• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 293
  • 10
  • Tagged with
  • 453
  • 453
  • 174
  • 174
  • 86
  • 73
  • 73
  • 73
  • 53
  • 27
  • 27
  • 26
  • 26
  • 25
  • 24
  • 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.

Terahertz Time Domain Spectroscopy of Anisotropic Systems: techniques, analysis and applications

Sahota, Derek G. 05 1900 (has links)
<p>The method of terahertz time domain spectroscopy (THz-TDS) allows determination of the broadband electromagnetic response of materials over a typical spectral region of 0.3 to 3 THz. Past work in this field has generally been dominated by the investigation of isotropic materials and the significant potential of using THz-TDS to study anisotropic materials has generally be under utilized. This work encompasses several stages on the path to develop THz-TDS for anisotropic material studies. First, the design, construction and optimization of a high sensitivity THz-TDS polarimetry setup is shown. The extinction ratio between electromagnetic field components in this setup is on the order of 105:1, over two orders of magnitude better than the typical 103:1 found in previous studies. Birefringent and dichroic polymer and crystalline materials are then studied to show the utility of the polarimetric system when compared to typical THz-TDS systems. To further the goal of developing broadband THz optics, a method for designing and constructing achromatic waveplates is discussed. Using this method, a proof of concept waveplate is fabricated and shown to induce an ellipticity of at least 0.75 over the THz bandwidth of 0.75 to 2.25 THz. Discussion then shifts to the field of gas spectroscopy using THz-TDS, and the THz absorption spectra of water, methanol, ethanol, isopropanol and acetone are measured. The measured water spectrum shows evidence for the formation of a tertramer of water molecules, which has a collective vibrational mode around 2.05 THz. The thesis concludes with a discussion of possibilities for measurements of circular dichroism using THz-TDS.</p> / Master of Applied Science (MASc)

Flow Boiling Heat Transfer in a Long, Small Diameter, Vertically Oriented, Uniformly Heated Tube

Statham, Allan Bradley January 2009 (has links)
<p>A thermalhydraulics experiment was constructed at McMaster University that is capable of measuring heat transfer data for test sections up to 1 m long at pressures up to 10.0 MPa. The test section was powered by a 96 kW DC power supply with digital control. Inlet temperature was controlled using a 40 kW RMS AC welding power supply. The experiment was pressurized using a 3.79 L bladdertype accumulator charged by a 13.8 MPa nitrogen cylinder and controlled using Swagelok pressure-reducing and back-pressure regulators. Up to 870 kPa of pump head was supplied using a Micropump GC-M25 pump.</p> <p>Commissioning data was gathered using a 93.2 cm long by 4.6 mm inside diameter Inconel 600 test section at 2.0 MPa with inlet temperatures from 126-180°C, representing inlet qualities of -0.2 to -0.08, and mass fluxes of 1500 and 2000 kg m<sup>-2</sup> S<sup>-1</sup>. Maximum outlet quality was 0.07. Heat transfer was measured using electrically isolated thermocouples 2, 4, 9, 14, 24, 34, and 44 cm from the test section outlet. Using the most reliable thermocouple 4 cm from the test section outlet, and including only data that had a heat balance error of less than ±2%, the PetukhovPopov and Gnielinski correlations for single phase heat transfer overpredicted experimental results with mean errors of 10.2% and 19.1% and standard deviations of ±3.0% and ±3.3% respectively. Several sub cooled boiling correlations showed good predictive capability for the present results. The Thom correlation predicted subcooled boiling heat transfer 4 cm from the test section outlet particularly well with a mean error of 0.5% and a standard deviation of ±14.1%. Low mass quality saturated boiling data was predicted with a mean error of 15.3% and a standard deviation of 18.0% by the modified Chen correlation. Overall the preliminary results show good quantitative agreement with existing correlations. More data will be gathered in the near future to corroborate these results and verify the experimental capabilities at a wider range of pressures and flow rates.</p> <p>The experiment will be used in the future to gather transient critical heat flux data. The experimental measurement accuracy, measurement speed, maximum inlet temperature, and flow control will be improved. This will be achieved by improving the thermocouple shielding and isolation, modifying and adding new data acquisition instrumentation, adding a heat exchanger at the test section outlet for inlet preheating, and adding an electronically controlled variac to control the pump voltage.</p> / Master of Applied Science (MASc)

Analysis of Intermittent Buoyancy Induced Flow in Asymmetrically Obstructed CANDU Nuclear Reactor Fuel Channels

Spencer, J. 04 1900 (has links)
<p>CANDU reactors have a large number of active and passive systems which help to mitigate events such as a loss of forced cooling or a loss of electrical power. During these events, decay heat must be removed using either emergency power driven active systems or through natural circulation phenomena. Depending on the configuration of the core at the time of the event, single or two-phase natural circulation is available to transport energy from the core to the steam generators which act as a heat sink. However, in some configurations (such as during a maintenance outage) natural circulation to the boilers may be precluded due to either the boilers or heat transport system being partially drained. Under these conditions flow may stagnate in the horizontal fuel channels which will initiated a mode of circulation known as Intermittent Buoyancy Induced Flow (IBIF).</p> <p>During IBIF, void generated in the center of the core will periodically reach a feeder and vent from the channel due to buoyancy induced forces, with liquid entering the channel from the opposite feeder, cooling the fuel. Analysis is typically performed to demonstrate that during the period of time from stagnation to venting fuel temperatures remain within their acceptance criteria. This mode of emergency heat removal can remove sufficient heat to preclude fuel failures until such time as forced flow can be re-established.</p> <p>It is assumed in most analysis that completely symmetrical configurations represent the worst possible configuration since most asymmetries (i.e., in channel axial heat flux, channel creep etc.), would lead to earlier venting and hence lower fuel temperatures. However, asymmetry in the form of a partial obstruction in the fuel channel during IBIF may occur due to maintenance or inspection activities- a scenario that has not been included in previous experimental and computational work on IBIF. This paper presents the analysis of the impact of partial flow obstruction on IBIF scenarios. A model is constructed using the code GOTHIC, and is benchmarked against experimental data from the Cold Water Injection Test (CWIT) facility for both the symmetrical and asymmetrical configurations. The work demonstrates that for single-phase IBIF, the impact of partial obstructions is not prohibitive. Computational demands precluded the completion of two-phase simulations in a reasonable timeframe; however useful insights and observations are drawn from the early stages that are successfully simulated.</p> / Master of Applied Science (MASc)

The Development of Trip Coverage Maps for the McMaster Nuclear Reactor

Stoll, J. L. 12 1900 (has links)
<p>Trip coverage maps indicate the reactor conditions under which instrument devices, manual scrams or passive safety systems are capable of arresting reactor transients initiated by specified postulated accidents before reaching safety boundaries. Trip maps are developed by simulating reactor transients with appropriate codes such as the PARET/ANL code. PARET/ANL has been validated against SPERT transient data with favorable results and is particularly suited for research reactor simulation of MTR reactors like the McMaster Nuclear Reactor (MNR).</p> <p>A conservative PARET/ANL model of MNR has been developed by considering the characteristics and operating limits of the MNR core. Conservative conditions of accident scenarios were adopted and PARET/ANL was used to simulate these conditions in MNR. During these P ARET power excursion simulations the MNR engineered safety system responses to loss of regulation rod control, sample handling and fuel handling accident scenarios were assessed and trip coverage maps were developed for each accident category. Forced convection and natural convection reactor conditions were considered.</p> <p>The PARET/ANL model of MNR predicts at least one engineered safety system is capable of arresting transients initiated from high power conditions (0.1 - 5.0 MW) in all the accident scenarios considered, -before the onset of bulk boiling. The model predicts at least one system prevents transients from reaching these thermal limits during transients initiated from low power conditions «0.1 MW) during loss of regulation rod control events. The withdrawal of SSR from low power conditions induce transients which may progress to bulk boiling in the hottest fuel channel. Fuel handling accident induced transients from a shutdown state are predicted to be arrested by the <3.8 s period scram and both 125% high flux scram instrument channels before thermal limits are reached.</p> / Master of Applied Science (MASc)


Gupta, Ruchi January 2007 (has links)
<p>The motivation for this project is to mimic an electronic microprocessor in the fluidic domain to enable on-chip decision making for lab-on-a-chip applications. Microfabrication can increase the economic feasibility of microfluidic computing by lowering the cost per chip. Monolithic integration also has the potential to reduce the packaging costs and reduce the interconnect delays.</p> <p>In this thesis a high reliability no-moving part microfluidic NOR gate was modeled and optimized using modern and widely-accepted computational fluid dynamics tools. Our optimized microfluidic NOR satisfies all the stringent device requirements needed to make a computing system. The transfer curves are non-linear, the fan-out is greater than 12, the input and output signals are in the same domain and the flow of information is only in one direction. Fabricating the microfluidic circuits with components of a single fixed geometry is very attractive. The NOR is a universal gate and thus all logic functions can be realized by a combination of NORs.</p> <p>Three important components of computing: a half adder, a static memory/latch and a clock were also modeled. We have also studied the dynamics of the device, and have understood the origin of the switching time. The performance of the device is only dependent on the Reynolds number of the supply jet. Thus the performance of the device for any fluid: air, water, oil etc, will remain unaltered at the same Reynolds number. Based on our understanding of the power vs. geometry we can predict the critical dimension of the device that can operate at the desirable power consumption.</p> <p>Finally, we enVISIon applying the designed microfluidic NOR to a newly emergmg technology - i.e. Lab-on-a-chip. We envision fabricating an integrated assembly of microfluidic devices to make a microfluidic processor for lab-on-a-chip systems. This work could have a major impact for biomedical applications.</p> / Master of Applied Science (MASc)

Study of the Applicability of the TRACE Code to CANDU Safety Analysis by Modeling the RD-14M Experimental Facility

Hummel, David 05 1900 (has links)
<p>A modern thermal-hydraulics system code is used to model the behaviour of a nuclear power plant's heat transport system in best-estimate safety analyses. The U.S. Nuclear Regulatory Commission's newly developed TRAC/RELAP Advanced Computational Engine (TRACE) code represents the state of the art in the field. Before a code can be accepted for use in safety analyses, however, it must first be demonstrated that it can produce meaningful results through a process of verification and validation. To demonstrate the applicability of the TRACE code to modeling CANDU type reactors, a model of the RD-14M integral test facility has thus been created using TRACE V5.0.</p> <p>The RD-14M facility is an electrically heated, scaled representation of a typical CANDU primary heat transport system. Tests at the facility are done to simulate various postulated accident scenarios, including loss of coolant accidents. A specific test (B9401) is of note for serving as benchmark data in an International Atomic Energy Agency (IAEA) code intercomparison and validation exercise, and has been modeled with TRACE.</p> <p>TRACE was demonstrated to reproduce the general trends of the test transient with fidelity comparable to other codes included in the IAEA exercise. Differences between the measured and predicted peak fuel sheath temperatures and break discharge rate were found to partially result from limitations in TRACE's constituent thermal-hydraulic models' ability to account for some horizontal flow stratification effects and break discharge phenomena common in CANDU accident analysis. Methods are proposed within the modeling methodology to account for these limitations. Ultimately, TRACE predicted the important test parameters as well as or better than some of the established codes used in the IAEA exercise, attesting to its maturity as an analysis tool.</p> / Master of Applied Science (MASc)

Fiber Optic Sensors for In-Situ Monitoring of Diesel Engine Exhaust Gas

Lakhian, Vickram 27 April 2010 (has links)
<p>A fiber optic carbon dioxide sensing system was developed for in-situ monitoring of carbon dioxide within a diesel engine exhaust environment. The fib er sensor was based upon the encapsulation of pyranine paired with tetraoctylammonium hydroxide within a hydrophobic glass formed using the sol-gel process. The sensitivity of the sensor to carbon dioxide was shown to follow a non linear trend with the highest sensitivity in the 0 - 5% CO<sub>2</sub> range. The lower detection limit was experimentally determined to be better than 0.3 % CO<sub>2</sub> . The fiber sensor's response was also characterized within an environment similar to that within an diesel engine exhaust stream. The fiber sensor was shown to be relatively unaffected by carbon monoxide and nitric oxide at concentrations which are typically found within a diesel engine exhaust gas. Nitrogen Dioxide, however, caused an effect in biasing the sensor response to erroneously report higher concentrations of carbon dioxide than were present . Higher concent rations of nitrogen dioxide were shown to permanently damage the fiber sensor and render it inoperative. The effects of increased environmental temperature and relative humidity were shown to decrease the sensitivity of the fiber sensor within the range of interest tor carbon dioxide sensing within diesel exhaust gases. An experiment within the exhaust stream of a single cylinder 2.4 kW diesel engine demonstrated that the fiber sensor was capable of monitoring the carbon dioxide levels for 6 minutes, however, longer exposure to this exhaust environment caused the destruction of the fiber.</p> / Master of Applied Science (MASc)

Dual-View Catadioptric Imaging System Design for Endoscopy

Wang, Chih Chung Roy 09 1900 (has links)
<p>Fluorescence endoscopy is a promising functional imaging technique to improve screening of early cancer lesions in the gastrointestinal (GI) tract. The intensity of tissue autofluorescence is weak and conventional forward viewing endoscopes are inefficient in light collection from objects of interest located on the GI tract wall. This thesis work presents the design and optimization of a catadioptric endoscope objective lens that is capable of acquiring simultaneous forward and radial views. The radial view optics is optimized for a balance between image quality and light collection by utilizing a pair of folded parabolic mirrors for redirecting the field of view and lenses for aberration control. The modulation transfer function, numerical aperture, track length, and field of view are parameters used in the optimization. Non-sequential ray tracing simulations of the light collection of various field locations along a cylindrical surface that simulates the GI tract suggest that the proposed design is more practical in light collection when compared to typical wide-angle, forward-viewing endoscope objectives. A prototype with additional optimization in an enlarged 3:1 scale design is manufactured by the Instrument Technology Research Center of the National Applied Research Laboratories (Hsinchu, Taiwan, Republic of China). Empirical verification of the modulation transfer function as well as relative light collection across the field of view is performed on the manufactured prototype. View synthesis digital image processing algorithms are proposed and tested using imagery acquired by the manufactured prototype.</p> / Master of Applied Science (MASc)

An In-Fiber Michelson Interferometer Long-Period Grating (LPG) With Integrated Sol-Gel and Aptamer Coatings for Biosensor Development

Xiao, Yao 08 1900 (has links)
<p>In this work, an in-fiber Michelson interferometer Long-Period Grating (LPG) biosensor with integrated sol-gel and aptamer coatingd was used for the development of a biosensor for adenosine triphosphate. A macroporous gold-nanoparticle doped sol-gel derived silica film was coated on the sensing head to enhance surface area and the sensitivity of the LPG based biosensor and to act as a surface for subsequent aptamer immobilization. The large surface area of the sol-gel film increases the number of immobilized aptamers, while the presence of the gold nanoparticles improves the refractive index match with the fiber cladding, enhancing sensitivity. The thin film, which is only two hundred nanometers thick, ensures the evanescent wave penetrates into the ambient environment. The LPG sensor has been demonstrated to work for the selective sensing of ATP in solution. The origin of the sensitivity enhancement is confirmed via simulation and experiments which included the design and fabrication of the LPG sensor.</p> / Master of Applied Science (MASc)

Validation of Computational Fluid Dynamic Tools for Single-Phase Flow Distribution in CANDU Headers

Muhana, Ala January 2009 (has links)
<p>Canada Deuterium Uranium, CANDU, nuclear reactors use forced convection cooling to remove heat from the nuclear fuel and transport it to the power production systems. Flow is supplied by large capacity heat transport pumps and is distributed to each separate fuel assembly through headers. The determination of thermalhydraulic parameters of the CANDU headers is important because hydraulic behavior in the headers governs the void fractions of fu el channels connected to them and influe nces the fuel bundles cooling efficiency during postulated accidents.</p> <p>This work presents the validation of FLUENT 6.3.26, a three dimensional Computational Fluid Dynamics (CFD) code, for header flow distribution simulations by comparing predictions to experimental data. The experimental data were obtained for three different header geo metries: horizontal header with four vertical outlets (case study data obtained from literature), horizontal header with two vertical inlets and header with two horizontal inlets (experiments done in this study). The experiments were carried out using 1.0 m long, 3.67 cm 10 horizo ntal cylindrical header with two symmetrical distributed vertical inlets or two horizo ntal inlets at the two header ends. The flow is distributed to five horizontal and five vertical outlets along the header with 0.92 cm 10.</p> <p>In the flrst validation, FLUENT provided good predictions of flow distribution and pressure gradients along the header for different inlet flow rates (Re number between 800 and 4,800). In the second and third validations, simulations for both vertical and horizontal inlet configurations were examined and with varying levels of inlet flow imbalance. The experimental data consists of a set of outlet flow rates as a function of inlet flow rates. The effects of flow inlet velocities, flow modeling and grid density on the computational accuracy are also presented. The CFD technique was found to be an efficient tool to predict the flow distribution in the headers studied.</p> / Master of Applied Science (MASc)

Page generated in 0.1305 seconds