A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Response of a Thermoacoustic Flashover Detector to Thermal Radiation(2014) Jeffrey, Zachary Tran; Sunderland, Peter; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thermoacoustic flashover detector is a device designed to be mounted on the helmet of a firefighter which creates a loud whistle when exposed to conditions that are consistent with flashover in order to provide firefighters with a warning and time to escape. The detector is based off a previous device designed at the University of Maryland which was operated using an electric band heater. This device was optimized by slightly altering the stack design and by the addition of approximately 0.3 mL of water to the stack, yielding an activation temperature of 125°C. Once the activation temperature was sufficiently lowered, the device was outfitted with copper fins which were designed to collect radiant heat from a propane-burning radiant panel and transfer it to the detector. When using four of these copper fins and exposed to a radiant heat flux of approximately 25 kW/m2, the detector activated around 125°C after 7 minutes. This was the first known activation of a thermoacoustic device to unconcentrated thermal radiation. The response time of the device was lowered after two more fins were added to the design. Once the detector was shown to work using radiant heat, it was tested at the Maryland Fire and Rescue Institute (MFRI) at the University of Maryland using full scale fires in order to replicate the conditions in which it would be expected to operate. While the detector did not activate during the full scale tests, the radiant panel tests proved that the design is feasible and that some slight design changes are needed in order for the detector to operate in a real fire environment.Item OPTIMIZATION AND IMPLEMENTATION OF A THERMOACOUSTIC FLASHOVER DETECTOR(2013) Hamburger, Kenneth A; Sunderland, Peter B; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thermoacoustic flashover detector is to be a helmet-mounted device that responds to deteriorating conditions in a compartment fire and produces an audible alarm to alert emergency personnel in time for an escape or change in tactics. An operational prototype device was designed at University of Maryland in 2011, and featured an aluminum, copper, and MACOR tube 178 mm long and 25.4 mm in diameter. The prototype was powered by an external heat band, which provided 44 watts of power at 308 deg C. Optimization of the prototype is conducted across several parameters including power consumption and temperature gradient. To that end, two scaled-down models of diameters 22 mm and 17 mm are constructed, both of which fail to produce sustained sound. Adding water to the device reduces the onset power consumption to 22 watts and the maximum temperature to 285 deg C, which represents the most efficient prototype of the device. A system of radiant heat collector panels and copper-water heat pipes is designed to replace the external heat band as a power source. A heat transfer analysis is conducted to determine the necessary size of the collector panels for proper activation, as well as the response time of the system. Total required surface area will depend on future design parameters, but reasonable estimates suggest that it will be between 0.02-0.03 sq meters. An acoustic analysis of the optimized device is conducted, revealing a fundamental frequency of 500Hz at 101 dB.Item Prototype Design for Thermoacoustic Flashover Detector(2012) Buda-Ortins, Krystyna Eva; Sunderland, Peter; diMarzo, Marino; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The thermoacoustic flashover detector integrates the phenomenon of thermoacoustics into a fire fighting application. This report presents the prototype design for the thermoacoustic flashover detector to ultimately be implemented in a firefighter's gear. Upon increases in compartment fire heat flux and temperature corresponding to the onset of flashover, the device will produce a loud warning tone to alert the firefighter that flashover is impending. This is critical because post-flashover, the fire transitions to an untenable environment for a firefighter, as well as compromised structural integrity of the building. The current design produces a tone at 115 dB at about 500 Hz upon heating from an external band heater and cooling via an ice/water bath. At 38 mm from the device, this sound level is louder than the 85 dB from fire alarms and distinct from the 3000 Hz tone of smoke detectors. The minimum power input to the device for sound onset is 44 Watts, corresponding to a temperature difference of 150 degrees Celsius at a mean temperature of 225 degrees Celsius across a 2 cm long porous steel wool stack. The temperatures at the hot and cold ends of the stack are 300 and 150 degrees Celsius respectively, which is achieved with a response time of ~100 seconds. The sound is sustained as long as there is a minimum power input of 31 Watts. Although the measurement uncertainties are estimated at 10 degrees Celsius for the temperatures and 5 Watts for the power input, this design provides a foundation for future improvement and quantification of the device. The mechanisms of the thermoacoustics at work and the materials selected for the prototype are presented. Different power level inputs to the device are analyzed and temperatures for operation are determined. Suggestions for future optimization and integration of the device into firefighters' gear are presented.