Development of a generalized integral jet model (original) (raw)
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Modelling the dispersion of flashing jets using CFD
Journal of Hazardous Materials, 2008
Risk assessments related to industrial environments where gas is kept in liquid form under high pressure rely on the results from predictive tools. Computational Fluid Dynamics (CFD) is one such predictive tool and it is currently used for a range of applications. One of the most challenging application areas is the simulation of multiphase flows resulting from a breach or leakage in a pressurised pipeline or a vessel containing liquefied gas. The present paper deals with the modelling of the post-flashing scenario of a jet emanating from a circular orifice. In addition to being based on the equations governing fluid flow, the models used are those related to turbulence, droplet transport, evaporation, break-up and coalescence. Some of these models are semi-empirical and based on the data from applications other than flashing. However, these are the only models that are currently available in commercial codes and that would be used by consulting engineers for the type of modelling discussed above, namely the dispersion of a flashing release. A method for calculating inlet boundary conditions after flashing is also presented and issues related to such calculations are discussed. The results from a number of CFD based studies are compared with available experimental results. The results show that whilst a number of features of the experimental results can be reproduced by the CFD model, there are also a number of important shortcomings. The shortcomings are highlighted and discussed. Finally, an optimum approach to modelling of this type is suggested and methods to overcome modelling difficulties are proposed.
A Unified 3D CFD Model for Jet and Pool Fires
In general, a fire accident involves various processes such as evaporation of fuel from a pool, formation of jets, laminar and turbulent diffusion, diffusion controlled and kinetics controlled reactions, smoke and soot formation and thermal radiation. The increased computational power enables use of more accurate CFD based models of these processes for large scale fire simulations. This work presents some results of the development and validation of a 3D CFD based model for dispersion of fuel vapours and associated fire hazards. In general, fires occur in a wide range of flow regimes. Unifying the simulation of this wide range of flow under a single combustion model is a challenge. In the present work, a unified model to deal with flames in different regimes such as slow pool fires and fires due to low speed laminar and high speed turbulent jets is implemented by modifying the eddy dissipation concept (EDC) model to include the effect of local laminar or turbulent burning velocities properly. Also, the local flame surface area, which determines local reaction rate, is estimated in a way such that the effect of discretization (mesh size) on the average reaction rate is minimal in order to obtain results which are reasonably grid independent. Spatial distribution of different quantities, such as temperature, mixture fraction, velocity and species concentrations are computed and compared with the experimental measurements available in relevant literature. It is found that the developed model using with an identical set of parameters was able to capture the qualitative behaviour of all the flames with a reasonably good quantitative comparison.
Computer modelling of turbulent gas explosions in complex 2D and 3D geometries
Journal of Hazardous Materials, 1993
Numerical simulation methods capable of predicting flame and pressure development in turbulent gas explosions are presented. Special attention is given to methods which adopt the k -E model of turbulence. Several verification calculations are presented, which include a variety of geometrical layouts as well as a range of different fuel-air mixtures. Comparisons between simulated and measured explosion data are in general in good agreement.
VALIDATION OF CFD CALCULATIONS AGAINST IGNITED IMPINGING JET EXPERIMENTS
2000
Computational Fluid Dynamics (CFD) tools have been increasingly employed for carrying out quantitative risk assessment (QRA) calculations in the process industry. However, these tools must be validated against representative experimental data in order to have a real predictive capability. As any typical accident scenario is quite complex, it is important that the CFD tool is able to predict combined release
Modeling of Flammable/Hazardous Gas Release and Dispersion
This presentation is an overview of recent customized applications of general-purpose Computational Fluid Dynamics (CFD) software, PHOENICS [1], to the CFD modeling of flammable/hazardous gas release and dispersion (GRAD) for risk and safety assessments.
CFD analysis of gas explosions vented through relief pipes
Journal of Hazardous Materials, 2006
Vent devices for gas and dust explosions are often ducted to safe locations by means of relief pipes. However, the presence of the duct increases the severity of explosion if compared to simply vented vessels (i.e. compared to cases where no duct is present). Besides, the identification of the key phenomena controlling the violence of explosion has not yet been gained. Multidimensional models coupling, mass, momentum and energy conservation equations can be valuable tools for the analysis of such complex explosion phenomena. In this work, gas explosions vented through ducts have been modelled by a two-dimensional (2D) axi-symmetric computational fluid dynamic (CFD) model based on the unsteady Reynolds Averaged Navier Stokes (RANS) approach in which the laminar, flamelet and distributed combustion models have been implemented. Numerical test have been carried out by varying ignition position, duct diameter and length. Results have evidenced that the severity of ducted explosions is mainly driven by the vigorous secondary explosion occurring in the duct (burn-up) rather than by the duct flow resistance or acoustic enhancement. Moreover, it has been found out that the burn-up affects explosion severity due to the reduction of venting rate rather than to the burning rate enhancement through turbulization.
CFD Modeling of Gas Release and Dispersion: Prediction of Flammable Gas Clouds
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.
Application of numerical simulations to predict aircraft combustor ignition
Comptes Rendus Mécanique, 2013
The present study aims at contributing to the development of a methodology to predict and improve the ignition performances of aircraft combustors. A model has been developed to investigate the early growth of a spherical ignition kernel in a two-phase flow mixture. It has been combined with a multiphysic code through two different approaches. The ignition kernel model is used to build the ignition probability map of a combustor. The output of the model can also be introduced as an initial condition in an unsteady simulation to test the flame propagation in the combustor. To validate both methods, RANS and LES simulations have been performed on an experimental combustion chamber, reproducing one sector of an industrial combustor. © 2012 Published by Elsevier Masson SAS on behalf of Académie des sciences.
ChemEngineering, 2018
Different kinds of explosions are driven by the internal energy accumulated in compressed gas or superheated liquid. A well-known example of such an explosion is the burst of a vessel with pressure-liquefied substance, known as Boiling Liquid Expanding Vapor Explosion (BLEVE). Hot BLEVE accident is caused mainly by direct heating (pool fire or jet fire) of the steel casing at the vapor side of the tank to temperatures in excess of 400 °C. Thermal insulation around the tank can significantly reduce and retard the excessive heating of the tank casings in a fire. This will allow fire fighters enough time to reach the accident location and to cool the LPG (Liquid Petroleum Gas) tank to avoid the BLEVE, to extinguish the fire or to evacuate the people in the vicinity of the accident. The proposed algorithm addresses several aspects of the BLEVE accident and its mitigation: Computational Fluid Dynamic (CFD) Simulation of jet fire by using fire dynamics simulator (FDS) software by using la...