In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).

In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).

Single cell analysis devices have become important tools to obtain unique information on cells to improve current medical techniques, such as tissue engineering, or diagnosis of cancer at an early stage. This thesis documents the development of a "cell cross flow system" (CFS), which aims to capture magnetically tagged (MT) cells from a heterogeneous population of cells, and array these cells in pre-determined locations using magnetic force. The CFS integrates a “magnetic single cell micro array” (MSCMA), and a gasket assembly to achieve this. Current single cell technology, relevant fluid and magnetic theory, CFS design process, finite element method (FEM) simulation, and cross flow experiments are detailed in this thesis. The CFS was successful in capturing MT Jurkat cells, and the experimental results were consistent with the FEM simulation analysis. It was found that the CFS was capable of capturing MT Jurkat cells up to a ratio of 1 to 103 (MT to non-magnetically tagged cells) using a cell concentration of 105 cells/mL. Although these results are promising, non-magnetically tagged Jurkat cells were found to adhere to the chip and could not be easily removed. Several recommendations were suggested for future iterations, including changing the gasket assembly design, optimizing the flow rate and cell concentration, and using smaller trap sizes for the MSCMA design.

The goal of the present work was to identify and implement modifications to a density-based unstructured RANS CFD algorithm, as typically used in turbomachinery flows (represented here via the RoIIs-Royce 'Hydra' code), for application to Iow Mach number gas-turbine combustor flows. The basic algorithm was modified to make it suitable for combustor relevant problems. Fixed velocity and centreline boundary conditions were added using a characteristic based method. Conserved scalar mean and variance transport equations were introduced to predict scalar mixing in reacting flows. Finally, a flarnelet thermochemistry model for turbulent non-premixed combustion with an assumed shape pdf for turbulence-chemistry interaction was incorporated. A method was identified whereby the temperature/ density provided by the combustion model was coupled directly back into the momentum equations rather than from the energy equation. Three different test cases were used to validate the numerical capabilities of the modified code, for isothermal and reacting flows on different grid types. The first case was the jet in confined cross flow associated with combustor liner-dilution jetcore flow interaction. The second was the swirling flow through a multi-stream swirler. These cases represent the main aerodynamic features of combustor primary zones. The third case was a methane-fueled coaxial jet combustor to assess the combustion model implementation. This study revealed that, via appropriate modifications, an unstructured density-based approach can be utilised to simulate combustor flows. It also demonstrated that unstructured meshes employing nonhexahedral elements were inefficient at accurate capture of flow processes in regions combining rapid mixing and strong convection at angles to cell edges. The final version of the algorithm demonstrated that low Mach RANS reacting flow simulations, commonly performed using a pressure-based approach, can successfully be reproduced using a density-based approach.

Mikrosiebe stellen auf Grund ihrer Geometrie einen geringeren Strömungswiderstand im System dar und ermöglichen somit eine höhere Filtrationsgeschwindigkeit. Der Einsatz solcher Mikrosiebe anstelle herkömmlicher Membranen in Filtrationsprozessen kann deren Effizienz enorm steigern. Im Rahmen der Diplomarbeit wurden mittels partikelassistierter Benetzung hergestellte Mikrosiebe charakterisiert. Hierfür wurde zunächst ein Filtermodul für Kreuzstromfiltrationen entwickelt, welches anschließend in einen Versuchsaufbau integriert und charakterisiert wurde. Neben den Strömungswiderständen der rechteckigen Kanäle des Moduls wurde außerdem der Strömungswiderstand für Mikrosiebe einer Porengröße bestimmt und mit der Theorie verglichen. Es zeigt sich, dass Theorie und Praxis gut übereinstimmen und es sich bei dem entwickelten Versuchsaufbau um eine gute Methode handelt Strömungswiderstände von Mikrosieben zu bestimmen.

Concerning management of smoke following an accidental fire within a building it is desirable to be able to estimate, within some understood, acceptable magnitude of error, the volume of smoke resulting from the combustion process of a predefined design fire scenario. Traditionally a range of first principle-based and empirically derived correlations are used to estimate the mass flow of smoke at a height of interest within the fire plume and are based upon the understanding that the mass flow of smoke at that height is a function only of the gravitational vector within the fire system, that is to say, that induced by the pressure differential between the naturally occurring hot plume gases and the surrounding quiescent bulk fluid. The statement that the fire plume is surrounded by a quiescent bulk fluid is in itself a significant simplification and is a key assumption required to facilitate the relative simplicity of the Froude-based entrainment correlations. It is of course quite intuitive to imagine that in real accidental fire scenarios in the built environment and across an array modern infrastructure, rarely does a fire exist submerged in a passive, quiescent atmosphere. This disconnect between the natural mechanics of the buoyant fire mechanism and the surrounding fluid in which it exists was necessary when the problem of entrainment by the fire plume was first described in the mainstream engineering literature around the middle of the twentieth century. Some 25 years later as ideal entrainment mechanics were beginning to be discussed specifically for application by a field of engineering in its infancy, a few researchers in the field of fire safety engineering published data that suggested that the addition of a relatively weak cross flow to the fire plume could have a significant impact upon the rate of air entrained by the plume, and by extension, the resultant smoke mass flow rate. The data published appeared more as a brief comment on an observation made during testing. It would be easily missed, nuzzled away in the middle of a lengthy doctoral thesis. Said thesis however happens to be one of the primary pieces of work that may be cited in reference to the formulation of perhaps the best known form of the axis-symmetric fire plume entrainment correlation, that of the so-called Zukoski correlation. It is perhaps curious then that the mention of a 3-fold increase in entrainment measurements following “small disturbances” in the atmosphere during the experimental work has seemingly been ignored by researchers, probably never-learned by students, and apparently forgotten by an industry. In a fire situation smoke can limit way-finding ability, severely irritate critical soft tissue like the eyes, trachea and oesophagus, impair cognitive function, contribute to significant property damage, facilitate the transfer of heat and carcinogens to locations remote to the fire source and it is well understood that most deaths due to fire are caused by asphyxiation following smoke inhalation. Significant portions of project budgets may be spent on designing, validating, installing and maintaining smoke management systems including the use of active systems such as extraction and pressurisation, passive curtains/reservoirs and detection such aspirating, video and beam detectors. Turbulent atmospheres may arise in any manner of situations such as modern buildings with large open spaces (airports, museums), hotel foyers and those with atriums spanning many floors, hangars and storage facilities/warehouses. Strong winds are normal on offshore oil platforms, outside the window on most floors of super-tall buildings or quite simply, anywhere on a blustery day. In specific cases the extraction systems designed to remove smoke and even normal HVAC systems can cause substantial air flow over large areas. In fact, a simple compartment with an uneven distribution of ventilation points (windows/doorways) has been shown to result in a directional fire flow that results in a significantly tilted flame, essentially inducing a cross flow scenario using the natural fire alone. With the coming-of-age of computational fluid dynamics models which are now a standard tool in all commercial fire engineering design offices, and probably in every smoke modelling report, it might be argued that there is little need to revisit the hand calculations from the ground up. Accepting, however, that a cross flow may increase the rate of entrainment of a fire plume and that this challenges the fundamental principles that all previous entrainment correlation knowledge is based on, and demonstrating the outcome (in terms of plume mass flow rate) with the use of a computational model, is an entirely different thing to understanding why this happens. Smoke management is one of the core design criteria, or questions at least, in practically all fire engineering design projects. In the literature there appears to be; no work quantitatively investigating cross flow fire plume entrainment rates; no work qualitatively describing the behaviour of the flame / fire plume under the influence of a cross flow (with respect to entrainment); and certainly no work framing this paradigm in the theoretical or practical context of the impact upon modern smoke control systems. This work aims to venture into these areas in the hope of beginning to piece together the overarching story of entrainment in the cross flow fire plume. The fundamental paradigm here is the addition of cross flow inertia (a horizontal pressure differential) to the axis-symmetric case where buoyancy (a zero initial momentum, vertical pressure differential) is the sole driver of the fluid flow system. How these flows then interact in a mixed convection sequence is investigated and described in terms that are useful for practical consideration by fire safety engineers. It is hoped that the concepts postulated and the questions raised will inspire further investigation into this poorly understood, but fundamental fire safety problem.

Cette thèse s'inscrit dans le cadre des énergies renouvelables au sein du programme HARVEST centré sur le développement d'un concept d'hydrolienne dérivé des turbines Darrieus et Gorlov. L'ajout d'un dispositif appelé carénage à la turbine permet à celle-ci d'extraire une portion de l'énergie cinétique du courant plus grande. Toutefois ce dernier peut favoriser la cavitation qui nuit à la turbine. Parmi les différents axes du programme, les travaux de thèse se situent dans cette problématique. En régime subcavitant et cavitant, l'analyse de l'hydrolienne a été menée suivant une approche numérique et expérimentale. Pour ce faire deux outils ont été mis en place. Du coté expérimental, le tunnel hydrodynamique du LEGI a été équipé d'une balance qui donne la mesure instantanée des forces et du couple qui s'exercent sur la turbine. Du coté numérique, les efforts ont été orientés sur l'amélioration et le développement du code de calcul universitaire, CAVKA. L'utilisation intensive de ces deux moyens, couplée à des modèles théoriques, a permis de mettre en évidence d'une part le fonctionnement de la turbine libre ou carénée et, d'autre part, les limites de fonctionnement vis-à-vis de la cavitation. / The general context of the present thesis is renewable energies within the HARVEST project, which consists in a water current turbine (WCT) development, inspired from the Darrieus and Gorlov geometries. The main advantage of the HARVEST WCT is the introduction of a channelling device, which allows extracting a bigger amount of the kinetic energy contained in the flowstream. However, the shrouding device can eventually increase cavitating risks, which generally damage the WCT itself and its performance. The main topic of this work is cavitation. The hydrodynamic behavior of the WCT is analyzed both numerically and experimentally, in non cavitating and cavitating conditions. For this analysis, two devices have been developed. On the one hand, the LEGI hydrodynamic channel is equipped with a measurement platform which provides the instantaneous and average measurements of two dimensional thrusts as well as the hydrodynamic torque. On the other hand, in the numerical domain, the work has been oriented to the improvement and the development of a CFD code, named Cavka. The intensive utilisation of these two devices, coupled to theoretical models, allow highlighting the functioning of the bare and shrouded WCTs and their limits in cavitating conditions.

Le but de cette thèse est le développement et l'optimisation de la chaine électrique d'une hydrolienne fluviale. L'approche est d'abord traitée en simulation pour ensuite finir par la conception et la mise au point d'un prototype. La partie simulation concerne la modélisation des ensembles turbines, génératrices et électronique de puissance mais aussi le développement des diverses lois de commandes. Ces commandes peuvent intervenir à différents niveaux du contrôle jusqu'à la supervision complète du système, permettant de gérer des défauts, des algorithmes de MPPT (extraction maximale de puissance), des synchronisations entre colonne, ... Le prototype d'hydrolienne fluviale sera ensuite présenté, de la mise au point des parties mécaniques jusqu'aux résultats expérimentaux. Les travaux nombreux autour de ce prototype ont permis d'obtenir des résultats satisfaisants et encourageants qui corroborent la théorie. / The purpose of this thesis is the development and optimization of the electrical system of a fluvial cross-flow current turbine. The approach is first treated in simulation and then eventually with the design and development of a prototype. The simulation section deals with the modeling of turbines groups, generators and power electronics, as well as the development of various control laws. These controls may have an influence at different levels of the control strategies up to the complete system supervision for fault management, MPPT (maximum power extraction) algorithms, turbine columns synchronization... The fluvial cross-flow current turbine prototype will then be presented, from the development of the mechanical parts to the experimental results. The various works involving the prototype have yielded satisfactory and encouraging results that corroborate the theory.

Estima-se que nos próximos 20 anos a energia hidráulica contribuirá com quase 30% da energia elétrica do planeta, atualmente esta participação é de 19%. Muitos países possuem iniciativas sérias de implementação de Pequenas Centrais Hidrelétricas, quer seja a médio ou a longo prazo. No Brasil, particularmente, um novo programa de incentivo as pequenas centrais hidrelétricas está sendo lançado pela ELETROBRÁS. Porém, a previsão do número de usinas de pequeno porte e a potência total a ser instalada dentro do plano decenal, 1997 2006, de geração é relativamente pequeno (15 PCH somando 93,71 MW de possíveis 2.161 totalizando 3.633 MW Fonte: SIPOT- ELETROBRÁS abr / 98). A média do consumo de energia elétrica por habitante no Brasil está abaixo da média do consumo mundial (1805 kWh/ano para 2160 kWh/ano. (Fontes: SIESE-Síntese anual 1999 e International Energy Outlook 1998 DOE / EIA). Quando comparamos as várias regiões do território brasileiro a discrepância se torna ainda maior. Vários tipos de turbinas hidráulicas podem ser usadas em pequenas, mini e micro centrais hidroelétricas, entre as quais podemos destacar: Pelton, Francis, Turgo, Kaplan, Hélice, Banki etc. No Brasil as mais utilizadas são: Francis e Kaplan seguidas de longe pela Pelton. O uso dos demais tipos é quase que desconhecido, principalmente a Turgo. A turbina de fluxo cruzado, também conhecida pelos nomes de: MichellBanki, Banki e MichellOssberger é definida como uma turbina de ação que pode ser instalada com quedas de 1 a 200 m de altura e vazões de 0,025 a 13 m3/s. Com a evolução apresentada principalmente nas últimas duas décadas por firmas tradicionais como: Ossberger Turbinenfabrick ou mais novas como a CINK, pode alcançar diâmetros de rotores próximos de 1,0 m com largura de até 3,0m e desenvolver potência de até 2000 kW, com rendimentos que já podem chegar a 90%. As principais evoluções estão concentradas em modificações no injetor da turbina, emprego de novos materiais nas pás, eixo e rolamentos do rotor e em tentativas de utilização do tubo de sucção. Um dos estudos de mostra a viabilidade técnica e econômica na implantação de uma turbina de fluxo cruzado em comparação com as turbinas Francis e Kaplan. As conclusões serão relatadas após a análise de viabilidade técnico-econômica entre os três tipos de turbinas. / It is forecasted that in next 20 years the hydraulic energy will contribute with almost 30% of the total electric power of the planet, while this participation is today near 19%. Many countries have firm initiatives of implementation on SHPs, in medium or long terms. In Brazil, a new incentive program for SHPs is being introduced by ELETROBRAS. However, the forecast for the number of small plants and output installed into Ten-Year Expansion Plan of Energy to the year 2006 is relatively small (15 SHP amount to 93.71 MW, compared to feasible levels of 2,161 SHPs and 3,633 MW. (Source: SIPOTELETROBRAS april / 98). The average electric power consumption per inhabitant in Brazil is below of the world average consumption (1,805 kWh/year against 2,160 kWh/year. Source: SIESE - Annual summary 1999 and International Energy Outlook 1998 DOE/EIA) and when compared with the different regions of the Brazilian territory this discrepancy becomes still larger. Several types of hydraulic turbines can be used in small hydropower, as Pelton, Francis, Turgo, Kaplan, Propeller, Banki, etc. In Brazil the more used are Francis and Kaplan followed by Pelton. The usage of the other types is almost that unknown, mainly the Turgo turbine. The cross flow turbine, also known by the names of: MichellBanki, Banki, and MichellOssberger is defined as an action turbine that can be applicable to falls from 1 to 200 m and flows from 0,025 to 13 m3/s. With the evolution technical presented mainly in the last two decades by traditional firms like Ossberger Turbinenfabrik and new firms like CINK, that turbine can reach diameters of rotors of 1,0 m with width of 2,6m and to develop capacity up to 2,000 kW, with efficiency near 90%. The main evolutions are concentrated in modifications presented in the injector of the turbine by several manufacturers, and the use of new materials in the blades of the runner, shafts, bearings and the use of the draft tube. Case study shows the technical and economical implications using a cross flow turbine in comparison to a Francis turbine and a Kaplan. The conclusions will be reported after technical and economical viability analysis among the three types of turbines.

There is a growing interest in tidal energy, owing to its predictable nature in comparison to other renewable sources. In the case of the UK, its importance also lies on the availability of exploitable areas as well as their total capacity, which is estimated to cover more than 20% of the country demand. However, the level of development of this kind of technology is still far behind other types of renewable energy. However, several studies focused on a variety of individual devices, followed by more recent research on the deployment of large arrays or tidal farms. Potential sites for energy extraction can be found in narrows between islands and the coast or estuaries. The latter present some advantages for the installation and the connection to the grid but estuaries are often prone to flood risk from tides and surges. Therefore, the objective of this thesis is to evaluate the effect that very large groups of turbines could have on peak water levels during flooding events in the case of being deployed in estuarine areas. For that purpose, a new methodology has been developed, which implies the use of a numerical model (MIKE 21 by DHI), and it has been demonstrated against a real case study in the UK: the Solway Firth estuary. Another objective has consisted of integrating in this thesis the results from detailed CFD modelling and optimisation techniques involved in the project. A literature review has been carried out in order to identify the current state of the art for the different subjects considered in the thesis. Different aspects of the numerical model used for this study (MIKE 21) have been presented and the modelling of the turbines within the code has been validated against experimental and CFD data. The procedure to include large numbers of turbines in the code is also developed. An analysis has been done of the different estuaries existing in the UK suitable for tidal energy extraction, identifying their main geometrical features. Based on this, idealised models of estuaries have been used to assess the influence that the channel geometry could have on the impact of tidal farms under extreme water levels. The effect has been measured by comparing the results of the numerical model between the case with and without turbines under different flooding scenarios. Finally, the same methodology has been applied to a real case study selected from the previous group of estuaries namely the Solway Firth. An initial model has been created, according to the available data at the start of the research, which contained some errors related to the water depth at the intertidal areas in the upper estuary. Therefore, when a more realistic dataset became available, an improved model was created. The improved model has been used to assess the effects of tidal farms in the estuary under a coastal flooding event. It is concluded that there is significant influence of the channel geometry over the locations where the maximum changes in water levels due to the tidal farms will happen. Nevertheless, the effects seem to be more relevant in terms of the decrease rather than the increase of peak water levels for all geometries and the maximum changes seem to be in the order of dm. This is in agreement with the results of the Solway Firth models and can be summarised as a positive net effect over flood risk. On the other hand, a concern has been raised about the impact on intertidal areas, which could be the subject of future research.