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Globally, there are vast amounts of low-grade heat sources from industrial waste and renewables that can be converted into electricity through advanced thermodynamic power cycles and appropriate working fluids. In this thesis, experimental research was conducted to investigate the performance of a small-scale Organic Rankine Cycle (ORC) system under different operating conditions. The experimental setup consisted of typical ORC system components, such as a turboexpander with a high speed generator, a scroll expander, a finned-tube condenser, an ORC pump, a plate evaporator and a shell and tube evaporator. R245fa was selected as the working fluid, on account of its appropriate thermophysical properties for the ORC system and its low ozone depletion potential (ODP). The test rig was fully instrumented and extensive experiments carried out to examine the influences of several important parameters, including heat source temperature, ORC pump speed, heat sink flow velocity, different evaporators and with or without a recuperator on overall R245fa ORC performances. In addition, in terms of the working fluid’s environmental impact, temperature match of the cycle heat processes and system compactness, CO2 transcritical power cycles (T-CO2) were deemed more applicable for converting low-grade heat to power. However, the system thermal efficiency of T-CO2 requires further improvement. Subsequently, a test rig of a small-scale power generation system with T-CO2 power cycles was developed with essential components connected; these included a plate CO2 supercritical heater, a CO2 transcritical turbine, a plate recuperator, an air-cooled finned-tube CO2 condenser and a CO2 liquid pump. Various preliminary test results from the system measurements are demonstrated in this thesis. At the end, a theoretical study was conducted to investigate and compare the performance of T-CO2 and R245fa ORCs using low-grade thermal energy to produce useful shaft or electrical power. The thermodynamic models of both cycles were developed and applied to calculate and compare the cycle thermal and exergy efficiencies at different operating conditions and control strategies. In this thesis, the main results showed that the thermal efficiency of the tested ORC system could be improved with an increased heat source temperature in the system with or without recuperator. When the heat source temperature increased from 145 oC to 155 oC for the system without recuperator, the percentage increase rates of turbine power output and system thermal efficiency were 13.6% and 14% respectively while when the temperature increased from 154 oC to 166 oC for the system with recuperator, the percentage increase rates were 31.2% and 61.97% respectively. In addition, the ORC with recuperator required a relative higher heat source temperature, which is comparable to a system without recuperator. On the other hand, at constant heat source temperatures, the working fluid pump speed could be optimised to maximise system thermal efficiency for ORC both with and without recuperator. The pressure ratio is a key factor impacting the efficiencies and power generation of the turbine and scroll expander. Maximum electrical power outputs of 1556.24W and 750W of the scroll expander and turbine were observed at pressure ratio points of 3.3 and 2.57 respectively. For the T-CO2 system, the main results showing that the CO2 mass flow rate could be directly controlled by varying the CO2 liquid pump speeds. The CO2 pressures at the turbine inlet and outlet and turbine power generation all increased with higher CO2 mass flow rates. When CO2 mass flow rate increased from 0.2 kg/s to 0.26kg/s, the maximum percentage increase rates of measured turbine power generation was 116.9%. However, the heat source flow rate was found to have almost negligible impact on system performance. When the thermal oil flow rate increased from 0.364kg/s to 0.463kg/s, the maximum percentage increase rate of measured turbine power generation was only 14.8%. For the thermodynamic analysis, with the same operating conditions and heat transfer assumptions, the thermal and exergy efficiencies of R245fa ORCs are both slightly higher than those of T-CO2. However, the efficiencies of both cycles can be enhanced by installing a recuperator at under specific operating conditions. The experiment and simulation results can thus inform further design and operation optimisations of both the systems and their components.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / O escopo deste trabalho foi compreender a gramÃtica polÃtica de Acarape (CearÃ) a partir do estudo dos ciclos polÃticos, das trajetÃrias de suas principais lideranÃas e das disputas locais pelo poder. Na ausÃncia de grupos polÃticos homogÃneos e hegemÃnicos na nova municipalidade, que se autonomizou em fins da dÃcada de 1980, buscou-se analisar os caminhos e mecanismos utilizados por lideranÃas polÃticas locais a fim de construir e fortalecer seu poder de mando de modo a alcanÃar a chefia do executivo municipal. O foco foi a forma como o mÃdico Franklin VerÃssimo (e porque ele) se inscreveu no campo polÃtico fragilizando o poder de mando de lideranÃas que hà 20 anos conseguiram manter afastados outros (novos) atores dos espaÃos polÃticos de concorrÃncia, conservando seus quadros dirigentes praticamente inalterados. O recorte temporal abrangeu o intervalo entre os anos de 1988 (primeira eleiÃÃo municipal de Acarape pÃs-emancipaÃÃo) a 2016, no qual buscou-se identificar a composiÃÃo das facÃÃes polÃticas, suas estratÃgias eleitorais e a alternÃncia no executivo local. O percurso metodolÃgico do trabalho envolveu, alÃm de levantamento bibliogrÃfico, a utilizaÃÃo de entrevistas, o acompanhamento de postagens de polÃticos nas redes sociais, o exame de dados disponibilizados pelo Tribunal Regional Eleitoral (TRE-CE), anÃlise documental e observaÃÃo de eventos pÃblicos e cenÃrios (prÃ)eleitorais em Acarape. O primeiro capÃtulo contextualizou a luta pela emancipaÃÃo de Acarape no cenÃrio da redemocratizaÃÃo brasileira dando Ãnfase aos personagens que protagonizaram o processo polÃtico. Dialogando com a perspectiva de ciclos polÃticos longevos na contemporaneidade, o segundo capÃtulo traÃou a genealogia do poder em Acarape reconstruindo as bases de recursos eleitorais das principais lideranÃas e as estratÃgias polÃticas e simbÃlicas utilizadas para se legitimarem (e se manterem) no poder. O Ãltimo capÃtulo abordou os operadores de entrada do mÃdico no cenÃrio polÃtico acarapense e a inauguraÃÃo de um novo ciclo polÃtico a partir da construÃÃo de uma nova chefia polÃtica e de uma profunda reorganizaÃÃo das facÃÃes polÃticas. O exemplo de Acarape pode revelar tendÃncias gerais na medida em que aponta para dependÃncia de municÃpios em relaÃÃo ao governo estadual, transfigurada no adesismo, interferindo no esvaziamento das oposiÃÃes a nÃvel local e na produÃÃo de ciclos de domÃnio de grupos polÃticos longevos. Espera-se contribuir para desenvolvimento de agendas de pesquisas que contemplem a anÃlise polÃtica municipal, sobretudo, no CearÃ, de modo a promover uma atualizaÃÃo de categorias que sÃo caras aos estudos do poder local. / O escopo deste trabalho foi compreender a gramÃtica polÃtica de Acarape (CearÃ) a partir do estudo dos ciclos polÃticos, das trajetÃrias de suas principais lideranÃas e das disputas locais pelo poder. Na ausÃncia de grupos polÃticos homogÃneos e hegemÃnicos na nova municipalidade, que se autonomizou em fins da dÃcada de 1980, buscou-se analisar os caminhos e mecanismos utilizados por lideranÃas polÃticas locais a fim de construir e fortalecer seu poder de mando de modo a alcanÃar a chefia do executivo municipal. O foco foi a forma como o mÃdico Franklin VerÃssimo (e porque ele) se inscreveu no campo polÃtico fragilizando o poder de mando de lideranÃas que hà 20 anos conseguiram manter afastados outros (novos) atores dos espaÃos polÃticos de concorrÃncia, conservando seus quadros dirigentes praticamente inalterados. O recorte temporal abrangeu o intervalo entre os anos de 1988 (primeira eleiÃÃo municipal de Acarape pÃs-emancipaÃÃo) a 2016, no qual buscou-se identificar a composiÃÃo das facÃÃes polÃticas, suas estratÃgias eleitorais e a alternÃncia no executivo local. O percurso metodolÃgico do trabalho envolveu, alÃm de levantamento bibliogrÃfico, a utilizaÃÃo de entrevistas, o acompanhamento de postagens de polÃticos nas redes sociais, o exame de dados disponibilizados pelo Tribunal Regional Eleitoral (TRE-CE), anÃlise documental e observaÃÃo de eventos pÃblicos e cenÃrios (prÃ)eleitorais em Acarape. O primeiro capÃtulo contextualizou a luta pela emancipaÃÃo de Acarape no cenÃrio da redemocratizaÃÃo brasileira dando Ãnfase aos personagens que protagonizaram o processo polÃtico. Dialogando com a perspectiva de ciclos polÃticos longevos na contemporaneidade, o segundo capÃtulo traÃou a genealogia do poder em Acarape reconstruindo as bases de recursos eleitorais das principais lideranÃas e as estratÃgias polÃticas e simbÃlicas utilizadas para se legitimarem (e se manterem) no poder. O Ãltimo capÃtulo abordou os operadores de entrada do mÃdico no cenÃrio polÃtico acarapense e a inauguraÃÃo de um novo ciclo polÃtico a partir da construÃÃo de uma nova chefia polÃtica e de uma profunda reorganizaÃÃo das facÃÃes polÃticas. O exemplo de Acarape pode revelar tendÃncias gerais na medida em que aponta para dependÃncia de municÃpios em relaÃÃo ao governo estadual, transfigurada no adesismo, interferindo no esvaziamento das oposiÃÃes a nÃvel local e na produÃÃo de ciclos de domÃnio de grupos polÃticos longevos. Espera-se contribuir para desenvolvimento de agendas de pesquisas que contemplem a anÃlise polÃtica municipal, sobretudo, no CearÃ, de modo a promover uma atualizaÃÃo de categorias que sÃo caras aos estudos do poder local.

The topic of this thesis is carbon dioxide (CO2) capture and storage (CCS), which is a technology that is currently being promoted by industries, scientists and governments, among others, in order to mitigate climate change despite a continued use of fossil fuels. Because of the complex nature of CCS and the risks it entails, it is controversial. The aim of this thesis is to analyse how the technology may be further developed in a responsible manner. In the first part of the thesis different methods for capturing CO2 from industrial processes as well as power plants are analysed. The aim is to identify early opportunities for CO2 capture, which is considered important because of the urgency of the climate change problem. Three potential early opportunities are studied: i) capturing CO2 from calcining processes such as cement industries by using the oxyfuel process, ii) capturing CO2 from pressurised flue gas, and iii) capturing CO2 from hybrid combined cycles. Each opportunity has properties that may make them competitive in comparison to the more common alternatives if CCS is realised. However, there are also drawbacks. For example, while capturing CO2 from pressurised flue gas enables the use of more compact capture plant designs as well as less expensive and less toxic absorbents, the concept is neither suitable for retrofitting nor has it been promoted by the large and influential corporations. The second part of the thesis has a broader scope than the first and is multidisciplinary in its nature with inspiration from the research field of Science and Technology Studies (STS). The approach is to critically analyse stakeholder percep-tions regarding CCS, with a specific focus on the CCS experts. The thesis sheds new light on the complexity and scientific uncertainty of CCS as well as on the optimism among many of its proponents. Because of the uncertain development when it comes to climate change, fossil fuel use and greenhouse gas emissions, the conclusion is that CCS has to be further developed and demonstrated. A responsible strategy for a future development of CCS would benefit from: i) a search for win-win strategies, ii) increasing use of appropriate analytical tools such as life-cycle analysis, iii) a consideration of fossil fuel scarcity and increasing price volatility, iv) funding of unbiased research and v) increasing simultaneous investments in long-term solutions such as renewable energy alternatives and efficiency improvements. / QC 20100727