Fire Protection Engineering

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End date: 2009Subject: search.filters.subject.Engineering, Mechanical

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    CHARACTERIZATION OF THE INITIAL SPRAY FROM A JET IN CROSSFLOW
    (2009) Zheng, Yinghui; Marshall, André; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    An experimental study on the initial spray from a liquid jet in air crossflow was conducted using Shadowgraphy and Particle Image Velocimetry (PIV) techniques. Momentum ratio and gas Weber number were varied to study their effects on the column trajectory, spray trajectory, breakup locations and spray characteristics after column breakup. Correlations for column trajectory, spray trajectory, breakup locations in terms of momentum ratio and gas Weber number were obtained using linear regression of the experimental data. Two breakup modes were recognized in the test (Column breakup and Bag breakup), a breakup mode regime map was provided including effects of momentum ratio and gas Weber number. Drop characteristics in the spray were also investigated.
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    SMOKE POINTS OF MICROGRAVITY AND NORMAL GRAVITY COFLOW DIFFUSION FLAMES
    (2009) Dotson, Keenan Thomas; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Smoke points were measured in microgravity aboard the International Space Station (ISS) as part of the Smoke Points in Coflow Experiment (SPICE), and in normal gravity conditions. In microgravity conditions increasing the coflow velocity or decreasing the burner diameter increased the smoke point flame length. A simplified prediction of centerline jet velocity did not yield residence-time-based criticalities or data collapse. Simulation of non-reacting flows showed that the simplified centerline velocity prediction was able to predict velocity decay for only relatively weak coflows. An improved model may yield different results. In normal earth gravity coflow velocity exhibited mixed effects. For burner diameters of 0.41, 0.76, and 1.6 mm, smoke points increased with increases of coflow velocity. For an unconfined coflow burner with a burner diameter of 13.7 mm smoke point length decreased with increasing coflow velocity for ethylene and propylene, while increasing for propane flames.
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    PYROLYSIS MODEL PARAMETER OPTIMIZATION USING A CUSTOMIZED STOCHASTIC HILL-CLIMBER ALGORITHM AND BENCH SCALE FIRE TEST DATA
    (2009) Webster, Robert Dale; Trouvé, Arnaud C; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study examines the ability of a stochastic hill-climber algorithm to develop an input parameter set to a finite difference one-dimensional model of transient conduction with pyrolysis to match experimentally determined mass loss rates of three sample materials exposed to a range of constant incident heat flux. The results of the stochastic hill-climber algorithm developed as part of the present study are compared to results obtained with genetic algorithms. Graphical documentation of the impact of single parameter mutation is provided. Critical analysis of the physical meaning of parameter sets, and their realistic range of application, is presented. Criteria are also suggested for stability and resolution of solid phase temperature and fuel mass loss rate in an implicit Crank-Nicolson scheme with explicit treatment of the heat generation source term.
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    Wind-Driven Plume Dispersion Near A Building
    (2008-05-05) Ling, Young Ern; Marshall, Andre W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The dispersions of smoke or hazardous materials during accidental releases are of concern in many practical applications. A technique combining salt-water modeling and Particle Image Velocimetry (PIV) is developed to study the dispersion of a buoyant plume in a complex configuration. Salt-water modeling based on the analogy between salt-water flow and fire induced flow has proven to be a successful method for the qualitative analysis of fire induced plumes. With the use of PIV, detailed measurements of the velocity field can be taken for quantitative analysis of the plume behavior. The technique is first validated for a canonical unconfined plume scenario by comparing the results with theory and previous experimental data, and subsequently extended to qualitatively and quantitatively analyze plume dispersion in a crossflow with the construction of a crossflow generation system for the salt-water modeling facility. Lastly, plume dispersion in a crossflow near a building is analyzed.
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    Energy Transport in Firefighter Protective Clothing
    (2008-01-24) Spangler, Kevin B; di Marzo, Marino; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Firefighting protective clothing is a highly advanced system designed to protect people from being burned in high temperature environments. Studies have shown a time delay from when a firefighter enters a high temperature environment until the skin feels a temperature increase. A similar time delay is found when the firefighter leaves the hot environment until the skin begins to cool. An experiment was conducted that used thermocouples to observe room temperatures, outside gear temperatures and skin temperatures of firefighters in high intensity and long duration heat exposures. Computer models were created to duplicate and understand the resulting temperature response in the tests. A multi-layered model uses defined material properties to replicate the results and understand the contribution of the individual layers. The computer models can recreate the testing results and it is found that air gaps throughout firefighter gear are critical in providing protection from heat for the firefighters.
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    Analysis of the initial spray from canonical fire suppression nozzles
    (2007-08-10) Ren, Ning; Marshall, André W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The performance of a fire suppression spray is governed by injector discharge characteristics. An atomization model based on the theoretical evolution of a radially expanding sheet generated by an impinging jet has been established in this study. The atomization model predicts characteristic initial drop location, size, and velocity based on injector operating conditions and geometry. These model predictions have been compared with measured discharge characteristics from three nozzle configurations of increasing geometrical complexity over a range of operating conditions. Differences between the predicted and measured initial spray are critically evaluated based on the experimentally observed atomization behavior.
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    Numerical Simulation of Ignition and Transient Combustion in Fuel Vapor Clouds
    (2007-07-31) Wiley, Jennifer; Trouvé, Arnaud; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Large-Eddy Simulation (LES) approach is used to model partially-premixed combustion (PPC) in confined and unconfined fuel vapor clouds. The model is based on the concept of a filtered reaction progress variable to describe the premixed combustion. The premixed combustion model is implemented into the Fire Dynamics Simulator (FDS), developed at the National Institute of Standards and Technology, USA, and is coupled with either an equilibrium-chemistry, mixture-fraction based model (FDS Version 4) or an eddy dissipation model (FDS Version 5) for non-premixed combustion. Modifications to the model are developed and implemented with the goal of reducing the grid resolution requirement while still producing physically sound results. The modified formulation is tested using both versions of the non-premixed combustion model, and the results are compared. It is found that the modifications are capable of reducing errors associated with poorly-resolved simulations in both versions of the model.
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    AN ASYMPTOTIC ANALYSIS OF SPONTANEOUS IGNITION OF HYDROGEN JETS
    (2007-04-26) lim, kianboon; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Analytical work is presented for the spontaneous ignition of a hydrogen jet emanating from a slot into air. A similarity solution of the flowfield was obtained. This was combined with the species and energy conservation equations, which were solved using activation energy asymptotics. Limits of spontaneous ignition were identified as functions of slot width, flow rate, and temperatures of the hydrogen jet and ambient air. Two scenarios are examined: a cool jet flowing into a hot ambient and a hot jet flowing into a cool ambient. For both scenarios, ignition is favored with an increase of either the ambient temperature or the hydrogen supply temperature. Moreover, for the hot ambient scenario, a decrease in local fuel Lewis number also promotes ignition. The Lewis number of the oxidizer only has a weak effect on ignition. Because spontaneous ignition is very sensitive to temperature, ignition is predicted to occur near the edge of the jet if the hydrogen is cooler than the air and on the centerline if the hydrogen is hotter than the air.
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    Discharge Characteristics of Canonical Sprinkler Sprays
    (2007-04-05) Blum, Andrew; Marshall, Andre; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Detailed characterization of spray behavior and its relationship to nozzle geometry, fluid properties, and injection characteristics is needed to advance water-based suppression technology and fire related computational fluid dynamics (CFD) tools. In this study, a series of experiments have been conducted to measure discharge characteristics of sprays produced by basic injector configurations modeled after conventional pendant sprinklers. Liquid jets of various sizes were injected downwards onto flat deflectors, tined deflectors, and boss-modified tined deflectors to establish the three canonical configurations explored in this study. Spray measurements including the initial angle of the sheet at the deflector exit, the sheet breakup radius, the drop size distribution 1 m below the deflector surface, and the volume density distribution were performed for these configurations. These systematic experiments provide discharge characteristics of practical interest while providing valuable data for CFD based atomization model development.
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    MODELING SOIL RESPONSE TO INTENSE HEATING FROM TUNNEL FIRES
    (2006-12-12) Hu, Xianxu; Marshall, André; Goodings, Deborah; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study investigates the response of saturated soils to intense heating from tunnel fires by numerical simulation. A general purpose commercial CFD code, FLUENT and a special porous media code, TOUGH2, are used. The conservation equations for porous media in each program are discussed and the numerical models are established. Two-dimensional simulations for the saturated coarse sand and the saturated fine sand are conducted and the results are compared with experimental data. It was found that models for capillary effects and relative permeability are required to describe the experimentally observed behavior. Without considering them, FLUENT predicts an inconsistent dry-out vapor zone in the soil column. TOUGH2 which includes these models gives the same two-zone structure observed in experiments, namely a liquid zone on the top and a two-phase zone at the bottom. The TOUGH2 results provide insight into the experimentally observed transient phenomena and agree well with experimentally observed trends.