CFD Modeling of Gas Release and Dispersion: Prediction of Flammable Gas Clouds

DOI: 10.1007/978-1-4020-6515-6_14

ABSTRACT Advanced computational fluid dynamics (CFD) models of gas release and dispersion (GRAD) have been developed, tested, validated
and applied to the modeling of various industrial real-life indoor and outdoor flammable gas (hydrogen, methane, etc.) release
scenarios with complex geometries. The user-friendly GRAD CFD modeling tool has been designed as a customized module based
on the commercial general-purpose CFD software, PHOENICS. Advanced CFD models available include the following: the dynamic
boundary conditions, describing the transient gas release from a pressurized vessel, the calibrated outlet boundary conditions,
the advanced turbulence models, the real gas law properties applied at high-pressure releases, the special output features
and the adaptive grid refinement tools. One of the advanced turbulent models is the multifluid model (MFM) of turbulence,
which enables to predict the stochastic properties of flammable gas clouds. The predictions of transient threedimensional
(3D) distributions of flammable gas concentrations have been validated using the comparisons with available experimental data.
The validation matrix contains the enclosed and nonenclosed geometries, the subsonic and sonic release flow rates and the
releases of various gases, e.g., hydrogen, helium, etc. GRAD CFD software is recommended for safety and environmental protection
analyses. For example, it was applied to the hydrogen safety assessments including the analyses of hydrogen releases from
pressure relief devices and the determination of clearance distances for venting of hydrogen storages. In particular, the
dynamic behaviors of flammable gas clouds (with the gas concentrations between the lower flammability level (LFL) and the
upper flammability level (UFL)) can be accurately predicted with the GRAD CFD modeling tool. Some examples of hydrogen cloud
predictions are presented in the paper. CFD modeling of flammable gas clouds could be considered as a costeffective and reliable
tool for environmental assessments and design optimizations of combustion devices. The paper details the model features and
provides currently available testing, validation and application cases relevant to the predictions of flammable gas dispersion
scenarios. The significance of the results is discussed together with further steps required to extend and improve the models.

1 Bookmark
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the comparison of IEC60079-10, CSA B108:99, NFPA 52 and API Standards requirements for determining sizes of hazardous locations with simulation results obtained by computational fluid dynamics (CFD) modeling. International standard IEC60079-10 determines the size of a hazardous location by a calculation of the hypothetical combustible volume caused by a fluid leak under specific temperatures, and ventilation rates. Canadian standard CSA B108:99 and American standard NFPA 52 use a prescriptive method to assign the size of a hazardous location depending on fuel quantities contained in the equipment. Considering hydrogen high buoyancy and diffusivity, requirements of both standards are likely too conservative. The PHOENICS CFD software package was used to solve the continuity, momentum and concentration equations with the appropriate boundary conditions, buoyancy model and turbulence models. Numerical results on hydrogen concentration predictions were obtained in the real industrial environment, which is the Hydrogen Energy Station (HES) produced by Stuart Energy Systems Corporation.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, CFD techniques were applied to the simulations of hydrogen release from a 400-bar tank to ambient through a Pressure Relieve Device (PRD) 6 mm (¼") opening. The numerical simulations using the TOPAZ software developed by Sandia National Laboratory addressed the changes of pressure, density and flow rate variations at the leak orifice during release while the PHOENICS software package predicted extents of various hydrogen concentration envelopes as well as the velocities of gas mixture for the dispersion in the domain. The Abel-Noble equation of state (AN-EOS) was incorporated into the CFD model, implemented through the TOPAZ and PHOENICS software, to accurately predict the real gas properties for hydrogen release and dispersion under high pressures. The numerical results were compared with those obtained from using the ideal gas law and it was found that the ideal gas law overestimates the hydrogen mass release rates by up to 35% during the first 25 seconds of release. Based on the findings, the authors recommend that a real gas equation of state be used for CFD predictions of high-pressure PRD releases.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Results are presented of measurements on turbulent round jets of air and of helium of the same nozzle momentum efflux, using, for the air jets, x-wire hot-wire probes mounted on a moving shuttle and, for He jets, a composite probe consisting of an interference probe of the Way-Libby type and an x-probe. Current models for scalar triple moments were evaluated. It was found that the performance of the model termed the Full model, which includes all terms except advection, was very good for both the air and the He jets.
    Journal of Fluid Mechanics 02/1993; · 2.29 Impact Factor

Full-text (2 Sources)

Available from
May 31, 2014