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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A study of directionally solidified Rene 80 subjected to short-term overtemperature

Smart, Heather 29 March 2017 (has links)
Effects of short-term overtemperature on Rene 80 DS were studied using Gleeble thermo-mechanical simulation apparatus. Volume fraction of gamma prime to gamma matrix was quantified and used to assess the effects of time, temperature and stress. Volume fraction was found to decrease with increasing temperature and time. Dissolution was found to occur through both solid and liquid state dissolution. Application of tensile stress was found to influence dissolution behaviour of gamma prime. / May 2017
2

Beam-Scanning Reflectarray Enabled by Fluidic Networks

Long, Stephen 2011 December 1900 (has links)
This work presents the design, theory, and measurement of a phase-reconfigurable reflectarray (RA) element for beamforming applications enabled by fluidic networks and colloidal dispersions. The element is a linearly polarized microstrip patch antenna loaded with a Coaxial Stub Microfluidic Impedance Transformer (COSMIX). Specifically, adjusting the concentration of highly dielectric particulate in the dispersion provides localized permittivity manipulation within the COSMIX. This results in variable impedance load on the patch and ultimately continuous, low-loss phase control of a signal reflected from the patch. Different aspects of design, modeling, and measurement are discussed for a proof-of-concept prototype and three further iterations. Initial measurements with manual injections of materials into a fabricated proof-of-concept demonstrate up to 200 degrees of phase shift and a return loss of less than 1.2 dB at the operating frequency of 3 GHz. The next design iteration addresses fabrication challenges as well the general cumbersomeness of the proof-of-concept by replacing the static material delivery system with a dynamic closed-loop fluidic network. It also makes use of a design procedure to maximize the phase sensitivity. Measurements demonstrate progressive phase shifts through dilution of the system reservoir; however, the initial measurements with this system are not in line with simulated predictions. Investigations suggest the primary culprit to be inaccurate material data. The dielectric constant of the particulate (colloidal BSTO) was overrated and the loss tangent of the fluid medium (a silicone-based oil) was underrated. After accounting for these issues the measurement a second measurement with the system demonstrates 270 degrees of phase shift with return loss of 9 dB. The next design iteration examines a trade-off between phase sensitivity and reduced losses. The design also features modifications to the fluidic system to allow for layered fabrication in the GND plane as well integration with a 2-port coaxial measurement cell. Attempted measurements discover the fluidic system cannot flow the higher concentrations of nanoparticles necessary for phase shifting. A final design iteration addresses this challenge by expanding and repositioning inlets to the fluidic system. Free space reflection measurements with this element initially demonstrate phase shifting until a buildup of nanoparticles form within the COSMIX.
3

Influence of a magnetic field on magnetic nanofluids for the purpose of enhancing natural convection heat transfer

Joubert, Johannes Christoffel January 2017 (has links)
Natural convection as a heat transfer mechanism plays a major role in the functioning of many heat transfer devices, such as heat exchangers, energy storage, thermal management and solar collectors. All of these have a large impact on the generation of solar power. Considering how common these devices are not only in power generation cycles, but in a majority of other thermal uses it is clear that increased performance for natural convection heat transfer will have consequences of a high impact. As such, the purpose of this study is to experimentally study the natural convection heat transfer behaviour of a relatively new class of fluids where nano-sized particles are mixed into a base fluid, also known as a nanofluids. Nanofluids have attracted widespread interest as a new heat transfer fluid due to the fact that the addition of nanoparticles considerably increases the thermophysical properties of the nanofluids when compared to those of the base fluid. Furthermore, if these nanoparticles show magnetic behaviour, huge increases in the thermal conductivity and viscosity of the nanofluid can be obtained if the fluid is exposed to a proper magnetic field. With this in mind, the study aimed to experimentally show the behaviour of these so-called magnetic nanofluids in natural convection heat transfer applications. In this study, the natural convection heat transfer of a magnetic nanofluid in a differentially heated cavity is investigated with and without an applied external magnetic field. The effects of volume concentration and magnetic field configuration are investigated. Spherical nanoparticles with a diameter of 20 nm are used with a volume concentration ranging between 0.05% and 0.3%, tested for the case with no magnetic field, while only a volume concentration of 0.1% was used in the magnetic cases. The experiments were conducted for a range of Rayleigh numbers in . The viscosity of the nanofluid was determined experimentally, while an empirical model from the literature was used to predict the thermal conductivity of the nanofluids. An empirical correlation for the viscosity was determined, and the stability of various nanofluids was investigated. Using heat transfer data obtained from the cavity, the average heat transfer coefficient, as well as the average Nusselt number for the nanofluids, is determined. It was found that a volume concentration of 0.05% showed an increase of 3.75% in heat transfer performance. For the magnetic field study, it was found that the best-performing magnetic field enhanced the heat transfer performance by 1.58% compared to the 0.1% volume concentration of the nanofluid with no magnetic field. / Dissertation (MEng)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / MEng / Unrestricted
4

Numerical Modeling and Analysis of Composite Beam Structures Subjected to Torsional Loading

Hsieh, Kunlin 16 May 2007 (has links)
Torsion of cylindrical shafts has long been a basic subject in the classical theory of elasticity. In 1998 Swanson proposed a theoretical solution for the torsion problem of laminated composites. He adopted the traditional formulation of the torsion problem based on Saint Venant's torsion theory. The eigenfunction expansion method was employed to solve the formulated problem. The analytical method is proposed in this study enabling one to solve the torsion problem of laminated composite beams. Instead of following the classical Saint Venant theory formulation, the notion of effective elastic constant is utilized. This approach uses the concept of elastic constants, and in this context the three-dimensional non-homogeneous orthotropic laminate is replaced by an equivalent homogeneous orthotropic material. By adopting the assumptions of constant stress and constant strain, the effective shear moduli of the composite laminates are then derived. Upon obtaining the shear moduli of the equivalent homogeneous material, the effective torsional rigidity of the laminated composite rods can be determined by employing the theory developed by Lekhnitskii in 1963. Finally, the predicted results based on the present analytical approach are compared with those by the finite element, the finite difference method and Swanson's results. / Master of Science
5

Development of the gas phase laser induced phosphorscence technique and soot measurements in flame using laser induced incandescence

Lawrence, Martin January 2013 (has links)
Thermometry measurements were carried out using planar laser induced phosphorescence in conjunction with thermographic phosphors in heated turbulent jets and laminar flames in order to further develop the technique for usage in flames. Two dimensional thermometry measurements are essential to improve the understanding of combustion processes, as temperature governs soot pyrolysis, leading to soot formation. Two particular thermographic phosphors, BAM and YAG:Dy were tested and compared and it was found that they were unsuitable for gas phase flame thermometry measurements. Soot volume fraction measurements were carried out using planar two colour laser induced incandescence in gaseous and liquid fuel flames. The gas fuel flames were diluted with nitrogen, carbon dioxide and hydrogen individually and then with nitrogen and hydrogen together, as well as carbon dioxide and hydrogen together, separately. Results revealed the dilution effects of the gases on the soot formation process, where increasing nitrogen percentage in the flow decreased SVF, carbon dioxide reduced it further and hydrogen showed no marked difference. Biodiesels were compared with each other and with diesel in a wick burner in order to analyse their compositional effects on soot. Biodiesel composition was measured using gas chromatography. The sooting tendencies of the biodiesels were as expected, fuels with a longer average carbon chain length and a higher degree of unsaturation were found to produce more soot than shorter, more saturated fuels. Diesel was sootier than all of the biofuels tested, due to containing aromatics and a lower oxygen content. A pilot study was also done, where the performance and emissions of biofuels and biofuel-diesel blends were tested in a gas turbine engine, in order to relate the investigation to real world situations.
6

VISUALIZATION AND CHARACTERIZATION OF ULTRASONIC CAVITATING ATOMIZER AND OTHER AUTOMOTIVE PAINT SPRAYERS USING INFRARED THERMOGRAPHY

Akafuah, Nelson Kudzo 01 January 2009 (has links)
The disintegration of a liquid jet emerging from a nozzle has been under investigation for several decades. A direct consequence of the liquid jet disintegration process is droplet formation. The breakup of a liquid jet into discrete droplets can be brought about by the use of a diverse forcing mechanism. Cavitation has been thought to assist the atomization process. Previous experimental studies, however, have dealt with cavitation as a secondary phenomenon assisting the primary atomization mechanism. In this dissertation, the role of the energy created by the collapse of cavitation bubbles, together with the liquid pressure perturbation is explicitly configured as a principal mechanism for the disintegration of the liquid jet. A prototype of an atomizer that uses this concept as a primary atomization mechanism was developed and experimentally tested using water as working fluid. The atomizer fabrication process and the experimental characterization results are presented. The parameters tested include liquid injection pressure, ultrasonic horn tip frequency, and the liquid flow rate. The experimental results obtained demonstrate improvement in the atomization of water. To fully characterize the new atomizer, a novel infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on the new atomizer and two automotive paint applicators. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the source in traveling through the spray is attenuated by the presence of the droplets. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the droplets as they are transferred from the applicator to the target surface. In addition, the thermal image is post-processed using theoretical and empirical equations to extract information from which the liquid volume fraction and number density within the spray are estimated.
7

The Study of Effects of Gas Bubbles on Acoustic Wave Attenuation Using AST-Sonar System

Wu, Cheng-kang 03 September 2007 (has links)
Bubbles are often present in the natural ocean. Bubbly liquid will have the significant influence the sound propagation, and creates a significant disturbance to under water target's detection. Therefore, it is an important research subject of bubble influence to the sound wave propagation. This study used the sonar training system which developed by British's iTP corporation, through suitable additional design discuss the attenuation of sound propagating through a bubble screen. At first this study collects and infers the formula by the literature review. Secondly, the experimental design of measuring the attenuation of sound wave. The experiment process by using two parallel iron boards to carry on the measurement of gas-volume fraction. Then correlate with the sound pressure from the measurement of hydrophone. After curve fitting, we can clearly know the each other correlation. Finally taking the result compare with the attenuation coefficient formula. The experimental consists of two parts. The first part is to measure the gas-volume fraction of the bubbly liquid contained in the screen; while the second part is to measure the sound attenuation of the bubble screen. The result display that the bubble screen can attenuate about 8 dB per centimeter as the gas-volume fraction stay at 1 percent. At high gas-volume fraction the coefficient of attenuation has increased, and is different from theoretical value. This is because the bubble's correlation has not been considered. In addition, the low frequency sound wave is close to theoretical value, but the high frequency sound wave has big different to theoretical value. Because the high frequency sound wave's wavelength is too small to satisfy the condition. At experiment I suggest to use more appropriate transducers and precise bubble's tube. Thus the experimental result will be better.
8

An Experimental Examination of a Progressing Cavity Pump Operating at Very High Gas Volume Fractions

Glier, Michael W. 2011 May 1900 (has links)
The progressing cavity pump is a type of positive displacement pump that is capable of moving nearly any fluid. This type of pump transports fluids in a series of discrete cavities formed by the helical geometries of its rigid rotor and elastomeric stator. With appropriate materials for the rotor and stator, this pump can move combinations of liquids, suspended solids, and gasses equally well. Because of its versatility, the progressing cavity pump is widely used in the oil industry to transport mixtures of oil, water, and sediment; this investigation was prompted by a desire to extend the use of progressing cavity pumps to wet gas pumping applications. One of the progressing cavity pump's limitations is that the friction between the rotor and stator can generate enough heat to damage the rotor if the pump is not lubricated and cooled by the process fluid. Conventional wisdom dictates that this type of pump will overheat if it pumps only gas, with no liquid in the process fluid. If a progressing cavity pump is used to boost the output from a wet gas well, it could potentially be damaged if the well's output is too dry for an extended period of time. This project seeks to determine how a progressing cavity pump behaves when operating at gas volume fractions between 0.90 and 0.98. A progressing cavity pump manufactured by seepex, model no. BN 130-12, is tested at half and full speed using air-water mixtures with gas volume fractions of 0.90, 0.92, 0.94, 0.96, and 0.98. The pump's inlet and outlet conditions are controlled to produce suction pressures of 15, 30, and 45 psi and outlet pressures 0, 30, 60, 90, 120, and 150 psi higher than the inlet pressure. A series of thermocouples, pressure transducers, and turbine flow meters measures the pump's inlet and outlet conditions, the flow rates of water and air entering the pump, and pressures and temperatures at four positions within the pump's stator. Over all test conditions, the maximum recorded temperature of the pump stator did not exceed the maximum safe rubber temperature specified by the manufacturer. The pump’s flow rate is independent of both the fluid's gas volume fraction and the pressure difference across the pump, but it increases slightly with the pump's suction pressure. The pump's mechanical load, however, is dependent only on the pressure difference across the pump and increases linearly with that parameter. Pressure measurements within the stator demonstrated that the leakage between the pump's cavities increases with the fluids gas volume fraction, indicating that liquid inside the pump improves its sealing capability. However, those same measurements failed to detect any appreciable leakage between the two pressure taps nearest the pump's inlet. This last observation suggests that the pump could be shortened by as much as 25 percent without losing any performance in the range of tested conditions; shortening the pump should increase its efficiency by decreasing its frictional mechanical load.
9

The Physico-Chemical Characterization of Soymilk Particles and Gelation Properties of Acid-Induced Soymilk Gels, as a Function of Soymilk Protein Concentration.

Ringgenberg, Elise 14 October 2011 (has links)
The physico-chemical characteristics of soymilk particles and the gelation properties of soymilk were investigated as a function of soymilk protein concentration, by preparing soymilk samples from different water-to-bean ratios. Particles from different soymilk protein concentrations showed similar protein composition and surface hydrophobicity, but different -potential, size and protein content. The particle voluminosity was derived using a relation between the effective refractive index of soymilk and the turbidity parameter determined experimentally. For the first time, experimental data was compared to theoretical models, drawing general conclusions about colloidal properties of soymilk particles. Protein concentration and the rate of acidification did not have a significant effect on the acid-induced gelation of soymilk. Results demonstrated that decreased charge is a prerequisite for particle aggregation, which is driven by hydrogen bridging. This thesis provides soymilk processors with general principles on the colloidal behaviour of soymilk, valuable information for new product development and better process design. / Soybean Growers of Ontario, Natural Sciences and Engineering Research Council of Canada
10

The Effect of Phase Morphology and Volume Fraction of Retained Austenite on the Formability of Transformation Induced Plasticity Steels

Lawrence, Benjamin 27 January 2010 (has links)
Transformation induced plasticity (TRIP) steels are a class of steels with exceptional formability properties, due mainly to the presence of meta-stable retained austenite which transforms to martensite under loading, locally hardening the steel. The volume fraction and mechanical stability of the retained austenite play an important role in producing the high formabilities of TRIP steels. In this thesis, two separate morphologies of retained austenite, equiaxed versus lamellar, have been produced through thermo-mechanical processing of a single common TRIP steel chemistry. The sheet formability characteristics of these two microstructures were examined, with varying volume fractions of retained austenite, through uniaxial tensile and in-plane plane-strain (IPPS) testing. It was found that higher levels of retained austenite produced better formability properties for both microstructures and strain paths. In uniaxial tension it was seen that the the lamellar microstructure attained higher strains at maximum load, and exhibited more sustained instantaneous n values than the equiaxed structure, despite having a lower volume fraction of retained austenite. IPPS testing was performed using an optical measurement of local strain and a comparative forming limit based on differences in strain rate between a developing neck and the surrounding material. It was found that the lamellar microstructure performed better than the equiaxed microstructure for this strain path, achieving higher strains before reaching the comparative forming limit. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-01-25 16:36:07.598

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