Call number: LD2668 .T4 1984 L56 / Master of Science

A thesis submitted in fulflment of the requirements for the degree of Doctor of Philosophy in the School of Computer Science and Applied Mathematics. November 2015 / The understanding of uid ow at microscale geometrics is an increasingly important eld in applied science and mechanics, especially in bioinspiration and biomimetics. These elds seek to imitate processes and systems in biology to design improved e cient engineering devices. In this thesis, inspired by the e ciency of the insect tracheal system in transporting respiratory gases at microscale, mathematical models that both mimic and explain the gas exchange process are developed. Models for the simultaneous movement of respiratory gases across the insect spiracle, gas transfer from one respiratory chamber to the next, end di usion and tissue absorption at the tracheole tips, and tracheal uid transport are presented. Expressions for tracheal partial pressures of the respiratory gases, rate of change of gas concentrations, rate of tracheal volume change, spiracle behaviour on net gas ow, cellular respiration and tissue absorption, and global gas movement within the insect are presented as well. Two versions of bioinspired pumping mechanism that is neither peristaltic nor belongs to impedance mismatch class of pumping mechanism are then presented. A paradigm for se- lectively pumping and controlling gases at the microscale in a complex network of channels is presented. The study is inspired by the internal ow distributions of respiratory gases produced by rhythmic wall contractions in dung beetle tracheal networks. These networks have been shown to e ciently manage uid ow compared to current produced micro uidic devices. The insect-like pumping models presented are expected to function e ciently in the microscale ow regime in a simple or complex network of channels. Results show the ability to induce a unidi- rectional net ow by using an inelastic channel with at least two moving contractions. These results might help in explaining some of the physiological systems in insects and may help in fabricating novel e cient micro uidic devices. In this study, both theoretical and the Di erential Transform Method are used to solve the exible trachea with gas exchange problem as well as the 2D viscous ow transport with or without prescribed moving wall contractions problem. Both Lubrication theory and quasi- steady approximations at low Reynolds number are used in the derivation of theoretical analysis. ii Moreover, an analytical investigation into the compressible gas ow with slight rarefactions through the insect trachea and tracheoles is undertaken, and a complete set of asymptotic analytical solutions is presented. Then, estimation of the Reynolds and Mach numbers at the channel terminal ends where the tracheoles directly deliver the respiratory gases to the cells is obtained by comparing the magnitude of the di erent forces in the compressible gas ow. The 2D Navier-Stokes equations with a slip boundary condition are used to investigate the compressibility and rare ed e ects in the respiratory channels.

Lorentz forces provide a unique method for the control and mixing of gas flows without the physical intrusion of objects into the flow. Lorentz forces arise when an electric current is passed through a volume in the presence of a magnetic field. The interaction between the electric current and the electric and magnetic fields produces a body force which affects the flow. These forces have been investigated experimentally by other researchers and show promise as a way to accelerate combustion in diffusion flames by increasing the mixing rate of fuel and oxidant streams. Theoretical and numerical models were developed to gain insight into this process. Alkali metal seeding raises the electrical conductivity of a flame by two to three orders of magnitude. This has two significant effects: the Lorentz force becomes stronger for the same applied electric current and magnetic field, and the alkali seed concentration becomes a dominant factor in determining electrical conductivity of seeded gases. This makes electrical conductivity much easier to predict, and so the Lorentz body force produced is easier to determine. A theoretical basis for numerical modeling of reactive flows with variable body forces has been developed. Many issues are important in simulating gas flows. Conservation of chemical species must be carefully maintained. Mass transport by gaseous diffusion, which limits combustion rates in a diffusion flame, must be appropriately modeled. Viscous action is also important, since it promotes mixing of the fuel and oxidant streams. Convective, conductive, and diffusive transport of energy must be carefully treated since energy transport directly affects the fluid flow. A numerical model of an incompressible gas flow affected by Lorentz forces was written and tested. Although assumptions made in the model, such as isothermal conditions and uniform density, are not found in diffusion flames, the numerical model predicts velocity vector patterns similar to those observed in actual Lorentz force tests on diffusion flames. A simulation code for compressible, reactive gas flows which include Lorentz forces has also been written. Several parts of the model have been validated, and the approach used appears likely to produce successful simulations. Further validation studies will be required, however, before complete modeling of the diffusion flame can proceed. / Graduation date: 1995

No description available.

It has been found through experiments at Southwest Research Institute that temperature differences between the gas and wall of the pipe through which the gas is flowing can greatly influence the gas flow in the pipe line and give different velocity magnitudes at the top and bottom half of the pipe. The effect on the flow is observed to worsen at low fluid flow and high temperature differences. This effect has been observed by ultrasonic flow meters which measure the chord average gas velocity at four heights across the pipe. A significant variance in chord averaged velocities is apparent at these conditions. CFD analysis was performed. Low flow velocities of 0.1524 m/sec, 0.3048 m/sec and 0.6096 m/sec and temperature differences of 5.5oK, 13.8oK and 27.7oK were considered. When these conditions were imposed onto the three different geometries, it was seen that the heating caused increased errors in the ultrasonic meter response. For the single elbow and double elbow pipe configurations, the errors were below 0.5% for constant wall temperature conditions but rose to 1% for sinusoid varying wall temperature conditions. The error was seen to increase as the axial velocity became more stratified due to momentum or temperature effects. The case of maximum error was noted for the double elbow geometry with sinusoid wall temperature condition where a swirl type of flow was noted to create localized velocity maxima at the center of the pipe. This part of the pipe was barely touched by the ultrasonic meter acoustic path giving maximum error of 1.4%. A thermal well was placed in the path of the gas flow in the pipe to observe the temperature response on the surface of the thermal well. It was noted that the thermal well surface temperature differed by 1.4% for most cases with gas velocity below 0.6096 m/sec.

In this thesis CIGS absorber layers have been deposited by gas flow sputtering with an extra supply of selenium, a method that displays promise for large scale production because of its one-step sputtering route which deposits low energy particles in a high deposition rate. In this thesis a method was developed where selenium was added to the sputtering process inside the sputter chamber in a controllable manner and in larger amount than done in previous projects. A total of five samples were manufactured with altered evaporation temperatures and an extra supply of selenium which then were finalized to solar cells using the standard baseline process of the Ångström solar center. The characteristics of the CIGS layer and solar cells were analyzed by XRF, IV- and QE measurements. A cell with a conversion efficiency of 11.6 %, Jsc of 27.9 mA/cm2, Voc of 0.63 V and fill factor of 66.2 % was obtained on a 0.5 cm2 cell area without an antireflective coating. All samples contained cells with obtained efficiencies above 10 %, but over the whole samples the efficiencies varied considerably. The samples that were deposited with moderately large selenium evaporation provided the highest efficiencies with a relatively good homogeneity over the substrate. Results show a deficiency of copper in the CIGS films compared to the target composition. The copper content was lower than 70 % expressed in Cu/(Ga+In), which probably resulted in a low diffusion length for electrons, leading to limited cell efficiencies.  Through the duration of the thesis issues that concerned the power supply- and the controls to the substrate heaters as well as the control of the evaporation temperature during the depositions arose that required problem solving and needs to be resolved for the future progression of this work. The conclusions drawn from this thesis are that it is possible to vary the temperature of the selenium source and thereby control the amount of selenium that evaporates during the deposition process even though there is a lot of additional heating in the sputter chamber from both the substrate heaters and the sputter source which could affect the ability to control the amount of selenium being evaporated. That the most likely reason for the limited efficiencies is due to the low copper content in the CIGS films and that a larger amount of evaporated selenium compared to previous work did not result in higher obtained efficiencies.

The present research describes an investigation of the flow through the inlet port and the cylinder of an internal combustion engine. The principal aim of the work is to interpret the effects of the port shape and valve lift on the engine's "breathing" characteristics, and to develop a better understanding of flow and turbulence behaviour through the use of Computational Fluid Dynamics (CFD), using a commercial available package STAR-CD. A complex computational mesh model was constructed, which presents the actual inlet port/cylinder assembly, including a curved port, a cylinder, moving valve and piston. Predictions have been carried out for both steady and transient flows. For steady flow, the influence of valve lift and port shape on discharge coefficient and the in-cylinder flow pattern has been examined. Surface static pressures predicted using the CFD code, providing a useful indicator of flow separation within the port/cylinder assembly, are presented and compared with experimental data. Details of velocity fields obtained by laser Doppler anemometry in a companion study at King's College London, using a steady flow bench test with a liquid working fluid for refractive index matching, compared favourably with the predicted data. For transient flow, the flow pattern changes and the turbulence field evolutions due to valve and piston movement are presented, and indicate the possible source of cyclic variability in an internal combustion engine.

Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: Nanoflow; microflow; unstructured; DSMC. Includes bibliographical references (leaves 171-178).

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 144-146). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.