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1
Idir, Anis. "Procédé thermochimique de production/stockage de froid pour le refroidissement et la valorisation de chaleur basse température de panneaux photovoltaïques." Thesis, Perpignan, 2022. http://www.theses.fr/2022PERP0016.
Анотація:
La technologie photovoltaïque (PV) est l’une des techniques de production d’électricité renouvelable la plus utilisée. La conversion photoélectrique génère cependant dans les cellules solaires une importante quantité de chaleur, entrainant une significative hausse de leur température de fonctionnement qui impacte fortement le rendement de conversion. Lorsque les panneaux opèrent dans des zones à fort ensoleillement et des conditions climatiques arides, les températures de fonctionnement atteignent des températures de 80°C à 100°C impactant également leur durabilité. Ainsi l’objectif des travaux de thèse réalisés repose sur l’amélioration de la conversion énergétique solaire par, d’une part, une limitation la hausse de température de fonctionnement des modules PV par un refroidissement actif pour en accroitre leurs performances électriques et d’autre par la valorisation en froid de l’énergie thermique générée par un procédé thermique à sorption de gaz. Le but visé est de démontrer la faisabilité technique d’un tel couplage et d’en évaluer la pertinence énergétique. Ainsi, un procédé à sorption de gaz exploitant une solution saturée, permettant d’exploiter la chaleur basse température générée des panneaux PV et la valoriser en froid a été défini, conçu, expérimenté et analysé. Un modèle numérique de ce couplage a été développé et a permis d’évaluer les performances électriques d’une centrale solaire et frigorifique du procédé à sorption couplé thermiquement, dans des conditions réalistes de fonctionnement. Un tel couplage qui permet ainsi une cogénération électricité/froid, montre ainsi qu’il est possible d’améliorer de 10.5 % le gain énergétique global en comparaison de celui de panneaux PV standard, tout en entrainant une faible perte exergétique globale de 1.3 % lié à la conversion supplémentaire de la chaleur en froidPhotovoltaic technology (PV) is one of the most widely used renewable electricity generation techniques. However, the photoelectric conversion process generates a large amount of heat in the solar cells, causing a significant increase in their operating temperature, which has a significant impact on the conversion efficiency. When the panels operate in areas with high solar irradiation and arid climatic conditions, the operating temperatures can reach 80°C to 100°C, which also impacts their durability. Thus, the objective of this thesis work is to improve the global solar energy conversion by limiting the operating temperature increase of PV modules through an active cooling in order to increase their electrical performance and to valorize in cold the thermal energy generated by a gas sorption thermal process. The aim is to demonstrate the technical feasibility of such a coupling and to evaluate its energy relevance. A gas sorption process exploiting a saturated solution, allowing to exploit the low temperature heat extracted from the PV panels and to valorize it in cold has thus been defined, designed, experimented and analyzed. A simulation tool has been developed to evaluate under realistic operating conditions the electrical performance a PV solar power plant and cooling performance of the thermally coupled sorption process. Such a coupling, which allows for electricity/cooling cogeneration, shows that it is possible to improve the overall energy gain by 10.5 % compared to that of standard PV panels, while resulting in a small overall energy loss of 1.3 % due to the additional conversion of heat to cold
2
Segond, Guillaume. "Etudes des couplages thermohydrauliques en régime variable d'un système thermique avec stockage : application à la production d'eau chaude sanitaire à partir de la valorisation d'une source de chaleur basse température." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4722.
Анотація:
Le travail présenté ici a pour objectifs d’étudier et d’optimiser les performances énergétiques d’un chauffe-eau thermodynamique couplé à un stockage par chaleur sensible. La ressource utilisée consiste en la récupération de chaleur sur l’air extrait d’un logement de type collectif. L’enjeu est de caractériser les conditions dans lesquelles le système est capable d’assurer les besoins avec des performances requises lorsque les conditions aux limites sont très fluctuantes. Sur le plan fonctionnel, le système doit être le plus simple possible du point de vue de sa configuration hydraulique et de sa stratégie de régulation.Pour cette étude, nous avons développé un modèle physico-corrélatif sur TRNSYS pour simuler et analyser les différents scenarios et les couplages thermohydrauliques entre les composants du système. En parallèle de cette démarche de modélisation, nous avons conçu et mis en œuvre un dispositif expérimental à l’échelle 1 à des fins de validation du modèle sur une large plage de conditions opératoires.L’analyse des résultats, notamment sur la nature des écoulements au sein du ballon de stockage, a mis en évidence l’influence majeure d’un certain nombre de paramètres sur les performances du système. En particulier, la robustesse des performances face à des fluctuations importantes des conditions aux limites peut être assurée grâce à une stratégie de régulation adaptée.Cette étude a finalement conduit à proposer un modèle réduit pour le dimensionnement du système qui prend en compte les paramètres le plus pertinents pour la stratégie de régulationThe work presented here aims to study and optimize the energy efficiency of a heat pump water heater coupled with a sensible heat storage. The resource used consists of heat recovery from exhaust air of a collective type of housing. The challenge is to characterize the conditions in which the system is capable of ensuring the needs with performance required when the boundary conditions are very volatile. Functionally, the system should be as simple as possible from the viewpoint of its hydraulic configuration and its control strategy.For this study, we developed a TRNSYS numerical model to simulate and analyze different scenarios and thermal hydraulic couplings between the system components. In parallel with this modeling approach, we designed and implemented an experimental set up with realistic scale to validate the model over a wide range of operating conditions.The analysis of the results, including the nature of flows within the storage tank, highlighted the major influence on a number of parameters on the system performance. In particular, the robust performance in the face of significant fluctuations of the boundary conditions can be ensured through appropriate control strategy.This study eventually led to propose a model for the design of the system that takes into account the most relevant parameters for the control strategy
3
Midtsjø, Alexander. "Power Production from Low Temperature Heat Sources." Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9902.
Анотація:
As part of the energy recovery part of the ROMA (Resource Optimization and recovery in the Materials industry) project, a laboratory prototype power production system is being built and completed in 2009. The laboratory prototype is based on a new technology for power production from low to medium temperature heat sources (the off gas from electrolysis cells in the aluminum industry) where CO2 is used as a working medium in a trans-critical Rankine cycle. The laboratory rig consists of the power cycle with a prototype expander as the core unit, an air loop to provide the heat, and an ethylene glycol loop to provide condensation of the working fluid in the power cycle. As a preparation to the assembling and instrumentation of the prototype rig, a simulation and an uncertainty analysis were conducted for the prototype rig in the autumn of 2008. This report focuses on the continuation of that work by an experimental investigation of the individual loops and the components of the prototype rig. The emphasis of this investigation has been put on the air loop and the expander unit of the power cycle. This is basically because these are of great importance to the performance of the power production prototype rig. The air loop was thoroughly tested, and from the investigations it was discovered that there was an unfavorable temperature distribution of the air going into the air-to-CO2 heat exchanger. This is the heat exchanger where heat is provided to the power cycle. The source for this temperature maldistribution was identified, and solutions were investigated to improve on the problem without results. The reduced performance of the air loop was incorporated in a new simulation of the power cycle in order to quantify the consequences for the optimization of the power cycle. The simulation was carried out for warm air temperature of 80 °C. The new calculations showed a reduction in maximum net work output of 27 % compared to the original simulation. The optimal conditions for the power cycle were also changed as a consequence of the reduced air loop performance. The investigation of the expander unit revealed that the expander isentropic efficiency was a strong function of the pressure difference across the expander, and a weak function of the expander inlet pressure. It also revealed that overall the isentropic efficiency was much less than the value of 80 % which was used in the original simulation. A new simulation of the power cycle was carried out where the expander isentropic efficiency was incorporated as a function of the pressure difference across the expander. This function was based on the data from the expander testing. The simulation showed a reduction in maximum net work output from 225 W to about 60 W, for warm air temperature of 80 °C. The new expander characteristics also affected the optimization of the power cycle. The simulation results and the results from the prototype investigation will be important in the optimization and control procedures of the assembled prototype power production system.
4
Pfaff, Michael. "Power Production from Low Temperature Heat Sources." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18330.
Анотація:
SummaryThis Master Thesis is a conclusion on work done as part of the Resource Optimizationand recovery in the Materials industry project (Roma). This project is involved in thedevelopment of a new technology for power production from low temperature heat sourcesfor off gases from aluminum production cells. The technology is based on an transcriticalRankine cycle with CO2 as a working fluid, as the work recovery circuit. The center ofthe test facility is the expander, a prototype provided by Obrist Engineering . 81 testswere perfomed to investigate the behavoir of the expander cycle. Effect of three mainparameters were investigated:• Effect CO2 massflow rate• Effect of heat source temperature• Effect of CO2 condensation pressureFor each parameter combination, the high pressure side of the expander cycle was variedin order to find the maximum power output.This study clearly showed limitation of the turbine which cannot maintain large pressuredifference probably due to large internal leakages. As a result, turbine outlet is highlysuperheated. This superheat is lost energy for the power cycle, and is simply dumpedinto the heat sink. One possible improvement would be to include a recuperator thatrecovers superheat after the pump.The results also indicate that the fan of the air loop is too small: increasing the CO2 flowrate to limit superheat at turbine outlet leads to turbine inlet temperature reduction.Last, for large CO2 mass flow rate (3.5 kgmin) which is required for proper operation ofthe turbine, the power generated is too large for the generator installed on the loop. Itstemperature reached 120 °C for some conditions. A new solution should be seeked.Based on experimental results, a mode of the power cycle was implemented in Pro/IIand simulations were run in order to find an improved design. The main goal is to beable to run the cycle at high CO2 mass flow rate: 3.5 kgmin. It was found that the airloop fan should be able to deliver up to 1 260 m3h . The new generator or braking systemshould be able to absorb up to 297 W.
5
Maalouf, Samer. "Étude et conception d'un système thermodynamique producteur du travail mécanique à partir d'une source chaude à 120°C." Thesis, Paris, ENMP, 2013. http://www.theses.fr/2013ENMP0074/document.
Анотація:
Les fumées à basse température (<120-150 °C) sortant des procédés industriels pourraient être récupérées pour la production d'électricité et constituent un moyen efficace de réduction de la consommation d'énergie primaire et des émissions de dioxyde de carbone. Cependant, des barrières techniques tels que la faible efficacité de conversion, la nécessité d'une grande zone de transfert de chaleur, et la présence de substances chimiques corrosives liées à une forte teneur en humidité lors du fonctionnement en environnement sévère entravent leur application plus large. Cette thèse porte particulièrement sur les secteurs industriels les plus énergivores rencontrant actuellement des difficultés à récupérer l'énergie des sources de chaleur à basse température dans des environnements hostiles. Des cycles thermodynamiques existants basés sur le Cycle de Rankine Organique (ORC) sont adaptés et optimisés pour ce niveau de température. Deux méthodes de récupération de chaleur classiques sont étudiées plus particulièrement : les déshumidifications à contact direct et indirect. Des méthodes de conception optimisées pour les échangeurs de chaleur sont élaborées et validées expérimentalement. Pour la déshumidification à contact indirect, des matériaux à revêtement anticorrosifs sont proposés et testés. Pour la déshumidification à contact direct, les effets du type et de la géométrie des garnissages sur les performances hydrauliques sont étudiés. Des cycles thermodynamiques innovants basés sur la technologie de déshydratation liquide sont proposés. Un cycle de régénération amélioré (IRC) est développé. Comparé aux technologies de récupération de chaleur classiques, l'IRC proposé améliore à la fois la puissance nette et le taux de détente de la turbine en prévenant par ailleurs les problèmes de corrosionLow-temperature waste-gas heat sources (< 120-150°C) exiting several industrial processes could be recovered for electricity production and constitute an effective mean to reduce primary energy consumption and carbon dioxide emissions. However, technical barriers such as low conversion efficiency, large needed heat transfer area, and the presence of chemically corrosive substances associated with high moisture content when operating in harsh environment impede their wider application. This thesis focuses on particularly energy-hungry industrial sectors characterized by presently unsolved challenges in terms of environmentally hostile low-temperature heat sources. Existing thermodynamic cycles based on Organic Rankine Cycle (ORC) are adapted and optimized for this temperature level. Two conventional heat recovery methods are studied more particularly: indirect and direct contact dehumidification. Optimized design methods for heat exchangers are elaborated and experimentally validated. For the indirect contact dehumidification, advanced anti-corrosion coated materials are proposed and laboratory tested. For the direct contact dehumidification, the effects of packing material and geometry on the corresponding hydraulic performances are underlined. Innovative thermodynamic cycles based on the liquid desiccant technology are investigated. An improved regeneration cycle (IRC) is developed. Compared to the conventional heat recovery technologies, the proposed “IRC” improves both net power and turbine expansion ratio besides preventing faced corrosions problems
6
Dahn, Douglas Charles. "Low temperature specific heat of LixNbS2 intercalation compounds." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25563.
Анотація:
This thesis describes a study of the low temperature specific heat of LiⅹNbS₂, where x is between 0 and 1. Samples were prepared by intercalating lithium into niobium disulfide in electrochemical cells. Structural data obtained by x-ray diffraction are presented. These, together with electrochemical measurements, show that staged phases exist for some values of x. The electronic specific heat of LiⅹNbS₂, is consistent with complete charge transfer from the intercalated lithium to the bands of the NbS2 host. The lattice specific heat also shows large changes as a function of x. A discussion of the data in terms of continuum elasticity theory suggests that intercalation produces large changes in the shear elastic constant C₄₄ . A brief discussion of superconductivity in LiⅹNbS₂, is also included.Science, Faculty of
Physics and Astronomy, Department of
Graduate
7
Farrokhpanah, Sonia. "Design of heat integrated low temperature distillation systems." Thesis, University of Manchester, 2009. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:228854.
Анотація:
This work addresses the challenges in design of heat integrated low-temperature separation processes. A novel, systematic and robust methodology is developed, which contributes to the design practice of heat-integrated separation sequence and the refrigeration system in the context of low-temperature separation processes. Moreover, the methodology exploits the interactions between the separation and refrigeration systems systematically in an integrated design context. The synthesis and optimisation of heat-integrated separation processes is complex due to the large number of design options. In this thesis, task representation is applied to the separation system to accommodate both simple and complex distillation columns. The stream conditioning processes are simulated and their associated costs are included in the overall cost of the process. Important design variables in separation systems, such as the separation sequence, type and operating conditions of the separation units (e.g. the operating pressure, feed quality and condenser type) are optimised. Various refrigeration provision strategies, such as expansion of a process stream, pure and mixed multistage refrigeration systems and cascades of multistage refrigeration cycles, are considered in the present work. A novel approach based on refrigeration system database is proposed, which overcomes the complexities and challenges of synthesis and optimisation of refrigeration systems in the context of low-temperature separation processes. The methodology optimises the key design variables in the refrigeration system, including the refrigerant composition, the number of compression stages, the refrigeration and rejection temperature levels, cascading strategy and the partition temperature in multistage cascaded refrigeration systems. The present approach has selected a matrix based approach for assessing the heat integration potentials of separation and refrigeration systems in the screening procedure. Non-isothermal streams are not considered isothermal and stream splitting and heat exchangers in series are taken into account. Moreover, heat integration of reboiler and condenser of a distillation column through an open loop heat pump system can be considered in this work. This work combines an enhanced simulated annealing algorithm with MILP optimisation method and develops a framework for simultaneously optimising different degrees of freedom in the heat integrated separation and refrigeration processes. Case studies extend the approach to the design of heat integrated separation sequences in above ambient temperature processes. The robustness of the developed framework is further demonstrated when it is utilised to design the LNG and ethylene plant fractionation trains.
8
Deng, Guangnan. "Embedded heat speaders in low temperature cofired ceramic substrates." FIU Digital Commons, 2002. http://digitalcommons.fiu.edu/etd/2770.
Анотація:
A new heat spreader that operates on a principle similar to heat pipes has been developed in Low Temperature Cofired Ceramic (LTCC) substrate. The heat spreader use sintered metal powder as the wick structure and water as the working fluid. Key topics related to the fabrication of embedded heat spreaders in LTCC substrate were studied. The conventional LTCC procedure has been improved to suit the requirement of heat spreader. A novel sintered porous silver powder has been developed to provide high capillary pressure and permeability for the wick structure. The maximum mass transport rate of the wick was about 0.692 (g/min) at wick height of 4.5cm. The thermal performance test demonstrated that the prototype heat spreader could work properly at power density of more than 70 W/cm2 without any sign of dry out occur. The successful fabrication of the prototype integrated heat spreader provides concept validation of using advanced two-phase heat management system to greatly improve the effective thermal conductivity of LTCC substrate.
9
Ploskic, Adnan. "Technical solutions for low-temperature heat emission in buildings." Doctoral thesis, KTH, Strömnings- och klimatteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133221.
Анотація:
The European Union is planning to greatly decrease energy consumption during the coming decades. The ultimate goal is to create sustainable communities that are energy neutral. One way of achieving this challenging goal may be to use efficient hydronic (water-based) heating systems supported by heat pumps. The main objective of the research reported in this work was to improve the thermal performance of wall-mounted hydronic space heaters (radiators). By improving the thermal efficiency of the radiators, their operating temperatures can be lowered without decreasing their thermal outputs. This would significantly improve efficiency of the heat pumps, and thereby most probably also reduce the emissions of greenhouse gases. Thus, by improving the efficiency of radiators, energy sustainability of our society would also increase. The objective was also to investigate how much the temperature of the supply water to the radiators could be lowered without decreasing human thermal comfort. Both numerical and analytical modeling was used to map and improve the thermal efficiency of the analyzed radiator system. Analyses have shown that it is possible to cover space heat losses at low outdoor temperatures with the proposed heating-ventilation systems using low-temperature supplies. The proposed systems were able to give the same heat output as conventional radiator systems but at considerably lower supply water temperature. Accordingly, the heat pump efficiency in the proposed systems was in the same proportion higher than in conventional radiator systems. The human thermal comfort could also be maintained at acceptable level at low-temperature supplies with the proposed systems. In order to avoid possible draught discomfort in spaces served by these systems, it was suggested to direct the pre-heated ventilation air towards cold glazed areas. By doing so the draught discomfort could be efficiently neutralized. Results presented in this work clearly highlight the advantage of forced convection and high temperature gradients inside and alongside radiators - especially for low-temperature supplies. Thus by a proper combination of incoming air supply and existing radiators a significant decrease in supply water temperature could be achieved without decreasing the thermal output from the system. This was confirmed in several studies in this work. It was also shown that existing radiator systems could successfully be combined with efficient air heaters. This also allowed a considerable reduction in supply water temperature without lowering the heat output of the systems. Thus, by employing the proposed methods, a significant improvement of thermal efficiency of existing radiator systems could be accomplished. A wider use of such combined systems in our society would reduce the distribution heat losses from district heating networks, improve heat pump efficiency and thereby most probably also lower carbon dioxide emissions.QC 20131029
10
Toal, B. R. H. "The application of heat pumps to low temperature drying." Thesis, University of Ulster, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378669.
11
Witwicky, Julien. "Heat dissipation due to microvibrations in low temperature experiments." Thesis, KTH, Fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293485.
Анотація:
Ultra-sensitive photodetectors on-board space missions need very low temperatures to keep a good resolution. Cryo-coolers, such as pulse-tubes, help maintaining these conditions within a cryostat. In return however, they generate micro-vibrations. These micro-vibrations dissipate enough heat to cause temperature fluctuations at the detector's support, thus lowering the detector's resolution. The first objective is to establish a test bench almost from scratch. The test bench includes a dummy representing the detector's support. The next objectives is to verify that we can measure heat dissipation at the dummy, corresponding to very low values of power ; and finally, to find a link between mechanics and heat dissipation. The dummy consists of a mass suspended by Kevlar chords and is mounted on the cold plate of a cryostat. From the cryostat enclosure, we were able to generate micro-vibrations at the suspended mass and to carry out acceleration and temperature measurements. At 4 K, we were able to measure heat dissipation only around the suspended mass resonance modes. As a first quantitative result, we found that an acceleration of thousands µg (g is the gravitational acceleration) on the cold plate dissipates hundreds of nano-watts. However, these are preliminary results and we will need to improve the test bench for future measurement campaigns.Ultrakänsliga fotodetektorer ombord rymduppdrag behover mycket låga temperaturer för att hålla en rätt upplösning. Kryokylare, såsom pulse-tubes, hjälper att upprätthålla dessa förhållanden i en kryostat. I gengäld genererar de dock mikrovibrationer. Dessa mikrovibrationer släpper ut tillräckligt med värme för att orsaka temperatursvängningar vid detektorns stöd, vilket sänker detektorns upplösning. Det första målet är att upprätta en testbänk från grunden. Testbänken innehåller en dummy som representerar detektorns stöd. Nästa mål är att kontrollera att vi kan mäta värmeavledning vid dummy, vilket motsvarar mycket låga effektvärden. Sista mål är att hitta en länk mellan mekanik och värmeavledning. Dummy består av en massa som är upphängd av Kevlar och är monterad på en kryostats kallplatta. Från kryostathöljet kunde vi generera mikrovibrationer vid den upphängda massan och genomföra accelerations- och temperaturmätningar. Vid 4 K kunde vi bara mäta värmeavledning runt upphängda massans resonanslägen. Som ett första kvantitativt resultat, upptäckte vi att en acceleration på tusentals µg (g är tyngdaccelerationen) på kylplattan försvinner hundratals nanowatt. Detta är dock preliminära resultat och vi kommer att behöva förbättra testbänken för framtida mätkampanjer.
12
Montanez, Morantes Maria Vanessa. "Operational optimisation of low-temperature energy systems." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/operational-optimisation-of-lowtemperature-energy-systems(a22bd339-1473-4401-bbc5-2e1280e57756).html.
Анотація:
Low-temperature energy systems are processes that operate below ambient temperatures and make use of refrigeration cycles, where the main energy consumption is due to the shaft work required to drive the compressors. Very-low-temperature energy systems, also known as cryogenic processes, operate at around -150°C and below. Due to increasing demand of products from cryogenic processes and tighter environmental regulations, existing plants need to be revamped to increase their energy efficiency or adapt to new processing capacities. So, accurate models of the performance of cryogenic processes are needed in order to optimise their operation. The present work proposes a new approach for optimising the operating conditions of existing refrigeration cycles in cryogenic processes, using pure refrigerants, for different plant operating conditions. In this work, the process conditions are considered as given and not considered as variables during the optimisation. The operational optimisation is achieved by integrating models for the part-load performance of centrifugal compressors and models for the simulation of plate-fin heat exchangers (PFHEs), into a single optimisation approach. An optimisation approach similar to the one proposed in this work was not found in the open literature. The optimisation approach varies the refrigerant evaporation temperatures, flow rates and cooling duties, minimum temperature difference in PFHEs, and rotational speed of compressors. The objective function seeks to minimise shaft work demand and the constraints consider the operational limitations of centrifugal compressors (minimum and maximum flow rates) and PFHEs (no temperature crosses and meeting the target temperatures of the process streams). In order to explore the solution space that is generated by the complex interactions between the variables and find an approximation to a global optimum, a multistart optimisation algorithm is implemented. The part-load centrifugal compressor model implemented in this work uses regressed data from their performance curves together with the fan laws. The proposed simulation model of PFHEs represents these units as a ‘fictitious’ heat exchanger network of two-stream matches. The simulation model accounts for single and two-phase streams and for the temperature-dependent physical properties of pure refrigerants (e.g. viscosity, heat capacity, etc.). In addition to the simulation model, design and rating models for PFHEs with single and two-phase streams are also proposed. The examples presented in this work for the design, simulation and rating of single and two-phase streams in PFHEs show that the models proposed can find feasible designs, and can predict the outlet temperature of the process streams within ±3°C for different inlet conditions. The example presented in this work for the operational optimisation of refrigeration cycles shows that savings of around 3% in shaft work consumption (up to £0.86 million per year), for different process throughput, can be achieved using the proposed methodology.
13
Hoegel, Benedikt. "Thermodynamics-based design of stirling engines for low-temperature heat sources." Thesis, University of Canterbury. Mechanical Engineering, 2014. http://hdl.handle.net/10092/9344.
Анотація:
Large amounts of energy from heat sources such as waste-eat and geothermal energy are available worldwide but their potential for useful power-generation is largely untapped. This is because they are relatively low temperature difference (LTD) sources, in the range from 100 to 200 °C, and it is thermodynamically diffcult, for theoretical and practical reasons, to extract useful work at these temperatures. This work explores the suitability of a Stirling engine (SE) to exploit these heat sources. Elsewhere much work has been done to optimise Stirling engines for high temperature heat sources, but little is known about suitable engine layouts, and their optimal design and operational aspects at lower temperature differences. With the reduced temperature difference, changes from conventional engine designs become necessary and robust solutions for this novel application have to be identified.
This has been achieved in four major steps: identification of a suitable engine type; thermodynamic optimisation of operating and engine parameters; optimisation of mechanical efficiency; and the development of conceptual designs for the engine and its components informed by the preceding analysis. For the optimisation of engine and operating parameters a model was set up in the commercial Stirling software package, Sage, which also has been validated in this thesis; suitable parameter combinations have been identified.
This work makes key contributions in several areas. This first is the identification of methods for better simulating the thermodynamic behaviour of these engines. At low temperature differences the performance of Stirling engines is very sensitive to losses by fluid friction (and thus frequency), adiabatic temperature rise during compression, and the heat transfer from and to the surroundings. Consequently the usual isothermal analytical approaches produce results that can be misleading. It is necessary to use a non-isothermal approach, and the work shows how this may be achieved.
A second contribution is the identification of the important design variables and their causal effects on system performance. The primary design variable is engine layout. For an engine having inherently low efficiency due to the low temperature difference it is important to choose the engine layout that provides the highest power density possible in order to minimise engine size and to save costs. From this analysis the double-acting alpha-type configuration has been identified as being the most suitable, as opposed to the beta or gamma configurations. An-other key design variable is working fluid, and the results identify helium and hydrogen as suitable, and air and nitrogen as unsuitable. Frequency and phase angle are other design variables, and the work identifies favourable values. A sensitivity analysis identifies the phase angle, regenerator porosity, and temperature levels as the most sensitive parameters for power and efficiency. It has also been shown that the compression work in low-temperature difference Stirling engines is of similar magnitude as the expansion work. By compounding suitable working spaces on one piston the net forces on the piston rod can be reduced significantly. In double-acting alpha-engines this can be achieved by choosing the Siemens as opposed to the Franchot arrangement. As a result friction and piston seal leakage which are two important loss mechanisms are reduced significantly and longevity and mechanical efficiency is enhanced. Design implications are identified for various components, including pistons, seals, heat exchangers, regenerator, power extraction, and crankcase. The peculiarities of the heat source are also taken into account in these design recommendations.
A third key contribution is the extraction of novel insights from the modelling process. For the heat exchangers it has been shown that the hot and cold heat exchangers can be identical in their design without any negative impact on performance for the low-temperature difference situation. In comparison the high temperature applications invariably require different materials and designs for the two heat exchangers. Also, frequency and phase angle are found to be quite different (lower frequency and higher phase angle) from the optimum parameters found in high temperature engines. Contrary to common belief the role of dead volume has been found to play a crucial and not necessary detrimental role at low temperature differentials.
Taken together, the work is positioned at the intersection of thermodynamic analysis and engineering design, for the challenging area of Stirling engines at low temperature differences. The work extracts thermodynamic insights and extends these into design implications. Together these help create a robust theoretical and design foundation for further research and development in the important area of energy recovery.
14
Mohammed, K. A. "Low temperature specific heat measurements of crystalline and amorphous magnetic materials." Thesis, University of Southampton, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356096.
15
Brown, Morgan J. (Brian James) Carleton University Dissertation Engineering Mechanical. "Low temperature boiling enhancement for the SLOWPOKE decay heat rejection system." Ottawa, 1989.
16
Chastin, S. "Low temperature specific heat and thermal conductivity of Kondo intermetallic compounds." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244320.
17
Mateu, Royo Carlos. "Development of High Temperature Heat Pumps for Industrial Waste Heat Recovery." Doctoral thesis, Universitat Jaume I, 2021. http://dx.doi.org/10.6035/14107.2021.744033.
Анотація:
One of the major challenges of this decade is developing more sustainable energy systems that contribute to environmental concern, especially climate change mitigation. Extending the operating conditions of the heat pump technology to higher temperatures will allow decarbonising the industrial sector from two slopes: recovering heat from waste heat sources that currently is being rejected to the ambient and produce heat at the required industrial thermal levels that become useful for the industrial processes. Both challenges will make possible reduce the equivalent CO2 emissions of the industrial sector and operate at high temperatures that conventional heat pumps. This thesis deals with the development of high temperature heat pumps through a comprehensive theoretical and experimental analysis to overcome different technology challenge: architecture, refrigerants, experimental prototype, advanced applications and system integration, providing new knowledge that represents a step forward in high temperature heat pump technology.Uno de los mayores desafíos de esta década recae en el desarrollo de sistemas energéticos más sostenibles que contribuyan a la preocupación medioambiental, especialmente la mitigación del cambio climático. Extender las condiciones de funcionamiento de la tecnología de bomba de calor a temperaturas más elevadas permitirá descarbonizar el sector industrial desde dos vertientes: recuperando calor de fuentes de calor residual, actualmente disipado al ambiente y producir calor a los niveles térmicos requeridos, útiles para los procesos industriales, reduciendo así las emisiones de CO2 equivalentes del sector industrial y contribuyendo al desarrollo sostenible. Esta tesis pretende abordar el desarrollo de bombas de calor de alta temperatura a través de un análisis teórico y experimental, para abordar diferentes desafíos tecnológicos: arquitectura, refrigerantes, prototipo experimental, aplicaciones avanzadas e integración de sistemas, generando nuevos conocimientos que representan un paso adelante en la tecnología de bombas de calor de alta temperatura.
Programa de Doctorat en Tecnologies Industrials i Materials
18
Gonçalves, De Azevedo Maria Filipa Couto Soares. "The effects of natural and forced convection on low temperature combustion." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648569.
19
Ploskic, Adnan. "Low - Temperature Basedboard Heaters in Built Environments." Licentiate thesis, KTH, Strömnings- och klimatteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25725.
Анотація:
The European Union has adopted a plan to decrease 20 % of total energy consumption through improved energy efficiency by 2020. One way of achieving this challenging goal may be to use efficient water-based heating systems supplied by heat pumps or othersustainable systems. The goal of this research was to analyze and improve the thermalperformance of water-based baseboard heaters at low-temperature water supply. Both numerical (CFD) and analytical simulations were used to investigate the heat efficiency of the system. An additional objective of this work was to ensure that the indoor thermal comfort was satisfied in spaces served by such a low-temperature heating system. Analyses showed that it was fully possible to cover both transmission and ventilation heatl osses using baseboard heaters supplied by 45 °C water flow. The conventional baseboards, however, showed problems in suppressing the cold air down-flow created by 2.0 m high glazing and an outdoor temperature of – 12 °C. The draught discomfort at ankle level was slightly above the upper limit recommended by international and national standards. On the other hand, thermal baseboards with integrated ventilation air supply showed better ability to neutralize cold downdraught at the same height and conditions. Calculations also showed that the heat output from the integrated system with one ventilation inlet was approximately twiceas high as that of the conventional one. The general conclusion from this work was that low-temperature baseboards, especially with integrated ventilation air supply, are an efficient heating system and able to be combined with devices that utilize the low-quality sustainable energy sources such as heat pumps.QC 20101029
20
Ssebabi, Brian. "Experimental evaluation of a low temperature and low pressure turbine." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86563.
Анотація:
Thesis (MEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: The potential benefits from saving energy have driven most industrial processing facilities to pay more attention to reducing energy wastage. Because the industrial sector is the largest user of electricity in South Africa (37.7% of the generated electricity capacity), the application of waste heat recovery and utilisation (WHR&U) systems in this sector could lead to significant energy savings, a reduction in production costs and an increase in the efficiency of industrial processes. Turbines are critical components of WHR&U systems, and the choice of an efficient and low cost turbine is crucial for their successful implementation. The aim of this thesis project is therefore to validate the use of a turbine for application in a low grade energy WHR&U system. An experimental turbine kit (Infinity Turbine ITmini) was acquired, assembled and tested in a specially designed and built air test bench. The test data was used to characterise the turbine for low temperature (less than 120 Celsius) and pressure (less than 10 bar) conditions. A radial inflow turbine rotor was designed, manufactured and then tested with the same test bench, and its performance characteristics determined. In comparison with the ITmini rotor, the as-designed and manufactured rotor achieved a marginally better performance for the same test pressure ratio range. The as-designed turbine rotor performance characteristics for air were then used to scale the turbine for a refrigerant-123 application. Future work should entail integrating the turbine with a WHR&U system, and experimentally determining the system’s performance characteristics.
AFRIKAANSE OPSOMMING: Die potensiële voordele wat gepaard gaan met energiebesparing het die fokus van industrie laat val op die bekamping van energievermorsing. Die industriële sektor is die grootse verbruiker van elektrisiteit in Suid-Afrika (37.7% van die totale gegenereerde kapasiteit). Energiebesparing in die sektor deur die toepassing van afval-energie-herwinning en benutting (AEH&B) sisteme kan lei tot drastiese vermindering van energievermorsing, ‘n afname in produksie koste en ‘n toename in die doeltreffendheid van industriële prosesse. Turbines is kritiese komponente in AEH&B sisteme en die keuse van ‘n doeltreffende lae koste turbine is noodsaaklik in die suksesvolle implementering van dié sisteme. Die doelwit van hierdie tesisprojek is dus om die toepassing van ‘n turbine in ‘n lae graad energie AEH&B sisteem op die proef te stel. ‘n Eksperimentele turbine stel (“Infinity Turbine ITmini”) is aangeskaf, aanmekaargesit en getoets op ‘n pasgemaakte lugtoetsbank. Die toetsdata is gebruik om die turbine te karakteriseer by lae temperatuur (minder as 120 Celsius) en druk (minder as 10 bar) kondisies. ‘n Radiaalinvloeiturbinerotor is ook ontwerp, vervaardig en getoets op die lugtoetsbank om die rotor se karakteristieke te bepaal. In vergelyking met die ITmini-rotor het die radiaalinvloeiturbinerotor effens beter werkverrigting gelewer by diselfde toetsdruk verhoudings. Die werksverrigtingkarakteristieke met lug as vloeimedium van die radiaalinvloeiturbinerotor is gebruik om die rotor te skaleer vir ‘n R123 verkoelmiddel toepassing. Toekomstige werk sluit in om die turbine met ‘n AEH&B sisteem te integreer en die sisteem se werksverrigtingkarakteristieke te bepaal.
21
Griffiths, Andrew. "Low temperature calorimetry of spin fluctuations in ZrZnâ†2 and Niâ†3Ga." Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262730.
22
Lloyd, Caleb Charles. "A Low Temperature Differential Stirling Engine for Power Generation." Thesis, University of Canterbury. Department of Electrical and Computer Engineering, 2009. http://hdl.handle.net/10092/2916.
Анотація:
There are many sources of free energy available in the form of heat that is often simply wasted for want of an effective way to convert it into useful energy such as electricity. The aim of this research project is to design and build a low temperature differential Stirling engine capable of generating electric power from heat sources such as waste hot water or geothermal springs.
The engine that has been developed is a research prototype model of a new type of design featuring a rotating displacer which is actuated by a pair of stepper motors. The rotating displacer design enables the use of readily available and comparatively cheap and robust steam pipe as the housing for the engine, and it also avoids problems associated with sealing and heat exchange that would be present in a large engine of a more traditional configuration. Owing to the fact that this engine is a research prototype, it has the ability to have some of its critical operating parameters such as phase angle and stroke length adjusted to investigate the effects on performance. When the next phase of development takes place most of these parameters will be fixed at the optimum values which will make manufacture cheaper and easier.
Unfortunately, construction of the prototype engine has not been completed at the time of writing so no power producing results have been achieved; however thorough results are presented on the operation of the control system for the stepper motors which actuate the displacer. Additionally, after a thorough history and background of Stirling engines was researched, the understanding gained of how these engines work has enabled a design process to take place which has hopefully led to a successful design. Analysis of various aspects of the engine have been carried out and results look promising for the engine to produce around 500 Watts of electrical power output whilst running on hot water up to around 90°C.
23
Kalua, Tisaye Bertram. "Analysis of factors affecting performance of a low-temperature Organic Rankine Cycle heat engine." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/17844.
Анотація:
Organic Rankine Cycle (ORC) heat engines convert low-grade heat to other forms of energy such as electrical and mechanical energy. They achieve this by vaporizing and expanding the organic fluid at high pressure, turning the turbine which can be employed to run an alternator or any other mechanism as desired. Conventional Rankine Cycles operate with steam at temperatures above 400 ℃. The broad aspect of the research focussed on the generation of electricity to cater for household needs. Solar energy would be used to heat air which would in turn heat rocks in an insulated vessel. This would act as an energy storage in form of heat from which a heat transfer fluid would collect heat to supply the ORC heat engine for the generation of electricity. The objective of the research was to optimize power output of the ORC heat engine operating at temperatures between 25℃ at the condenser and 90 to 150℃ at the heat source. This was achieved by analysis of thermal energy, mechanical power, electrical power and physical parameters in connection with flow rate of working fluid and heat transfer fluids.
24
Ntsendwana, Bulelwa. "Advanced low temperature metal hydride materials for low temperature proton exchange membrane fuel cell application." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8494_1307431585.
Анотація:
Energy is one of the basic needs of human beings and is extremely crucial for continued development of human life. Our work, leisure and our economic, social and physical welfare all depend on the sufficient, uninterrupted supply of energy. Therefore, it is essential to provide adequate and affordable energy for improving human welfare and raising living standards. Global concern over environmental climate change linked to fossil fuel consumption has increased pressure to generate power from renewable sources [1]. Although substantial advances in renewable energy technologies have been made, significant challenges remain in developing integrated renewable energy systems due primarily to mismatch between load demand and source capabilities [2]. The output from renewable energy sources such as photo-voltaic, wind, tidal, and micro-hydro fluctuate on an hourly, daily, and seasonal basis. As a result, these devices are not well suited for directly powering loads that require a uniform and uninterrupted supply of input energy.
25
Mohamed, Mahmoud. "Physical Properties of Iron-based Superconductors Probed by Low-Temperature Specific-Heat Measurements." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-98736.
Анотація:
In this thesis, specific heat, magnetic susceptibility and resistivity studies on the iron-pnictide superconductors LiFeAs, NaFe1-xCoxAs, AFe2As2 (A = K, Ca, Ba), M1-xNaxFe2As2 (M = Ca, Ba), and Ca(Fe1-xCox)2Fe2As2 are presented, from which different intrinsic physical properties are resolved. The combined first-order spindensity wave/structural transition which occurs in the parent compounds of the 122 pnictide systems is shown to gradually shift to lower temperature for low doping levels. Upon higher doping, this transition is completely suppressed and simultaneously, superconductivity appears at lower temperature. In contrast, the phase diagram in Ca(Fe1-xCox)2Fe2As2 is shown to exhibit a pronounced region of coexistence of magnetism and superconductivity. Further important results reported in this work concern the electronic properties and superconducting-gap characteristics. In LiFeAs, the zero-field temperature dependence of the electronic specific heat can be well described by two s-wave gaps, whose magnitudes are in agreement with ARPES results. Our gap analysis in KFe2As2, Ca0.32Na0.68Fe2As2, and Ba0.65Na0.35Fe2As2 single crystals also implies the presence of two s-wave-like gaps. The magnetic phase diagram of LiFeAs and KFe2As2 for magnetic fields along both principal orientations has been constructed and an anisotropy of Hc2(T) of 3 and 5, respectively, has been obtained.
26
Latcham, Jacob G. (Jacob Greco). "Heat exchanger design for thermoelectric electricity generation from low temperature flue gas streams." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54513.
Анотація:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 33).
An air-to-oil heat exchanger was modeled and optimized for use in a system utilizing a thermoelectric generator to convert low grade waste heat in flue gas streams to electricity. The NTU-effectiveness method, exergy, and thermoelectric relations were used to guide the modeling process. The complete system design was optimized for cost using the net present value method. A number of finned-tube compact heat exchanger designs were evaluated for high heat transfer and low pressure loss. Heat exchanger designs were found to favor either power density or exergy effectiveness to achieve optimal net present value under different conditions. The model proved capable of generating complete thermoelectric flue gas systems with positive net present values using thermoelectric material with a ZT value of 0.8 and second law efficiency of 13%. Complete systems were generated for a number of economic conditions. The best complete system achieved a first law efficiency of 1.62% from a 1500 C flue gas stream at an installed cost of $0.79 per watt.
by Jacob G. Latcham.
S.B.
27
Hegarty, M. "The development of low temperature heat capacity results : a heat capacity study of some chlorammine cobalt(III) compounds." Thesis, University of Stirling, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306811.
28
Kirkconnell, Carl Scott. "Numerical analysis of the mass flow and thermal behavior in high-frequency pulse tubes." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/16434.
29
Yucel, Ayse Tugce. "Modeling And Control Of High Temperature Oven For Low Temperature Co-fired Ceramic (ltcc) Device Manufacturing." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614918/index.pdf.
Анотація:
In the electronics the quality, reliability, operational speed, device density and cost of circuits are fundamentally determined by carriers. If it is necessary to use better material than plastic carrier, it has to be made of ceramics or glass-ceramics. This study dealt with the ceramic based carrier production system. The types of the raw ceramics fired at low temperature (below 1000°C) are called Low Temperature Co-Fired Ceramics (LTCC). In this study, a comprehensive thermal model is described for the high temperature oven which belongs to a Low Temperature Co-fired Ceramic (LTCC) substance production line. The model includes detailed energy balances with conduction, convection and radiation heat transfer mechanisms, view factor derivations for the radiative terms, thermocouple balances, heating filaments and cooling mechanisms for the system. Research was conducted mainly on process development and production conditions along with the system modeling of oven. Temperature control was made in high temperature co-firing oven. Radiation View Factors for substrate and thermocouples are determined. View factors between substrate and top-bottom-sides of the oven are calculated, and then inserted into the energy balances. The same arrangement was made for 3 thermocouples at the bottom of the oven. Combination of both expressions gave the final model. Modeling studies were held with energy balance simulations on MATLAB. Data analysis and DOE study were held with JMP Software.
30
Demirkaya, Gökmen. "Theoretical and Experimental Analysis of Power and Cooling Cogeneration Utilizing Low Temperature Heat Sources." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3069.
Анотація:
Development of innovative thermodynamic cycles is important for the efficient utilization of low-temperature heat sources such as solar, geothermal, and waste heat sources. Binary mixtures exhibit variable boiling temperatures during the boiling process, which leads to a good thermal match between the heating fluid and working fluid for efficient heat source utilization. This study presents a theoretical and an experimental analysis of a combined power/cooling cycle, which combines the Rankine and absorption refrigeration cycles, uses ammonia-water mixture as the working fluid and produces power and refrigeration, while power is the primary goal. This cycle, also known as the Goswami Cycle, can be used as a bottoming cycle using waste heat from a conventional power cycle or as an independent cycle using low to mid-temperature sources such as geothermal and solar energy. A thermodynamic analysis of power and cooling cogeneration was presented.
The performance of the cycle for a range of boiler pressures, ammonia concentrations, and isentropic turbine efficiencies were studied to find out the sensitivities of net work, amount of cooling and effective efficiencies. The thermodynamic analysis covered a broad range of boiler temperatures, from 85 °C to 350 °C. The first law efficiencies of 25-31% are achievable with the boiler temperatures of 250-350 °C. The cycle can operate at an effective exergy efficiency of 60-68% with the boiler temperature range of 200-350 °C. An experimental study was conducted to verify the predicted trends and to test the performance of a scroll type expander. The experimental results of vapor production were verified by the expected trends to some degree, due to heat transfer losses in the separator vessel. The scroll expander isentropic efficiency was between 30-50%, the expander performed better when the vapor was superheated. The small scale of the experimental cycle affected the testing conditions and cycle outputs. This cycle can be designed and scaled from a kilowatt to megawatt systems. Utilization of low temperature sources and heat recovery is definitely an active step in improving the overall energy conversion efficiency and decreasing the capital cost of energy per unit.
31
Trædal, Stian. "Analysis of the Trilateral Flash Cycle for Power Production from low Temperature Heat Sources." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26347.
Анотація:
SummaryIn this study, the Trilateral Flash Cycle (TFC) and the Partially Evaporating Cycle (PEC) have been analyzed and compared to the Organic Rankine Cycle (ORC) for power production from low temperature heat sources. This study is a continuation of the work done in my project thesis fall 2013.The ORC is a well-known technology that is in use in several plants today. The TFC and PEC on the other hand are still in a state of technical development. The biggest challenge for the TFC and PEC is the required two-phase expansion. Lately, two-phase expanders with high efficiencies have been developed, which makes the TFC and PEC economically interesting.Currently, only a few studies on the TFC and PEC can be found, and most of them are theoretical considerations. All of these studies finds the TFC promising for low temperature heat sources, which was also the findings of my project thesis. The PEC is found to be promising for smaller systems where the working fluid pump efficiency is low.The TFCs main difference from the ORC is that the heating process ends at the boiling point of the working fluid, i.e. there is no evaporation and superheating. This leads to a better temperature match between the working fluid and the heat source, such that more heat can be transferred to the working fluid. Power is produced in a two-phase expander after the heating process. The cost pr. kWh for TFC systems have been estimated to be lower than for ORC systems due to the elimination of the evaporator, separator drum, gear box, lube oil system and the fact that simpler heat exchangers can be used.In the PEC, the working fluid is allowed to be partially evaporated during the heating process. This is done in an attempt to combine the advantages of the TFC and the ORC.The ORC, TFC and PEC have been simulated in a Microsoft Excel calculation tool, using Visual Basic for Applications. The simulations include detailed heat exchanger models to calculate heat transfer coefficients and pressure losses, and two-phase expander efficiency models for the TFC and PEC. The three cycles have been simulated and optimized for maximum net power production for three cases using different heat source temperatures. Air with a mass flow of 10 kg/s and temperatures of 100, 150 and 200 °C are used for Case I, Case II and Case III respectively. Water at 20 °C is used as the heat sink. The three cases are simulated with eight different working fluids, R123, R134a, R245fa, R1234ze(E), butane, pentane, isopentane and propane with maximum heat exchanger areas of 1000, 1500, 2000, 2500, 3000, 3500 and 4000 m2. Different performance parameters are calculated and used to compare the performance of the ORC, TFC and PEC, and the different working fluids. The results show that the TFC has the lowest power production for all cases, and the largest estimated system size. Both the total heat exchanger area and expander outlet volume flow are generally higher for the TFC systems, especially for the lower heat source temperature cases. For the 100 °C and 150 °C cases the power production for the TFC and ORC is in the same range. Since TFC systems are estimated to have a lower cost than ORC systems, they can be suitable for systems with heat sources in this range when system size is not a critical factor. The PEC does not show any advantage over the ORC for the cases analyzed here. This study shows less promising results for the TFC than my project thesis and other published studies. This is mainly due to the variable two-phase expander efficiency used here, and that none of the other studies considers pressure losses in the system or calculation of heat transfer coefficients for each working fluid.A scientific paper on the main results from the study before the simulation of the PEC and inclusion of the heat exchanger models is given in Appendix C. This paper has been submitted to the journal Energy. A scientific paper on the final results of the study is given in Appendix D. This paper has been submitted to the Gustav Lorentzen Conference.
32
Wakelin, Jonathan Peter. "Low temperature specific heat and thermal conductivity of doped YBa2Cu3O7 and other ceramic superconductors." Thesis, University of Sussex, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284082.
33
Matthews, Jason E. "Thermoelectric and Heat Flow Phenomena in Mesoscopic Systems." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/12108.
Анотація:
xvii, 189 p. ： ill. (some col.)Low-dimensional electronic systems, systems that are restricted to single energy levels in at least one of the three spatial dimensions, have attracted considerable interest in the field of thermoelectric materials. At these scales, the ability to manipulate electronic energy levels offers a great deal of control over a device's thermopower, that is, its ability to generate a voltage due to a thermal gradient. In addition, low-dimensional devices offer increased control over phononic heat flow. Mesoscale geometry can also have a large impact on both electron and phonon dynamics. Effects such as ballistic transport in a two-dimensional electron gas structure can lead to the enhancement or attenuation of electron transmission probabilities in multi-terminal junctions. The first half of this dissertation investigates the transverse thermoelectric properties of a four-terminal ballistic junction containing a central symmetry-breaking scatterer. It is believed that the combined symmetry of the scatterer and junction is the key component to understanding non-linear and thermoelectric transport in these junctions. To this end, experimental investigations on this type of junction were carried out to demonstrate its ability to generate a transverse thermovoltage. To aid in interpreting the results, a multi-terminal scattering-matrix theory was developed that relates the junction's non-linear electronic properties to its thermoelectric properties. The possibility of a transverse thermoelectric device also motivated the first derivation of the transverse thermoelectric efficiency. This second half of this dissertation focuses on heat flow phenomena in InAs/InP heterostructure nanowires. In thermoelectric research, a phononic heat flow between thermal reservoirs is considered parasitic due to its minimal contribution to the electrical output. Recent experiments involving heterostructure nanowires have shown an unexpectedly large heat flow, which is attributed in this dissertation to an interplay between electron-phonon interaction and phononic heat flow. Using finite element modeling, the recent experimental findings have provided a means to probe the electron-phonon interaction in InAs nanowires. In the end, it is found that electron-phonon interaction is an important component in understanding heat flow at the nanoscale. This dissertation includes previously unpublished co-authored material.
Committee in charge: Dr. Richard Taylor， Chair； Dr. Heiner Linke， Advisor； Dr. David Cohen， Member； Dr. John Toner， Member； Dr. David Johnson， Outside Member
34
Rattner, Alexander S. "Single-pressure absorption refrigeration systems for low-source-temperature applications." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53912.
Анотація:
The diffusion absorption refrigeration (DAR) cycle is a promising technology for fully thermally driven cooling. It is well suited to applications in medicine refrigeration and air-conditioning in off-grid settings. However, design and engineering knowhow for the technology is limited; therefore, system development has historically been an iterative and expensive process. Additionally, conventional system designs require high-grade energy input for operation, and are unsuitable for low-temperature solar- or waste-heat activated applications.
In the present effort, component- and system-level DAR engineering analyses are performed. Detailed bubble-pump generator (BPG) component models are developed, and are validated experimentally and with direct simulations. Investigations into the BPG focus on the Taylor flow pattern in the intermediate Bond number regime, which has not yet been thoroughly characterized in the literature, and has numerous industry applications, including nuclear fuel processing and well dewatering. A coupling-fluid heated BPG design is also investigated experimentally for low-source-temperature operation. Phase-change simulation methodologies are developed to rigorously study the continuously developing flow pattern in this BPG configuration. Detailed component-level models are also formulated for all of the other DAR heat and mass exchangers, and are integrated to yield a complete system-level model. Results from these modeling studies are applied to develop a novel fully passive low-source-temperature (110 - 130°C) DAR system that delivers refrigeration grade cooling. This design achieves operation at target conditions through the use of alternate working fluids (NH3-NaSCN-He), the coupling-fluid heated BPG, and a novel absorber configuration. The complete DAR system is demonstrated experimentally, and evaluated over a range of operating conditions. Experimental results are applied to assess and refine component- and system- level models.
35
White, Kathleen Madara. "Low Temperature Synthesis and Characterization of Some Low Positive and Negative Thermal Expansion Materials." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11582.
Анотація:
LOW TEMPERATURE SYNTHESIS AND CHARACTERIZATION OF SOME LOW POSITIVE AND NEGATIVE THERMAL EXPANSION MATERIALS
Kathleen Madara White
151 pages
Directed by Dr. Angus P. Wilkinson
Low temperature non-hydrolytic sol-gel synthesis was used to explore the possibility of lowering the crystallization temperatures of some known AIVMV2O7 compounds. Crystallization temperatures for ZrP2O7 and ZrP2O7 were unaffected by the use of non-hydrolytic sol-gel methods; however, successful synthesis of these compounds broadens the range of materials that can be produced using this method and suggests the possibility of synthesizing solid solutions (or composites) including ZrP2O7 or ZrV2O7.
This research presents for the first time the direct synthesis of ZrP2O7 from separate zirconium and phosphorus starting materials using mild autoclave methods.
Characterization of some AIVMV2O7 compounds, using lab and high resolution synchrotron powder XRD, led to the assignment of a new symmetry for CeP2O7 and to the suggestion that the reported structure for PbP2O7 was inadequate. Studies using in situ high temperature lab and synchrotron powder XRD for PbP2O7 and CeP2O7 provided the opportunity to report their thermal properties for the first time, and to compare their behavior to that of some other AIVMV2O7. High pressure diffraction measurements on CeP2O7 provided data for the estimation of bulk moduli and suggested two possible pressure-induced phase transitions.
A broad range of MIIIMVP4O14 compounds were prepared using low temperature hydrolytic sol-gel synthesis. Thermal studies revealed nearly linear trends in CTEs and lattice constants with respect to the sizes of MIIIMV cations. Some lower ionic radii compounds had CTEs comparable to that of ZrP2O7 at low temperature, suggesting a similar superstructure. Three compounds were found to exhibit temperature-induced phase transitions.
36
Weng, Chuan. "Experimental study of evaporative heat transfer for a non-azeotropic refrigerant blend at low temperature." Ohio : Ohio University, 1990. http://www.ohiolink.edu/etd/view.cgi?ohiou1183475091.
37
Lauterbach, Christoph [Verfasser]. "Potential, System Analysis and Preliminary Design of Low-Temperature Solar Process Heat Systems / Christoph Lauterbach." Kassel : Kassel University Press, 2014. http://d-nb.info/1065320620/34.
38
Hargreaves, T. E. "The low temperature heat capacity of high Tc superconductors and related materials in magnetic fields." Thesis, University of Sussex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320366.
39
Lundberg, Axel. "Temperature profiles and hardness estimation of laser welded heat affected zone in low carbon steel." Thesis, Malmö högskola, Fakulteten för teknik och samhälle (TS), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-20830.
Анотація:
Termisk modellring av hårdhet genom beräkning och simulering av den värmepåverkade zonen i en lasersvetsad stålplatta är en omfattande process. Dock är analysen viktig då mikrostrukturella fastransformationer förorsakade av svetsningen kan ge oönskade hårdhetsnivåer av den värmepåverkade zonen jämfört med hårdeheten i basmaterialet. I denna avhandling har analytiska ekvationer implementerats och testats för validitet mot simuleringar gjorda av andra författare och mot experimentella värden.Eftersom termisk modellering av svetsar är ett omfattande område var avhandlingen tvungen att smalnas av för att göra analysen mer fokuserad. Begränsningar gjordes för den matematiska modelleringen genom att endast titta på två-dimensionellt värmeflöde i svetsade plattor där endast den analytiska lösningen är av intresse. Arbetet har också inriktats mot stål då detta material är vida använt över hela världen. Då lasersvetsning är en snabb och kostnadseffektiv process så är hårdhetsanalysen av största vikt. Avhandlingen är uppdelad i tre övergripande delar; den första är att ta fram och förstå arbetet som gjorts inom termisk modellering av svetsar, alltså förstå matematiken bakom problemet. Modelleringen är till för att producera diagram parametrar från en termisk cykel, för att kunna fortgå med korrekt hårdhets analys. För det andra så sätts den matematiska modelleringen på prov i ett antal situationer som var och en simulerar olika förutsättningar. Detta gjordes i ett grafiskt användargränssnitt av ren bekvämlighet. Detta gör att ingenjörer lätt kan implementera olika egenskaper för materialet och få fram diagram och kurvor.Sist, ett liknande grafisk användargränssnitt för att simulera hårdheten i valfri punkt i den värmepåverkade zonen programmerades och därigenom implementerades ekvationerna som denna avhandling handlar om i grund och botten. En teoretisk bakgrund till fasomvandlingen är också inkluderad som förklaring till grundproblemet med oönskad hårdhet i den värmepåverkade zonen i lasersvetsat stål.Huvudslutsatser i avhandlingen:•Matematisk modellering av värmeöverföring i svetsar genomförd av Rosenthal är fortfarande applicerbar på modern lasersvetsningsapparatur. •Den empiriska modellen från Ion et al. (1984) är ej applicerbar med godkänt resultat för hårdhetsuppskattning.•Ekvationerna från Ion (2005) är statistiskt godkända för att simulera hårdhet.•Den analytiska lösningen är överlägsen den numeriska när det gäller snabb och enkel implementering för att simulera termiska cykler och hårdhet, medan den numeriska lösningen kan ta i beaktning mera avancerade egenskaper.•Förvärming av stålet innan svetsning kan vara mycket fördelaktigt för hårdheten i den värme-påverkade zonen, speciellt vid högre kolekvivalent.Thermal modelling of hardness in the heat-affected zone (HAZ) in a laser welded steel plate is a cumbersome process both in calculation and simulation. The analysis is however important as the microstructural phase transformations induced by welding may cause unwanted hardness levels in the HAZ compared with that of the parent material. In this thesis analytical equations have been implemented and checked for validity against simulations made by other authors and against experimental values.With such a large field as thermal modelling, the thesis had to be narrowed down to make the analysis more subject focused. Limitations made were for mathematical modelling only looking at a two-dimensional heat flow in welded plates; in this thesis only the analytical solution to the heat flow is considered. The work was also directed towards steel; such a material as used largely all over the globe. As laser welding is a fast and cost-effective process, an analysis of hardness is of great importance. Work was divided into three overlapping parts; the first was to derive and understand the work done in the field of thermal modelling of welds, thus understanding the mathematics behind the basic problem. This modelling provides a number of curves and parameters from a thermal cycle, thus enabling one to do the hardness analysis correctly. Secondly, this mathematical modelling was applied to a number of cases, simulating different circumstances. This was done using self-programmed Graphical User Interfaces (GUI) for convenience. This enables engineers to easily plug in the materials and processing properties and thus simulate the required parameters and curves for further analysis.Lastly, a GUI for simulating the hardness of any point in the HAZ was programmed and used, thus implementing and validating the equations. A theoretical introduction of the phases induced in the HAZ is also included, in order of understanding the problems of unwanted hardness in the HAZ of laser-welded steel.Main conclusions of this thesis:•Mathematical modelling of heat transfer in welds by Rosenthal (1946) is still applicable for modern laser welding apparatus.•The empirical model presented by Ion et al. (1984) is not applicable with experimental results of hardness in the HAZ of the steels investigated here.•Equations by Ion (2005) are accurate for simulating the hardness.•The analytical solutions investigated are superior to numerical solutions with regard to quick, simple simulations of thermal cycles and hardness. Numerical solutions allows for more advanced modelling, which can be lengthy.•Preheating the steel prior to welding is favourable in reducing hardness levels, especially with steel of higher carbon equivalent.
40
Hegana, Ashenafi B. "Low Temperature Waste Energy Harvesting by Shape Memory Alloy Actuator." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1461631046.
41
Svensson, Klas, and Jonas Wallenskog. "Low Temperature Waste Heat Solutions : with proposals for energy technological actions based on Scania’s building 64." Thesis, Linköping University, Linköping University, Energy Systems, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-28211.
Анотація:
The report comprises two separate parts:
- part 1: Temperature needs for district heating in the paint shop for axles in building 210
- part 2: Energy and low temperature waste heat solutions in heating and cooling systems for building 64 with surroundings
The paint shop for axles in part 1 has air quality requirements in places for coating of axles. Toachieve desired air properties there are different process ventilation systems, which consist ofventilation coils for heating and cooling, plus air humidifier. The ventilations coils for heating usedistrict heating. Today the ventilation coils use water of 100°C to achieve necessary air demands inthe coating boxes. This part of the report investigates whether the existing system would achievethe air requirements with a water temperature of 75°C instead of 100°C in the ventilation coilsduring the coldest parts of the year. The conclusion is that it is not possible; the existing system isadjusted for a water temperature of 100°C to achieve the air requirements. To use a watertemperature of 75°C, more or major ventilation coils are needed.
The focus of the report is at part 2. In this part, possibilities for low temperature waste heatsolutions are investigated. Those partly aim at specific local solutions for building 64 withsurroundings and on the other part of general waste heat solutions for new buildings andreconstructions in the future. To make these parts possible, the systems for heating and cooling inbuilding 64 have been identified. During this identification, potential savings that are not of wasteheat character have also been observed.
The most profitable saving concerns the control of temperature for the inner hardening vat. It isthe hardening vat for gas carburizing oven SV16838 that has been studied in this report. Today thetemperature of the hardening vat is controlled very ineffective. The conclusion is that a betteradjustment of the controller would save 180 000 SEK/year with a pay off time around two months.Worth mentioning (SV16838 included), is that there are at least five similar gas carburizing ovens atthe Scania area in Södertälje.
A pinch analysis has also been done for building 64, with it’s primarily conclusion that the groundheating is violating the pinch rules during long periods of the year. To remedy the ground heatingwill only need a different control and will lead to a saving between 20 000 – 75 000 SEK/year. Tomore accurate determine the saving, an investigation of the ground heating during winter time isneeded. Another conclusion concerning the pinch analysis is that the method for a real scenariorather shows the potential of the system than gives you an optimal solution possible to implement.More actions are to use the exhaustions of the endo gas generators and that the washing andrinsing systems if possible not should be heated with electricity. The exhaustions from the endo gasgenerators have a very high temperature, more then 300°C. If these, instead of hot water boilers,could warm the closely located water for the LPG (liquefied petroleum gas) evaporation, 125 000SEK/year can be saved. Today the hot water boilers are heated with electricity. If the washing andrinsing systems existing electricity heating instead can be heated with secondary heat (˜ districtheating), a save of 500 000 SEK/year is possible.
For waste heat solutions there are a few different approaches. Close to building 64, the largestpotential to use waste heat is in building 62 and 75, where air heaters are assessed with the largestpotential. In difference to other investigated buildings, building 210 has the possibility to use wasteheat even during the summer. This building is located 1 km from building 64. To use waste water inbuilding 210, a complex net of waste heating will be required where several buildings with asurplus of waste heat can be connected. A net like this has calculated pipe costs of 5, 2 million SEK.The saving for the use of waste heat only in building 210 will be around 1,4 million SEK/year. Thissave corresponds to the air handling systems that occur in part 1.
42
Bai, Lijun. "Life Cycle Assessment of Electricity Generation from Low Temperature Waste Heat : The Influence of Working Fluid." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19234.
Анотація:
In the metallurgical industry and in refineries and process industries, there is significant amount of waste heat, it is a challenged field to do the research for producing electricity from the energy of waste heat. Traditionallay, Organic Rankine Cycle(ORC)is used for generating electricity from low temperature heat source. Recently researchers are focusing on the supercritical Rankine cycle which uses CO2 as working fluid for which is more environmental friendly working fluid, possilbe reduced size and better utilization of lower temperature heat source.Currently this technology is under development and there is no manufacturing of this technology that can be observed. In this Master's thesis, the overall environmental impacts caused by the CO2 supercritical cycle will be evaluated:1. What are technologies available for producing electricity from low temperature heat?2. What is the electricity that can be generated from a given amount of heat and what type of equipment is needed for this?3. What are the environmental and resource impacts of this type of equipment, based on analyses of similar types of equipment?4. what is the environmental benefit from energy generation comparing with other fossil and renewable electricity production? 5. A brief economic analysis cosidering the waste heat electricity generation
43
Gustafsson, Marcus. "Energy efficient and economic renovation of residential buildings with low-temperature heating and air heat recovery." Licentiate thesis, KTH, Strömnings- och klimatteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172982.
Анотація:
With the building sector accounting for around 40% of the total energy consumption in the EU, energy efficiency in buildings is and continues to be an important issue. Great progress has been made in reducing the energy consumption in new buildings, but the large stock of existing buildings with poor energy performance is probably an even more crucial area of focus. This thesis deals with energy efficiency measures that can be suitable for renovation of existing houses, particularly low-temperature heating systems and ventilation systems with heat recovery. The energy performance, environmental impact and costs are evaluated for a range of system combinations, for small and large houses with various heating demands and for different climates in Europe. The results were derived through simulation with energy calculation tools. Low-temperature heating and air heat recovery were both found to be promising with regard to increasing energy efficiency in European houses. These solutions proved particularly effective in Northern Europe as low-temperature heating and air heat recovery have a greater impact in cold climates and on houses with high heating demands. The performance of heat pumps, both with outdoor air and exhaust air, was seen to improve with low-temperature heating. The choice between an exhaust air heat pump and a ventilation system with heat recovery is likely to depend on case specific conditions, but both choices are more cost-effective and have a lower environmental impact than systems without heat recovery. The advantage of the heat pump is that it can be used all year round, given that it produces DHW. Economic and environmental aspects of energy efficiency measures do not always harmonize. On the one hand, lower costs can sometimes mean larger environmental impact; on the other hand there can be divergence between different environmental aspects. This makes it difficult to define financial subsidies to promote energy efficiency measures.Byggnader står för omkring 40 % av den totala energianvändningen i EU. Energieffektivisering av byggnader är och fortsätter därför att vara en viktig fråga. Även om stora framsteg har gjorts när det gäller att minska energianvändningen i nya byggnader så är det stora beståndet av befintliga byggnader med dålig energiprestanda förmodligen ett ännu viktigare område att fokusera på. Denna avhandling behandlar energieffektiviseringsåtgärder som kan lämpa sig för renovering av befintliga hus, i synnerhet lågtemperaturvärmesystem och ventilationssystem med värmeåtervinning. Energiprestanda, miljöpåverkan och kostnader utvärderas för en rad systemkombinationer, för små och stora hus med olika värmebehov och för olika klimat i Europa. Resultaten togs fram genom simuleringar med energiberäkningsprogram. Lågtemperatursystem och värmeåtervinning framstod båda som lovande lösningar för energieffektivisering av europeiska hus, särskilt i norra Europa, eftersom dessa åtgärder har större effekt i kalla klimat och på hus med stort värmebehov. Prestandan för värmepumpar, såväl av utelufts- som frånluftstyp, förbättrades med lågtemperaturvärmesystem. Valet mellan frånluftsvärmepump och värmeåtervinning till ventilationsluft kan antas bero på specifika förhållanden för varje fall, men de är båda mer kostnadseffektiva och har lägre miljöpåverkan än system utan värmeåtervinning. Värmepumpen har fördelen att den kan återvinna värme året runt, förutsatt att den producerar varmvatten. Ekonomiska och miljömässiga aspekter av energieffektiviseringsåtgärder stämmer inte alltid överens. Dels lägre kostnad ibland betyda större miljöpåverkan, dels kan det finnas divergens mellan olika miljöaspekter. Detta gör det svårt att fastställa subventioner för att främja energieffektiviseringsåtgärder.
QC 20150904
44
Adluru, Hari Kishore. "Design and analysis of micro-channel heat-exchanger embedded in Low Temperature Co-fire Ceramic (LTCC)." FIU Digital Commons, 2004. http://digitalcommons.fiu.edu/etd/1160.
Анотація:
Increased device density, switching speeds of integrated circuits and decrease in package size is placing new demands for high power thermal-management. The convectional method of forced air cooling with passive heat sink can handle heat fluxes up-to 3-5W/cm2; however current microprocessors are operating at levels of 100W/cm2, This demands the usage of novel thermal-management systems. In this work, water-cooling systems with active heat sink are embedded in the substrate.
The research involved fabricating LTCC substrates of various configurations - an open-duct substrate, the second with thermal vias and the third with thermal vias and free-standing metal columns and metal foil. Thermal testing was performed experimentally and these results are compared with CFD results. An overall thermal resistance for the base substrate is demonstrated to be 3.4oC/W-cm2. Addition of thermal vias reduces the effective resistance of the system by 7times and further addition of free standing columns reduced it by 20times.
45
Benafan, Othmane. "Design, Fabrication and Testing of a Low Temperature Heat Pipe Thermal Switch with Shape Memory Helical Actuators." Master's thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6222.
Анотація:
This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states are actuated by shape memory alloy elements while heat is transferred by a heat-pipe. The motivation for such a switch comes from NASA's need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. For example, as the temperature can approximately vary between 40 K to 400 K during lunar day/night cycles, such a switch can reject heat from a cryogen tank in to space during the night cycle while providing thermal isolation during the day cycle. By utilizing shape memory alloy elements in the thermal switch, the need for complicated sensors and active control systems are eliminated while offering superior thermal isolation in the open state. Nickel-Titanium-Iron (Ni-Ti-Fe) shape memory springs are used as the sensing and actuating elements. Iron (Fe) lowers the phase transformation temperatures to cryogenic regimes of operation while introducing an intermediate, low hysteretic, trigonal R-phase in addition to the usual cubic and monoclinic phases typically observed in binary NiTi. The R-phase to cubic phase transformation is used in this application. The methodology of shape memory spring design and fabrication from wire including shape setting is described. Heat transfer is accomplished via heat acquisition, transport and rejection in a variable length heat pipe with pentane and R-134a as working fluids. The approach used to design the shape memory elements, quantify the heat transfer at both ends of the heat pipe and the pressures and stresses associated with the actuation are outlined. Testing of the switch is accomplished in a vacuum bell jar with instrumentation feedthroughs using valves to control the flow of liquid nitrogen and heaters to simulate the temperature changes. Various performance parameters are measured and eported under both transient and steady-state conditions. Funding from NASA Kennedy Space Center for this work is gratefully acknowledged.M.S.
Masters
Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
46
Juhas, Mary Catherine. "The effect of low temperature isothermal heat treatments on the intergranular corrosion of AISI 316 stainless steel simulated weld heat affected zones /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487673114115915.
47
Bryson, Matthew John, and mbryson@bigpond net au. "The conversion of low grade heat into electricity using the Thermosyphon Rankine Engine and Trilateral Flash Cycle." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080130.162927.
Анотація:
Low grade heat (LGH) sources, here defined as below 80ºC, are one group of abundant energy sources that are under-utilised in the production of electricity. Industrial waste heat provides a convenient source of concentrated LGH, while solar ponds and geothermal resources are examples of sustainable sources of this energy. For a number of years RMIT has had two ongoing, parallel heat engine research projects aimed at the conversion of LGH into electricity. The Thermosyphon Rankine Engine (TSR) is a heat engine that uses water under considerable vacuum. The other research stream uses a hydrocarbon based working fluid in a heat engine employing the Trilateral Flash Cycle (TFC). The TSR Mk V was designed and built as a low cost heat engine for the conversion of LGH into electricity. Its main design advantages are its cost and the employment of only one moving part. Using the data gained from the experimental rig, deviations from the expected results (those derived theoretically) were explored to gain insight for further development. The results from the TSR rig were well below those expected from the design specifications. Although the experimental apparatus was able to process the required heat energy, the efficiency of conversion fell well below the expected 3% and was approximately 0.2%. The inefficiency was explained by a number of contributing factors, the major being form drag upon the rotor that contributed around 2/3 of the losses. Although this was the major cause of the power loss, other factors such as the interference with the rotor by the condensate on its return path contributed to the overall poor performance of the TSR Mk V. The RMIT TFC project came about from exploration of the available academic literature on the subject of LGH conversion. Early work by researchers into applying Carnot's theory to finite heat sources led them to explore the merits of sensible heat transfer combined with a cycle that passes a liquid (instead of a gas) though an expander. The results showed that it was theoretically possible to extract and convert more energy from a heat source of this type using this method than using any other alternative. This previous research was targeted at heat sources above 80ºC and so exploration of the theoretical and empirical results for sources below this temperature was needed. Computer models and an experimental rig using isopentane (with a 28ºC boiling point at atmospheric pressure) were produced to assess the outcomes of employing low temperature heat sources using a TFC. The experimental results from the TFC research proved promising with the efficiency of conversion ranging from 0.8% to 2.4%. Although s uch figures seem poor in isolation, it should be noted that the 2.4% efficiency represents an achievement of 47% of the theoretical ideal conversion efficiency in a rig that uses mainly off-the-shelf components. It also confirms that the TFC shows promise when applied to heat sources less than 80ºC.
48
NADELLA, Venkata Raghurama Swaroop. "CFD Simulation of MQL with low temperature and high-pressure coolant." Thesis, KTH, Industriell produktion, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244417.
Анотація:
Att använda stora mängder skärvätskor vid en bearbetningsprocess har potentiellt negativ inverkan inte bara för operatören men också på miljön. Utöver detta tillkommer ökade kostnader för tillverkningsprocessen. För att minska skärvätskekonsumtionen under maskinbearbetning införs en teknik som kallas minimalsmörjning(MQL=Minimum Quantity Lubrication) som använder mycket mindre mängd skärvätska men ändå är effektivare än standard kylspolning med skärvätska. Denna avhandling fokuserar på att bestämma konvektionen över ett skär med en konstant värmekälla placerad inuti ett kvadratiskt hölje och beräkningsdomänen för den CFD-modell som presenteras, vilken består av flytande och fasta domäner och interaktion mellan dessa. Möjligheten att använda MQL då lågtemperatur- och högtryckskylmedel appliceras undersöks och hur temperaturen sjunker efter applicering av kylmedel/kylvätskor observeras genom att simulera förhållandena i ANSYS flytande arbetsbänk. Denna tekniks effektivitet bestäms med avseende på huruvida högtrycks- och lågtemperaturkylvätska kan avleda värme och transportera bort spånor från ingreppszonen. Slutligen sammanställs resultaten och därpå dragna slutsatserna.Employing huge amount of cutting fluids in machining process has potential negative impacts not only to the operator but also to the environment along with increased cost of manufacturing process. To reduce the cutting fluid consumption during machining, a technique called Minimum Quantity Lubrication (MQL) is introduced which uses very less amount of cutting fluid yet being effective than flood cooling. This thesis focuses on determining the convection over a cutting insert with a constant heat source inside a square enclosure and the computational domain of the CFD model presented consists of fluid and solid domains with fluid-solid interaction. The feasibility of MQL using low temperature and high-pressure coolant and observing how temperature is dropping after the application of coolant/coolants by simulating the conditions in ANSYS fluent workbench. The effectiveness of this technique is determined in terms of whether high pressure and low temperature coolant can dissipate heat and remove chips from the cutting interface. Finally drawing conclusion based on results.
49
Manap, Mohd Yazid B. Hj Abd. "The effects of low temperature storage and thermisation on the quality of raw and heat treated milk." Thesis, University of Glasgow, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385626.
50
Mureddu, Alessandro. "Thermodynamic analysis of an ORC plant and a transcritical CO2 plant for low temperature waste heat recovery." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Анотація:
La domanda di energia nel mondo è in continuo aumento e, contemporaneamente, l'aumento dell'inquinamento ambientale spinge verso una diminuzione dell'utilizzo di combustibili fossili. Per questo motivo, oggi è fondamentale sia lo sviluppo di nuove fonti energetiche pulite, sia il recupero di calore di scarto da varie applicazioni che, in passato, veniva perso. Lo scopo di questo lavoro è un'analisi termodinamica di impianti ORC e impianti a CO2 transcritica, entrambi usati per il recupero di calore di scarto industriale a bassa temperatura (=200°C). In particolare, verranno analizzati due diversi layout per ogni tipologia di impianto: il layout semplice e quello recuperato. Le quattro simulazioni son state sviluppate in Matlab, implementando le equazioni di bilancio entalpico per ogni ciclo, in modo tale da poter calcolare le performance termodinamiche e, dunque, poter confrontare i diversi layout, in modo da scegliere quello che assicura le migliori prestazioni. Le quattro simulazioni son state svolte considerando un set di parametri di progetto, in linea con lo stato dell'arte attuale, e per diversi valori della pressione massima del ciclo, in modo tale da trovarne il valore che massimizzi l'efficienza termodinamica. In seguito, son stati confrontati tutti i valori calcolati, così da scegliere l'impianto più adatto al recupero di calore di scarto a bassa temperatura. Successivamente, le simulazioni son state svolte con un diverso valore della temperatura di uscita dei fumi e della temperatura di uscita dell'acqua di raffreddamento, per motivi di impatto ambientale. In seguito, i cicli son stati valutati per diversi valori della temperatura di ingresso dei fumi caldi e per diversi valori del rendimento isoentropico di turbina, così da valutare l'effetto di una variazione di tali parametri sul rendimento termodinamico di ogni ciclo.