Browsing by Author "Dr. William L. Roberts, Committee Chair"

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Controlled Particle Transport in a Human Airway Replica
(2007-12-07) Rojas, Carlye Rimmele; Dr. William L. Roberts, Committee Chair; Dr. Clement Kleinstreuer, Committee Member; Dr. Stefan Seelecke, Committee Member
The goal of this research is a proof-of-concept for targeted aerosol delivery and validation of computational results. Sodium chloride particles, with a monodisperse particle size of one micrometer are used to represent a drug aerosol in the experimental validation of computational results. A complex oral airway, including a mouth, larynx, pharynx, and trachea was constructed out of laser cured resin, using a three-dimensional printing method. A symmetric three generation (G0 to G3) bifurcating bronchial airway was constructed using the same process. Two-phase flow was conducted through these models to yield particle transport results. The bulk air flow was 2 liters per minute, the highest observed flow rate that will allow the flow to remain laminar throughout the airway model. The flow rate of the particle seeded flow was maintained at 20 milliliters per minute. The velocities of these two flow rates remain within an order of magnitude of each other to inhibit vortices created by shear forces when the two flows were introduced. A series of nozzles (constructed using SL) were used to control the particle injection location. A one millimeter inner diameter seed nozzle is offset, from the center, a given percent of the radius. There were five nozzles, with increasingly offset seed tubes, 0% (centerline of axisymmetric nozzle), 20%, 40%, 60%, and 80%. The airway model was attached to the nozzle so that the nozzle exit is in the same plane as the mouth entrance. The nozzle was rotated so that the seed tube exit can be positioned at various angles within the circular cross-section. By controlling the particle release position, the deposition efficiency can be increased, dramatically, as compared to the uniform injection of the drug. The results show the controlled particle release can determine which branch or branches of the third generation bifurcating bronchial airway the particles will exit. While numerous previous researchers have studied the deposition effects of a uniform injection of aerosol particles in the human airways, the controlled position of particle release is an original idea.
The Effect of Elevated Pressure on Soot Formation in a Laminar Jet Diffusion Flame
(2003-07-18) McCrain, Laura L.; Dr. William L. Roberts, Committee Chair; Dr. Stefan Franzen, Committee Member; Dr. Jack R. Edwards, Committee Member
Soot volume fraction (f[subscript sv]) is measured quantitatively in a laminar diffusion flame at elevated pressures up to 25 atmospheres as a function of fuel type in order to gain a better understanding of the effects of pressure on the soot formation process. Methane and ethylene are used as fuels; methane is chosen since it is the simplest hydrocarbon while ethylene represents a larger hydrocarbon with a higher propensity to soot. Soot continues to be of interest because it is a sensitive indicator of the interactions between combustion chemistry and fluid mechanics and a known pollutant. To examine the effects of increased pressure on soot formation, Laser Induced Incandescence (LII) is used to obtain the desired temporally and spatially resolved, instantaneous f[subscript sv] measurements as the pressure is incrementally increased up to 25 atmospheres. The effects of pressure on the physical characteristics of the flame are also observed. A laser light extinction method that accounts for signal trapping and laser attenuation is used for calibration that results in quantitative results. The local peak f[subscript sv] is found to scale with pressure as p[superscript 1.2] for methane and p[superscript 1.7] for ethylene.
Experimental Investigations of Liquid Fueled Pulsejet Engines
(2006-10-17) McCalley, Christian Talbot; Dr. William L. Roberts, Committee Chair; Dr. Ronald O. Scattergood, Committee Member; Dr. Andrey V. Kuznetsov, Committee Member; Dr. Terry Scharton, Committee Member
Various sizes of pulsejets are used to study the effects of heavy liquid fuels like kerosene and military grade JP-8. A hobby scale pulsejet, commercially available from Bailey Machine Services (BMS), is used with gasoline to verify data acquisition techniques, and attempts are made to use kerosene to fuel the jet to prove the viability of using kerosene to power pulsejet engines. A large valved pulsejet, predicted to deliver 25 lbs of thrust, is designed to be used with kerosene for initial testing to prove the feasibility of using such a propulsion device for personal troop transport. A 25 cm valveless pulsejet is designed, fabricated, and tested using propane, gasoline, and kerosene to determine if such an engine is practical for propelling a small, high speed Unmanned Aerial Vehicle (UAV) for military application. Temperatures, average and instantaneous combustion chamber pressure, sound pressure levels and jet operating frequencies were recorded at various fuel flow rates.
The Frequency Response of Counterflow Diffusin Flames
(2003-01-06) Welle, Eric James; Dr. Clement Kleinstreuer, Committee Member; Dr. Richard D. Gould, Committee Member; Dr. William L. Roberts, Committee Chair; Dr. H. Christopher Frey, Committee Member
Most practical combustion processes rely on turbulent diffusion flames due to their higher heat release rates when compared to laminar diffusion flames. The higher heat release rates occur because of the increased mixing that results from the flame's interaction with the turbulent flow field. Unfortunately, the turbulent combustion process is very complex; therefore, simplified models have been constructed. Flamelet Theory is a method that characterizes turbulent diffusion flames as a collection of strained, laminar, one-dimensional flamelets. One caveat of this model is the flamelets are assumed to respond quasi-steadily to the applied flow field. The focus of my research has been to elucidate the influence of a time varying flow field on the combustion process. To test the response, the reaction zone of a propane-air counter-flow diffusion flame was subjected to time varying flow fields using speakers. The results of the experiments illustrate a reaction zone that responds quasi-steadily at forcing frequencies up to 50 Hz. Above this threshold, significant departures occur from steady flame behavior. At elevated frequencies, conditions were found where the reaction zone temperature was found to be in phase with the strain rate, signaling a significant deviation from the quasi-steady state assumption. In diffusion flames, the limiting step for the transport of reactants to the flame front is a diffusion process. The time associated with the increasing phase difference is likely a result of the time necessary for reactants to travel through the diffusion layer. As the forcing frequency is increased, the time rate of change of reactants delivered to the edge of the diffusive zone increases; however, a finite amount of time is still necessary for the reactants to diffuse to the flame front. As the forcing frequency increases, this diffusion time becomes larger relative to the cycle time of the oscillation, which in turn shows up as an increasing phase difference. Another aspect of this research was to determine the effects of the transient flow field on soot formation. The formation of soot is of great concern as it is considered to be highly carcinogenic. Unlike other flame parameters such as flame temperature and thickness that responded quasi-steadily at low forcing frequencies, the soot volume fraction showed significant deviations from steady flame behavior at lower frequencies. At higher forcing frequencies, it was found that the soot field asymptotes to a steady structure. The cause of the low frequency response is a result of the long time scales associated with soot production. The results from this work help illuminate the fundamental physics that governs a flame's response to a time varying flow field. It has shown that significant errors can occur when following the quasi-steady state assumption of the traditional Flamelet Theory. It was also shown that even moderately forced flames exhibit a dramatically different sooting structure when compared to steady flames.