The characteristics of the proton exchange membrane fuel cell (called PEMFC) stacks made with the graphite unipolar/bipolar plates are studied in this thesis. Using pure hydrogen as fuel, certain experimental work is conducted to help us to understand the factors which influence on the performance of a HFC stack. The experimental work under various operating conditions starts from single cell stacks to multi-cell stacks. The maximum power is about 200 W, which is made with two 10-cell stacks in series. For simplification, all of the flow channels in the cathode are open type in which air is directly supplied from ambient by fan. The comparison of the performance of two single cells, which are made with both a graphite unipolar plate and a new-type carbon fiber unipolar plate, is conducted. The total resistances of the two types of bipolar plates with gas diffusion layers are tested to help us to understand their strong or weak points. The experimental results display that the double inlets has better performance than the single inlet due to larger entrance space. Increasing the applied torque will reduce the contact resistance between bipolar plate and diffusion layer and also the gaps between the fibers of carbon cloth. Reducing the contact resistance is helpful in increasing the performance of the cell, but reducing the gaps between fibers will inhibit the entering of reactive gas and is unfavorable for performance; therefore, the proper torque is necessary to obtain the best voltage output. When air is used as an oxidizer and the flow channel is an open type channel, the fan in high rotating speed is helpful at high current density. The high air volume flow rate can supply sufficient oxidizer and avoid the decay of the voltage output at high current density. At the current density 1 A/cm2, the power density of the single-cell stack is about 400 mW/cm2 and the power density of the 10-cell stack is down to about 310 mW/cm2 in our experiment. The rib of the carbon fiber unipolar/bipolar plate is soft, so there is no deformation in the gas diffusion layer in stack assembly. Only slight compression is needed to assemble a stack; therefore, the reactive gas can easily flow into the most of active area. This type unipolar/bipolar plate is made with low density plastic except that the rib is made with carbon fiber bunches. Thus the new plate is weight light, cost low and volume small. So it is quite possible that the new-type of carbon fiber plate is used as substitution for the graphite bipolar plate in the future. In that case the light, low cost and high performance choice can be achieved.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work reports an experimental investigation related to the drop-in process of HCFC22 in a commercial refrigeration system with a maximum capacity of 15 kW. Among the alternative refrigerants there are hydrocarbons (HCs) and synthetic refrigerants, HFC. The experimental facility is basically composed of analternative variable speed compressor (VSC), tube in tube heat exchangers and an electronic expansion valve (EEV). Different methodologies were addressed to this document. Initially, the systemoperated at the nominal frequency and has been configured to the same openning condition in the expansion valve. The limits of the refrigeration system were operated by factorial experimental designs. Therefore,there were presented response surfaces and metamodels, showing consistent tools to predict the cooling system behavior. Also, an analysis of the individual performance of each refrigerant was held in three different evaporation temperatures: -15ºC, -10ºC and -5ºC. All fluids, except R134a can be suitable to replace R22 in these specific applications. Both HCs and HFC32 provide the refrigeration capacity and COP greater than the original system. In addition, the environmental impact of each fluid was estimated by the TEWI method. HCs showed the lowest impacts, while HFC404A promoted the greatest damage to the environment. Finally, the analysis of the operating system with a Scroll compressor was made. Among the seven options to R22, only five refrigerants operated in stable condition. Moreover, even with handling system parameters, this class of compressors was less flexible to the proposed drop-in. In general, as a great technical contribution for refrigeration systems, this study found that, regardless of the installation capacity, the EEV/VSC pair functionality is an essential tool not only for the adaptation of an alternative fluid to the original compression cycle, as well as to reduce environmental impacts. / O presente trabalho relata uma investigação experimental do processo de drop-in(substituição direta) do HCFC22 em um sistema de refrigeração comercial com capacidade máxima de 15kW. Entre os refrigerantes alternativos testados, encontram-se hidrocarbonetos e refrigerantes sintéticos da classe HFC.A bancada experimental é composta, basicamente, de um compressor de velocidade variável(CVV) alternativo, trocadores de calor de tubos concêntricos e uma válvula de expansão eletrônica (VEE). Inicialmente, o sistema operou à frequência nominal e foiconfigurado à mesma condição de abertura no dispositivo de expansão. Posteriormente, os limites de cada refrigeranteforam explorados por meio de ferramentas estatísticas DOE,design of experiments. Nesta segunda etapa, foram apresentadas superfícies de respostas e metamodelos, que se mostraram ferramentas coerentes na previsão do comportamento do sistema de refrigeração.Em sequência,foirealizada uma análise do desempenho individual de cada refrigerante, em três diferentes temperaturas de evaporação: -15ºC, -10ºC e -5ºC. Todos os refrigerantes, com exceção do R134a, podem substituir o R22 nestas aplicações específicas. Ambos os hidrocarbonetos (HCs) e o HFC32 proporcionaram capacidades de refrigeração e COPs superiores ao sistema original. Em complemento, a estimativa dos impactos ambientais de cada fluidofoi estimada através do método TEWI, total equivalent warming impact. Os HCs apresentaram os menores impactos, enquanto o HFC404A promoveu os maiores danos ao meio ambiente.Por fim, realizou-se a análise do sistema operando com um compressor tipoScroll. Entre as sete opções ao R22, apenas cinco refrigerantes operaram em condições estáveis. Além disso, mesmo com a manipulação de parâmetros do sistema, esta classe de compressores mostrou-se menos flexível à proposta de drop-in.Em geral, como maior contribuição técnica aos sistemas de refrigeração, o presente trabalho comprovou que, independentemente da capacidade da instalação, a funcionalidade do par VEE/CVV é uma ferramenta essencial não só para a adaptação de um fluido alternativo ao ciclo de compressão original, como também para a reduçãodos impactos ambientais. / Doutor em Engenharia Mecânica

Orientadores: Hermano Medeiros Ferrera Tavares, Marcos Carneiro da Silva / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e Computação / Made available in DSpace on 2018-08-07T03:17:59Z (GMT). No. of bitstreams: 1 Navarro_MaristelaDomeni_M.pdf: 2037867 bytes, checksum: a858cc3260dae4659d1b3cdfece3f4f9 (MD5) Previous issue date: 2006 / Resumo: Este trabalho objetiva verificar a viabilidade da utilização da rede das operadoras de televisão à cabo para medição remota e tarifação diferenciada de energia elétrica para consumidores alimentados em baixa tensão - Grupo B. Envolve a criação de protótipos de hardware e software para controle da comunicação, obtenção dos dados e controle operacional dos medidores de energia executados remotamente a partir de uma central. A arquitetura implementada tem três elementos principais: o Ponto de Presença, instalado no quadro de medidores do consumidor; o Controlador Central de Comunicação, instalado na operadora de televisão à cabo, responsável pela comunicação com os Pontos de Presença monitorados e pela concentração e envio de informações ao Centro de Aplicações, o último elemento da arquitetura. Resultados foram coletados e avaliados, abordando aspectos como a viabilidade técnica, vantagens e desvantagens. Esse trabalho proporcionou ainda um breve estudo de novas formas de comunicação remota com medidores usando outros meios físicos de comunicação / Abstract: This work was developed to verify the viability to use the cable TV infra-structure for remote measurement and billing for consumers fed in low tension - Group B. It involved the creation of hardware and software prototypes for control of the communication to collecting data remotely of the energy meter from a central office. The implemented architecture has three main elements: the Point of Presence, installed at the consumer side; the Central Controller, installed in the Cable TV headend, responsible for the communication with the Points of Presence and for the concentration and sending of information to the Application Center, the last element of the architecture. Results had been collected and evaluated, taking into account aspects as the viability technique, advantages and disadvantages. This work still provided a briefing study of new ways of remote communication with the energy meters using other infra-structure of communication / Mestrado / Automação / Mestre em Engenharia Elétrica

[EN] Climate change is one of the short term threats for the humanity because it can affect seriously to the environment and, consequently, to vegetal and animal life. If it is not stopped in next years, maybe this effect will be irreversible. Climate change is produced by anthropogenic emissions of Greenhouse Gas to Earth's atmosphere. Vapour compression systems are one of the main contributors to this phenomenon. Among them, commercial refrigeration applications, through HFC usage, can be highlighted. Since 1990s, developed countries supermarkets are using refrigerants (mainly R134a, R404A and R507A) with great impact (high GWP values) on the climate change due to leakages, especially from parallel compressor rack DX systems. Recently, some regulations and directives have been approved to limit GWP values of HFC used in most extended refrigeration and air conditioning applications, directly affecting to commercial refrigeration. In this thesis, some low-GWP alternatives to replace the most commonly used HFC refrigerants in commercial refrigeration are evaluated, taking into account the limitations imposed by these regulations. To carry out this evaluation, the current status of parallel compressor rack refrigeration systems and their fluids has been reviewed. Then, the different low-GWP options to replace R134a and R404A have been studied. HFOs and their mixtures with HFC have been highlighted as the most promising drop-in or retrofit alternatives. Thus, R1234yf, R1234ze(E) and R450A were proposed to replace R134a and R448A to substitute R404A. The theoretical performance of the different low-GWP alternative fluids, as an overview of their potential use, has been studied at typical parallel compressor rack refrigeration operating conditions using the basic thermodynamic vapour compression cycle. Given the good theoretical performance of these refrigerants, they have been tested in a vapour compression test bench. From the experimental results it is depicted that R1234yf and R1234ze(E) are not acceptable as drop-in or light retrofit refrigerants from an energetic point of view. These fluids, when used in R134a systems, require system modifications (more severe in the case of R1234ze(E)) to achieve acceptable energy efficiency values. Moreover, due to the large refrigerant charge in PCRRS, both HFOs could present problems relating to security. Thus, while R450A presents a GWP value of 547, it appears as the best option to replace R134a due to the similar energy efficiency and properties. Its experimental mass flow rate and cooling capacity are slightly lower than R134a, but the final COP is approximately the same. The best R450A results when compared to R134a are obtained at higher CRs. Although can obtain better efficiency results in new systems, with a minor TXV adjustment R448A shows very high performance when it is used in R404A systems. Despite R448A lower cooling capacity than that R404A, this HFC/HFO mixture can achieve great CO2 equivalent emission reductions and it is recommended as lower-GWP replacement for R404A. / [ES] El cambio climático es una amenaza para la humanidad ya que puede afectar seriamente al medio ambiente y, en consecuencia, a la vida animal y vegetal. Si en los próximos años no se actúa para detenerlo, tal vez este efecto sea irreversible. Entre otros factores, el incremento de la temperatura global es producido por las emisiones antropogénicas de gases de efecto invernadero a la atmósfera. La refrigeración comercial, basada en sistemas de compresión de vapor, contribuye de forma relevante a este fenómeno a través del uso de fluidos sintéticos como refrigerantes y del consumo de energía eléctrica procedente de combustibles fósiles. Desde la última década del siglo XX, los supermercados de países desarrollados utilizan HFCs como fluidos de trabajo, principalmente R134a, R404A y R507A. Estos gases, de alto potencial de calentamiento atmosférico (PCA), contribuyen al cambio climático al fugarse accidentalmente de los sistemas de refrigeración, destacando las centrales de compresores en paralelo conectadas a sistemas de expansión directa. El valor máximo de PCA de los HFCs utilizados en aplicaciones de refrigeración y aire acondicionado va a ser controlado por normativas comunitarias, afectando directamente a los fluidos usados comúnmente en refrigeración comercial. Esta tesis evalúa diferentes alternativas de bajo PCA para sustituir los refrigerantes HFC más utilizados en refrigeración comercial, teniendo en cuenta las limitaciones impuestas por las normativas actuales. Para llevar a cabo dicho estudio, se revisa el estado actual de los sistemas de centrales de compresores en paralelo y sus fluidos. A continuación, se analizan las diferentes opciones de bajo PCA para sustituir al R134a y R404A. Al destacar los HFOs y sus mezclas con HFCs como alternativas para realizar un reemplazo con pocas modificaciones del sistema (propiedades similares); R1234yf, R1234ze(E) y R450A son propuestos para sustituir al R134a y R448A para R404A. El rendimiento teórico de los diferentes fluidos alternativos de bajo PCA, para obtener una visión general del potencial de su uso, se estudia simulando las condiciones operativas típicas de las centrales de compresores en paralelo, usando el ciclo termodinámico de compresión de vapor básico. Dado el buen rendimiento mostrado por estos refrigerantes, son ensayados en un banco de pruebas de compresión de vapor. De los resultados experimentales se observa que R1234yf y R1234ze(E) no son aceptables desde un punto de vista energético como sustitutivos directos o con menores modificaciones. Dichos fluidos, cuando son utilizados en sistemas de R134a, requieren modificaciones del sistema (más severas en el caso del R1234ze(E)) para alcanzar valores aceptables de eficiencia energética. Por otra parte, debido a la gran carga necesaria en PCRRS, ambos HFOs podrían presentar problemas en cuanto a la seguridad. Así, mientras que el R450A presenta un valor de PCA de 547, aparece como la mejor opción para sustituir al R134a debido a una eficiencia energética y propiedades similares. El caudal másico y la capacidad frigorífica del R450A son ligeramente inferiores en comparación con las del R134a, pero por otra parte, el COP resultante es aproximadamente el mismo. Los mejores resultados obtenidos para R450A son obtenidas a altas tasas de compresión. Aunque puede ser obtenida una eficiencia energética más alta en sistemas de nuevo diseño, con sólo un ajuste menor de la válvula de expansión termostática, el R448A muestra valores muy altos de rendimiento en sistemas utilizados con R404A. A pesar de que la capacidad frigorífica del R448A es menor que la del R404A, esta mezcla de HFC y HFO puede dar lugar a grandes reducciones de emisiones de CO2 equivalentes, siendo así recomendado como reemplazo del R404A con menor PCA. / [CA] El canvi climàtic és una amenaça per a la humanitat ja que pot afectar seriosament el medi ambient i, en conseqüència, la vida animal i vegetal. Si en els propers anys no s'actua per aturar-lo, potser aquest efecte siga irreversible. Entre altres factors, l'increment de la temperatura global és produït per les emissions antropogèniques de gasos d'efecte hivernacle a l'atmosfera. La refrigeració comercial, basada en sistemes de compressió de vapor, contribueix de manera rellevant a aquest fenomen per l'ús de fluids sintètics com refrigerants i pel consum d'energia elèctrica procedent de combustibles fòssils. Des de l'última dècada del segle XX, els supermercats dels països desenvolupats utilitzen HFCs com fluids de treball, principalment R134a, R404A i R507A. Aquests gasos, d'alt potencial d'escalfament atmosfèric (PCA en castellà), contribueixen al canvi climàtic quan s'escapen accidentalment dels sistemes de refrigeració. D'aquest tipus de sistemes destaquen com a grans emissors de diòxid de carboni les centrals de compressors en paral·lel connectades a sistemes d'expansió directa. El valor màxim de PCA dels HFCs utilitzats en aplicacions de refrigeració i aire condicionat serà controlat per normatives comunitàries, cosa que afectarà directament els fluids utilitzats a la gran majoria de sistemes de refrigeració comercial. Aquesta tesi avalua diferents alternatives de baix PCA per substituir els refrigerants HFC més utilitzats en refrigeració comercial sense oblidar les limitacions imposades per les normatives actuals. Per dur a terme aquest estudi, es revisa l'estat actual dels sistemes de centrals de compressors en paral·lel i els seus fluids. A continuació, s'analitzen les diferents opcions de baix PCA per substituir l'R134a i l'R404A. Els HFOs i les seves mescles amb HFCs com alternatives destaquen per permetre una substitució amb poques modificacions del sistema (propietats similars); R1234yf, R1234ze(E) i R450A són proposats per substituir l'R134a i R448A per l'R404A. Per obtenir una visió general del potencial de l'ús dels diferents fluids alternatius de baix PCA, s'estudia el seu rendiment teòric mitjançant una simulació de les condicions operatives típiques de les centrals de compressors en paral·lel. Per a aquesta simulació s'empra el cicle termodinàmic de compressió de vapor bàsic. Com a conseqüència del bon rendiment mostrat per aquests refrigerants, són assajats en un banc de proves de compressió de vapor. Dels resultats experimentals s'observa que R1234yf i R1234ze(E) no són acceptables des d'un punt de vista energètic com a substitutius directes o amb menors modificacions. Aquests fluids, quan són utilitzats en sistemes de R134a, requereixen modificacions del sistema (més severes en el cas de l'R1234ze(E)) per assolir valors acceptables d'eficiència energètica. D'altra banda, a causa de la gran càrrega necessària en PCRRS, tots dos HFOs podrien presentar problemes en temes de seguretat. Així, mentre que el R450A presenta un valor de PCA de 547, apareix com la millor opció per substituir l'R134a a causa de una eficiència energètica i propietats similars. El cabal màssic i la capacitat frigorífica de l'R450A són lleugerament inferiors en comparació amb les de l'R134a, però d'altra banda, el COP resultant és aproximadament el mateix. Els millors resultats de l'R450A són obtinguts a altes taxes de compressió. Tot i que pot ser obtinguda una eficiència energètica més alta en sistemes de nou disseny, amb només un ajust menor de la vàlvula d'expansió termostàtica, l'R448A mostra valors molt alts de rendiment en sistemes utilitzats amb R404A. Encara que la capacitat frigorífica de l'R448A és menor que la de l'R404A, aquesta barreja de HFCs i HFO pot aconseguir grans reduccions d'emissions de CO2 equivalents, i es per tant es recomanada com a reemplaçament amb menor PCA de l'R404A. / Mota Babiloni, A. (2016). ANALYSIS OF LOW GLOBAL WARMING POTENTIAL FLUORIDE WORKING FLUIDS IN VAPOUR COMPRESSION SYSTEMS. EXPERIMENTAL EVALUATION OF COMMERCIAL REFRIGERATION ALTERNATIVES [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62680 / Premios Extraordinarios de tesis doctorales

Le présent document obéit à un plan strict inhérent à tous les manuscrits de thèsepassée en Validation des Acquis de l’Expérience (VAE). Après un CV détaillé ledocument présente tout d’abord un retour réflexif sur le parcours professionnel c'està-dire, une synthèse sur les taches effectuées d’un travail de type projet vers uneimplication de plus en plus forte vers un travail de recherche à proprement parlé. Aprèsce retour réflexif qui permet d’avoir une vue d’ensemble de la progression du parcours,une synthèse est proposée, non pas de la totalité des travaux, mais de trois domainesbien précis et représentatifs du parcours de recherche. Ce choix s’est fait en cherchantun fil d’Ariane qui est tout simplement la nature chimique de la céramique étudiée ;dans le présent document il s’agit de carbures et plus précisément de SiC, TiC, ZrC,HfC. Tout d’abord le travail sur les céramiques monolithiques pour les applicationsnucléaires est abordé puis, les applications spatiales avec la mise au point deprotections contre l’oxydation à partir de poudres revêtues enfin, le document s’achèvepar des travaux d’infiltration de céramiques à partir d’un matériau intermétallique oucomment il est possible de faire des céramiques ultra réfractaires à basse température.Ces travaux étant originaux ils ont fait l’objet de brevets et de publications qui serontabordés dans la troisième partie. / This document obeys a strict plan inherent in all PhD manuscripts passed in Validationof the Assets of Experiment (VAE). After a detailed resume this document first of all,presents a reflexive return on the career i.e., from a work of type project towards anincreasingly strong implication to a research task. After this reflexive return whichmakes it possible to have an overall picture of the progression of the course, asynthesis is proposed, not of total work, but of three fields quite precise andrepresentative of the course of research. This choice was done by seeking a wire ofARIANE which is the chemical nature of the studied ceramics; in this document it isabout carbides and more precisely about SiC, TiC, ZrC, HfC. First of all monolithicceramics for the nuclear applications is approached then, the space applications withthe elaborating of protections against oxidation made by core shell powders finally, thedocument is completed by ceramics infiltrations from an intermetallic material or howit is possible to make ultra refractory ceramics at low temperature. As these works areoriginal they were the object of patents and publications which will be approached inthe third part.

Les paramètres physiques à la base des fuites du fluide frigorigène HFC-134a dans les systèmes de climatisation automobile ne sont pas encore pleinement compris. Le but de ce travail de recherche est d'établir une méthode de mesures des débits de fuite de fluide frigorigène des systèmes de climatisation automobile ainsi que des composants de ces systèmes, et aussi de développer une approche générique de prévision de ces émissions. Dans la thèse, les fuites chroniques des différents composants des systèmes de climatisation automobile sont évaluées et hiérarchisées. Une méthode d'essais de laboratoire, basée sur la mesure de concentration dans un volume d'accumulation, est présentée pour déterminer les débits de fuite de systèmes et de composants. La précision de la mesure est aussi justifiée. Des mesures en régime permanent et pour plusieurs températures contrôlées sont effectuées afin de comparer le débit de fuite de l'ensemble du système et la somme des débits de fuite de tous les composants. Les simulations de la variation de température permettent de prédire les impacts des conditions climatiques annuelles quel que soit le climat. Les essais en régime dynamique sont également traités pour analyser la contribution du temps de fonctionnement du système aux émissions annuelles du système. Afin de vérifier la méthode d'essai en laboratoire, des opérations de récupération du fluide frigorigène ont été effectuées sur une quarantaine de véhicules avec une précision de +0 / -1 g. Sur la base des résultats des essais en laboratoire et de ceux obtenus sur la flotte de véhicules, un facteur de corrélation a été établi pour corréler les tests en laboratoire aux émissions mesurées sur le terrain. Les prévisions des émissions de tuyauteries flexibles utilisées dans les systèmes de climatisation automobile ont été développées en prenant en compte les effets de la température et de la pression. Les joints toriques typiques sont étudiés et deux modes de fuite: la perméation à travers des matériaux polymères et l'écoulement du gaz dans les micro-canaux sont distingués. Les performances d'étanchéité d'un joint torique radial sont étudiées en utilisant la méthode des éléments finis. Le comportement non-linéaire des déformations des polymères est pris en compte. L'analyse des facteurs principaux tels que la contrainte, la pression de contact maximale et le contact est basée sur les résultats de simulations numériques. Les deux modes de fuites permettent de comprendre les phénomènes clés des émissions et donc d'améliorer les performances d'étanchéité. En résumé, le débit de fuite d'un système de climatisation automobile est la somme des débits de fuite de toutes les sources de fuites. Ces sources sont de deux types: la perméabilité du gaz dans les polymères et l'écoulement du gaz dans les micro-canaux existant entre les joints et les parties métalliques des raccords. Pour chaque mode d'émission, une loi de comportement a été développée et les modèles prédictifs permettent de prévoir les débits de fuite avec un nombre limité de mesures.

The environmental concerns in recent times have grown especially after signing Montreal protocol. In the last ten years, researchers have focussed mainly on understanding the boiling and condensation phenomena of HFC refrigerants in minichannels. As global warming concerns are growing day by day, due to high global warming potential, HFCs are not the ultimate option. In the near future, HFCs will probably be replaced by environmentally friendly refrigerants. Therefore, to find the potential replacements of HFCs and also to get a deeper understanding of the boiling phenomena in minichannels, more and more fluids having low GWP (Global Warming Potential) and ODP (Ozone Depletion Potential) should be tested. Recent efforts to protect the environment have led to a growing interest for natural refrigerants. However in the literature, flow boiling data of natural refrigerants in minichannels are scarce. To meet the environmental concerns and to understand the behaviour of natural refrigerants in minichannels and the performance compared to HFCs, flow boiling experiments in single circular vertical minichannels of internal diameters of 1.70 and 1.224 mm were performed using ammonia and propane as working fluids. Flow boiling heat transfer results of ammonia and propane with 1.70 mm channel showed that the heat transfer coefficient was a function of heat flux and the effect of mass flux was insignificant. The heat transfer coefficient of ammonia in 1.224 mm was dependent on heat flux at low vapour qualities then a clear dependence of the heat transfer coefficient on the mass flux was observed at higher vapour qualities. The heat transfer results of ammonia and propane were compared with well known correlations and among them Cooper (1989) correlation in case of ammonia and Liu and Winterton (1991) and Cooper (1984) pool boiling correlations in case of propane best predicted the experimental heat transfer data. Results of the two phase pressure drop studies of ammonia and propane showed that the two phase pressure drop increased with the increase of mass flux, with the increase of heat flux and with the decrease of saturation temperature. The comparison of the two phase pressure drop experimental data with well known predicting models showed that none of the correlations predicted the ammonia data well and that Müller Steinhagen and Heck (1986) was well in agreement with the propane data. Dryout of propane in 1.70 mm and 1.224 mm internal diameter channels was also investigated. Dryout heat flux was observed to increase with the increase of mass flux, with the decrease of vapour quality and with the increase of internal diameter. The effect of saturation temperature on the dryout heat flux was insignificant. The experimental dryout data were compared with macro and micro scale correlations and among them Bowring (1972) and Callizo et al. (2010a) gave best predictions. The heat transfer and pressure drop results of ammonia and propane and dryout results of propane were compared with R134a data taken on the same test rig by Owhaib (2007) and Ali (2010). The comparison of heat transfer showed that the heat transfer coefficient was a function of heat flux and the effect of mass flux was insignificant in all tested conditions except ammonia in 1.224 mm tube where the heat transfer coefficient was dependent on heat flux at lower vapour qualities and a clear dependence of mass flux was observed at higher vapour qualities. The heat transfer data of ammonia, propane and R134a were compared with correlations and among them Cooper (1989) correlation gave best predictions. The comparison of pressure drop results showed that the two phase pressure drop of all fluids was increased with the increase of mass flux, with the increase of heat flux and with the decrease of saturation temperature. At equal heat flux and mass flux, the two phase pressure drop of ammonia was increased with the decrease of internal diameter but the diametric effects of R134a were unclear. Müller Steinhagen and Heck (1986) and Zhang and Webb (2001) best predicted the experimental data of two phase pressure drop of ammonia, propane and R134a among the correlations considered for comparison. The dryout data of propane were also compared with dryout data of R134a and it was observed that the dryout heat flux of propane and R134a increased with the increase of mass flux, with the decrease of vapour quality and with the increase of internal diameter. The effect of saturation temperature on the dryout heat flux of propane and R134a was insignificant. The correlation of Bowring (1972) for conventional channels and the microscale correlation of Callizo et al. (2010a) were among the correlations which gave best predictions of experimental data of dryout. / QC 20120210

The purpose of this work is to assess and propose possible methods for increasing the transmission speed of the cable television distribution, concretely the UPC network in Brno. The first part of work collectively processes general knowledge and gives the reader into the issue. After that follows an analysis of TV cable networks UPC in Brno, especially view of data transmission. After familiarization with the physical aspect of the network is described data communications itself, including standard DOCSIS, respectively EuroDOCSIS. Particular attention is paid to factors that have effect on data transmission and speed. Benefit is the calculation of dividing ratio in different parts of the network and compared with the real load. As far as possible in the given work results of measurements with regard to the quality of the network. The last part is about how to increase speeds. Perspective solution is mainly a technology which is based on standard EuroDOCSIS 3.0, which introduces the concatenation of individual channels. Result of made tests of first cable modem EuroDOCSIS 3.0 confirms the very high speeds and currently preparedness for other major step in so long development of TV cable network.

A comprehensive field investigation was conducted at Potrero Hills Landfill (PHL) located in Suisun City, California to quantify emissions of twelve (hydro)chlorofluorocarbons (i.e. F-gases). The specific target constituents for this study included CFC-11, CFC-12, CFC-113, CFC-114, HCFC-21, HCFC-22, HCFC-141b, HCFC-142b, HCFC-151a, HFC-134a, HFC-152a, and HFC-245fa. The majority of the F-gas emission studies have been conducted outside of the United States and very limited field landfill emission data are available in the United States. Because of historical usage of blowing agents in insulation foams including CFC-11, HCFC-142b, HFC-134a, and HFC-245fa, models reported in literature predicted high F-gas emissions from a landfill environment, but very limited field data are available to verify such predictions. In this investigation, the surface flux of the twelve F-gases, methane, and carbon dioxide was quantified from various landfill cover systems and in areas with different waste ages, waste heights, and cover thicknesses at Potrero Hills Landfill. In addition, destruction efficiencies for the twelve F-gases were determined based on inlet and outlet concentrations of the onsite flare system. Lastly, the surface flux values were scaled up to a facility-wide emission value to estimate the total fugitive emissions from the landfill. The F-gas flux values for the daily covers were in the 10 -8 to 10-1 g m-2 day -1 range and 10-7 to 10-2 g m-2 day-1 range for the wet and dry season, respectively. The F-gas flux values for the intermediate covers in the -10-6 to 10-4 g m-2 day-1 range and -10-6 to 10-4 g m-2 day-1 range for the wet and dry season, respectively. The F-gas flux values for the final covers were in the 10-7 to 10-5 g m-2 day-1 range and -10-7 to 10-6 g m-2 day-1 range for the wet and dry season, respectively. F-gas fluxes for the final covers had the highest number of below detection limit cases as well as lower than R2 threshold cases. Thest F-gas fluxes were measured from daily cover system constructed with auto shredder residue (i.e. auto fluff) for the both the wet and dry seasons. The highest fluxes were measured for CFC-11, HCFC-21, and HCFC-141b in the wet season and for CFC-11, HCFC-141b, and HFC-134a in the dry season across the seven cover locations. Lower level of variation was observed for methane and carbon dioxide with flux values ranging over five orders of magnitude for the seven tested locations. The methane flux values for the daily covers were in the 10-2 to 10+1 g m-2 d-1 range and 1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The carbon dioxide flux values for the daily covers were in the -10+1 to 10+2 g m-2 day-1 range and -10+1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The methane flux values for the intermediate covers were in the -10-2 to 10+1 g m-2 d-1 range and -10-3 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The carbon dioxide flux values for the intermediate covers were in the 1 to 10+2 g m-2 day-1 range for both seasons. The methane fluxes for the final cover were -10 -3 g m-2 day-1 and 10-4 g m-2 day-1 for the wet and dry season, respectively. The carbon dioxide flux values for the final cover were in the 10+1 g m-2 d-1 range and 1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. Negative flux values were typically observed during the wet season and at the intermediate and final covers. The destruction efficiencies for the twelve F-gases were above 99.5% for the onsite flare. Highest F-gas raw gas concentrations were measured for HFC-134a while the lowest F-gas concentration was measured for CFC-113. The F-gas concentrations in the raw gas ranged from 103 to 106 pptv. Similar to what has been reported in the literature, the landfill gas flare system was an efficient abatement device in controlling F-gas emissions. The surface emission measurement values from the field investigation were scaled up to estimate facility-wide fugitive emission values using the relative surface areas of the daily, intermediate, and final cover distributions in the landfill. The total fugitive emissions from the landfill including twelve F-gases, methane, and carbon dioxide ranged from 6,900 to 94,000 CO2E tonnes per year during the wet season, from 21,000 to 47,000 CO2E tonnes per year during the dry season, and from 13,000 to 75,000 CO2E tonnes per year during the year, prorated by the season (representing weighted average of 58% wet season emission rate and 42% dry season emission rate in a 12-month calendar year). The total fugitive F-gas emissions ranged from 1,600 to 4,800 CO2E tonnes per year during the wet season, from 140 to 600 CO2E tonnes per year during the dry season, and from 1,000 to 3,000 CO2E tonnes per year, prorated by the season. The total fugitive methane emissions ranged from 530 to 75,000 CO2E tonnes per year during the wet season, 17,000 to 35,000 CO2E tonnes per year during the dry season, and from 7,500 to 58,000 CO2E tonnes per year, prorated by the season. The total fugitive carbon dioxide emissions ranged from 5,000 to 14,000 CO2E tonnes per year during the wet season, 4,200 to 12,000 CO2E tonnes per year during the dry season, and from 4,500 to 13,000 CO2E tonnes per year, prorated by the season. In comparison to the total fugitive emission value derived from the first-order decay (FOD) model reported by USEPA and the total fugitive emission values calculated using waste-in-place (WIP) – landfill gas correlation equation presented in Spokas et al. (2015), the field-derived methane emission values were one to three orders of magnitude lower.

Hydraulic devices play an essential role in mechanical engineering due to their high-power density, good controllability, flexible application and high robustness, which expose innovative methods of energy transmission. However, in applications where there is an increased risk of fire or explosion, the commonly used combustible mineral oils represent an unacceptable safety hazard. In such cases, fireresistant, water-based hydraulic fluids are in demand. A special feature of these liquids is their high cavitation tendency and the associated strong erosion wear. The aim of this research is to predict the cavitation behaviour of HFC and the subsequent erosion phenomena using numerical methods and to validate the results with experiments. Additionally, experimental results for HFC were compared with HLP. The findings help to implement further developments to decrease the erosive effect of cavitation in high-pressure differences in hydraulic components. For this purpose, flow geometries of typical hydraulic components, e.g. valve and pump, are used for experimental and numerical investigation. The large-eddy simulation (LES) turbulent modelling is used with Zwart-Gerber cavitation model. The cavitation aggressiveness is quantified by cavitation erosion indices according to Nohmi.