A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Quantification of Flame Heat Feedback in Cone Calorimetry Tests(2017) Tilles, Jessica; Stoliarov, Stanislav; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In order to understand material flammability, accurate pyrolysis models must be developed. Understanding flame heat feedback is essential in developing accurate pyrolysis models. The most widely used standard to quantitatively assess material flammability is the cone calorimeter. The goal of this project was to develop a spatially-resolved flame heat feedback model for 10 cm square horizontal specimens under buoyancy-driven flames to represent the conditions of the cone calorimeter and reasonably, the Fire Propagation Apparatus (FPA). Standard cone calorimeter experiments were performed on several thermoplastics in order to obtain heat release rate (HRR) and mass loss rate (MLR) data. In addition to standard cone calorimetry, side and center flame heat flux was measured under the cone calorimeter using two water-cooled heat flux gauges. The heat flux results show relatively good agreement with prior studies. Heat transfer coefficients were developed from the heat flux measurements in order to quantify heat feedback. It was found that the heat flux in the center of the burning materials is dominated by radiation and the side is dominated by convection. A two-zone heat feedback model with one convection and one radiation dominated zone was then developed, using a heat transfer correlation from the literature. The heat feedback model developed in this study will later be implemented into an in-house numerical pyrolysis model, ThermaKin.Item FORWARD HEATING IN WIND-DRIVEN FLAMES(2017) Tang, Wei; Gollner, Michael J.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wildland fires pose a significant threat to the environment and society at large. The large number of unknowns makes wildland fire predictions much harder than those typically encountered within the built environment, especially under the influence of wind. The spread rate of a fire depends largely on forward heating from the flame to unburnt fuels, however few measurements of heat fluxes from wind-driven flames exist. In wildland fires, the intermittent nature of flame is also thought to be uniquely important to the flame spread process. In this work, both averaged and time-dependent aspects of the flame are studied, including the total heat flux distribution on the downstream surface, flame extension and attachment, and frequencies of intermittent flame movements. Correlations of these properties, dependent on both fire size and ambient wind, will provide a means to describe the thermal exposure during fuel heating and ignition in wind-driven wildland fires. This data will provide a basis for both understanding and model development for wildland fire spread as well as provide a dataset for future numerical validation of computational fluid dynamic models. Detailed laboratory experiments were performed on line fires under forced flow with a variety of ambient wind velocities and fire sizes. Local heat fluxes were measured onto a nearly adiabatic surface downstream of a line burner. The downstream heat flux distribution was correlated as a piecewise function with the local Richardson number in two regimes, the first with higher heat fluxes, where the flame remained attached the downstream surface and the second with a steeper decay of heat fluxes. This observation was further corroborated by analysis of side-view images of the flame, which showed the attachment location was linearly correlated with the location where the Rix equaled unity. The flame forward pulsation frequency and the flame-fuel contact frequency were also extracted. Scaling analysis indicates that they can be well correlated with Fr, Q*, and local Rix respectively. The location of maximum pulsation frequency, xmax, for each burner/wind configuration was also obtained using the VITA technique. Further study indicates that xmax can be well estimated using mean flame properties.Item PROCEDURES TO OBTAIN ACCURATE MEASUREMENT FROM A GAS FUELD BURNER(2014) Kim, Hyeon; Sunderland, Peter B; Quintiere, James G; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Procedures to obtain accurate heat flux measurements from a 50 mm diameter gas-fueled burner using a diluent fuel gas mixture were examined that required following steps. Local heat flux measurements on the surface of a thick porous copper plate burner were corrected with a pure convective burning assumption and stagnant layer solution. Calibration procedures for thermopile-type heat flux gauge was developed and compared with NIST BFRL heat flux gauge calibration system. Calibration of gauges has found to be possible without controlling the temperature. The absorptivity and emissivity of the coating used on the burner and heat flux gauges were measured via calibrated heat flux gauges and copper slug calorimeter. Independently, an apparatus was designed, built, and calibrated to measure burner flame radiant fraction. The heat flux distribution at the burner was measured. Sample measurements were taken to show accurate measurements and potential analysis of the collected burner data is examined.