The focus of the world is on the reduction of greenhouse gases, such as carbon dioxide, which contribute to the global warming currently experienced. Because most of the carbon dioxide emitted into the atmosphere is from fossil fuel combustion, alternative energy sources were developed and others are currently under study to see whether they will be good alternatives. One of these alternative sources of energy is the combustion of wood instead of coal. The advantages of wood are that it is a neutral carbon fuel source and that currently installed infrastructure used to combust coal can be retrofitted to combust wood or a mixture of wood and coal in an attempt to reduce the carbon dioxide emissions. Spent nuclear fuel has to be cooled so that the decay heat generated does not melt the containment system, which could lead to the unintentional release of radioactive material to the surroundings. The heat transfer mechanisms involved in the cooling have historically been analysed by assuming that the fluid and solid phases are at local thermal equilibrium (LTE) in order to simplify the analysis. The exergy destruction of the combustion of pine wood in an adiabatic combustor was investigated in this thesis using analytical and computational methods. The exergy destruction of the combustion process was analysed by means of the second law efficiency, which is the ratio of the maximum work that can be achieved by a Carnot engine extracting heat from the combustor, and the optimum work of the combustor. This was done for theoretical air combustion and various excess air combustions, with varied inlet temperatures of the incoming air. It was found that the second law efficiency reached an expected maximum for theoretical air combustion, and this held true for all varying air inlet temperatures. However, it was found that as the air inlet temperature was increased more and more, the maximum second law efficiency was the same for all excess air combustions, including the theoretical air combustion. It was also found that the results of the analytical and commercial computational fluid dynamics code compared well. Another analysis was conducted of irreversibilities generated due to combustion in an adiabatic combustor burning wood. This was done for a reactant mixture varying from a rich to a lean mixture. A non-adiabatic non-premixed combustion model of a numerical code was used to simulate the combustion process where the solid fuel was modelled by using the ultimate analysis data. The entropy generation rates due to the combustion and frictional pressure drop processes were computed to eventually arrive at the irreversibilities generated. It was found that the entropy generation rate due to frictional pressure drop was negligible when compared with that due to combustion. It was also found that a minimum in irreversibilities generated was achieved when the air-fuel mass ratio was 4.9, which corresponded to an equivalent ratio of 1.64, which was lower than the respective air-fuel mass ratio and equivalent ratio for complete combustion with theoretical amount of air of 8.02 and 1. Studieswere conducted to numerically analyse irreversibilities generated due to combustion in an adiabatic combustor burning wood. The first study analysed the effect of changing the incoming air temperature from 298 K to 400 K. The second study analysed the effect of changing the wall condition of the combustor from adiabatic to negative heat flux (that is heat leaving the system) for an incoming air temperature of 400 K. The irreversibilities generated in the combustor were calculated by computing the entropy generation rates due to the combustion, heat transfer and frictional pressure drop processes. For the first part of the study, it was found that for the minimum irreversibilities generated in the adiabatic combustor, the optimal air-fuel ratio (AF) corresponding to minimum irreversibilities slightly reduced from 4.9 to 4.8. In the second part of the study, it was found that by changing the wall condition from adiabatic to heat flux on the combustor, the AF corresponding to the minimum irreversibilities increased from 4.8 to 6. For the third part of the study, the combustor with a heat flux wall condition and a wall thickness simulated at an AF of 6, the sum of twice the wall thickness and the optimum diameter always added up to 0.32 m, resulting in the minimum irreversibilities. An analytical model was developed to minimise the thermal resistance of an air-cooled porous matrix made up of solid spheres with internal heat generation. This was done under the assumption of LTE. It was found that the predicted optimum sphere diameter and the minimum thermal resistance were both robust in that they were independent of the heat generation rate of the solid spheres. Results from the analytical model were compared with those from a commercial numerical porous model using liquid water and air for the fluid phase, and wood and silica for the solid phase. The magnitudes of the minima of both the temperature difference and the thermal resistance seemed to be due to equal contribution from the thermal conduction heat transfer inside the solid spheres and heat transfer in the porous medium. Because the commercial numerical porous model modelled only the heat transfer occurring in the porous medium, it expectedly predicted half of the magnitudes of the minima of the temperature difference and thermal resistance of those by the analytical model. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

According to the Intergovernmental Panel on Climate Change, Carbon Dioxide Removal (CDR) technologies play a significant role in deep mitigation pathways to limit global temperature rise to 1.5°C. As a result, interest in them is becoming increasingly prevalent, the most widely discussed being Direct Air Capture (DAC), or active removal of carbon dioxide from atmospheric air. While DAC processes have indeed been successfully tested, one of the most prominent being that developed by Canadian company Carbon Engineering, their widespread deployment faces significant headwinds due to prohibitively high energy consumption and its associated costs. Before DAC can be considered to exist in a state of technological readiness, reductions to the installations' energy demand must be realized. This thesis analyzes the thermodynamic behavior of Carbon Engineering's proposed 1 Mt-CO2/year natural gas fuelled DAC plant, which they describe as “a low-risk starting point rather than a fully optimized least-cost design” [Keith et al., Joule 2, 1573], with the aim to illustrate key areas to which energy efficiency improvement measures must target. With an understanding built of the mechanisms by which energy is utilized and irreversibly lost within their plant, suggestions are put forth for directions to pursue for process improvements, with further analysis included on potential alternative plant configurations which would reduce overall heat and power consumption. A thermodynamic work loss analysis is performed on their plant design at a system level, which finds 92.2% of incoming exergy being lost to thermodynamic irreversibilities. A component-level analysis is then performed to detail the mechanisms by which these losses occur in the most energy-intensive plant segments, namely, the calciner and preheat cyclones, air separation unit, water knockout system, CO2 compression system, and power island. The dissipation of chemical exergy in the air contactor component, i.e., the release of stored chemical exergy as low-grade heat to the environment due to the exothermic reaction of CO2 and aqueous KOH, was determined as the largest unavoidable source of work loss. The most avoidable losses were found to be associated with use of natural gas as a feedstock for heat and power, namely, through its introduction of additional CO2 and water to be processed within the plant, and due to gas turbine power production's inherent Carnot efficiency limits. Additional analysis and discussion follows regarding possible loss reduction measures and modifications, the key concept presented being the use of renewable energy to provide plant power, combined with a calciner using electric resistance heating to meet its reduced thermal demand. Use of a readily-available high-temperature heat source for calciner heat is also considered, with thorough description included of its thermodynamic advantages. Finally, the all-electric plant concept is analyzed at a system level, and its advantages compared to the original natural gas fuelled case. / Graduate

No / Online games require small data of 3D models for low storage costs, quick transmission over the Internet, and efficient geometric processing to achieve real-time performance, and new techniques of facial blendshapes to create natural facial animation. Current geometric modelling and animation techniques involve big data of geometric models and widely applied facial animation using linear interpolation cannot generate natural facial animation and create special facial animation effects. In this paper, we propose a new approach to integrate the strengths of ODE (ordinary differential equation) sweeping surfaces and Newton's second law-based facial blendshapes to create 3D models and their animation with small data, high efficiency, and ability to create special facial effects.

Technological advancement has thrust MEMS design and fabrication into the forefront of modern technologies. It has become sufficiently self-sustained to allow mass production. The limiting factor which is stalling commercialization of MEMS is the packaging and device reliability. The challenging issues with MEMS packaging are application specific. The function of the package is to give the MEMS device mechanical support, protection from the environment, and electrical connection to other devices in the system. The current state of the art in MEMS packaging transcends the various packaging techniques available in the integrated circuit (IC) industry. At present the packaging of MEMS includes hermetic ceramic packaging and metal packaging with hermetic seals. For example the ADXL202 accelerometer from the Analog Devices. Study of the packaging methods and costs show that both of these methods of packaging are expensive and not needed for majority of MEMS applications. Due to this the cost of current MEMS packaging is relatively high, as much as 90% of the finished product. Reducing the cost is therefore of the prime concern. This Thesis explores the possibility of an inexpensive plastic package for MEMS sensors like accelerometers, optical MEMS, blood pressure sensors etc. Due to their cost effective techniques, plastic packaging already dominates the IC industry. They cost less, weigh less, and their size is small. However, porous nature of molding materials allows penetration of moisture into the package. The Thesis includes an extensive study of the plastic packaging and characterization of three different plastic package samples. Polymeric materials warp upon absorbing moisture, generating hygroscopic stresses. Hygroscopic stresses in the package add to the thermal stress due to high reflow temperature. Despite this, hygroscopic characteristics of the plastic package have been largely ignored. To facilitate understanding of the moisture absorption, an analytical model is presented in this Thesis. Also, an empirical model presents, in this Thesis, the parameters affecting moisture ingress. This information is important to determine the moisture content at a specific time, which would help in assessing reliability of the package. Moisture absorption is modeled using the single phase absorption theory, which assumes that moisture diffusion occurs freely without any bonding with the resin. This theory is based on the Fick's Law of diffusion, which considers that the driving force of diffusion is the water concentration gradient. A finite difference simulation of one-dimensional moisture diffusion using the Crank-Nicolson implicit formula is presented. Moisture retention causes swelling of compounds which, in turn, leads to warpage. The warpage induces hygroscopic stresses. These stresses can further limit the performance of the MEMS sensors. This Thesis also presents a non invasive methodology to characterize a plastic package. The warpage deformations of the package are measured using Optoelectronic holography (OEH) methodology. The OEH methodology is noninvasive, remote, and provides results in full-field-of-view. Using the quantitative results of OEH measurements of deformations of a plastic package, pressure build up can be calculated and employed to assess the reliability of the package.

Thermal energy storage (TES) is an advanced technology for storing thermal energy that can mitigate environmental impacts and facilitate more efficient and clean energy systems. Thermochemical TES is an emerging method with the potential for high energy density storage. Where space is limited, therefore, thermochemical TES has the highest potential to achieve the required compact TES. Principles of thermochemical TES are presented and thermochemical TES is critically assessed and compared with other TES types. The integration of TES systems with heating, ventilating and air conditioning (HVAC) applications is examined and reviewed accounting for various factors, and recent advances are discussed. Thermodynamics assessments are presented for general closed and open thermochemical TES systems. Exergy and energy analyses are applied to assess and compare the efficiencies of the overall thermochemical TES cycle and its charging, storing and discharging processes. Examples using experimental data are presented to illustrate the analyses. Some important factors related to design concepts of thermochemical TES systems are considered and preliminary design conditions for them are investigated. Parametric studies are carried out for the thermochemical storage systems to investigate the effects of selected parameters on the efficiency and behavior of thermochemical storage systems. / UOIT

This study focused on a numerical second law analysis and optimisation of a receiver tube op- erating in a parabolic trough solar collector for small-scale application. The receiver functioned in a Rankine cycle. The focus was on entropy generation minimisation in the receiver due to the high quality exergy losses in this component. Water functioned as the working uid and was heated from ambient conditions (liquid) to a superheated state (vapour), consequently, the receiver tube was subject to both single phase as well as two-phase ow. Entropy generation in the receiver tube was mainly due to nite temperature di erences as well as uid friction. The contribution of each of these components was investigated. Geometrical as well as operating conditions were investigated to obtain good guidelines for receiver tube and plant design. An operating pressure in the range of 1 MPa (Tsat = 180 C) to 10 MPa (Tsat = 311 C) was considered. Furthermore a mass ow range of 0:15 kg=s to 0:4 kg=s was investigated. Results showed that beyond a diameter of 20 mm, the main contributor to the entropy generation was the nite temperature di erences for most conditions. Generally, operating pressures below 3 MPa showed bad performance since the uid friction component was too large for small operating pressures. This phenomenon was due to long two-phase lengths and high pressure drops in this region. The nite temperature di erence component increased linearly when the tube diameter was increased (due to the increase in exposed area) if the focused heat ux was kept constant. However, the uid friction component increased quadratically when the diameter was reduced. In general when the concentration ratio was increased, the entropy generation was decreased. This was due to more focused heat on each section of the receiver pipe and, in general, resulted in shorter receiver lengths. Unfortunately, there is a limit to the highest concentration ratio that can be achieved and in this study, it was assumed to be 45 for two-dimensional trough technology. A Simulated Annealing (SA) optimisation algorithm was implemented to obtain certain optimum parameters. The optimisation showed that increasing the diameter could result in a decrease in entropy generation, provided that the concentration ratio is kept constant. However, beyond a certain point gains in minimising the entropy generation became negligible. Optimal operating pressure would generally increase if the mass ow rate was increased. Finally, it was seen that the highest operating pressure under consideration (10 MPa) showed the best performance when considering the minimisation of entropy in conjunction with the maximisation of the thermodynamic work output. / Dissertation (MEng)--University of Pretoria, 2014. / tm2015 / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Future 450mm semiconductor wafer foundries are expected to produce billions of low cost, leading-edge processors, memories, and wireless sensors for Internet of Everything applications in smart cities, smart grids, and smart infrastructures. The problem has been a lack of wise investment decision making using traditional semiconductor industry models. The purpose of this study was to design decision-making models to conserve financial resources from conception to commercialization using real options to optimize production capacity, to defer an investment, and to abandon the project. The study consisted of 4 research questions that compared net present value from real option closed-form equations and binomial lattice models using the Black-Scholes option pricing theory. Three had focused on sensitivity parameters. Moore's second law was applied to find the total foundry cost. Data were collected using snowball sampling and face-to-face surveys. Original survey data from 46 Americans in the U.S.A. were compared to 46 Europeans in Germany. Data were analyzed with a paired-difference test and the Box-Behnken design was employed to create prediction models to support each hypothesis. Data from the real option models and survey findings indicate American 450mm foundries will likely capture greater value and will choose the differentiation strategy to produce premium chips, whereas higher capacity, cost leadership European foundries will produce commodity chips. Positive social change and global quality of life improvements are expected to occur by 2020 when semiconductors will be needed for the $14 trillion Internet of Everything market to create safe self-driving vehicles, autonomous robots, smart homes, novel medical electronics, wearable computers with streaming augmented reality information, and digital wallets for cashless societies.

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

1. There is a crisis in economics. The discipline evolved in nineteenth century Europe and is difficult to adapt to modern conditions, even in the West, and particularly in alien cultures. Application of conventional economic analysis to economic activity in a culture as alien as traditional China highlights the biases in assumptions of the paradigm. 2. The concepts, models and vocabulary evolved over one hundred years ago predate important developments in the natural sciences. It is now necessary for economists to concede no goods can ever be 'produced', and they are not 'consumed' either. In clear terms matter is transformed, but is not created or destroyed (First Law of Thermodynamics). 3. When people transform matter, in lay language we say energy is 'used'. In a simple cottage industry, 'raw material' is transformed into a commodity in front of our eyes by the use of human energy and the release of energy from a 'fuel'. In modem complex economic activity, it is difficult or impossible to keep track of the processes from raw matter to transformed 'product' although the principle is the same. 4. The Second Law of Thermodynamics states that in any transformation, energy is not created or destroyed, but becomes 'less available'. In short, entropy increases. This appears to work well for pure physics and chemistry, but its application to analysis of economic activity has only been notional. 5. There is a reason why economists borrowing terms from hard science experience difficulty. It is because physicists and chemists have addressed specific laboratory and engineering problems, but not the broader economic issues. The hypothesis gradually evolved in this research program that not only economic concepts and terms needed reworking, but those in physics as well. The definitions of energy as 'ability to do works and of entropy as 'unavailable energy' jar the logic of our commonsense. 6. The notion of 'available energy' was traced back to the phenomenon in physical chemistry known as exothermicity, or the release of energy during a chemical reaction. It was reasoned that while scientists had focussed on this phenomenon and measured it carefully they saw no need to ask where the energy came from, or to measure its transformation. From the perspective of analysing economic activity, the question was important. 7. It was hypothesised that the energy released from a fuel as electromagnetic radiation (mainly heat) was the residual of the set of coulombic forces within atoms that maintain the structure of shells of electrons around the protons. This idea in turn came from the presumption that molecular bonding is a residual of vectors of the set of coulombic forces within atoms, and the likelihood that in an exothermic reaction, after the reactants are said (by scientists) to 'seek equilibrium', product molecules have a portion of the coulombic forces 'left over' and not required to maintain their structures. An estimate was made of the coulombic forces extant in various fuels, and compared with the known data for their release of energy. 8. The idea was developed in detail. The concept we call in economics, 'production', and should call 'transformation' can only occur when forces locked within atoms are released as electromagnetic forces. (Gravitational forces exist because matter has been put 'there' by electromagnetic radiation). When 100 grams of dry grass fuel is burnt, about 2 megajoules of electromagnetic radiation are released. It was estimated that the coulombic forces between each electron and proton in that amount dry grass total 150 gigajoules (or giganewtons, since the reference is to forces). 9. Within the boundary of a simple economic activity, the ratio of aggregated coulombic forces locked up within atoms to the electromagnetic forces radiated out was estimated at the beginning of the activity, and then after a duration. The ratio of forces always tends towards 'evening out'. This measurement captures the entropy phenomenon which has been said by Georgescu-Roegen to be the basis of all economic activity. 10. At the roots of the economic paradigm founded by Adam Smith is the premise that the material world, as a set of substances, is a stage on which economic actors 'add value', bid prices up and down, and by their rational perception manage their livelihoods and surroundings well. From the findings of this research program it is contended that the surroundings of economic actors can be classed into two categories: locked up (coulombic) electromagnetic forces, and radiated electromagnetic forces. The former has a tendency to convert to the latter. All action, including all economic activity, and all life can be traced to a point in space and time where this conversion is (naturally) occurring. The phenomenon is analogous to a slope where water cascades, and gravitational potential energy converts to other (either useless or useful) forms of energy. To appreciate the nature of this phenomena, and to attempt to fathom its dimensions, sets our perceptions of ourselves as economic actors in a quite different and very humbling context.