A. James Clark School of Engineering
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Item Measurement and Simulation of Suppression Effects in a Buoyant Turbulent Line Fire(2016) White, James Patrick; Sunderland, Peter B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental and numerical study of turbulent fire suppression is presented. For this work, a novel and canonical facility has been developed, featuring a buoyant, turbulent, methane or propane-fueled diffusion flame suppressed via either nitrogen dilution of the oxidizer or application of a fine water mist. Flames are stabilized on a slot burner surrounded by a co-flowing oxidizer, which allows controlled delivery of either suppressant to achieve a range of conditions from complete combustion through partial and total flame quenching. A minimal supply of pure oxygen is optionally applied along the burner to provide a strengthened flame base that resists liftoff extinction and permits the study of substantially weakened turbulent flames. The carefully designed facility features well-characterized inlet and boundary conditions that are especially amenable to numerical simulation. Non-intrusive diagnostics provide detailed measurements of suppression behavior, yielding insight into the governing suppression processes, and aiding the development and validation of advanced suppression models. Diagnostics include oxidizer composition analysis to determine suppression potential, flame imaging to quantify visible flame structure, luminous and radiative emissions measurements to assess sooting propensity and heat losses, and species-based calorimetry to evaluate global heat release and combustion efficiency. The studied flames experience notable suppression effects, including transition in color from bright yellow to dim blue, expansion in flame height and structural intermittency, and reduction in radiative heat emissions. Still, measurements indicate that the combustion efficiency remains close to unity, and only near the extinction limit do the flames experience an abrupt transition from nearly complete combustion to total extinguishment. Measurements are compared with large eddy simulation results obtained using the Fire Dynamics Simulator, an open-source computational fluid dynamics software package. Comparisons of experimental and simulated results are used to evaluate the performance of available models in predicting fire suppression. Simulations in the present configuration highlight the issue of spurious reignition that is permitted by the classical eddy-dissipation concept for modeling turbulent combustion. To address this issue, simple treatments to prevent spurious reignition are developed and implemented. Simulations incorporating these treatments are shown to produce excellent agreement with the experimentally measured data, including the global combustion efficiency.Item FLAMMABILITY CHARACTERISTICS OF WATER-BASED POLYCRYLIC AND OIL-BASED POLYURETHANE COATED OAK VENEER PLYWOOD SAMPLES SUBJECTED TO INCIDENT HEAT FLUXES(2005-12-13) Thompson, Sarah Elizabeth; Mowrer, Frederick W.; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The flammability characteristics of oak veneer plywood were evaluated in the Cone Calorimeter. Samples of 6.35 mm (1/4 in.) thick and 19.05 mm (3/4 in.) thick oak veneer plywood were coated with 3, 6, and 9 coats of either oil-based polyurethane or water-based polycrylic clear finishes and tested at incident heat fluxes of 35, 50, and 75 kW/m2 along with uncoated samples. Both the type of finish and the number of coatings were found to influence the ignition time, the measured peak heat release rate, and the minimum flux for ignition of the samples. The ignition times for the coated samples were 2 to 3 times lower than the unfinished samples. Predicted times to ignition differed by a factor of 2 to 3 from the measured values (with the exception of the samples with nine coats of finish.) The predicted ignition temperatures differed by as much as 100 ºC from the measured temperatures. The Quintiere flammability parameter, b, was found to be positive for all testing scenarios, suggesting a propensity for flame spread at the incident heat fluxes evaluated.