UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    IMAGING PYROMETRY OF WOOD EMBERS UNDER SIMULATED MOVEMENT
    (2022) Baldwin, James H; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A major mechanism for wildland fire spread are spot fires, where small combusted organic particulate (firebrands) are lofted and transported to a remote location where they can then ignite new fires. The modeling of these spot fire ignitions is limited by the unknown surface temperature and emissivity of firebrands, which is challenging to measure due to the small size of firebrands (precluding the use of intrusive temperature methods such as thermocouples) as well as the dependency of conventional non-intrusive temperature measurements (e.g. Infrared Imagers) on emissivity. A solution to this is presented in Color Pyrometry, which uses color pixel intensities to determine an object's temperature based on a calibration against an object of known temperature/emissivity. The presented method is a Ratio Pyrometry approach between green and red pixel intensities normalized to camera settings, which demonstrates the benefit of being independent of object emissivity as validated by Planck's Law, and is based on a Blackbody Furnace calibration. To determine the method's applicability to realistic firebrand imaging conditions, which would provide the most comprehensive understanding of firebrand ignition, the individual impact of firebrand movement speed on the pyrometry's surface temperature predictions is considered. An apparatus is developed that decouples firebrand movement speed from the surface wind speed (which is known to impact firebrand surface temperature) as well as allows for modulation of the firebrand's simulated movement speed, and involves rotating the imaging device about a fixed axis relative to a stationary firebrand. Five trials at a set orientation were conducted to verify the apparatus' repeatability, and subsequent trials of varying rotation speed, distance, applied wind speed, and mounting orientation were conducted. Both qualitatively and through a statistical analysis consisting of ANOVA and non-parametric distribution testing, firebrand movement speed and orientation are shown to have no individual impact on surface temperature. Average ember surface temperatures were found to be 922.1 ± 20.4 °C with a 1 m/s applied wind speed and 955.0 ± 20.2 °C with a 2 m/s applied wind speed, which is in agreement with previous studies. It is proven that the presented Pyrometry method's results are independent of a major complicating factor associated with realistic firebrands, which thereby further supports future efforts into wildland fire spread modeling.
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    THE INFLUENCE OF WIND ON THE STRUCTURE OF INCLINED FLAMES
    (2020) Heck, Michael; Gollner, Michael J; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Experiments were performed using stationary gas burners in order to characterize the flame geometry and downstream heating from stationary flames under inclined configurations under an applied forced flow. Stationary flames exhibit behavior similar to spreading wildland fires but are an ideal configuration for carefully studying fundamental wildland fire behavior characteristics that play a critical role in downstream heating, which subsequently drive fire spread. Two conditions were applied to a small-scale apparatus during experimentation, a sloped surface and forced-flow wind. The experiments were performed at multiple heat-release rates for angles from 0 to 28 degrees from the horizontal and wind speeds of 0 to 0.5 m/s.Flame geometry such as center-line flame length, flame tilt angle, and flame attachment length along the downstream surface were determined from side-view video imaging. Downstream heating was also measured through fine-wire thermocouple temperature measurements and surface total heat heat flux measurements. The measurements provided a heating profile depicting the magnitude of heating that would be applied to unburned fuels at distances in front of a spreading fire. These profiles were compared to the flame attachment observed from imaging, and to one another. While the surface heat flux cannot be scaled to larger fires, it’s relation to temperature profiles will be useful to further interpret large-scale experiments and as validation data for numerical modeling of fire behavior of the combined effects of slope and wind