a b s t r a c tAccurate representation of the fire sprinkler spray enables quantitative engineering analysis of fire suppression performance. Increasingly, fire sprinkler systems are analyzed with computational fluid dynamics (CFD) fire models where the sprinkler spray is simulated with Lagrangian particles dispersed throughout the fire induced flow. However, there is limited guidance for representing the complex, spatio-stochastic characteristics of the initial sprinkler sprays in terms of these Lagrangian particles. The present work establishes a descriptive analytical framework for the initial sprinkler spray that is rigorously grounded in statistical theory, related to local spray properties, and capable of translating highfidelity measurements into CFD inputs. This framework describes the initial sprinkler spray as a unified probability distribution function, varying over an initialization surface, and statistically representing measurements of near field local spray properties (volume flux, drop size distribution, and drop sizevelocity correlation). Lagrangian particles accurately representing the sprinkler spray may be initialized by a stochastic sampling of this probability distribution function. This novel representation enables highfidelity initialization of the sprinkler spray in CFD fire models, improving their utility in quantitative engineering analysis.
The objective of this study is to bring basic information on the mechanisms that control flame cooling effectiveness in water mist fire suppression systems. The study is based on well-resolved large eddy simulations (LES) of buoyancy-driven, turbulent, methane-air diffusion flames exposed to water mist injected through a controlled air co-flow. Simulations are performed using an LES solver called FireFOAM and using a modified version recently enhanced with a new flame extinction model based on the concepts of a critical flame Damköhler number for extinction and a critical gas temperature for re-ignition. The numerical simulations provide global information on the flame response to changes in the water mist load as well as spatially-resolved information on the structure of the flame-based heat release rate processes and mist-based evaporation processes. The results suggest that maximum suppression is obtained when mist droplets are entrained into the flame base region.While water-based fire suppression systems provide an attractive and 2 popular solution to the problem of fire safety in the built environment, a 3 fundamental understanding of the factors that control the performance of 4 these systems is still lacking [1][2][3]. When evaluating the fire suppression per-5 formance of water sprays, it is useful to differentiate between systems that 6 achieve suppression by flame cooling, i.e., systems that reduce the fire in-7 tensity by acting directly on combustion (e.g., by increasing the probability 8 of flame extinction), and systems that achieve suppression by fuel cooling, 9 i.e., systems that reduce the fire intensity by acting on fuel formation (e.g., 10by wetting active fuel surfaces and decreasing the rate of pyrolysis, or by 11 wetting inactive fuel surfaces and inhibiting further flame spread). The abil-12 ity of a given system to achieve flame cooling or fuel cooling depends on 13 its ability to deliver the liquid water to the location of the flame or to that 14 of the fuel surfaces and is therefore strongly related to the droplet size dis-15 tribution in the liquid spray. Conventional sprinkler systems produce large 16 droplets (larger than 100 microns) that penetrate the gas flow and evaporate 17 slowly; large droplets have a low probability of acting (i.e., evaporating) at 18 the flame location and a high probability of wetting fuel surfaces; sprinkler 19 systems achieve fire suppression primarily by fuel cooling. In contrast, mist 20 systems produce small droplets (smaller than 100 microns) that move with 21 the gas flow and evaporate quickly; small droplets have a relatively high 22 23low probability of wetting fuel surfaces; mist systems achieve fire suppression 24 primarily by flame cooling (note that mists systems have also the ability to 25 block radiation transport via droplet absorption and scattering effects and 26 can therefore also provide some form of fuel cooling). 27One of the main objectives of fire suppression research is to fill the 28 knowledge gap between the engineering-level perf...
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