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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.
31

Bubble Free Electrodes for Electroosmotic Pumping

Subramani, Ganapathy Balasubramanian 08 1900 (has links)
<p>Electroosmotic (EO) pumping is a widely used micro fluidic pumping technique due to its advantages such as simple design, applicability to wide range of conductive fluids and favorable scaling of electrical forces. Electrodes are necessary to establish the electrical forces and hence fluid flow inside the micro channel. One of the major problems associated with inert electrodes such as gold or platinum used in EO pumping is gas evolution, whereas redox electrodes have a shorter life time. In this thesis, EO pumping is demonstrated using two different bubble free electrodes with longer lifetime.</p> <p>The first of the two types demonstrated is thick silver/ silver chloride electrodes embedded in poly di-methylsiloxane (PDMS) micro channels. However, embedding thick electrodes inside PDMS channels using traditional micro fabrication will lead to a gap near the electrodes which can result in leakage of the working fluid. A new surface micromachining technique in PDMS has been developed to address the leakage problem.</p> <p>Surface micromachining with PDMS as a structural material and photoresist as a sacrificial material allows the fabrication of PDMS microchannels on substrates with significant topography. Adhesion of the structural layer with the substrate is characterized for different prepolymer ratios using standard tensile test. 1:3 (curing agent: base) combination was found to have the highest bonding strength with an adhesion strength of7.2 MPa. The effectiveness of this technique is demonstrated by the fabrication of microchannels with embedded 61lm thick silver/ silver chloride electrodes. The micro channels are leak proof and conformal contact between the PDMS and electrode is confirmed through SEM. The release time for micro channels was reduced to 1 min irrespective of the length of the micro channel. The flexibility and versatility of this technique for fabrication of multi layered micro channel structure is demonstrated through a micro fluidic valve. The valve closure occurred at 6.37 kPa.</p> <p>The Voltage-current density of the Ag/AgCl electrodes was characterized. The limiting current density of the electrode is 2.7 mAlcm2. The capacity of the electrodes is 1680 μA-sec. EO pumping has been demonstrated with an applied voltage of 1-2 V and a maximum velocity of 44 μm/sec is obtained.</p> <p>The second bubble free electrode demonstrated is an inert liquid electrode which has an extended life unlike the metal electrodes. The device consists of two upper PDMS micro channels and a lower micro channel with a 6μm thick nanoporous polycarbonate sheet placed in between them. An electro osmotic pump has been demonstrated using this liquid electrode configuration with a maximum velocity of 118 μm/sec at 60 V.</p> / Master of Applied Science (MASc)
32

Stretch Forming of Sheet Metal. A Review of Some Instability Theories and The Design and Construction of A Testing Rig For Formability Studies of Thicker Guage Materials

Paul-Chowdhury, Sisir R. 11 1900 (has links)
<p>Some instability theories relating to the stretch forming of sheet metal are reviewed, and a comprehensive computer programme based on Marciniak's modified mathematical model is developed to determine, theoretically, the Forming Limit Diagram. Also, Kasper's Shape Analysis technique is analyzed in the form of an Optimization model, and an attempt is made to correlate it with the theoretically determined FLD in order to predict the formability of sheet metal in advance. At the same time, a testing rig is designed, built and tested for the determination of the FLD of thicker guage materials under laboratory conditions.</p> / Master of Engineering (ME)
33

Validation of Computational Fluid Dynamics for Atria Geometries

Rundle, Charles 09 1900 (has links)
<p>A systematic validation of the computational fluid dynamics code ANSYS CFX for atria geometries is presented. Turbulent natural convection, radiation heat transfer and conjugate heat transfer are essential to the performance of an atrium and are all validated separately. In order to be thorough, the initial validations involve the fundamental simulations for each phenomenon. A simulation of a complete atrium is also presented using the conclusions reached in the previous validations.</p> <p>The validation of each of the phenomena was successful. Turbulent natural convection simulations yielded two suitable turbulence models, with the preference for k-ω model being decided by a narrow margin. The radiation validations proved that the Discrete Transfer model was an accurate model and the best offered by ANSYS CFX. Conjugate heat transfer showed that ANSYS CFX was capable of capturing the qualitative aspects of the phenomenon. The final atrium simulations showed the expected over prediction of temperature in the atrium, and an under prediction of the stratification. The atrium simulation proved insensitive to façade emissivity. The magnitude of the solar radiation heat flux did change the temperature and velocity field. It was shown that ANSYS CFX was capable of modeling the important phenomena but more accurate boundary conditions are required to obtain the best results possible.</p> / Master of Applied Science (MASc)
34

Chipping and Breakage of Carbide Tools

Masood, Abdel Meged Zaher 05 1900 (has links)
<p>The purpose of this project was to study the failure mechanisms of carbide tools in turning operations due to fracture of the cutting edge. The study consisted of a combination of turning tests, examination of fracture surfaces and an analysis of the stresses in the tool as produced by the cutting force. Thermal stresses are so far not considered. It is concluded that chipping is a ductile failure due to high shear stresses at the cutting edge and breakage is brittle fracture originating at the rake face at a local maximum of tensile stress.</p> <p>For the finite element stress analysis a new method of successively refining mesh while diminishing the analysed area is introduced which is rather effective and economical in that all computation except for the final field is done only once for various loading cases.</p> / Master of Engineering (ME)
35

Noise Sources Characterization of Automotive HVAC Systems

Madani, Vahid 10 1900 (has links)
<p>The noise sources and mechanisms of the front and rear HVAC systems of an automotive are characterized experimentally. The front system has three main outlet ducts equipped with louvers and operates in two modes of bypass and recirculation. The inlet and outlet sides of the rear system are both located in the cabin; hence, it always works only on the recirculation mode. The outlet duct of the rear system is covered by a ten-hole curved plate which is found to be a strong source of noise. Both systems are tested at the highest possible flow rate, as it is the most annoying condition of noise generation. The noise coming out of each duct of the front and rear systems and their fan units are measured separately. Since the fan is an important part of the systems, it is studied at different speeds with more details. In order to compare the effect of the noise generated by the fan section with the noise produced by the complete system, the impeller is replaced with a speaker generating an overall sound level similar to the fan noise. Under this condition, the flow noise due to the evaporator core, distributive ducts and louvers are cancelled. It is concluded that at low frequencies the duct flow-noise is dominant. At high frequencies, the effects of both duct flow-noise and fan noise are impor1ant. To find out how the combination of the outgoing sound from the vents and fans inlet affect on the driver and passengers, some measurements are carried out inside the cabin of the automobile.</p> / Master of Applied Science (MASc)
36

Computer Adaptive Control in Milling

MacNeil, Peter R. 04 1900 (has links)
<p>The purpose of this project was to develop a CNC software base and an Adaptive Control system for a CNC milling machine. The CNC software base consists mainly of Assembly language routines written for the HP-2100 minicomputer for the editing and debugging of N/C data programs. The Adaptive Control system consists of a cutting force transducer, and an Analog to Digital Processor which supply input to an A/C routine resident in the HP-2100 minicomputer. The Adaptive Control system and the cutting forces encountered in milling were simulated in computer programs. The system was stabilized by using the simulation to predict the response of the actual system.</p> / Master of Engineering (ME)
37

An Experimental Study of the Hydrodynamic Suspension of Cylinders in a Vertical Pipeline

Lee, Stephen W. 12 1900 (has links)
<p>This thesis describes an experimental study of hydrodynamically suspended cylinders and cylinders modified by end cap(s) in a vertical pipeline, using water and polymer solution as the fluid medium.</p> <p>The experiments involved hydrodynamically suspending steel and aluminium cylinders in a pipeline for the sphere to pipe diameter ratios of 0.434 to 0.864. Drag coefficients were found from a force balance which involved measuring the average velocity of flow near the cylinders as well as the pressure drops across the cylinders. The experiments on cylinders were done in both water and dilute aqueous polymer solutions, while the tests on cylinders modifies by end caps were done in water only. The length to diameter ratios of cylinders used in this study ranged from three to fourteen.</p> <p>Comparison of results from this study of those obtained by other authors especially Hoerner(¹³), McNown & Newlin(¹⁸) and Aly^(³⁰) were made.</p> / Master of Engineering (ME)
38

Laminar Flow Development Downstream of an Abrupt Circular Channel Expansion

Pike, Graham K. 06 1900 (has links)
<p>This dissertation reports the development of a flow visualisation technique which was used to study the flow pattern generated by an abrupt expansion in a circular section conduit, Experiments were performed at Reynolds numbers (based on upstream tube diameter) ranging from 222 to 755 and for tube diameter ratios of 0.63, 0.79 and 0.93.</p> <p>Velocity profiles were obtained at each of two different stations beyond the vortex and these were used as upstream boundary conditions for the linearized axial Navier-Stokes equation for the purpose of predicting development lengths. A correlation was obtained for development length as follows:</p> <p>L/D = 0.27 Re⁰˙⁹⁴, D [1- (d/D)²˙⁷⁷] Measurements of vortex length were made for a tube diameter ratio of 0.63 and the results correlated in the form</p> <p>xR/h = 0.048 Re¹˙¹ d</p> <p>Hence both vortex length and development length increase almost linearly with Reynolds number.</p> / Master of Engineering (ME)
39

Diffusion of Drag Reducing Aqueous Polymer Solutions in External Flow

El, Riedy K. F. 04 1900 (has links)
<p>This thesis describes an experimental study of the diffusion of dilute squeous drag reducing polymers when ejected from a thin wall slot into a developing turbulent boundary layer (external flow).</p> <p>A horizontal flat plate located in a 0.1524 m. (6 in.) I.D. plexiglass pipe was specifically designed for obtaining diffusion data. Water or aqueous polymer solutions which were dyed with a fluorescing dye were injected tangentially into the boundary layer through a slot situated near the leading edge of the flat plate. Samples were taken from the flow field and by using a spectrophotometer, concentration profiles were established. The investigation was carried out for a constant free stream velocity of 5.4 m./sec. for various injection flow rates and concentrations in the range 0 to 1500 w.p.p.m.</p> <p>It was found that the diffusion rate will increase for very low polymer concentrations (of the order of 0.75 w.p.p.m.), while the diffusion rate will be reduced for higher concentrations. The resulting data have been compared to Newtonian diffusion phenomena as well as the available data for polymer additives.</p> <p>Correlations for the concentration profiles, diffusion boundary Layer growth, wall concentration and eddy diffusivity are presented. The research covers the four important zones of diffusion with emphasis on the earlier developing zones for which there are virtually no data available. The results indicate that a universal diffusion correlation exists which represents the data for both Newtonian and polymer solutions for the far region downstream but indicate decidedly different phenomena near the injection region, confirming a previously published theoretical analysis.</p> / Master of Engineering (ME)
40

Analysis of a Numerical and Adaptive Control Servomechanism

Elbestawi, Abdel Aziz Mohamed 04 1900 (has links)
<p>The purpose of this project was to analyze the Numerical and Adaptive Control system of a CNC milling machine, in order to improve the time response of the system while maintaining its stability. The available linear control theory as well as the state space method were used to study and simulate the behaviour of the N/C loop. The N/C system was tested to determine the practically optimum values of position and velocity gains. The Adaptive Control system consists of a cutting force transducer, and an Analog to Digital Processor which supply input to an A/C routine resident in the HP-2100A minicomputer. Both classical control theory and the state space technique were also used to investigate the operation of the A/C loop and to predict the response of the actual system.</p> / Master of Engineering (ME)

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