In this work, several materials possessing a layered structure were investigated using a technique of exfoliation in liquid phase to produce few- to mono-layers of the material. Materials exfoliated in such a way included graphite, boron nitride, molybdenum disulfide and tungsten disulfide. Subsequent transmission electron microscopy and accompanying electron diffraction patterns revealed that few and mono layer forms of these materials have been realized through this exfoliation method. Ultraviolet-visible spectroscopy confirmed the shifting of the band gaps in molybdenum and tungsten disulfides that is predicted in reducing the number of layers of these materials and was also used to confirm the band gap of the boron nitride. As a potential application, exfoliated molybdenum disulfide was used in the construction of electrodes for electrical charge storage in an electrochemical double layer capacitor, or supercapacitor, style device. Cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy measurements were performed using three different electrolytes, which showed good capacitive behavior for these devices. Using the data from electrochemical impedance spectroscopy, equivalent circuit models were generated to represent the systems in different electrolytes. From this, it was determined that the capacitive behavior of these systems was partially diffusion limited.

The magnetocaloric and thermomagnetic properties of the MnNiGe1-xAlx, Ni50Mn35(In1−xCrx)15 and (Mn1−xCrx)NiGe1.05 systems have been studied by x-ray diffraction, differential scanning calorimetry (DSC), and magnetization measurements. Partial substitution of Al for Ge in MnNiGe1−xAlx results in a first-order magnetostructural transition (MST) from a hexagonal ferromagnetic to an orthorhombic antiferromagnetic phase at 186 K (for x = 0.09). A large magnetic entropy change of ∆SM = -17.6 J/kg K for ∆H = 5 T was observed in the vicinity of TM = 186 K for x = 0.09. This value is comparable to those of well-known giant magnetocaloric materials, such as Gd5Si2Ge2, MnFeP0.45As0.55, and Ni50Mn37Sn13 [1]. The values of the latent heat (L = 6.6 J/g) and corresponding total entropy changes (∆ST = 35 J/kg K) have been evaluated for the MST using DSC measurements. Large negative values of ∆SM of -5.8 and -4.8 J/kg K for ∆H = 5 T in the vicinity of TC were observed for x = 0.09 and 0.085, respectively. Partial substitution of Cr for Mn in(Mn1−xCrx)NiGe1.05 results in a MST from a hexagonal paramagnetic to an orthorhombic paramagnetic phase near TM ~ 380 K (for x = 0.07). Partial substitution of Cr for In in Ni50Mn35(In1−xCrx)15 shifts the magnetostructural transition to a higher temperature (TM ~ 450 K) for x = 0.1. Large magnetic entropy changes of ∆SM = -12 (J/kgK) and ∆S = -11 (J/kgK), both for a magnetic field change of 5 T, were observed in the vicinity of TM for (Mn1−xCrx)NiGe1.05 and Ni50Mn35(In1−xCrx)15, respectively. The concentration-dependent (T-x) phase diagram of transition temperatures (magnetic, structural, and magnetostructural) has been generated using magnetic, XRD, and DSC data. The role of magnetic and structural changes on transition temperatures are discussed.

Accessibility to clean water which is necessary for a healthy lifestyle is a problem that spans the globe. Many societies that lack clean water are also without the energy resources such as electricity or gas that are used for purification. This project is on the development of a solar powered water purification system with Phase Change Material (PCM) energy storage and experimental studies on the system. Water distillation was achieved and analyses were performed on the effects of weather conditions on the distillate production. Solar systems are affected by limited sunshine which occurs only during daylight hours. A second part of the research involved adding a PCM heat exchanger to the system to extend distillation beyond the daylight hours. The analyses evaluated distillate production against outdoor conditions such as temperature, wind speed, and use of the PCM heat exchanger, to determine how they affect the performance of the system. Results show that increased outdoor temperature and clear atmospheric conditions yield greater distillate production. The effects of wind speed were less conclusive. Use of the PCM heat exchanger shifted production to later in the day, but overall, resulted in lower daily production than when the heat exchanger was bypassed. The most definite indicator of distillate production was the temperature differential between the water entering the still and the outdoor temperature.

A technology that has the potential to liquefy hydrogen and natural gas efficiently is an Active Magnetic Regenerative Liquefier (AMRL). An AMRL exploits the magnetocaloric effect displayed by magnetic materials whereby a reversible temperature change is induced when the material is exposed to a magnetic field. This effect can be used to produce cooling. By using the magnetic materials in a regenerator as the heat storage medium and as the means of work input, one creates an Active Magnetic Regenerator (AMR). Because the adiabatic temperature change is a strong function of temperature for most materials, to span a large temperature range such as that needed to liquefy hydrogen, a number of different materials may be needed to make up one or more regenerators. Single material AMRs have been proven, but layering with more than one material has not. This thesis is a study of AMRs using magnetic refrigerants displaying second-order paramagnetic to ferromagnetic ordering. An analysis of AMR thermodynamics is performed and results are used to define properties of ideal magnetic refrigerants. The design and construction of a novel test apparatus consisting of a conduction-cooled superconducting solenoid and a reciprocating AMR test apparatus are described. A numerical model is developed describing the energy transport in an AMR. Experiments using Gd are performed and results are used to validate the model. A strong relationship between flow phasing is discovered and possible reasons for this phenomenon are discussed. Simulations of AMRs operating in unconventional modes such as at temperatures greater than the transition temperature reveal new insights into AMR behaviour. Simulations of two-material layered AMRs suggest the existence of a jump phenomenon occurring regarding the temperature span. These results are used to explain the experimental results reported by other researchers for a two-material AMR. / Graduate

Flow distribution chambers are devices commonly used by the water industry to distribute flows in water and sewage treatment plants. These have simple designs, and are required to operate over a range of volumetric flowrates. Many chambers surveyed (Herbath and Wong, 1997b) were found to perform poorly. They suffered from flow mal-distribution, where the flow was not distributed according to design. The most common cause of flow mal-distribution was hypothesised to be due to the presence of a pipe bend below the chamber (Herbath and Wong, 1997a, 1997b). Therefore, an experimental and numerical study of the flow within a distribution chamber was conducted in this thesis to prove this hypothesis. A novel large-scale model (1: 13) of a typical distribution chamber was constructed. This allowed the collection of high quality and novel velocity and turbulence measurements near the free surface using hot film anemometry. The free surface location was measured using a vernier point gauge while the flow distribution between the outlets was metered by orifice plates. Records of the flow patterns were also kept. The experimental results showed that flow mal-distribution did not occur as expected since the model distribution chamber was designed with a long length of straight inlet pipe, to eliminate the suspected cause of flow mal-distribution. Novel velocity and water surface data were also collected in the experiments, which contributed towards the small body of knowledge in this area of research into flow distribution. CFD models of the physical model were created and solved using a commercial CFD code, CFX 4.1, developed by CFX International of AEA Technology. Steady state and transient two- and three-dimensional calculations of the symmetrical chamber were carried out in the course of the study. A novel adaptation of the existing code was made in obtaining solutions to the numerical models. A new solution strategy was made and refined in this stage of the research using the two-dimensional representation of the distribution chamber, for reasons of reduced computational time. Differencing schemes, surface sharpening, mass residuals, mesh refinement and different turbulence models were investigated during model refinement. The accuracies of the calculated results were determined by comparison with experimental results. It was found that the 3D model, incorporating the RNG k-c model, without surface sharpening, and using the Van Leer differencing scheme, gave good quantitative agreement with the experimental velocities, free surface location and flow distribution. The 2D results gave qualitatively good predictions. Quantitatively, the results were over-predicted which was due, to dimensional effects. The volume of the 2D model was reduced from the 3D model, while the inlet velocity was made the same. This replicated the momentum effects near the free surface that were the governing causes of flow mal-distribution. Nevertheless, this approach was much more practical in terms of computational effort. More importantly, the correct trends for flow mal-distribution could be predicted accurately. Therefore, the next stage of the research used the 2D model developed and validated here. This part of the research involved the novel adaptation of the existing symmetrical 2D results for investigating the asymmetric effects of pipe bends. Three different approaches for modelling the asymmetric effects of a pipe bend were investigated. The first, and the most simplistic, was to incline the incoming flow at an angle to the vertical. The second was to calculate the velocities and turbulence at the outlet of a simple 2D pipe bend, separate from the chamber. These calculated variables were then input into the chamber, to build up a picture of the asymmetric flow, iteratively. The third, and the most accurate method, was to couple the bend to the chamber. It was found that only the third method was capable of accurately representing the conditions within the chamber. Two different pipe bend. lengths were examined using the third approach. The distances chosen were typical of the bend distances found in some treatment plants. The results . from both simulations produced large flow mal-distribution and asymmetric flows within the chamber. A value of 10% difference between the flows from the two outlets was taken to be the maximum limit for mal-distribution. However, values of 44.5 % and 22.8 % were obtained for the larger pipe distance and short pipe distance respectively. Novel remediation strategies using numerical techniques were used to determine the most effective means of improving the flow distribution. The first, used a vertical flow splitter, placed directly above the chamber inlet. Although it altered the path of the jet, it was felt that it would be ineffective for all situations. Although the magnitude of the asymmetry was improved with the use of the splitter, the improvement was insufficient to warrant its recommendation. The other device tested was a horizontal plate located at a certain distance from the chamber inlet. For the longer bend case, a separation distance equivalent to two inlet hydraulic diameters was sufficient to deflect the jet, and reduced the magnitude of the flow asymmetry to around 2%. When the same plate location was used for the shorter bend case, the efficiency of the plate was reduced. Although there was an improvement in the distribution, the magnitude of the asymmetry was greater than 10%. The plate was subsequently lowered by half a hydraulic diameter. This gave a large improvement to the effectiveness of the plate, and the resulting asymmetry was reduced to 7.31 %. The horizontal plate was considered more promising since its function was to deflect and reduce the peak velocities of the jet. With the reduction in velocities, the magnitudes of the nonlinear terms in the Navier-Stokes equations are reduced. The solution to the equations would be more likely to be symmetrical.

More and more transient gas-liquid operations in pipes are being successfully applied in the oil and gas industry. Pigging in two-phase pipelines, to remove liquid accumulation or for cleaning purposes, is an important transient operation. Another important operation is the injection of (-)-as to transport the accumulated liquid in the pipeline to process facilities. Analysis of such transient two-phase flow in a pipeline is necessary not only for designing the liquid and gas handling facilities, but also for safe operating procedure. In pipeline-fiser system such operations cause even more severe changes in flow conditions. A two-fluid model has been developed to determine the transient behaviour of fluids during these operations. The derived one-dimensional set of equations for each flow pattern describe the flow of fluids in all regions. Semi-implicit finite difference schemes were used to solve the initial and boundary value problem for each phase of the process - gas/pig injection, gas shut-in, slug production and gas flow out of the system. An extensive experimental program has been carried out to acquire two-phase transient flow and pigging data on a 67m long, 0.0525m diameter, 9.9m high pipeline-riser system. A computer based data acquisition system has been utilised to obtain rapidly changing and detailed information of the flow behaviour during the transient tests. The model results compare well with the experimental data for characteristics such as inlet pressure, hold-up and pig velocity.

Solid propellant is the highly energetic fuel burnt in the combustion chamber of ballistic weapons. It is manufactured, for this purpose, in either granular or stick form. Internal ballistics describes the behavior within the combustion chamber throughout the ballistic cycle upto projectile exit from the muzzle of the gun barrel. Over the last twenty years this has been achieved by modelling the process using two-phase flow equations. The solid granules or sticks constitute the first phase, which can be assumed to be incompressible over typical pressure ranges within the chamber. The gas-phase is composed of both the original ambient gas contained around the propellant and additional gas produced by the propellant gasifying on heating. Equations can be derived that describe the conservation of mass, momentum and energy in terms of average flow variables. The equations are a highly non-linear system of partial-differential- equations. High-speed flow features are observed in internal ballistics and ordinary fini te- difference methods are unsuitable numerical methods due to inaccurate prediction of discontinuous flow features. Modern shock-capturing methods are employed, which solve the system of equations in conservation form, with the ability to capture shocks and contact discontinuities. However, although the numerical solutions compare well with experiment over the bulk of the combustion chamber, the ignition models used in internal ballistics are unreliable. These are based on either gas or solid-surface temperature achieving some empirically measured 'ignition temperature' after which the propellant burns according to an empirical pressure dependent burning law. Observations indicate that this is not an adequate representation of ignition. Time differences between first solid gasification and ignition imply two distinct processes occurring. ]Further, ignition occurring in gas-only regions indicates that ignition is controlled by a gas-phase reaction. This thesis develops simple ideas to describe possible mechanisms for these physical observations. The aim is to provide an improved model of the ignition of solid propellant. A two stage reaction process is described involving endothermic gasification of the solid, to produce a source of reactant gas, followed by a very exothermic gas-phase ignition reaction. Firstly the gas-phase ignition is considered. A very simple reaction is suggested which is assumed to control the combustion of reactant gas, produced by solid gasification. Ignition is, by definition, the initiation of this exothermic reaction. Chemical kinetics are included in the gas-phase flow equations to explore the evolution of the reactant gas that is subject to changes in temperature and pressure. By assuming spatial uniformity, analytical solutions of the problem are deduced. The physical interpretation of the solution is discussed, in particular, the relationship between temperature, reactant concentration and ignition is explored. Numerical methods are required to solve the one-dimensional flow equations. Development of suitable CFD methods provides a method of solution. Finite-volume schemes, based on the original work by Godunov, are used to solve the conservation form of the equations. A simple test problem is considered whereby reactant gas is injected into a cylindrical combustion chamber. By examining the resulting flow histories, valuable information is gathered about the complicated coupling of chemistry and flow. Chemistry is included into a system of two-phase flow equations. By using standard averaging methods along with an equation for gas-phase species, equations are derived that describe the rate of change of average flo%v variables for both gas and particle phases. Numerical schemes are developed and some of the difficulties involved in two-phase flow systems, that are not an issue in single-phase flow, are presented. An internal ballistics application is considered as a test case and the solution discussed. The other important reaction involved in the combustion cycle, solid gasification, is explored. The model is based on detailed description of interphase mass and energy transfer at the solid-gas interface. This involves the solution of the heat conduction equation with a moving boundary that divides the solid and gas regions. Similar numerical schemes are constructed to solve the equations. Finally, this model is coupled with the equations of gas-phase reaction. This describes the complete cycle whereby increases in gas temperature cause the solid to increase in temperature and gasify. Subsequent gas-phase combustion of the reactant gases produces heat-transfer between the solid and gas and continues to accelerate gasification. Eventually this results in selfsustained combustion of the solid propellant.

No description available.

The Fourier transform (spectrum) of a signal is a complex function and is characterized by the magnitude and phase spectra. Phase retrieval is the reconstruction of the phase spectrum from the measurements of the magnitude spectrum. Such problems are encountered in imaging modalities such as X-ray crystallography, frequency-domain optical coherence tomography (FDOCT), quantitative phase microscopy, digital holography, etc., where only the magnitudes of the wavefront are detected by the sensors. The phase retrieval problem is ill-posed in general, since an in nite number of signals can have the same magnitude spectrum. Typical phase retrieval techniques rely on certain prior knowledge about the signal, such as its support or sparsity, to reconstruct the signal. A classical result in phase retrieval is that minimum-phase signals have log-magnitude and phase spectra that satisfy the Hilbert integral equations, thus facilitating exact phase retrieval. In this thesis, we demonstrate that there exist larger classes of signals beyond minimum-phase signals, for which exact phase retrieval is possible. We generalize Hilbert integral equations to 2-D, and also introduce a variant that we call the composite Hilbert transform in the context of 2-D periodic signals. Our first extension pertains to a particular type of parametric modelling of 2-D signals. While 1-D minimum-phase signals have a parametric representation, in terms of poles and zeros, there exists no such 2-D counterpart. We introduce a new class of parametric 2-D signals that possess the exact phase retrieval property, that is, their magnitude spectrum completely characterizes the signal. Starting from the magnitude spectrum, a sequence of non-linear operations lead us to a sum-of-exponentials signal, from which the parameters are computed employing concepts from high-resolution spectral estimation such as the annihilating filter and algebraically coupled matrix-pencil methods. We demonstrate that, for this new class of signals, our method outperforms existing techniques even in the presence of noise. Our second extension is to continuous-domain signals that lie in a principal shift-invariant space spanned by a known basis. Such signals are characterized by the basis combining coefficients. These signals need not be minimum-phase, but certain conditions on the coefficients lead to exact phase retrieval of the continuous-domain signal. In particular, we introduce the concept of causal, delta dominant (CDD) sequences, and show that such signals are characterized by their magnitude spectra. This condition pertains to the time/spatial-domain description of the signal, in contrast to the minimum-phase condition, which is described in the spectral domain. We show that there exist CDD sequences that are not minimum-phase, and vice versa. However, finite-length CDD sequences are always minimum-phase. Our method reconstructs the signal from the magnitude spectrum up to ma-chine precision. We thus have a class of continuous-domain signals that are neither causal nor minimum phase, and yet allow for exact phase retrieval. The shift-invariant structure is applicable to modelling signals encountered in imaging modalities such as FDOCT. We next present an application of 2-D phase retrieval to continuous-domain CDD signals in the context of quantiative phase microscopy. We develop sufficient conditions on the interfering reference wave for exact phase retrieval from magnitude measurements. In particular, we show that when the reference wave is a plane wave with magnitude greater that the intensity of the object wave, and when the carrier frequency is larger than the band-width of the object wave, we can reconstruct the object wave exactly. We demonstrate high-resolution reconstruction of our method on USAF target images. Our final and perhaps the most unifying contribution is in developing Hilbert integral equations for 2-D first-quadrant signals and in introducing the notion of generalized minimum-phase signals for both 1-D and 2-D signals. For 2-D continuous-domain, first-quadrant signals, we establish partial Hilbert transform relations between the real and imaginary parts of the spectrum. In the context of 2-D discrete-domain signals, we show that the partial Hilbert transform does not suffice and introduce the notion of composite Hilbert transform and establish the integral equations. We then introduce four classes of signals (combinations of 1-D/2-D and continuous/discrete-domain) that we call generalized minimum-phase signals, which satisfy corresponding Hilbert integral equations between log-magnitude and phase spectra, hence facilitating exact phase retrieval. This class of generalized minimum-phase signals subsumes the well known class of minimum-phase signals. We further show that, akin to minimum-phase signals, these signals also have stable inverses, which are also generalized minimum-phase signals.

abstract: A control method based on the phase angle is used to control oscillating systems. The phase oscillator uses the sine and cosine of the phase angle to change key properties of a mass-spring-damper system, including amplitude, frequency, and equilibrium. An inverted pendulum is used to show a further application of the phase oscillator. Two methods of control based on the phase oscillator are used for swing-up and balancing of the pendulum. The first control method involves two separate stages. The scenarios where this control works are discussed. The second control method uses variable coefficients to result in a smooth transition between swing-up and balancing. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2015