PhD / Electrostatics of aerosols for inhalation is a relatively new research area. Charge properties of these particles are largely unknown but electrostatic forces have been proposed to potentially influence lung deposition. Investigation on the relationship between formulation and aerosol charging is required to understand the fundamental mechanisms. A modified electrical low pressure impactor was employed to measure the particles generated from metered dose inhalers and dry powder inhalers. This equipment provides detailed size and charge information of the aerosols. The particles were sized by impaction onto thirteen stages. The net charges in twelve of the size fractions were detected and recorded by sensitive electrometers. The drug deposits were quantified by chemical assay. The aerosol charge profiles of commercial metered dose inhalers were product-dependent, which was due to differences in the drug, formulation, and valve stem material. The calculated number of elementary charges per drug particle of size ≤ 6.06 μm ranged from zero to several ten thousands. The high charge levels on particles may have a potential effect on the deposition of the aerosol particles in the lung when inhaled. New plastic spacers marketed for use with metered dose inhalers were found to possess high surface charges on the internal walls, which was successfully removed by detergent-coating. Detergent-coated spacer had higher drug output than the new ones due to the reduced electrostatic particle deposition inside the spacer. Particles delivered from spacers carried lower inherent charges than those directly from metered dose inhalers. Those with higher charges might be susceptible to electrostatic forces inside the spacers and were thus retained. The electrostatic low pressure impactor was further modified to disperse two commercial Tubuhaler® products at 60 L/min. The DPIs showed drug-specific responses to particle charging at different RHs. The difference in hygroscopicity of the drugs may play a major role. A dual mechanistic charging model was proposed to explain the charging behaviours. The charge levels on drug particles delivered from these inhalers were sufficiently high to potentially affect deposition in the airways when inhaled. Drug-free metered dose inhalers containing HFA-134a and 227 produced highly variable charge profiles but on average the puffs were negatively charged, which was thought to be due to the electronegative fluorine atoms in the HFA molecules. The charges of both HFAs shifted towards neutrality or positive polarity with increasing water content. The spiked water might have increased the electrical conductivity and/or decreased the electronegativity of the bulk propellant solution. The number of elementary charges per droplet decreased with decreasing droplet size. This trend was probably due to the redistribution of charges amongst small droplets following electrostatic fission of a bigger droplet when the Raleigh limit was reached.

Numerical simulation of mold filling in low pressure die casting is considered in this study. The physical model includes modeling of free surface flow, heat transfer with phase change, surface tension, natural convection together with effect of trapped air in the mold. The governing equations are discretized by control volume finite difference method. The pressure field is computed by two-step projection method and the free surface is tracked by PLIC-VOF method. Water analog model is used for the validation purpose. Good agreement between numerical and experimental results is observed which supports the feasibility of the presented method.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 195-202).

No description available.

This dissertation research focused on the growth of 4H-SiC epitaxial layers in low-pressure horizontal hot-wall chemical vapor deposition (CVD) reactors. The goal of the research was to develop a growth process that maximized the growth rate and produced films of smooth morphology. The epitaxial growth of SiC was carried out in two different reactor sizes, a 75 mm reactor and a 200 mm reactor. The maximum repeatable growth rate achieved was 30-32 um/h in the 200 mm reactor using the standard chemistry of hydrogen-propane-silane (H2-C3H8-SiH4) at growth temperatures <̲ 1600 °C, which is the highest growth rate reported to date in a horizontal hot-wall reactor at these temperatures. This growth rate was achieved with a silane flow rate of 30 sccm. The process development and characterization of 4H-SiC epitaxial films grown using the standard chemistry are presented. There are many ways to increase the growth rate, such as changing the pressure, increasing the reactant flow rates, or increasing the temperature. The method of choice for this dissertation work was to first increase the reactant flow rates, i.e. silane flow rate, and then to alter the growth chemistry by using a growth additive. When the silane flow is increased, while maintaining a specific growth temperature, supersaturation of silicon may occur. When this happens, particulates may form and deposit onto the sample surface during growth which degrades the film morphology of the epitaxial layers. In order to overcome this severe limitation in the growth of SiC, hydrogen chloride (HCl) was added to the standard chemistry of H2-C3H8-SiH4 during growth when the SiH4 flow was increased beyond 30 sccm. With the addition of HCl, the Si supersaturation was suppressed and the growth rate was increased from ~32 um/h to ~ 49 um/h by increasing the silane precursor up to 45 sccm, while maintaining the Si/C ratio of the standard chemistry process. The addition of HCl to the standard chemistry for growth of SiC films was pioneering work that has since been duplicated by several research groups.

Fundamental to the future of space exploration is the development of advanced life support systems capable of maintaining crews for significant periods without re-supply from Earth. Bioregenerative life support systems harness natural ecosystem processes and employ plant photosynthesis and transpiration to produce food, supply oxygen, and regenerate water while consuming carbon dioxide. Proposed Lunar and Martian exploration has prompted interest into the effects of hypobaria on plant development. Reduced atmospheric pressure conditions will reduce the pressure gradient between the structure and the local environment thereby decreasing the engineering requirements, leakage and mass required to construct the growth facility. To establish the optimal conditions for reduced pressure plant growth structures it is essential to determine the atmospheric pressure limits required for plant development and growth. Due to its physiological importance, oxygen will compose a significant portion of this atmosphere. The effects of reduced atmospheric pressure and decreased oxygen partial pressures on plant germination, growth and development were assessed in the University of Guelph’s hypobaric plant growth chambers. Treatments included a range of total pressures from 10 to 98 kPa and oxygen partial pressures from 2 to 20 kPa. Results demonstrated that reduced atmospheric pressure had minimal effect on plant growth, net carbon exchange rate and transpiration if the physiologically important gases including carbon dioxide, oxygen and water vapour, were maintained above threshold levels. The reduction of oxygen partial pressures below 7 kPa had drastic consequences across all atmospheric pressures with poor germination, seedling establishment and growth. It is evident that the response of plants grown at reduced pressures from young seedlings differs from that of older plants that were established at ambient conditions and then subjected to the atmospheric adjustment. The young plant tissues adapt in response to the extreme conditions and maintain productivity despite the limited atmosphere. / Natural Science and Engineering Research Council, Canadian Space Agency, Ontario Graduate Student Program, Canadian Foundation for Innovation, Ontario Innovation Trust

The reduction of fuel consumption and the reduction of toxic emissions are the main goals of research and development in the area of internal combustion engines. The use of exhaust gas recirculation (EGR) to come further in that direction is today an established method for diesel engines. EGR reduces the emissions of nitrogen oxides with a low penalty in fuel consumption. The increasingly hard regulations on emissions put high pressure on the manufacturers to improve these systems. The present work aims at increasing the knowledge in the area of EGR. Two of the main challenges when applying EGR are addressed, efficiency and mixing. The efficiency of the EGR-system is analyzed, focusing on keeping the fuel penalty low for a given EGR-rate. Different layouts of the EGR system are studied and compared regarding their stationary and transient properties. Exergy analysis is used to show the potential for improvement in different system components. In the same time, exergy analysis as a tool is introduced and compared to energy analysis of a system. The usefulness of exergy analysis of the entire gas exchange is shown by the example of a heavy-duty diesel engine. The problem of EGR and air mixing is approached by a detailed study of the mixing process in a heavy-duty diesel engine. Different methods for the measurement of EGR distribution are presented and compared. Additionally, the possibility to predict the mixing effects by 1-D and 3-D simulation is assessed. It is shown that the mixing between air and EGR is highly dependent on the pulsating nature of the flow. The EGR is shown to be transported in packets in the air flow. This leads to the conclusion that mixing not only at the mixing point, but also mixing in flow direction needs to be optimized, as the distribution of EGR between the cylinders is dependent on the timing between the passage of the EGR packets and the valve opening time. / <p>QC 20140203</p>

Superheated steam (SS) drying of distillers’ spent grain (DSG) is a more energy efficient alternative to conventional hot air drying. SS drying at sub-atmospheric pressure (also referred to as low pressure) can prevent burning and lowering the quality of the food product. The objective of this study was to design, fabricate, and test a SS drying system that could operate at sub-atmospheric pressure for drying DSG. After the custom designed system was constructed, major problems associated with the system were identified. A number of tests were carried out and modifications were made to the system to resolve technical problems. Distillers’ spent grain was then successfully dried using the system under various levels of temperature from 95 to 115°C and pressure of either -25 or -20 kPa, with a SS velocity from 0.100 to 0.289 m/s.

The flow field around a low pressure turbine blade is examined using smoke-wire flow visualization, static surface pressure measurements, and particle image velocimetry (PIV). The purpose of the experimental study is to investigate the transition and separation characteristics on low pressure turbine blades under low Reynolds number (Re) and varying freestream turbulence intensity (FSTI). A cascade model consisting of 6 Pratt andamp; Whitney PAK-B low pressure turbine blades was examined in a wind tunnel using PIV and flow visualization. Smoke-wire visualization was performed for test section exit angles of 93°, 95°, and 97°, in the range Re = 3 · 104 to 9 · 104 and three levels of FSTI varied with a passive grid. The locations of separation and transition were determined to be approximately 45% and 77% of the suction surface length, respectively, based upon the smoke stream lines observed in the images, and appear to be independent of Re, turning angle, and FSTI. The maximum size of the separation bubble was found to decrease with increasing Re, turning angle, and FSTI. PIV images from three camera views were processed for an exit angle of 95° and a Re range of 3:0 · 104 to 30:0 · 104 and three levels of FSTI. Velocity, vorticity, and reversed flow probability field plots were generated along with velocity, vorticity, and RMS velocity profiles. The point of separation point was determined to be from 63% SSL to 67% SSL. The area of reversed flow was computed for each image pair from camera views 1 and 3, as an approxiamtion of the relative size of the separation region. For low Re and FSTI cases the area was much larger than for higher FSTI cases at any Re. The raw PIV images include some of the rst clear pictures of the turbulent flow structures forming in the unsteady shear layer over the suction surface of low pressure turbine blades. Several movies are compiled that show how the geometry and location of the shear layer evolve in time for a given set of flow conditions.

The flow field around a low pressure turbine (LPT) blade cascade model with and without flow control is examined using ejector nozzle (EN) and vortex generator jet (VGJ) geometries for separation control. The cascade model consists of 6 Pak-B Pratt andamp; Whitney low pressure turbine blades with Re = 30,000-50,000 at a free-stream turbulence intensity of 0.6%. The EN geometry consists of combined suction and blowing slots near the point of separation. The VGJs consist of a row of holes placed at an angle to the free-stream, and are tested at two locations of 69% and 10.5% of the suction surface length (SSL). Results are compared between flow control on and flow control off states, as well as between the EN, VGJs, and a baseline cascade with no flow control geometry for steady and pulsatile blowing. The EN geometry is shown to control separation with both steady and pulsatile blowing. The VGJs at 69% SSL are shown to be much more aggressive than the EN geometry, achieving the same level of separation control with lower energy input. Pulsed VGJs (PVGJ) have been shown to be just as effective as steady VGJs, and results show that a 10% duty cycle is almost as effective as a 50% duty cycle. The VGJs at 10.5% SSL are shown to be inefficient at controlling separation. No combination of duty cycle and pulsing frequency tested can eliminate the separation region, with only higher steady blowing rates achieving separation control. Thus, the VGJs at 69% SSL are shown to be the most effective in controlling separation.