Ce mémoire considère l'évolution des stéréotypes racistes et sexistes qui sont contestés dans trois œuvres littéraires afro-américaines, soit Not Without Laughter de Langston Hughes, The Bluest Eye de Toni Morrison et Citizen : An American Lyric de Claudia Rankine. L'analyse de ces livres vise à déterminer comment la double contrainte des femmes noires sous-tend les stéréotypes et préjugés qui sont apparus pendant l'esclavage et qui persistent dans la culture du vingt-et-unième siècle. Ces stéréotypes, tels que la Mammy, la Jezebel ou la femme en colère, ont été créés et maintenus afin de fournir une justification idéologique à la marginalisation et à l'exploitation des femmes noires. De plus, ils ont servi à soutenir les intérêts et objectifs de la société blanche patriarcale telle que manifestée aux États-Unis à travers le temps. Encore aujourd'hui, ces images discriminatoires et non représentatives contribuent à la perpétuation du racisme et du sexisme, et continuent de contrôler le corps, l'esprit, et la sexualité des femmes noires aux États-Unis. À travers une analyse chronologique des œuvres, publiées respectivement en 1930, 1970, et 2014, mon argumentaire postule que les performances de féminité noire étudiées dans chaque roman révèlent un désir de contester et réfuter ces stéréotypes, s'avérant ainsi des actes de résistance et d'autodétermination. Mon approche, éclairée par les théories de l'intersectionnalité et du féminisme noir, étudie la manière dont Hughes, Morrison, et Rankine revisitent, remettent en question, et déconstruisent les stéréotypes raciaux afin de mettre en évidence la multiplicité des identités féminines Afro-Américaines et ainsi, rejeter la fausse perception monolithique des femmes noires. / This thesis investigates the evolution of racist and sexist stereotypes forced onto black women in three African American works: Langston Hughes's Morrison's The Bluest Eye , and Claudia Rankine's Not Without Laughter Citizen: An American Lyric , Toni . The thesis aims to show the pervasiveness of the double bind of African American women that emerged during slavery and that persists in the culture of the twenty-first century as the Mammy, the Jezebel, or the angry black woman, among . Stereotypes, such others, were created and maintained to provide an ideological justification for the marginalization and exploitation of black women, which, in turn, were used to support the interests of the white mainstream and patriarchal society. To this day, these cont rolling images black female body, mind, and sexuality perpetuate racism and regulate the in the United States. Through a chronological analysis of the works, respectively published in 1930, 1970, and 2014, my argumentation posits that the chosen iterations of black womanhood talk back to their racial heritage, a vexed history of misrepresentation and misconception, thereby allowing for new performances and scripts of the black female self to be inscribed in culture. My approach to this thesis, grounded in theorizations related to intersectionality and black feminism, demonstrates that Hughes, Morrison, and Rankine revisit, challenge, and deconstruct racial stereotypes to highlight the multiplicity of African American female identities and, ultimately, reject the monolithic perception of black women.

The waste heat recovery technologies have become very relevant since many industrial plants continuously reject large amounts of thermal energy during normal operation which contributes to the increase of the production costs and also impacts the environment. The simulation programs used in industrial engineering enable development and optimization of the operational processes in a cost-effective way. The company Chematur Engineering AB, which supplies chemical plants in many different fields of use on a worldwide basis, was interested in the investigation of the possibilities for effective waste heat recovery from the hydrogenation of dinitrotoluene, which is a sub-process in the toluene diisocyanate manufacture plant. The project objective was to implement waste heat recovery by application of the Organic Rankine Cycle and the Absorption Refrigeration Cycle technologies. Modeling and design of the Organic Rankine Cycle and the Absorption Refrigeration Cycle systems was performed by using Aspen Plus® simulation software where the waste heat carrier was represented by hot water, coming from the internal cooling system in the hydrogenation process. Among the working fluids investigated were ammonia, butane, isobutane, propane, R-123, R-134a, R-227ea, R-245fa, and ammonia-water and LiBr-water working pairs. The simulations have been performed for different plant capacities with different temperatures of the hydrogenation process. The results show that the application of the Organic Rankine Cycle technology is the most feasible solution where the use of ammonia, R-123, R-245fa and butane as the working fluids is beneficial with regards to power production and pay-off time, while R-245fa and butane are the most sustainable choices considering the environment.

In this study, the feasibility of using an organic Rankine cycle (ORC) in trigeneration plants is examined through thermodynamic modeling and thermoeconomic optimization. Three novel trigeneration systems are considered. Each one of these systems consists of an ORC, a heating-process heat exchanger, and a single-effect absorption chiller. The three systems are distinguished by the source of the heat input to the ORC. The systems considered are SOFC-trigeneration, biomass- trigeneration, and solar-trigeneration systems. For each system four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Comprehensive thermodynamic analysis on each system is carried out. Furthermore, thermoeconomic optimization is conducted. The objective of the thermoeconomic optimization is to minimize the cost per exergy unit of the trigeneration product. The results of the thermoeconomic optimization are used to compare the three systems through thermodynamic and thermoeconomic analyses. This study illustrates key output parameters to assess the trigeneration systems considered. These parameters are energy efficiency, exergy efficiency, net electrical power, electrical to cooling ratio, and electrical to heating ratio. Moreover, exergy destruction modeling is conducted to identify and quantify the major sources of exergy destruction in the systems considered. In addition, an environmental impact assessment is conducted to quantify the amount of CO2 emissions in the systems considered. Furthermore, this study examines both the cost rate and cost per exergy unit of the electrical power and other trigeneration products. This study reveals that there is a considerable efficiency improvement when trigeneration is used, as compared to only electrical power production. In addition, the emissions of CO2 per MWh of trigeneration are significantly lower than that of electrical power. It was shown that the exergy destruction rates of the ORC evaporators for the three systems are quite high. Therefore, it is important to consider using more efficient ORC evaporators in trigeneration plants. In addition, this study reveals that the SOFC-trigeneration system has the highest electrical energy efficiency while the biomass-trigeneration system and the solar mode of the solar trigeneration system have the highest trigeneration energy efficiencies. In contrast, the SOFC-trigeneration system has the highest exergy efficiency for both electrical and trigeneration cases. Furthermore, the thermoeconomic optimization shows that the solar-trigeneration system has the lowest cost per exergy unit. Meanwhile the solar-trigeneration system has zero CO2 emissions and depends on a free renewable energy source. Therefore, it can be concluded that the solar-trigeneration system has the best thermoeconomic performance among the three systems considered.

Low-grade heat sources, here defined as below 300 ºC, are abundantly available as industrial waste heat, solar thermal, and geothermal, to name a few. However, they are under-exploited for conversion to power because of the low efficiency of conversion. The utilization of low-grade heat is advantageous for many reasons. Technologies that allow the efficient conversion of low-grade heat into mechanical or electrical power are very important to develop. This work investigates the potential of supercritical Rankine cycles in the conversion of low-grade heat into power. The performance of supercritical Rankine cycles is studied using ChemCAD linked with customized excel macros written in Visual Basic and programs written in C++. The selection of working fluids for a supercritical Rankine cycle is of key importance. A rigorous investigation into the potential working fluids is carried out, and more than 30 substances are screened out from all the available fluid candidates. Zeotropic mixtures are innovatively proposed to be used in supercritical Rankine cycles to improve the system efficiency. Supercritical Rankine cycles and organic Rankine cycles with pure working fluids as well as zeotropic mixtures are studied to optimize the conversion of lowgrade heat into power. The results show that it is theoretically possible to extract and convert more energy from such heat sources using the cycle developed in this research than the conventional organic Rankine cycles. A theory on the selection of appropriate working fluids for different heat source and heat sink profiles is developed to customize and maximize the thermodynamic cycle performance. The outcomes of this research will eventually contribute to the utilization of low-grade waste heat more efficiently.

Water and energy crises have forced researchers to seek alternative water and energy sources. Seawater desalination can contribute towards meeting the increasing demand for fresh water using alternative energy sources like low-grade heat. Industrial waste heat, geothermal, solar thermal, could help to ease the energy crisis. Unfortunately, the efficiency of the conventional power cycle becomes uneconomically low with low-grade heat sources, while, at the same time, seawater desalination requires more energy than a conventional water treatment process. However, heat discarded from low-grade heat power cycles could be used as part of desalination energy sources with seawater being used as coolant for the power cycles. Therefore a study of desalination using low-grade heat is of great significance. This research has comprehensively reviewed the current literature and proposes two systems that use low-grade heat for desalination applications or even desalination/power cogeneration. The proposed two cogeneration systems are a supercritical Rankine cycle-type coupled with a reverse osmosis (RO) membrane desalination process, and a power cycle with an ejector coupled with a multi-effect distillation desalination system. The first configuration provides the advantages of making full use of heat sources and is suitable for hybrid systems. The second system has several advantages, such as handling highly concentrated brine without external electricity input as well as the potential of water/power cogeneration when it is not used to treat concentrated brine. Compared to different stand-alone power cycles, the proposed systems could use seawater as coolant to reject low-grade heat from the power cycle to reduce thermal pollution.

In this study, the feasibility of using an organic Rankine cycle (ORC) in trigeneration plants is examined through thermodynamic modeling and thermoeconomic optimization. Three novel trigeneration systems are considered. Each one of these systems consists of an ORC, a heating-process heat exchanger, and a single-effect absorption chiller. The three systems are distinguished by the source of the heat input to the ORC. The systems considered are SOFC-trigeneration, biomass- trigeneration, and solar-trigeneration systems. For each system four cases are considered: electrical-power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Comprehensive thermodynamic analysis on each system is carried out. Furthermore, thermoeconomic optimization is conducted. The objective of the thermoeconomic optimization is to minimize the cost per exergy unit of the trigeneration product. The results of the thermoeconomic optimization are used to compare the three systems through thermodynamic and thermoeconomic analyses. This study illustrates key output parameters to assess the trigeneration systems considered. These parameters are energy efficiency, exergy efficiency, net electrical power, electrical to cooling ratio, and electrical to heating ratio. Moreover, exergy destruction modeling is conducted to identify and quantify the major sources of exergy destruction in the systems considered. In addition, an environmental impact assessment is conducted to quantify the amount of CO2 emissions in the systems considered. Furthermore, this study examines both the cost rate and cost per exergy unit of the electrical power and other trigeneration products. This study reveals that there is a considerable efficiency improvement when trigeneration is used, as compared to only electrical power production. In addition, the emissions of CO2 per MWh of trigeneration are significantly lower than that of electrical power. It was shown that the exergy destruction rates of the ORC evaporators for the three systems are quite high. Therefore, it is important to consider using more efficient ORC evaporators in trigeneration plants. In addition, this study reveals that the SOFC-trigeneration system has the highest electrical energy efficiency while the biomass-trigeneration system and the solar mode of the solar trigeneration system have the highest trigeneration energy efficiencies. In contrast, the SOFC-trigeneration system has the highest exergy efficiency for both electrical and trigeneration cases. Furthermore, the thermoeconomic optimization shows that the solar-trigeneration system has the lowest cost per exergy unit. Meanwhile the solar-trigeneration system has zero CO2 emissions and depends on a free renewable energy source. Therefore, it can be concluded that the solar-trigeneration system has the best thermoeconomic performance among the three systems considered.

Energikontor Sydost har startat demonstrationsprojekt inom småskalig kraftvärme. Ronneby Miljö och Teknik AB driver en demonstrationsanläggning för småskalig elproduktion med ORC-turbin på värmeverk i Bräkne-Hoby. I samband med installation av ORC-turbin gjordes även ombyggnation av fjärrvärmeledning till närliggande sågverk. Detta examensarbete är en teknisk- och lönsamhetsanalys för utvärdering av investeringen. Elverkningsgrad uppgick för denna fjärrvärmesäsong till 2,23 %, alfa-värde till 2,3 %, systemverkningsgrad för ORC-system till 99,54 %. Ledningsförluster minskade från 19,7 till 17,25 % efter ombyggnation. Det visades även att sänkning av fjärrvärmereturtemperatur ökar elproduktionen. Investeringskalkyl visade en icke lönsam investering om el säljs externt. Att producera och använda el internt inom anläggningen visade sig lönsamt även utan investeringsstöd. Ombyggnation av fjärrvärmeledning visades även vara lönsamt. Tekniken är vid anslutning till värmeverk förnybar, lokal och har hög tillgänglighet vid högbelastningstider.

Made available in DSpace on 2016-06-02T20:28:26Z (GMT). No. of bitstreams: 1 3559.pdf: 499785 bytes, checksum: 08c3a73aa07cbea987903f5c2a785444 (MD5) Previous issue date: 2011-03-23 / Financiadora de Estudos e Projetos / We study scalar conservation laws, with the deduction of an explicit formula of a smooth solution with compact support, we also present the behavior of the solution given by the formula when the initial value is zero outside a finite interval. In order to study the uniqueness of a given conservation law under certain hypotheses. / Neste trabalho estudamos leis de conservação escalar, com a dedução de uma fórmula explícita de uma solução suave de suporte compacto, também apresentamos o comportamento da solução dada pela fórmula quando o dado inicial é nulo fora de algum intervalo limitado e por fim estudamos a unicidade para uma dada lei de conservação sob certas hipóteses.

New technologies to converting heat into usable energy are constantly being developed for renewable use. This means that more interactions between different energy grid will be applied, such as utilizing low thermal waste heat to convert its energy to electricity. With high electricity price, such technology is quite attractive at applications that develop low waste heat. In the case of excess heat in district heating (DH) grid and the electricity price are high, the waste heat can be converted to electricity, which can bring a huge profit for DH companies. Candidate technologies are many and the focus in this degree rapport is on the so-called Organic Rankine Cycle (ORC) that belongs to the steam Rankine cycle. Instead of using water as a working fluid, organic working fluid is being used because of its ability to boil at lower temperature. Because this technique is available, it also needs to be optimized, developed, etc. to achieve the highest appropriate efficiency. This can be done, for example, by modeling different layouts, analyzing functionality, performance and / or do a simulation of various suitable working fluids.  This is the purpose of this degree project and the research parts are to select working fluids suitable at low temperatures (70-120) °C, the difference analysis between the selected fluids and identification of the parameters that most affect the performance. There are many suitable methods to apply to achieve desired results. The method used in this rapport degree is commercial software such as Mini REFPROP, CoolPack, Excel but the most important part is simulation with AspenPlus. The selected and suitable working fluids between the chosen temperature interval are R236ea, R600, R245fa and n-hexane. Three common layouts were investigated, and they are The Basic ORC, ORC with an internal heat exchanger (IHE) and regenerative ORC. The results show that in comparison between 120°C and 70°C as a temperature source and without an internal heat exchanger (IHE), R600 at 70°C, has the highest efficiency about 13.55%. At 110°C n-hexane has the highest efficiency about 18.10%. R236ea has the lowest efficiency 13.16% at 70°C and 16.29% at 110°C. R236ea kept its low efficiency through all results. Without an IHE and a source range from 70 °C up to almost 90 °C, R600 has the highest efficiency and at 90°C n-hexane has the highest efficiency. With an IHE and between (70-90) °C R245fa still has the highest efficiency. With or without IHE and a heat source of 110 °C n-hexane has the highest efficiency 18.10% and 18.40%. R236ea gets the greatest increase 5.2% in efficiency but remains with the lowest efficiency. With Regenerative ORC, n-hexane had an optimal middle pressure about 0.76 bar. The optimal pressure corresponds to a thermal efficiency of 17.52%. The most important identified parameters are the fluid characteristics such as higher critical temperature, temperature source, heat sink, application placement and component performance.         The current simulations have been run at some fixed data input such as isentropic efficiencies, no pressure drops, adiabatic conditions etc. It was therefore expected that the same efficiency curve would repeat itself. This efficiency pattern would differ with less or higher values depending on the layout performance. However, this pattern was up to 90 degrees Celsius and gets a very noticeable change by the change of the efficiency for n-hexane. Therefore n-hexane is chosen with Regenerative ORC because it had the highest efficiency at the highest temperature source tested. This is due definitive to the fluid properties like its high critical temperature compared to the other selected fluids. R236ea remains the worst and that’s also related to the fluid properties. It is also important to note that these efficiencies are only from a thermodynamic perspective and may differ when combining both thermal and economic perspectives as well as application placement. These high efficiencies will certainly be lower at more advanced or real processes due to various factors that affect performance. Factors such as component´s efficiency and selection, pipe type and size, etc. To maintain a constant temperature when it’s not, flow regulation is then necessary and that’s also affects the performance.   The conclusion is that the basic ORC which does not have an IHE and from 70 up to 90 degrees Celsius, R600 has the highest efficiency. Higher temperature gives n-hexane the highest efficiency. With an IHE and between (70-90) °C R254fa has the highest efficiency. At higher temperature source n-hexane has the highest efficiency. ORC with an IHE has the best performance. The R236ea has the worst performance through all results. With regenerative ORC, an optimal meddle-pressure for n-hexane is 0.76 bar. Important parameters are The properties of the fluid, temperature source, heatsink, Application placement and component performance. / Nej

The present work addresses the thermodynamic optimization of small binary-cycle geothermal power plants. The optimization process and entropy generation minimization analysis were performed to minimize the overall exergy loss of the power plant, and the irreversibilities associated with heat transfer and fluid friction caused by the system components. The effect of the geothermal resource temperature to impact on the cycle power output was studied, and it was found that the maximum cycle power output increases exponentially with the geothermal resource temperature. In addition, an optimal turbine inlet temperature was determined, and observed to increase almost linearly with the increase in the geothermal heat source. Furthermore, a coaxial geothermal heat exchanger was modeled and sized for minimum pumping power and maximum extracted heat energy. The geofluid circulation flow rate was also optimized, subject to a nearly linear increase in geothermal gradient. In both limits of the fully turbulent and laminar fully-developed flows, a nearly identical diameter ratio of the coaxial pipes was determined irrespective of the flow regime, whereas the optimal geofluid mass flow rate increased exponentially with the Reynolds number. SeveORCs were observed to yield maximum cycle power output. The addition of an IHE and/or an Oral organic Rankine Cycles were also considered as part of the study. The basic types of the FOH improved significantly the effectiveness of the conversion of the available geothermal energy into useful work, and increased the thermal efficiency of the geothermal power plant. Therefore, the regenerative ORCs were preferred for high-grade geothermal heat. In addition, a performance analysis of several organic fluids was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for the basic type of ORCs, whereas those with lower vapour specific heat capacity, such as butane, were more suitable for the regenerative ORCs. / Dissertation (MEng)--University of Pretoria, 2013. / Mechanical and Aeronautical Engineering / unrestricted