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

DOI: 10.1007/978-1-4020-6515-6_14 In book: Advanced Combustion and Aerothermal Technologies, pp.179-195


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.

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    • "It computes local Reynolds numbers in every cell of the computational mesh and applies the local effective viscosity based on this number. A detailed description of the CFD tool PHOENICS is given in [15] [16]. The same computational domain of 100 m  18 m  25 m was considered in all the runs and the grid of 40  20  30 was used in the reported six-tank configuration. "
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    ABSTRACT: The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and methane is studied using computer fluid dynamics simulations performed with FLACS Hydrogen. Results for constant flow rate through a 6.35 mm diameter pressure relief Device (PRD) orifice from 100 barg, 250 barg, 400 barg, 550 barg and 700 barg compressed gas systems are presented for both horizontal hydrogen and methane jets. To quantify the effect of a horizontal surface on the jet, the jet exit is positioned at various heights above the ground ranging from 0.1 m to 10 m. Free jet simulations are performed for comparison purposes. Also, for cross-validation purposes, a number of cases for 100 barg releases were simulated using proprietary models developed for hydrogen within commercial CFD software PHOENICS. It is found that the presence of a surface and its proximity to the jet centreline result in a pronounced increase in the extent of the flammable cloud compared to a free jet.
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    ABSTRACT: This article summarizes the first part of a benchmark exercise comparing seven different commercial three dimensional codes used for dispersion modeling in the context of major accident risk assessments. The aim of this first stage was twofold: First, the project intended to better understand the potential magnitude of the variation in results for a relatively simple study case. The benchmark case confirmed that, just as with integral models, the use of different codes can cause significant variation in the dispersion results. Second, the study wanted to identify the key assumptions which had a predominant influence on the uncertainty of the results, with the intention of providing clear guidance in engineering specifications for the definition of the scope of work of a computational fluid dynamics dispersion study. This article summarizes the key drivers identified, to date, for the variation in results, and the work shows this variation can be reduced to an acceptable margin by clearly specifying these key assumptions. © 2013 American Institute of Chemical Engineers Process Saf Prog, 2013
    No preview · Article · May 2013 · Process Safety Progress
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    Full-text · Dataset · Mar 2015