This thesis research aims to develop an improved, efficient, low-capacity heat engine, running on an Organic Rankine Cycle (ORC) to generate power. The ORC is driven by low or moderate temperature heat sources, such as; renewable energy in the form of a hot gas derived from biomass/biogas/biofuel combustion streams, waste heat recovery, process heat recovery, etc. The ORC is more suitable and flexible than a conventional steam Rankine cycle, especially when it is applied to low power range. In this research, an extended surface heat exchanger is used to boil the pressurised working fluid, R134a, using a hot air as heat source. The expander used is a scroll type, coupled to a generator, which is able to produce maximum 1.6 kW output. Experimental data of the heat engine are measured under different operating conditions and utilized in the analysis and comparisons. Power generation under various conditions is investigated in order to determine the optimum performance parameters for the heat engine. The isentropic efficiency of the expander is found to be over 40% and reaches 80% for the improved expansion conditions. For the boiler, it is determined that the overall heat transfer coefficient multiplied with the heat transfer area is around 150 W/K. The energy efficiency of the experimental ORC is around 3% for hot air as the low temperature heat source at about 105oC where exergy efficiency reaches 22%, respectively. / UOIT

Cette étude présente une analyse thermomécanique du comportement en fatigue oligocyclique du polyamide 6.6 vierge et renforcé de fibres de verre courtes. Des bilans d'énergie sont réalisés en utilisant, de façon combinée, des techniques d'imagerie quantitative visible et infrarouge. Les champs de température sont obtenus par thermographie et les champs de déformation par corrélation d'images. Sur un cycle de chargement, on montre comment il est possible d'estimer séparément les sources de chaleurs moyennes par cycle, sources associées aux mécanismes dissipatifs et induites par les effets de couplage thermomécanique. On montre ensuite, pour différentes fréquences de chargement, l'évolution du bilan de puissance moyen par cycle sur une zone matérielle correspondant à la partie utile de l'éprouvette. Ce bilan prend en compte le taux de l'énergie de déformation, les chaleurs mises en jeu et les variations d'énergie interne. On observe que la forme du bilan de puissance est très fortement dépendante, pour un rapport de charge donné, à la fréquence de sollicitation, à la teneur en eau, à l'orientation des fibres de verre mais aussi aux niveaux de contrainte appliqués. / This study presents a thermomechanical analysis of fatigue behavior of pure and short glass- fiber reinforced polyamide 6.6. The energy balances are drew up using the combined application of visible and infrared quantitative imaging techniques. Temperature fields are obtained by thermography and strain fields by image correlation. Over one complete cycle, we show how it is possible to separately estimate the heat sources averaged over the cycle, associated with dissipative mechanisms and induced by thermomechanical coupling source effets. Then we show, for different loading rates, the time courses of the energy rate balance for a physical area corresponding to the gage part of the specimen. This balance takes into account the deformation energy rate, the heat sources and the internal energy variations. It is observed that the shape of the energy rate balance is highly dependent, for a given load ratio, to the load rate, the water content, the orientation of the glass fibers and the applied stress levels.

There are numerous experiments for the exploration of the corium spreading behaviour, but comparable data have not been available up to now in the field of the long term behaviour of a corium expanded in a core catcher. The difficulty consists in the experimental simulation of the decay heat that can be neglected for the short-run course of events like relocation and spreading, which must, however, be considered during investigation of the long time behaviour. Therefore the German GRS, defined together with Battelle Ingenieurtechnik a benchmark problem in order to determine particular problems and differences of CFD codes simulating an expanded corium and from this, requirements for a reasonable measurement of experiments, that will be performed later. First the finite-volume-codes Comet 1.023, CFX 4.2 and CFX-TASCflow were used. To be able to make comparisons to a finite-element-code, now calculations are performed at the Institute of Safety Research at the Forschungszentrum Rossendorf with the code ANSYS/FLOTRAN.For the benchmark calculations of stage 1 a pure and liquid melt with internal heat sources was assumed uniformly distributed over the area of the planned core catcher of a EPR plant. Using the Standard-k-e-turbulence model and assuming an initial state of a motionless superheated melt several large convection rolls will establish within the melt pool. The temperatures at the surface do not sink to a solidification level due to the enhanced convection heat transfer. The temperature gradients at the surface are relatively flat while there are steep gradients at the ground where the no slip condition is applied. But even at the ground no solidification temperatures are observed. Although the problem in the ANSYS-calculations is handled two-dimensional and not three-dimensional like in the finite-volume-codes, there are no fundamental deviations to the results of the other codes.

These days, the cooling of new generation electronic servers is a challenge due to the immense heat generated by them. In order to avoid overheating caused by the important rise in temperature appropriate cooling procedures must be used in order to meet the thermal requirement. The current study aims at addressing the issue of overheating in this field, and focuses on the thermal management of electronic devices modelled as a discrete heat sources (mounted in a rectangular cavity) with uniform heat flux applied from the bottom. A review of the literature published regarding the convective heat transfer from heated sources as well as a thorough background on the theory of the cooling of discrete sources by forced convection in rectangular channel is provided in this study. It was showed that the heat transfer performance in channel is strongly influenced by the geometric configurations of heat sources. Therefore, the arrangement and geometric optimisation are the main considerations in the evaluation of thermal performance. Unlike experimental methods that were carried out widely in the past, which provided less cost-effective and more time-consuming means of achieving the same objective, in this study we first explore the possibilities and the advantages of using the CD-adapco's CFD package Star-CCM+ to launch a three dimensional investigation of forced convection heat transfer performance in a channel mounted with equidistant heatgenerating blocks. Numerical results were validated with available experimental data, and showed that the thermal performance of the heat transfer increases with the strength of the flow. The second objective was to maximise the heat transfer density rate to the cooling fluid and to minimise both the average and the maximum temperature in the channel by using the numerical optimisation tool HEEDS/Optimate+. The optimal results showed that better thermal performance was not obtained when the heated sources followed the traditional equidistance arrangement, but was achieved with a specific optimal arrangement under the total length constraint for the first case. Subsequently, for the second case study, on the volume constraints of heat sources, the results proved that optimal configurations that maximise the heat transfer density rate were obtained with a maximum of either the height-to-length ratio or the height-to-width ratio. It was concluded that the heat transfer rate to the cooling fluid increases significantly with the Reynolds number and the optimal results obtained numerically are found to be fairly reliable. / Dissertation (MSc)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / MSc / Unrestricted

There are numerous experiments for the exploration of the corium spreading behaviour, but comparable data have not been available up to now in the field of the long term behaviour of a corium expanded in a core catcher. The difficulty consists in the experimental simulation of the decay heat that can be neglected for the short-run course of events like relocation and spreading, which must, however, be considered during investigation of the long time behaviour. Therefore the German GRS, defined together with Battelle Ingenieurtechnik a benchmark problem in order to determine particular problems and differences of CFD codes simulating an expanded corium and from this, requirements for a reasonable measurement of experiments, that will be performed later. First the finite-volume-codes Comet 1.023, CFX 4.2 and CFX-TASCflow were used. To be able to make comparisons to a finite-element-code, now calculations are performed at the Institute of Safety Research at the Forschungszentrum Rossendorf with the code ANSYS/FLOTRAN.For the benchmark calculations of stage 1 a pure and liquid melt with internal heat sources was assumed uniformly distributed over the area of the planned core catcher of a EPR plant. Using the Standard-k-e-turbulence model and assuming an initial state of a motionless superheated melt several large convection rolls will establish within the melt pool. The temperatures at the surface do not sink to a solidification level due to the enhanced convection heat transfer. The temperature gradients at the surface are relatively flat while there are steep gradients at the ground where the no slip condition is applied. But even at the ground no solidification temperatures are observed. Although the problem in the ANSYS-calculations is handled two-dimensional and not three-dimensional like in the finite-volume-codes, there are no fundamental deviations to the results of the other codes.

This master thesis focuses on the testing of the combustion equipment and the wood fuel combustion process. The aim of the thesis is to get acquainted with this issue and to analyze solutions for monitoring and control of heat source parameters according to valid legislation. The result of this thesis is the realization and verification of the software design of the combustion test system using the NI LabVIEW development environment.

The diploma thesis is dedicated to the development and maintenance of the central heating supply system in Plzeň. The first part of the thesis is devoted to a brief overview of the city's history and to the development of the energy sector and the beginnings of the construction of energy sources producing thermal energy in Plzeň. The next part contains the analysis of the administrative development of heat sources and the history of their construction in the city. In the middle of the 19th century, important industrial enterprises started to establish their first own energy sources. The energy source of the Škoda Plzeň plant, which was one of the first in the city, also used to heat the city's flats after the World War II and later incorporated into the central heating system. In order to supply heat, the city began to build heating plants in several parts of the city in the late 60s of the 20th century and followed this process with the construction of a central heating source in the early 70s. The last part of the thesis deals with the period after privatisation, when the legal form of business was changed and the Plzeňská teplárenská a. s. joint-stock company was established. The final summary compares the reasons for the construction of heat sources in Plzeň, which can be divided into three...

4th generation district heating (4GDH) and varying the indoor temperature to store heat are both important concepts that can make it easier to implement more renewable energy and reduce costs of heating. This study looks at these concepts from a customer perspective using one building and looking at how energy can be stored and the performance of 4GDH. Low temperature heat sources from industry, supermarkets, and datacentres are used in combination with heat from a combined heat and power plant to get the required heating. A heat pump has also been modelled as a part of the 4GDH structure. In addition to looking at heat storage in 4GDH a scenario with direct electric heating has also been evaluated. In conclusion 4GDH has lower operating costs than 3rd generation district heating, but it is not worth varying the indoor temperature to store energy when using 4GDH. It is, however, profitable to vary indoor temperature if direct electric heating is used.

Em projetos de oleodutos e gasodutos utilizam-se aços de alta resistência e baixa liga (ARBL), como o aço API 5L X80. Na soldagem multipasse destas tubulações, a zona afetada pelo calor (ZAC) do passe de raiz é submetida a um novo ciclo térmico pelos passes de soldagem subsequentes. Isto resulta em alterações nos valores das propriedades físicas. Nos aços ARBL, a ZAC de grãos grosseiros reaquecida intercriticamente (IC-ZACGG) pode se tornar uma zona frágil localizada, isto é, uma zona com maior dureza. Consequentemente, falhas estruturais podem ocorrer, ocasionando paradas não desejadas no transporte de fluidos. O objetivo deste trabalho é desenvolver uma metodologia baseada no modelo de fontes de calor distribuídas de Mhyr e Gröng, para avaliar o fluxo de calor na soldagem considerando as propriedades físicas dependentes da temperatura. Estender a aplicação desta ferramenta em soldagens multipasses para identificar sub-regiões da ZAC de um passe anterior sendo afetada pela ZAC de passes subsequentes. As isotermas simuladas foram validadas através de medições realizadas em macrografias de juntas soldadas. Os ciclos térmicos simulados foram validados através das temperaturas máximas atingidas e pelos tempos de resfriamento de 800 a 500 ºC (?t8-5) dos ciclos térmicos experimentais. Ao aplicar a metodologia proposta, foi possível delimitar com acurácia as regiões reaquecidas da ZAC e analisar os efeitos dos passes subsequentes em cada uma das sub-regiões da ZAC do passe de raiz. A IC-ZACGG na região do passe de raiz foi localizada, mas não se comportou como zona frágil devido à boa soldabilidade do aço API 5L X80 comprovada pelos ensaios de dureza e de tenacidade ao impacto Charpy-V. / In pipelines projects, the high strength low alloy (HSLA) steels are used, such as the API 5L X80 steel. During the multipass welding of these pipes, the heat affected zone (HAZ) of the root pass is subjected to a new thermal cycle by the subsequent welding passes. This results in changes in the values of the physical properties. In the HSLA steels, the intercritical reheated coarse-grained heat-affected zone (IR-CGHAZ) can become a local brittle zone, that is, a region with greater hardness. Consequently, structural failures could happen, causing undesired shutdowns in fluid transportation. The objective of this work is to develop a methodology based on the distributed heat sources model of Mhyr and Gröng, to evaluate the heat flux in the welding considering the temperature-dependent physical properties. Extend the application of this tool in multipass welds to identify HAZ subregions of a previous pass being affected by the HAZ of subsequent passes. The simulated isotherms were validated through measurements made on macrographs of welded joints. The simulated thermal cycles were validated through the maximum temperatures reached and the cooling times from 800 °C to 500 ºC (?t8-5) of the experimental thermal cycles. By applying the proposed methodology, it was possible to accurately delimit reheated HAZ regions and analyze the effects of subsequent passes in each of the root pass HAZ subregions. The IRCGHAZ in the root pass region was localized, but it did not behave as a brittle zone due to the good weldability of the API 5L X80 steel as proven by the hardness and Charpy-V impact tests.

L’utilisation d'énergie en milieu urbain est essentielle pour le bon fonctionnement de notre société, en particulier pour les besoins de chauffage qui est un élément central de notre système énergétique souvent considéré comme allant de soi. Dans ce cadre, les systèmes énergétiques urbains et en particulier les réseaux de chaleur urbains ont besoin d’évoluer pour s'adapter à la transition à venir vers un système énergétique durable. Ce travail de recherche a pour objectif de présenter, de discuter et d’évaluer, du point de vue technico-économique, le concept de micro-réseaux de chaleur urbains basse température comme réseaux secondaires de distribution de chaleur actifs. Dans cette thèse, une approche méthodologique mixte basée sur la simulation analytique pour l'évaluation des alternatives est développée et discutée pour étudier une combinaison de technologies associées aux sous-stations basse température. Les principaux résultats de ce travail couvrent : le développement d’un modèle amélioré de charges thermiques agrégées ; la comparaison des performances des réseaux basse température ; l’analyse des avantages et des inconvénients des sous-stations actives couplées à des sources de chaleur ou du stockage distribuées ; et les effets d’une température de retour du réseau primaire plus basse. Les conclusions révèlent que la conception et le fonctionnement intégrés du micro-réseau de chaleur urbain actif ont le potentiel d'améliorer les performances de l'ensemble du système, afin de relever ses défis d'une manière efficace et rentable. Ce travail fait progresser les connaissances actuelles sur le chauffage urbain en identifiant les synergies et les enjeux associés, en vue de que ces technologies jouent un rôle clé dans le futur système énergétique intelligent et durable. / Energy use in the urban environment is vital for the proper functioning of our society, and in particular, comfort heating –and cooling– is a central element of our energy system that is often taken for granted. Within this context, district energy systems and especially, district heating (DH) systems must evolve to adapt to the upcoming decades-long transition towards a sustainable energy system. This dissertation seeks to introduce, discuss, and asses from a techno-economic perspective, the concept of low-temperature based thermal micro-grids (subnets) as active distribution thermal networks. For this purpose, a mixed methodological approach based on analytical simulation for the assessment of alternatives is developed and discussed to evaluate a set of technologies. Key findings of this research include: an updated and improved model of aggregated heat loads; the identification of differences in load and temperature patterns for certain LT subnets; the analysis of benefits and drawbacks of active substations with distributed heat sources and/or storage; and the impact of the reduction of the primary network return temperature, which leads to lower generation & operating costs. These outcomes reveal that the integrated design and operation of the active thermal micro-grid have the potential to improve the performance of the entire system, to address the matter of providing comfort heating in an effective and cost-efficient manner. This work advances the current DH knowledge by identifying synergies and challenges that arise with these new developments, in order for DH to play a key role in the future smart and sustainable energy system.