Dispersion in confined building : a coupled approach

International Journal of Impact Engineering, 2011

The paper presents a study aiming at simulation of some characteristics of an interior explosion within a room with an opening, that is initially closed by a heavy cover, and is gradually opened due to the pressures exerted by the explosion products. An effective simplified model of explosion venting due to separation of the protective cover has been developed. The developed model with lumped parameters is based on the Bernoulli equation and describes the quasi-stationary venting phase of the interior explosion. The initial internal gas pressure induced by the very short non-stationary phase is predicted by the developed approximate analytical formula, based on the full energy conservation law. The formula yields very good agreement with experimental data and with numerical analysis results. The simulation of the unsteady outflow from a cylindrical high-pressure vessel upon a sudden separation of the cover has shown that the developed simplified model yields the integral characteristics of the outflow process (such as a maximum cover's velocity and displacement etc.) with reasonable accuracy.

2000

PresentationConsiderable developmental work has gone into modeling dispersion of accidental outdoor releases; less has been applied to indoor releases. Indoor dispersion is characterized by the influence of a ventilation system and confining surfaces that facilitate aerosol rainout. Stratification can occur so that only part of a room contains flammable vapors, giving rise to so-called partial volume deflagrations. Indoor explosions are more complex to treat because there are two important regimes: before and after explosion vents, windows, or other panels open. We describe here a model, WELMIX, to calculate time-varying concentration changes within a room from time-varying inputs such as occur with pool evaporation. The model allows for gas sensors in the room connected to automatic controls of the fresh air/recycle ratio and ventilation rate. We illustrate here the influence of ventilation rate and fresh air/recycle ratio on concentrations. A mixing efficiency is applied that is u...

HVAC&R Research, 2014

This study presents numerical investigation of an air supply device based on wall confluent jets in a ventilated room. Confluent jets can be described as multiple round jets issuing from supply device apertures. The jets converge, merge, and combine at a certain distance downstream from the supply device and behave as a united jet, or so-called confluent jet. The numerical predictions of the velocity flow field of isothermal confluent jets with three Reynolds-averaged Navier-Stokes turbulence models (renormalization group k-ε, realizable k-ε, and shear stress transport k-ω) are reported in the present study. The results of the numerical predictions are verified with detailed experimental measurements by a hot wire anemometer and constant temperature anemometers for two airflow rates. The box method is used to provide the inlet boundary conditions. The study of the airflow distribution shows that a primary wall jet (wall confluent jet) exists close to the supply device along the wetted wall, and a secondary wall jet is created after the stagnation region along the floor. It is presented that the flow field of the primary and secondary wall jet predicted by turbulence models is in good agreement with the experimental data. The current study is also compared with the literature in terms of velocity decay and the spreading rate of the primary and secondary wall jet, the results of which are consistent with each other. Velocity decay and the spreading rate of the secondary wall jet in vertical and lateral directions were studied for different inlet airflow rates and inlet discharge heights. The comparative results demonstrate that the flow behavior is nearly independent of the inlet flow rate. Inlet discharge height is found to have impact close to the inlet, where the velocity decays faster when the jet discharges at higher level. The decay tendency is similar as the jet enters into the room for all discharge heights.

Introduction. In many industries, there are serious safety concerns related to the use of flammable gases in indoor and outdoor environments. It is important to develop reliable methods of analyses of flammable gas release and dispersion (GRAD) in real-life complex geometry cases. Computational fluid dynamics (CFD) is considered as one of the promising cost-effective approaches in such analyses. Over the last 6 years, the authors have been collaborating in CFD modeling of GRAD processes. As a result, the advanced robust CFD models 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 PHOENICS. Advanced CFD models include the following: the dynamic boundary conditions, describing the transient gas release from a pressurized vessel, the calibrated outlet boundary conditions, the real gas law properties applied at high-pressure releases, the special output features and the local adaptive grid refinement (LAGR) tools. The predictions of transient 3D distributions of flammable gas concentrations have been validated using the comparisons with available experimental data. The validation matrix contains the enclosed and non-enclosed geometries, the subsonic and sonic release flow rates and the releases of various gases, e.g. hydrogen, helium, methane, etc. GRAD CFD module is recommended for safety and environmental protection analyses. It has been extensively 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)) are accurately predicted with this module, which

Fire

Recent explosions with devastating consequences have re-emphasized the relevance of fire safety and explosion research. From earlier works, the severity of the explosion has been said to depend on various factors such as the ignition location, type of a combustible mixture, enclosure configuration, and equivalence ratio. Explosion venting has been proposed as a safety measure in curbing explosion impact, and the design of safety vent requires a deep understanding of the explosion phenomenon. To address this, the Explosion Venting Analyzer (EVA)—a mathematical model predicting the maximum overpressure and characterizing the explosion in an enclosure—has been recently developed and coded (Process Saf. Environ. Prot. 99 (2016) 167). The present work is devoted to methane explosions because the natural gas—a common fossil fuel used for various domestic, commercial, and industrial purposes—has methane as its major constituent. Specifically, the dynamics of methane-air explosion in vented...

Journal of Wind Engineering and Industrial Aerodynamics, 1997

Some wind tunnel investigations of gas dispersion around a rectangular building placed in a simulated atmospheric boundary layer have been conducted. Numerical simulations of these experiments have been performed by solving the Reynolds-averaged Navier-Stokes equations, combined with a Reynolds-stress turbulence model, and two variants of the two-layer model due to Rodi. It appears that only the second moment closure correctly predict the recirculating zones on the faces. In this case, calculated values of gas concentrations on the building model faces agree generally well with measurements.

Environmental Engineering and Management Journal

The current paper is an overview on previous and ongoing research carried out by the authors concerning the use of Computational Fluid Dynamics for the accurate classification of hazardous Ex areas generated by flammable gases, for the optimization of computational simulation of air-methane mixture explosions by using ANSYS CFX and FLUENT and for calibrating computational simulations of gas explosions using the Schlieren effect. These research works containing analytic studies have led to the observation of basic principles which come to support the benefit of computational approaches for estimating gas dispersion within technological installations in which are handled or stored flammable materials and in which there are likely to occur explosive atmospheres. Preliminary results have led to the idea of developing a computational method for assessing the hazardous area extent in case of gas leak explosions in confined spaces. The computational method intended to be developed has to be validated in the lab using an experimental chamber as domain for analysing accidental flammable gas leaks from transportation installations and for studying the formation, ignition and burning of air-flammable gas mixtures in confined spaces. Results obtained from physical experiments will be used for calibrating the mathematical models. Further, verification and validation of computational simulations carried out based on physical experiments will be performed by a comparative analysis of virtual results with the experimental ones. In the end, the mathematical model will be implemented on a small-scale reproduction of a confined industrial area with explosion hazard.

2018

Vented deflagrations are one of the most common and simplest methods to reduce damages that might be caused to buildings and enclosures due to accidental explosions. Various engineering models are available in the literature in the form of published papers, European and USA standards. However, none of these have been sufficiently validated for the vented explosions of hydrogen-air mixtures, especially for realistic explosion scenarios in the presence of obstacles. In addition, a new engineering model based on external cloud explosions (ECE) has been developed by the authors. The foundation of the ECE is the proposed new methodology to calculate the external cloud formation, which is described in another paper (Sinha and Wen, 2018a) also submitted to this conference. The present paper further describes the following up procedures to calculate both the overpressures generated by the external cloud combustion and internal explosion. . The model has also been extended to cover the vente...

Chemical Engineering Transactions, 2016

In most vented explosions the peak overpressure is controlled by turbulent flame propagation external to the vent. This has been known for many years, but a method to predict the overpressure from the external flame speed has not been developed. Current vent modelling is based on the assumption that the unburned gas flow through the vent controls the overpressure and does not address the issue of the external explosion. This work shows that the external flame speeds in a small vented explosion test facility can be predicted from Taylors's acoustic theory (1946). Vented explosion data is presented for vent coefficients from 3 – 22 for the most reactive mixtures of methane, propane and ethylene in terms of the overpressure and the external flame speed. The overpressure from Taylors's acoustic theory give a good prediction of the measured overpressure.