • Basic Usage
  • Simple Example
  • Streamlit Application
  • Example Files
• Examples
  • Vessel Depressurization
  • Vessel Filling
  • Fire Scenario
  • Relief Valve Sizing
  • Two-Phase Calculations

API Reference

• hdclass - Main Calculation Engine
  • HydDown
  • Key Classes
  • Implementation Notes
• transport - Heat and Mass Transfer
  • Gr()
  • Pr()
  • Nu()
  • h_inside()
  • h_inner()
  • h_inside_mixed()
  • h_inner_mixed()
  • h_inside_liquid()
  • h_inside_wetted()
  • hem_release_rate()
  • gas_release_rate()
  • relief_valve()
  • api_psv_release_rate()
  • cv_vs_time()
  • control_valve()
  • Dimensionless Numbers
  • Heat Transfer Coefficients
  • Mass Flow Rate Calculations
  • Valve Types
• fire - Fire Heat Load Modeling
  • stefan_boltzmann()
  • pool_fire_api521()
  • pool_fire_scandpower()
  • jet_fire_api521()
  • jet_fire_scandpower()
  • jet_fire_peak_large_scandpower()
  • jet_fire_peak_small_scandpower()
  • pool_fire_peak_scandpower()
  • sb_fire()
  • Predefined Fire Scenarios
  • Stefan-Boltzmann Calculation
  • Usage Example
• thermesh - 1-D Transient Heat Conduction
  • solve_ht()
  • Domain
  • isothermal_model()
  • piecewise_linear_model()
  • Mesh
  • Element
  • LinearElement
  • QuadraticElement
  • Overview
  • Key Features
  • Applications
  • Wall Heat Conduction Modes
  • Composite Materials
  • Two-Phase Modeling
• validator - Input Validation
  • validate_mandatory_ruleset()
  • heat_transfer_validation()
  • valve_validation()
  • validation()
• materials - Material Properties
  • von_mises()
  • ATS()
  • UTS()
  • steel_Cp()

Additional Information

• Citing HydDown
• Changelog

[AMdeMiguel+14]

B. Acosta, P. Moretto, N. de Miguel, R. Ortiz, F. Harskamp, and C. Bonato. Jrc reference data from experiments of on-board hydrogen tanks fast filling. International Journal of Hydrogen Energy, 39(35):20531–20537, 2014. doi:10.1016/j.ijhydene.2014.03.227.

[And21]

Anders Andreasen. Hyddown: a python package for calculation of hydrogen (or other gas) pressure vessel filling and discharge. Journal of Open Source Software, 6(66):3695, 2021. URL: https://doi.org/10.21105/joss.03695, doi:10.21105/joss.03695.

[And24]

Anders Andreasen. Hyddown – user guide and technical reference. 2024. URL: https://hal.science/hal-04858235v1.

[ABZN+18]

Anders Andreasen, Filippo Borroni, Marcos Zan Nieto, Carsten Stegelmann, and Rudi P. Nielsen. On the adequacy of api 521 relief-valve sizing method for gas-filled pressure vessels exposed to fire. Safety, 2018. doi:10.3390/safety4010011.

[AS25]

Anders Andreasen and Carsten Stegelmann. Open source pressure vessel blowdown modeling under partial phase equilibrium. Process Safety Progress, 2025. doi:10.1002/prs.70035.

[API14a]

API. API 520 Sizing, Selection, and Installation of Pressure-relieving Devices. American Petroleum Institute, 2014.

[Bel25]

Caleb Bell. Fluids: fluid dynamics component of chemical engineering design library (chedl). https://github.com/CalebBell/fluids, 2025.

[BLVikramGovindarajanr24]

Caleb Bell, Pierre Lesouhaitier, VikramGovindarajan, and jeremy rutman. CalebBell/ht: 1.0.8. December 2024. URL: https://doi.org/10.5281/zenodo.14321704, doi:10.5281/zenodo.14321704.

[BWQL14]

Ian H. Bell, Jorrit Wronski, Sylvain Quoilin, and Vincent Lemort. Pure and pseudo-pure fluid thermophysical property evaluation and the open-source thermophysical property library coolprop. Industrial & Engineering Chemistry Research, 53(6):2498–2508, 2014. URL: http://pubs.acs.org/doi/abs/10.1021/ie4033999, arXiv:http://pubs.acs.org/doi/pdf/10.1021/ie4033999, doi:10.1021/ie4033999.

[BEA+17]

Michael Bjerre, Jacob G. I. Eriksen, Anders Andreasen, Carsten Stegelmann, and Matthias Mandø. Analysis of pressure safety valves for fire protection on offshore oil and gas installations. Process Safety and Environmental Protection, 105:60–68, 2017. doi:10.1016/j.psep.2016.10.008.

[Bor98]

Guy Borden, editor. Control Valves – Practical Guides for Measurement and Control. Instrument Society of America, 1998.

[BRR64]

W. R. Byrnes, R. C. Reid, and F. E. Ruccia. Rapid depressurization of gas storage cylinder. Industrial & Engineering Chemistry Process Design and Development, 3(3):206–209, 1964. doi:10.1021/i260011a004.

[DMM17]

M. Dadashzadeh, D. Makarov, and V. Molkov. Non-adiabatic blowdown model: a complimentary tool for the safety design of tank-TPRD system. In Proceedings of the Internationsl Conference On Hydrogen Safety, 1–18. Hamburg, Germany, September 2017. International Association for Hydrogen Safety. URL: https://hysafe.info/uploads/papers/2017/186.pdf.

[DM07]

C. J. B. Dicken and W. Mérida. Modeling the transient temperature distribution within a hydrogen cylinder during refueling. Numerical Heat Transfer, Part A: Applications, 53(7):685–708, 2007. doi:10.1080/10407780701634383.

[EB15]

Jacob Gram Iskov Eriksen and Michael Skov Bjerre. Analysis of the application and sizing of pressure safety valves for fire protection on offshore oil and gas installations. Master's thesis, Aalborg University, 2015. URL: https://projekter.aau.dk/projekter/files/213880237/Analysis_of_the_application_and_sizing_of_pressure_safety_valves_for_fire_protection_on_offshore_oil_and_gas_installations._By_PECT10_1_F15.pdf.

[Gea93]

C.J. Geankoplis. Transport Processes and Unit Operations. Chemical Engineering. PTR Prentice Hall, 1993.

[Gro]

Walter Grouve. Thermesh – finite element code for transient one-dimensional heat conduction in python. https://github.com/wjbg/thermesh. Accessed: 2024-12-25.

[HR24]

C. Hall and V. Ramasamy. Modelling the conjugate heat transfer during the fast-filling of high-pressure hydrogen vessels for vehicular transport. International Journal of Thermofluids, 21:100527, 2024. doi:10.1016/j.ijft.2023.100527.

[HRS+92]

M. A. Haque, M. Richardson, G. Saville, G. Chamberlain, and L. Shirvill. Blowdown of pressure vessels. Pt. II: Experimental validation of computer model and case studie. Trans. IChemE B, 70:10–17, 1992.

[HS04]

B. Hekkelstrand and P. Skulstad. Guidelines for the Protection of Pressurised Systems Exposed to Fire. Scandpower Risk Management AS, 2004.

[IEC11]

IEC. Iec 60534-2-1 industrial-process control valves – part 2-1: flow capacity – sizing equations for fluid flow under installed conditions. Technical Report, IEC, 2011.

[ISA95]

ISA. Flow Equations for Sizing Control Valves, ANSI/ISA S75.01 Standard, ISA-S75.01-1985 (R 1995). Instrument Society of America, 1995.

[JSRB04]

J. M. Saiz Jabardo, E. Fockink da Silva, G. Ribatski, and S. F. de Barros. Evaluation of the rohsenow correlation through experimental pool boiling of halocarbon refrigerants on cylindrical surfaces. Journal of the Brazilian Society of Mechanical Sciences and Engineering, 26:218–230, 2004. doi:10.1590/S1678-58782004000200015.

[KNP+21]

Taichi Kuroki, Kazunori Nagasawa, Michael Peters, Daniel Leighton, Jennifer Kurtz, Naoya Sakoda, Masanori Monde, and Yasuyuki Takata. Thermodynamic modeling of hydrogen fueling process from high-pressure storage tank to vehicle tank. International Journal of Hydrogen Energy, 46(42):22004–22017, 2021. doi:10.1016/j.ijhydene.2021.04.037.

[MBAI+17]

D. Melideo, D. Baraldi, B. Acosta-Iborra, R. Ortiz Cebolla, and P. Moretto. Cfd simulations of filling and emptying of hydrogen tanks. International Journal of Hydrogen Energy, 42(11):7304–7313, 2017. doi:10.1016/j.ijhydene.2016.05.262.

[MDKM21]

V. Molkov, M. Dadashzadeh, S. Kashkarov, and D. Makarov. Performance of hydrogen storage tank with tprd in an engulfing fire. International Journal of Hydrogen Energy, 46(73):36581–36597, 2021. doi:10.1016/j.ijhydene.2021.08.128.

[MCD+88]

K. Moodie, L.T. Cowley, R.B. Denny, L.M. Small, and I. Williams. Fire engulfment tests on a 5 tonne lpg tank. Journal of Hazardous Materials, 20:55–71, 1988. doi:10.1016/0304-3894(88)87006-7.

[Pio99]

I. l Pioro. Experimental evaluation of constants for the Rohsenow pool boiling correlation. International Journal of Heat and Mass Transfer, 42(11):2003–2013, 1999. doi:10.1016/S0017-9310(98)00294-4.

[Roh51]

Warren M. Rohsenow. A method of correlating heat transfer data for surface boiling of liquids. Technical Report, Cambridge, Mass. : M.I.T. Division of Industrial Cooporation, [1951], 1951. URL: https://dspace.mit.edu/handle/1721.1/61431 (visited on 2025-03-27).

[SVNA96]

J. M. Smith, H. C. Van Ness, and M. M. Abbott. Introduction to Chemical Engineering Thermodynamcis. McGraw-Hill, fifth edition, 1996.

[SBSK14]

Michael Striednig, Stefan Brandstätter, Markus Sartory, and Manfred Klell. Thermodynamic real gas analysis of a tank filling process. International Journal of Hydrogen Energy, 39(16):8495–8509, 2014. doi:https://doi.org/10.1016/j.ijhydene.2014.03.028.

[vdBW05]

C.J.H. van den Bosch and R.A.P.M. Weterings, editors. Methods for the calculation of physical effects (Yellow Book) – CPR 14E. Committee for the Prevention of Disasters, 3 edition, 2005.

[Wik08]

WikiMedia. First law open system diagram. 2008. Adapted from DOE-HDBK-1012/1-92, Thermodynamics, Heat Transfer, and Fluid Flow, Volume 1 of 3, 2014. U.S. Department of Energy. URL: https://commons.wikimedia.org/wiki/File:First_law_open_system.svg.

[Won98]

Shan Meng Angela Wong. DEVELOPMENT OF A MATHEMATICAL MODEL FOR BLOWDOWN OF VESSELS CONTAINING MULTICOMPONENT HYDROCARBON MIXTURES. PhD thesis, University College London, 1998. URL: https://discovery.ucl.ac.uk/id/eprint/1317912/1/299471.pdf.

[WMM07]

Peter Lloyd Woodfield, Masanori Monde, and Yuichi Mitsutake. Measurement of averaged heat transfer coefficients in high-pressure vessel during charging with hydrogen, nitrogen or argon gas. Journal of Thermal Science and Technology, 2(2):180–191, 2007. doi:10.1299/jtst.2.180.

[API14b]

API. Pressure-relieving and Depressuring Systems, API Standard 521. Technical Report API Standard 521, Sixth Edition, January, American Petroleum Institute, 2014.

[deMiguelAMC15]

N. de Miguel, B. Acosta, P. Moretto, and R. Ortiz Cebolla. The effect of defueling rate on the temperature evolution of on-board hydrogen tanks. International Journal of Hydrogen Energy, 40(42):14768–14774, 2015. doi:10.1016/j.ijhydene.2015.06.038.

[RuizMaraggiM23]

Leopoldo M. Ruiz Maraggi and Lorena G. Moscardelli. Modeling hydrogen storage capacities, injection and withdrawal cycles in salt caverns: introducing the geoh2 salt storage and cycling app. International Journal of Hydrogen Energy, 48(69):26921–26936, 2023. doi:10.1016/j.ijhydene.2023.03.293.

Indices and tables

• Index

• Module Index

• Search Page