Zugl.: München, Techn. Universiẗat, Diss., 2008.

Thesis--Technische Universität München, 2008. / Includes bibliographical references.

La présente thèse s’intéresse à la conception et la caractérisation des procédés microstructurés mettant en œuvre des réseaux de microcanaux de différentes dimensions. L’analyse de tels réseaux multi-échelles, représentatifs d’une parallélisastion de microsystèmes élémentaires, a essentiellement servi à identifier les principaux paramètres géométriques et physiques contrôlant les performances de ces réseaux complexes. On a cherché à quantifier l’influence des paramètres géométriques comme le rapport de résistances hydrodynamiques internes, le nombre de canaux et d’échelles opérant ainsi que leur répartition sur le réseau, sur des critères hydrodynamiques comme la maldistribution du fluide et la perte de charge résistive. Il est révélé qu’en fonction des contraintes imposées, un arrangement optimal des canaux sur un nombre pair d’échelles permet de réduire considérablement la maldistribution interne des flux et les pertes de charge résultantes. L’analyse thermique associée à l’analyse hydrodynamique a montré que les performances thermiques des réseaux sont fortement liées à leurs structurations géométriques internes. En présence de réactions catalytiques consécutives, ces mêmes réseaux enregistrent des déviations du rendement du produit désiré. Ces déviations peuvent être levées par une structuration appropriée du réseau catalytique multi-canal. La même architecture de ces réseaux peut être adaptée pour permettre le déroulement des opérations de mélange et/ou des réactions multi-phasiques. Ainsi, pour ces réseaux complexes, où un nombre élevé de variables imbriquées est considéré, des lignes directrices sont ressorties pour aider à leur conception et dimensionnement / This PhD thesis focuses on the design and the characterization of microstructured processes including microchannel networks of various dimensions. The analysis of such multi-scale networks, representative of elementary microsystems parallelization, is mainly used to identify the main geometrical and physical parameters controlling the network performances. Influence of geometrical parameters, such as the internal hydrodynamic resistances ratio, the number of channels and scales and their arrangement in the network, on hydrodynamic criteria like fluid maldistribution and pressure drop is investigated. It is shown that according to some specific constraints, an optimal arrangement of the channels on an even number of scales, allows to reduce significantly the internal flow maldistribution and the consequential pressure losses. The thermal analysis coupled with the hydrodynamic analysis illustrates that the thermal performances of microchannel networks are strongly affected by their internal geometrical arrangement. Nevertheless, the various mixture points located in the network compensate the fluid maldistribution resulting from a non appropriate geometrical arrangement. When consecutive catalytic reactions are performed inside these networks, deviations of the desired product rate can be recorded. These deviations can be reduced by an optimal catalytic network arrangement. The same architecture of these networks is also adapted to allow multi-phase mixing and /or reactions. Thus, using these complex networks, where several variables are considered, guidelines are derived in order to improve their design and their dimensionless

No description available.

This thesis contains the numerically investigations of the performance of a run-around membrane energy exchanger (RAMEE) at different outdoor air conditions and the effects of non-uniform exchanger channels. The RAMEE is a new type of building ventilation air energy recovery system that allows heat and moisture to be transferred between isolated supply and exhaust air streams. Two liquid-to-air membrane energy exchangers (LAMEEs) are placed in the supply and exhaust air ducts and transfer heat and moisture between air and a circulating liquid desiccant that couples the two LAMEEs together. The ability of the system to transfer heat and moisture between isolated supply and exhaust ducts makes it appropriate for numerous HVAC applications (e.g., hospitals and building energy retrofits). <p> The performance of the RAMEE at different outdoor air conditions is shown to be highly variable due to the coupling of the heat and moisture transfer by the desiccant. This coupling allows the humidity ratio between the indoor and outdoor air to influence the heat transfer and the moisture transfer is influenced by the difference between the indoor and outdoor air temperatures. The coupling produces some complex RAMEE performance characteristics at some outdoor air conditions where the effectiveness values (i.e., sensible, latent, and total) were shown to be less than 0% or greater than 100%. Effectiveness and operating correlations are developed to describe these complex behaviours because existing correlations do not account for the coupling effects. The correlations can serve as design and operation tools for the RAMEE which do not require the use of an iterative computational numerical model.<p> Non-uniform exchanger channels are present in the RAMEE because of pressure differences between the air and solution channels which deform the membrane into the air channel. The non-uniform channels are analytically shown to create maldistributed fluid flows and variable heat and mass transfer coefficients. The combined effects of these two changes lead to a reduction in the RAMEE effectiveness, which increases as the size of the membrane deformation increases. The reduction in total effectiveness for an exchanger where the membrane has a peak deflection of 10% of the nominal air channel thickness operating at a NTU of 12 was shown to be 12.5%. These results of non-uniform exchanger channels agree with previously conducted experimental results.

This thesis contains the numerically investigations of the performance of a run-around membrane energy exchanger (RAMEE) at different outdoor air conditions and the effects of non-uniform exchanger channels. The RAMEE is a new type of building ventilation air energy recovery system that allows heat and moisture to be transferred between isolated supply and exhaust air streams. Two liquid-to-air membrane energy exchangers (LAMEEs) are placed in the supply and exhaust air ducts and transfer heat and moisture between air and a circulating liquid desiccant that couples the two LAMEEs together. The ability of the system to transfer heat and moisture between isolated supply and exhaust ducts makes it appropriate for numerous HVAC applications (e.g., hospitals and building energy retrofits). <p> The performance of the RAMEE at different outdoor air conditions is shown to be highly variable due to the coupling of the heat and moisture transfer by the desiccant. This coupling allows the humidity ratio between the indoor and outdoor air to influence the heat transfer and the moisture transfer is influenced by the difference between the indoor and outdoor air temperatures. The coupling produces some complex RAMEE performance characteristics at some outdoor air conditions where the effectiveness values (i.e., sensible, latent, and total) were shown to be less than 0% or greater than 100%. Effectiveness and operating correlations are developed to describe these complex behaviours because existing correlations do not account for the coupling effects. The correlations can serve as design and operation tools for the RAMEE which do not require the use of an iterative computational numerical model.<p> Non-uniform exchanger channels are present in the RAMEE because of pressure differences between the air and solution channels which deform the membrane into the air channel. The non-uniform channels are analytically shown to create maldistributed fluid flows and variable heat and mass transfer coefficients. The combined effects of these two changes lead to a reduction in the RAMEE effectiveness, which increases as the size of the membrane deformation increases. The reduction in total effectiveness for an exchanger where the membrane has a peak deflection of 10% of the nominal air channel thickness operating at a NTU of 12 was shown to be 12.5%. These results of non-uniform exchanger channels agree with previously conducted experimental results.

Les échangeurs multifluides à plaques brasées (EPB) sont d’une technologie complexe qui permet de très fortes intégrations énergétiques, mais rend leur conception très délicate. Ces travaux ont pour objectif la modélisation et la simulation en 3D des EPB. Ils intègrent la maldistribution des fluides sur la largeur des passages qui peut dégrader fortement les performances thermiques de l’échangeur. La carte 3D des températures obtenue permettra le calcul des contraintes mécaniques. Le parcours d’un fluide est assimilé à un réseau hydraulique défini grâce à la théorie des graphes. Une méthode de maillage a été spécifiquement adaptée pour le couplage thermo-hydraulique. Ce dernier impose une résolution simultanée des équations de bilans matière, thermique et de quantité de mouvement par un système non linéaire de grande dimension et creux, avec mise en place de méthodes numériques adaptées. Enfin, des études de cas industriels sont présentées pour illustrer le simulateur 3D.

This PhD work was motivated by the CEA R&D program to provide solid technological basis for the use of Brayton power conversion system in Sodium-cooled Fast nuclear Reactors (SFRs). Multi-channel compact heat exchangers are necessary for the present application because of the low heat transfer capacity of the gas foreseen. In ASTRID project, a minimum size of Na channels section is required to avoid the plugging risk. However, this induces very low pressure losses in the bundle. Considering an additional inlet flow condition, a real risk of bad flow distribution remains. As a result, the thermal performance and thermal loading of the heat exchanger degrades due to it. The main goal of this work was to overcome the flow maldistribution problem by means of an innovative design of sodium distribution system (PATENT FR1657543), the development of a numerical strategy and the construction of an experimental database to validate all theoretical studies. The innovative sodium distribution system consists on an inlet header which tries to guide the evolution of the impinging jet flow while a system of bifurcating pre-distribution channels increases pressure drops in the bundle. Lateral communications between pre-distribution channels are introduced to further homogenize the flow. Two experimental facilities have been conceived to study the flow behavior in bifurcating channels and in the inlet header, respectively. At the same time, their effect on the flow distribution between channels is evaluated. The acquired PIV aerodynamic database allows to validate the numerical models and to prove the design basis for the proposed distribution system. Once having validated the CFD turbulence models and the strategy to study the flow maldistribution in the SGHE module, a decisive and trustworthy optimization of each component of the sodium distribution system has been performed. Finally, an optimal configuration has been proposed for the actual phase of ASTRID project.

Magister Economicae - MEcon / The provision of health care in South Africa is undergoing major restructuring. The aim is to achieve substantial, visible and sustainable improvements to the efficiency and accessibility of primary healthcare (PHC) services for all South Africans. One of the country's most critical problems is the weak and fragmented public sector PHC system. The most critical problems contributing to this are the maldistribution of resources (financial, physical and human) between hospitals and the primary care system, and between rural and urban areas. The health sector, therefore, faces the challenge of a complete restructuring and transformation of the national health care delivery system and related institutions. Choices need to be made about which services to cut, which to streamline and where savings can be made. Ways need to be found to use ALL of South Africa's resources optimally. This process of restructuring would be facilitated by the availability of accurate information on resource utilisation in the health sector. This study estimates the difference in the cost of primary diabetes treatment at dayhospitals and a provincial hospital in the Western Cape in 1992/93. Health economics is in its infancy in South Africa and serious data limitations exist. This study is therefore a pioneering effort in many ways. An appropriate methodological framework in which to conduct the costing had to be developed. The South African health sector, health spending arid the cost of primary diabetes treatment at day-hospitals and the provincial hospital are reviewed. Theoretical perspectives of the health care market and the methodologies of cost analysis are discussed. The cost analysis method of study is chosen, and arguments are advanced for its suitability in the South African context. A simple method of calculating the direct costs to obtain the average cost is proposed for the purpose of the study. Direct costs consist of staff costs and other related costs, such as medical supplies, non-medical supplies, building operations, equipment etc. These costs are then used to calculate the average costs per diabetic patient at the day-hospitals and the provincial hospital. The average cost per diabetic patient at day-hospitals amounted to R18.76, while at the provincial hospital the cost was R59.60.

[ES] Las regulaciones medioambientales imponen el uso de refrigerantes con cada vez menor Poder de Calentamiento Atmosférico (PCA), y obligan a que la búsqueda de refrigerantes alternativos a los actuales sea una necesidad real acorde a las tendencias del sector. El paso de los refrigerantes actuales a la utilización de refrigerantes alternativos no es inmediato ni mucho menos sencillo. La complejidad a nivel tecnológico es muy elevada, dado que el uso de un nuevo refrigerante exige diseñar y desarrollar de cero todos los componentes del circuito, puesto que poseen unas especificaciones y requerimientos de funcionamiento totalmente diferentes de los que poseen los refrigerantes actuales. La motivación principal de la tesis doctoral es la de plantear lo primeros pasos para el desarrollo de un equipo de bomba de calor para climatización que utilice un refrigerante con un bajo índice de PCA como el propano, en sustitución del que emplea la unidad actualmente (R410A), reduciendo así el impacto medioambiental del equipo y mejorando sus propiedades. Todo esto se encuentra incluido en los siguientes puntos: - Anticipar el cambio de tecnología necesario para el cumplimiento de la regulación F-GAS, asegurando menores emisiones para el medio ambiente y manteniendo la eficiencia energética actual mediante el desarrollo de equipos de bomba de calor con capacidad de modulación y con propano como fluido refrigerante. - Desarrollar herramientas de modelado y simulación para las diferentes plataformas objetivo. - Obtener conocimiento específico sobre el comportamiento de la bomba de calor mediante el análisis experimental con prototipos funcionales bajo las condiciones de trabajo especificadas, con la intención de conocer su funcionamiento, además de sus limitaciones, exigencias prácticas y sus necesidades de control. - Facilitar el diseño y desarrollo industrial de nuevos equipos de climatización mediante las herramientas de simulación y los datos experimentales obtenidos a través de prototipos funcionales. Motivada por este nuevo escenario, esta tesis se centra en estudiar qué posibilidades existen en medio-largo plazo en el desarrollo de bombas de calor para ajustarse a la regulación existente, no solo en cuanto a requerimientos ambientales sino también energéticos. Para ello, el primer paso ha sido el de realizar una sustitución directa del refrigerante original de la unidad aerotérmica, el R410A, por R290 para establecer el punto de referencia y poder conocer qué prestaciones es capaz de desarrollar esa misma unidad sin un rediseño del circuito de refrigerante. Tras esta primera evaluación, se ha llevado a cabo un estudio teórico de distintas configuraciones de circuito frigorífico con propano para evaluar las ventajas e inconvenientes entre ellas, con el objetivo de elegir la que mejor se ajuste al cumplimiento de los objetivos marcados. Este estudio se ha efectuado en tres ámbitos distintos: calefacción a baja temperatura, alta temperatura y condiciones de alta temperatura de impulsión de agua hasta 75ºC. En todos ellos, el resultado principal que se ha considerado ha sido el de eficiencia, lo que ha permitido obtener un orden de las tipologías estudiadas en función de los resultados obtenidos. A pesar de esto, esta evaluación también ha puesto de manifiesto otra característica intrínseca a cada uno de ellos como es su límite de funcionamiento en relación con la máxima temperatura de impulsión de calefacción. Tras ello, se ha construido un prototipo de bomba de calor funcional completo para ejecutar la fase experimental, que incluya hasta tres de las tipologías evaluadas en la fase teórica previa, para que, con todos los ensayos pertinentes, los resultados permitan seleccionar la tipología de circuito de refrigerante que se integre en un prototipo final. Este prototipo permitirá caracterizar el funcionamiento del sistema tanto para una plataforma aire-agua, como para una plataforma salm / [CA] Les regulacions mediambientals imposen l'ús de refrigerants amb cada vegada menor Poder d'Escalfament Atmosfèric (PCA), i obliguen a que la recerca de refrigerants alternatius als actuals sigui una necessitat real d'acord amb les tendències del sector. El pas dels refrigerants actuals a l'utilització de refrigerants alternatius no és immediat ni tampoc fàcil. La complexitat a nivell tecnològic és molt elevada, ja que l'ús d'un nou refrigerant exigeix dissenyar i desenvolupar de zero tots els components del circuit, tenint en conta que tenen unes especificacions i requeriments de funcionament totalment diferents dels que posseeixen els refrigerants actuals. La motivació principal de la tesi doctoral és la de plantejar el primers passos per al desenvolupament d'un equip de bomba de calor per a climatització que utilitzi un refrigerant amb un baix índex de PCA com el propà, en substitució del què empra la unitat actualment (R410A), reduint així l'impacte mediambiental de l'equip i millorant les seves propietats. Tot això es troba inclòs en els següents punts: - Anticipar el canvi de tecnologia necessari per al compliment de la regulació F-GAS, assegurant menors emissions per al medi ambient i mantenint l'eficiència energètica actual mitjançant el desenvolupament d'equips de bomba de calor amb capacitat de modulació i amb propà com a fluid refrigerant. - Desenvolupar ferramentes de modelatge i simulació per a les diferents plataformes objectiu. - Obtenir el coneixement específic sobre el comportament de la bomba de calor mitjançant l'anàlisi experimental amb prototips funcionals en les condicions de treball especificades, amb la intenció de conèixer el seu funcionament, a més de les seues limitacions i exigències pràctiques i les seues necessitats de control. - Facilitar el disseny i desenvolupament industrial de nous equips de climatització mitjançant les ferramentes de simulació i les dades experimentals obtingudes a través de prototips funcionals. Motivada per aquest nou escenari, aquesta tesi es centra a estudiar quines possibilitats hi ha al mitjá-llarg termini en el desenvolupament de bombes de calor per a ajustar-se a la regulació existent, no només en relació amb el requeriments ambientals sinó també energètics. Per això, el primer pas ha sigut el de fer una substitució directa del refrigerant original de la unitat aerotèrmica, el R410A, per R290 per establir el punt de referència i poder conèixer quines prestacions és capaç de desenvolupar aquesta mateixa unitat sense un redisseny del circuit de refrigerant. Després d'aquesta primera avaluació, s'ha dut a terme un estudi teòric de diferents configuracions de circuit frigorífic amb propà per avaluar els avantatges i inconvenients entre elles, amb l'objectiu de triar la que millor s'ajusti a l'acompliment dels objectius marcats. Aquest estudi s'ha efectuat en tres àmbits diferents: calefacció a baixa temperatura, alta temperatura i condicions d'alta temperatura d'impulsió d'aigua fins a 75ºC. En tots ells, el resultat principal que s'ha considerat ha sigut el d'eficiència, el que ha permès obtenir un ordre de les tipologies estudiades en funció dels resultats obtinguts. Tot i això, aquesta avaluació també ha posat de manifest una altra característica intrínseca a cada un d'ells com és el seu límit de funcionament en relació amb la màxima temperatura d'impulsió de calefacció. Després d'això, s'ha construït un prototip de bomba de calor funcional complet per executar la fase experimental, que inclogui fins a tres de les tipologies avaluades en la fase teòrica prèvia, perquè, amb tots els assajos pertinents, els resultats permeten seleccionar la tipologia de circuit de refrigerant que s'integri en un prototip final. Aquest prototip permetrà caracteritzar el funcionament de sistema tant per a una plataforma aire-aigua, com per a una plataforma salmorra-aigua, a través del canvi del bescanviador / [EN] Environmental regulations impose the use of refrigerants with less and less Global Warming Potential (GWP), and force that the search for alternative refrigerants in order to substitute the current ones is a real need according to the trends in the sector. The transition from current refrigerants to the use of alternative refrigerants is neither immediate nor simple. The complexity at the technological level is very high, since the use of a new refrigerant requires a new design and a new development for all the components along the refrigerant circuit, since they may have totally different specifications and operating requirements compared to the traditional refrigerants. The main motivation of this thesis is to present the initial stages concerning the development of a heat pump unit for space heating that uses a lo GWP refrigerant like propane, replacing the current refrigerant of the unit (R410A), leading to a reduction of the environmental impact of this equipment and improving its properties. All this has been included on the following points: - Anticipate the required technology change to be compliant with the F-GAS regulation, ensuring low-impact emissions to the atmosphere and keeping a similar energy efficiency through the development of heat pump units with heating capacity modulation and with propane as refrigerant. - Develop modelling and simulation tools for the different platforms approaches. - Obtain specific knowledge about the heat pump performance through experimental analysis with functional prototypes under the specified working conditions, with the aim of acquiring knowledge not only about its operation, but also about its limitations, practical requirements and its control needs. - Contribute to the industrial design and development of new space heating equipment using simulation tools and experimental data obtained through functional prototypes. Motivated by this new scenario, this thesis focuses on studying the available options in the medium-long term concerning the heat pump development in order to be compliant with the applicable regulations, not only in terms of environmental requirements but also energy requirements. To do this, the first step has been related to carry out a direct replacement of the original refrigerant of the aerothermal unit, R410A, with R290 to establish the reference point and to be able to know the performance of the original unit without considering a redesign of the refrigerant circuit. After this initial evaluation, a theoretical study of different refrigerant circuit configurations with propane has been carried out with the purpose of evaluating the advantages and disadvantages among them, in order to choose the one that fulfils the performance requirements the best. This study has been executed in three different areas: low heating temperature, high heating temperature and high water flow temperature conditions up to 75ºC. In all of them, the main result considered has been the efficiency, which has enabled to obtain a priority order based on the results obtained. Despite this, this evaluation has also revealed another attached feature, such as their operating limit in relation to the maximum heating flow temperature. After that, a complete functional heat pump prototype has been built to execute the experimental phase, which includes up to three of the typologies evaluated in the previous theoretical phase, so that, with all the corresponding tests, the results allow to select the typology of refrigerant circuit to be integrated into a final prototype. This prototype has also enabled the performance characterization for two different types of platforms, air-water and brine-water, by changing of the corresponding exchanger using cutting valves. In parallel to this, a certain phenomenon related to the behaviour of the refrigerant have been studied through different operating conditions for each typology as well as the proper measures to improve the system control. As / López Juárez, E. (2021). Desarrollo de una bomba de calor doméstica que usa propano como fluido de trabajo [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/174570