A resistance emulation approach to optimize the wave energy harvesting for a direct drive point absorber

In general, a major challenge for the exploitation of renewable energies is to improve their efficiency. In electricity generation from the energy of ocean waves, not unlike other technologies, the converter must be optimized to make the energy harvesting economically feasible. This paper proposes a passive tuning control strategy of a point absorber in which the power captured is maximized by controlling the electromagnetic force of the generator with a resistance emulation approach. The proposed strategy consists of mapping the optimal values for regular waves and applying them to irregular waves. This strategy is tested in a wave energy converter in which the generator is connected to a boost rectifier converter whose controller is designed to emulate a resistance. The power electronics system implemented is validated by comparing its performance with the case in which the generator is directly connected to a resistive load. The simulation results show the effectiveness of the proposed strategy as the maximum captured power is concentrated around the optimal values previously calculated and with the same behavior for both excitations.

Tuning the current ratio of a CPV system to maximize the energy harvesting in a particular location

A method based on experimental data is proposed to optimize the energy harvesting of a silicone-on-glass Fresnel-lens based CPV system. It takes into account the spectral variations along the year in a particular location as well as the thermal and spectral sensitivities of the optics and solar cell. In addition, different alternatives to tune the top/middle subcells current ratio in a CPV module are analyzed and their capacity to maximize the annually produced energy is quantified.

Localization and Tracking in Energy-Constrained Networks with Dynamic Connectivity

Systems used for target localization, such as goods, individuals, or animals, commonly rely on operational means to meet the final application demands. However, what would happen if some means were powered up randomly by harvesting systems? And what if those devices not randomly powered had their duty cycles restricted? Under what conditions would such an operation be tolerable in localization services? What if the references provided by nodes in a tracking problem were distorted? Moreover, there is an underlying topic common to the previous questions regarding the transfer of conceptual models to reality in field tests: what challenges are faced upon deploying a localization network that integrates energy harvesting modules? The application scenario of the system studied is a traditional herding environment of semi domesticated reindeer (Rangifer tarandus tarandus) in northern Scandinavia. In these conditions, information on approximate locations of reindeer is as important as environmental preservation. Herders also need cost-effective devices capable of operating unattended in, sometimes, extreme weather conditions. The analyses developed are worthy not only for the specific application environment presented, but also because they may serve as an approach to performance of navigation systems in absence of reasonably accurate references like the ones of the Global Positioning System (GPS). A number of energy-harvesting solutions, like thermal and radio-frequency harvesting, do not commonly provide power beyond one milliwatt. When they do, battery buffers may be needed (as it happens with solar energy) which may raise costs and make systems more dependent on environmental temperatures. In general, given our problem, a harvesting system is needed that be capable of providing energy bursts of, at least, some milliwatts. Many works on localization problems assume that devices have certain capabilities to determine unknown locations based on range-based techniques or fingerprinting which cannot be assumed in the approach considered herein. The system presented is akin to range-free techniques, but goes to the extent of considering very low node densities: most range-free techniques are, therefore, not applicable. Animal localization, in particular, uses to be supported by accurate devices such as GPS collars which deplete batteries in, maximum, a few days. Such short-life solutions are not particularly desirable in the framework considered. In tracking, the challenge may times addressed aims at attaining high precision levels from complex reliable hardware and thorough processing techniques. One of the challenges in this Thesis is the use of equipment with just part of its facilities in permanent operation, which may yield high input noise levels in the form of distorted reference points. The solution presented integrates a kinetic harvesting module in some nodes which are expected to be a majority in the network. These modules are capable of providing power bursts of some milliwatts which suffice to meet node energy demands. The usage of harvesting modules in the aforementioned conditions makes the system less dependent on environmental temperatures as no batteries are used in nodes with harvesters--it may be also an advantage in economic terms. There is a second kind of nodes. They are battery powered (without kinetic energy harvesters), and are, therefore, dependent on temperature and battery replacements. In addition, their operation is constrained by duty cycles in order to extend node lifetime and, consequently, their autonomy. There is, in turn, a third type of nodes (hotspots) which can be static or mobile. They are also battery-powered, and are used to retrieve information from the network so that it is presented to users. The system operational chain starts at the kinetic-powered nodes broadcasting their own identifier. If an identifier is received at a battery-powered node, the latter stores it for its records. Later, as the recording node meets a hotspot, its full record of detections is transferred to the hotspot. Every detection registry comprises, at least, a node identifier and the position read from its GPS module by the battery-operated node previously to detection. The characteristics of the system presented make the aforementioned operation own certain particularities which are also studied. First, identifier transmissions are random as they depend on movements at kinetic modules--reindeer movements in our application. Not every movement suffices since it must overcome a certain energy threshold. Second, identifier transmissions may not be heard unless there is a battery-powered node in the surroundings. Third, battery-powered nodes do not poll continuously their GPS module, hence localization errors rise even more. Let's recall at this point that such behavior is tight to the aforementioned power saving policies to extend node lifetime. Last, some time is elapsed between the instant an identifier random transmission is detected and the moment the user is aware of such a detection: it takes some time to find a hotspot. Tracking is posed as a problem of a single kinetically-powered target and a population of battery-operated nodes with higher densities than before in localization. Since the latter provide their approximate positions as reference locations, the study is again focused on assessing the impact of such distorted references on performance. Unlike in localization, distance-estimation capabilities based on signal parameters are assumed in this problem. Three variants of the Kalman filter family are applied in this context: the regular Kalman filter, the alpha-beta filter, and the unscented Kalman filter. The study enclosed hereafter comprises both field tests and simulations. Field tests were used mainly to assess the challenges related to power supply and operation in extreme conditions as well as to model nodes and some aspects of their operation in the application scenario. These models are the basics of the simulations developed later. The overall system performance is analyzed according to three metrics: number of detections per kinetic node, accuracy, and latency. The links between these metrics and the operational conditions are also discussed and characterized statistically. Subsequently, such statistical characterization is used to forecast performance figures given specific operational parameters. In tracking, also studied via simulations, nonlinear relationships are found between accuracy and duty cycles and cluster sizes of battery-operated nodes. The solution presented may be more complex in terms of network structure than existing solutions based on GPS collars. However, its main gain lies on taking advantage of users' error tolerance to reduce costs and become more environmentally friendly by diminishing the potential amount of batteries that can be lost. Whether it is applicable or not depends ultimately on the conditions and requirements imposed by users' needs and operational environments, which is, as it has been explained, one of the topics of this Thesis.

Determination of Maximum Mechanical Energy Efficiency in Energy Galloping Systems

Transverse galloping is a type of aeroelastic instability characterized by large amplitude, low frequency, normal to wind oscillations that appear in some elastic two-dimensional bluff bodies when subjected to a fluid flow, provided that the flow velocity exceeds a threshold critical value. Such an oscillatory motion is explained because of the energy transfer from the flow to the two-dimensional bluff body. The 7 amount of energy that can be extracted depends on the cross section of the galloping prism. Assuming that the Glauert-Den Hartog quasistatic criterion for galloping instability is satisfied in a first approximation, the suitability of a given cross section for energy harvesting is evaluated by analyzing the lateral aerodynamic force coefficient, fitting a function with a power series in tan a (a being the angle of attack) to 10 available experimental data. In this paper, a fairly large number of simple prisms (triangle, ellipse, biconvex, and rhombus cross sections, as well 11 as D-shaped bodies) is analyzed for suitability as energy harvesters. The influence of the fitting process in the energy harvesting efficiency evaluation is also demonstrated. The analysis shows that the more promising bodies are those with isosceles or approximate isosceles cross sections.

Energy and power aware scheduling algorithm modeling for battery powered embedded systems

Energy management has always been recognized as a challenge in mobile systems, especially in modern OS-based mobile systems where multi-functioning are widely supported. Nowadays, it is common for a mobile system user to run multiple applications simultaneously while having a target battery lifetime in mind for a specific application. Traditional OS-level power management (PM) policies make their best effort to save energy under performance constraint, but fail to guarantee a target lifetime, leaving the painful trading off between the total performance of applications and the target lifetime to the user itself. This thesis provides a new way to deal with the problem. It is advocated that a strong energy-aware PM scheme should first guarantee a user-specified battery lifetime to a target application by restricting the average power of those less important applications, and in addition to that, maximize the total performance of applications without harming the lifetime guarantee. As a support, energy, instead of CPU or transmission bandwidth, should be globally managed as the first-class resource by the OS. As the first-stage work of a complete PM scheme, this thesis presents the energy-based fair queuing scheduling, a novel class of energy-aware scheduling algorithms which, in combination with a mechanism of battery discharge rate restricting, systematically manage energy as the first-class resource with the objective of guaranteeing a user-specified battery lifetime for a target application in OS-based mobile systems. Energy-based fair queuing is a cross-application of the traditional fair queuing in the energy management domain. It assigns a power share to each task, and manages energy by proportionally serving energy to tasks according to their assigned power shares. The proportional energy use establishes proportional share of the system power among tasks, which guarantees a minimum power for each task and thus, avoids energy starvation on any task. Energy-based fair queuing treats all tasks equally as one type and supports periodical time-sensitive tasks by allocating each of them a share of system power that is adequate to meet the highest energy demand in all periods. However, an overly conservative power share is usually required to guarantee the meeting of all time constraints. To provide more effective and flexible support for various types of time-sensitive tasks in general purpose operating systems, an extra real-time friendly mechanism is introduced to combine priority-based scheduling into the energy-based fair queuing. Since a method is available to control the maximum time one time-sensitive task can run with priority, the power control and time-constraint meeting can be flexibly traded off. A SystemC-based test-bench is designed to assess the algorithms. Simulation results show the success of the energy-based fair queuing in achieving proportional energy use, time-constraint meeting, and a proper trading off between them. La gesti��n de energ��a en los sistema m��viles est�� considerada hoy en d��a como un reto fundamental, not��ndose, especialmente, en aquellos terminales que utilizando un sistema operativo implementan m��ltiples funciones. Es com��n en los sistemas m��viles actuales ejecutar simultaneamente diferentes aplicaciones y tener, para una de ellas, un objetivo de tiempo de uso de la bater��a. Tradicionalmente, las pol��ticas de gesti��n de consumo de potencia de los sistemas operativos hacen lo que est�� en sus manos para ahorrar energ��a y satisfacer sus requisitos de prestaciones, pero no son capaces de proporcionar un objetivo de tiempo de utilizaci��n del sistema, dejando al usuario la dif��cil tarea de buscar un compromiso entre prestaciones y tiempo de utilizaci��n del sistema. Esta tesis, como contribuci��n, proporciona una nueva manera de afrontar el problema. En ella se establece que un esquema de gesti��n de consumo de energ��a deber��a, en primer lugar, garantizar, para una aplicaci��n dada, un tiempo m��nimo de utilizaci��n de la bater��a que estuviera especificado por el usuario, restringiendo la potencia media consumida por las aplicaciones que se puedan considerar menos importantes y, en segundo lugar, maximizar las prestaciones globales sin comprometer la garant��a de utilizaci��n de la bater��a. Como soporte de lo anterior, la energ��a, en lugar del tiempo de CPU o el ancho de banda, deber��a gestionarse globalmente por el sistema operativo como recurso de primera clase. Como primera fase en el desarrollo completo de un esquema de gesti��n de consumo, esta tesis presenta un algoritmo de planificaci��n de encolado equitativo (fair queueing) basado en el consumo de energ��a, es decir, una nueva clase de algoritmos de planificaci��n que, en combinaci��n con mecanismos que restrinjan la tasa de descarga de una bater��a, gestionen de forma sistem��tica la energ��a como recurso de primera clase, con el objetivo de garantizar, para una aplicaci��n dada, un tiempo de uso de la bater��a, definido por el usuario, en sistemas m��viles empotrados. El encolado equitativo de energ��a es una extensi��n al dominio de la energ��a del encolado equitativo tradicional. Esta clase de algoritmos asigna una reserva de potencia a cada tarea y gestiona la energ��a sirvi��ndola de manera proporcional a su reserva. Este uso proporcional de la energ��a garantiza que cada tarea reciba una porci��n de potencia y evita que haya tareas que se vean privadas de recibir energ��a por otras con un comportamiento m��s ambicioso. Esta clase de algoritmos trata a todas las tareas por igual y puede planificar tareas peri��dicas en tiempo real asignando a cada una de ellas una reserva de potencia que es adecuada para proporcionar la mayor de las cantidades de energ��a demandadas por per��odo. Sin embargo, es posible demostrar que s��lo se consigue cumplir con los requisitos impuestos por todos los plazos temporales con reservas de potencia extremadamente conservadoras. En esta tesis, para proporcionar un soporte m��s flexible y eficiente para diferentes tipos de tareas de tiempo real junto con el resto de tareas, se combina un mecanismo de planificaci��n basado en prioridades con el encolado equitativo basado en energ��a. En esta clase de algoritmos, gracias al m��todo introducido, que controla el tiempo que se ejecuta con prioridad una tarea de tiempo real, se puede establecer un compromiso entre el cumplimiento de los requisitos de tiempo real y el consumo de potencia. Para evaluar los algoritmos, se ha dise��ado en SystemC un banco de pruebas. Los resultados muestran que el algoritmo de encolado equitativo basado en el consumo de energ��a consigue el balance entre el uso proporcional a la energ��a reservada y el cumplimiento de los requisitos de tiempo real.

Jupiter power generation with electrodynamic tethers at constant orbital energy

An electrodynamic tether system for power generation at Jupiter is presented that allows extracting energy from Jupiter's corotating plasmasphere while leaving the system orbital energy unaltered to first order. The spacecraft is placed in a polar orbit with the tether spinning in the orbital plane so that the resulting Lorentz force, neglecting Jupiter's magnetic dipole tilt, is orthogonal to the instantaneous velocity vector and orbital radius, hence affecting orbital inclination rather than orbital energy. In addition, the electrodynamic tether subsystem, which consists of two radial tether arms deployed from the main central spacecraft, is designed in such a way as to extract maximum power while keeping the resulting Lorentz torque constantly null. The power-generation performance of the system and the effect on the orbit inclination is evaluated analytically for different orbital conditions and verified numerically. Finally, a thruster-based inclination-compensation maneuver at apoapsis is added, resulting in an efficient scheme to extract energy from the plasmasphere of the planet with minimum propellant consumption and no inclination change. A tradeoff analysis is conducted showing that, depending on tether size and orbit characteristics, the system performance can be considerably higher than conventional power-generation methods.

Analytical study and evaluation results of power optimizers for distributed power conditioning in PV arrays

The use of modular or ���micro��� maximum power point tracking (MPPT) converters at module level in series association, commercially known as ���power optimizers���, allows the individual adaptation of each panel to the load, solving part of the problems related to partial shadows and different tilt and/or orientation angles of the photovoltaic (PV) modules. This is particularly relevant in building integrated PV systems. This paper presents useful behavioural analytical studies of cascade MPPT converters and evaluation test results of a prototype developed under a Spanish national research project. On the one hand, this work focuses on the development of new useful expressions which can be used to identify the behaviour of individual MPPT converters applied to each module and connected in series, in a typical grid-connected PV system. On the other hand, a novel characterization method of MPPT converters is developed, and experimental results of the prototype are obtained: when individual partial shading is applied, and they are connected in a typical grid connected PV array

Single-Stage Grid-Connected Forward Microinverter with Boundary Mode Control

This paper presents a microinverter to be integrated into a solar module. The proposed solution combines a forward converter and a constant off-time boundary mode control, providing MPPT capability and unity power factor in a single-stage converter. The transformer structure of the power stage remains as in the classical DC-DC forward converter. Transformer primary windings are utilized for power transfer or demagnetization depending on the grid semi-cycle. Furthermore, bidirectional switches are used on the secondary side allowing direct connection of the inverter to the grid. Design considerations for the proposed solution are provided, regarding the inductance value, transformer turns ratio and frequency variation during a line semi-cycle. The decoupling of the twice the line frequency power pulsation is also discussed, as well as the maximum power point tracking (MPPT) capability. Simulation and experimental results for a 100W prototype are enclosed

Modelado de materiales piezoel��ctricos para aplicaciones de autoalimentaci��n en entornos viales

Este proyecto continua con el estudio iniciado en los proyectos: Alimentaci��n ���Energy Harvesting��� basada en fuentes piezoel��ctricas, Alimentaci��n aut��noma: aplicaci��n a fuente piezoel��ctrica y Banco de pruebas para sistemas autoalimentados en aplicaciones viales, que se realizaron anteriormente. Este estudio se basa en la b��squeda de soluciones de alimentaci��n Energy Harvesting centrados en fuentes piezoel��ctricas. El objetivo de este estudio es conocer las posibilidades que pueden ofrecer los materiales piezoel��ctricos para alimentaci��n aut��noma cuando son excitados por veh��culos en diferentes circunstancias y entornos viales. Para la realizaci��n de este estudio se han utilizado se��ales provenientes del banco de ensayos, as�� como se��ales obtenidas de una instalaci��n construida en un vial del Campus. Para poder realizar el estudio de los diversos materiales piezoel��ctricos utilizados en este proyecto, se necesitan conocer las caracter��sticas de los modelos el��ctricos. Para obtener estas caracter��sticas se ha dise��ado un programa basado en LabView, este programa adem��s puede modificar la se��al para que simule las diversas circunstancias a las que pueden estar sometidos los diferentes materiales piezoel��ctricos. En este estudio se ha tenido en cuenta la distancia de seguridad entre veh��culos para diferentes velocidades y la posibilidad de poder amplificar la excitaci��n que pueden recibir los diversos materiales. Utilizando el programa PSpice OrCAD�� se realizan los diferentes modelos con el objetivo de observar el comportamiento de los materiales bajo diversas circunstancias. Tambi��n se han utilizado varias topolog��as rectificadoras diferentes para poder comprobar en que situaci��n se puede obtener la m��xima tensi��n acumulada posible. Adem��s tambi��n se ha evaluado la m��xima potencia que puede entregar cada material en cada situaci��n. Por ultimo se han realizado varias pruebas pr��cticas con el banco de ensayos para comprobar la acumulaci��n energ��tica real que se puede obtener de los materiales instalados en ��l. Tambi��n se ha realizado el estudio de una aplicaci��n pr��ctica que sea capaz de alimentar peque��os circuitos o sensores de poco consumo. Abstract This Project goes on with the study started in the projects Feeding ���Energy Harvesting��� based on piezoelectric sources, independent feeding: application to piezoelectric source and testing bench to self fed systems in roads applications that were previously done. This study is based on the search of feeding solutions Energy Harvesting focus on piezoelectric sources. The aim of this study is know the different piezoelectric materials possibilities that can offer to independent feeding when different circumstances and road surroundings are excited by vehicles in. To develop this study several signals of the testing bench have been used and also signals get from an installation constructed on a Campus road. As far as the study of the different piezoelectric materials used in this project is concerned we should know the electrical models features. In order to obtain these characteristics a program based on LabView was designed, this program can modify the signal so that it simulates the diverse circumstances to which they can be put under the different piezoelectric materials. In this study I have bearded in mind the safe distance between vehicles for different speeds and the possibility of being able to amplify the excitation that can receive the diverse materials. Using the program PSpice OrCAD�� the different models with the objective are made to observe the behaviour of the materials under diverse circumstances. Also several different rectifying topologies have been used to be able to verify the maximum overvoltage accumulated. In addition I have assessed the maximum power that can give each material in each situation. Last but not least different practical proofs with the testing bench have been done to check the actual energy accumulation that can be obtained from the materials installed on it. Also the study of a practical application has been made that is able to feed small circuits or low consumption sensor.

Caracterizaci��n y modelado de grandes centrales fotovoltaicas

La presente tesis doctoral propone un conjunto de ensayos de corta duraci��n destinados a cubrir la ausencia de est��ndares internacionales espec��ficamente adaptados a la tecnolog��a y al panorama fotovoltaico actual que indiquen como realizar los procedimientos de control de calidad para comprobar que las grandes centrales fotovoltaicas ejecutadas responden a las expectativas establecidas durante la fase de proyecto. Dichos ensayos buscan, desde el punto de vista estrictamente t��cnico, obtener en un corto periodo de tiempo (t��picamente una semana) resultados altamente repetitivos y representativos del comportamiento de la instalaci��n bajo an��lisis, a la vez que minimizar al m��ximo la incertidumbre global, aspectos fundamentales para los procedimientos de control general de la calidad de una central. Los ensayos propuestos comprueban tanto el comportamiento general de la central, en t��rminos de su capacidad de producci��n energ��tica, como el de sus principales componentes, generadores fotovoltaicos e inversores, en t��rminos de potencia m��xima y eficiencia, respectivamente. Tambi��n se aconseja una revisi��n de la calidad y seguridad de la instalaci��n y de los materiales empleados en la ejecuci��n de la central para evitar un envejecimiento prematuro de los mismos. Todos los ensayos recogidos en el texto se apoyan en la experiencia recopilada por el ���Grupo de Sistemas Fotovoltaicos del Instituto de Energ��a Solar de la Universidad Polit��cnica de Madrid���, que ha estado involucrado en procedimientos de control de calidad de unas 50 centrales fotovoltaicas, con una potencia acumulada cercana a 250 MW, la mayor��a de ellas instaladas en Espa��a. ABSTRACT This PhD thesis proposes a set of short-duration tests to establish quality control procedures to ensure that large photovoltaic plants fulfil the initial expectations. The motivation for this work is the lack of international standards specifically adapted to the present photovoltaic technology and its state of the art. From a strict technical point of view, these tests seek to obtain highly repetitive and representative results about the behaviour of the installation under study in a short period of time (typically one single week); and to minimize the global uncertainty. These are the two keys aspects required in quality control procedures. The proposed tests evaluate the general behaviour of the photovoltaic plants, in terms of energy production, as well as the particular behaviour of their main devices, photovoltaic arrays and inverters, in terms of maximum power and efficiency, respectively. A review of the installation quality and safety, and the employed materials in its execution to avoid premature aging is also recommended. The tests here presented are based on the experience accumulated by the ���Grupo de Sistemas Fotovoltaicos del Instituto de Energia Solar de la Universidad Politecnica de Madrid���. This group has been involved in quality control procedures of about 50 photovoltaic plants, with an accumulated power close to 250 MW, most of them installed in Spain.

Pre-Feasibility Study of Hybrid Wind Power-H-2 System Connected to Electrical Grid

The growth of wind power as an electric energy source is profitable from an environmental point of view and improves the energetic independence of countries with little fossil fuel resources. However, the wind resource randomness poses a great challenge in the management of electric grids. This study raises the possibility of using hydrogen as a mean to damp the variability of the wind resource. Thus, it is proposed the use of all the energy produced by a typical wind farm for hydrogen generation, that will in turn be used after for suitable generation of electric energy according to the operation rules in a liberalized electric market.

Modeling Piezoelectric Harvesting Materials in Road Traffic Applications.

En esta comunicaci��n se presenta el m��todo para obtener modelos equivalentes el��ctricos de materiales piezoel��ctricos utilizados en entornos con tr��fico vial para aplicaciones "Energy Harvesting". Los resultados experimentales se procesan para determinar la estructura topol��gica ��ptima y la tecnolog��a de los elementos semiconductores utilizados en la etapa de entrada del sistema de alimentaci��n "harvesting". Asimismo se presenta el modelo de la fuente de alimentaci��n no regulada bajo demanda variable de corriente. Abstract: The method to obtain electrical equivalent models of piezoelectric materials used in energy harvesting road traffic environment is presented in this paper. The experimental results are processed in order to determine the optimal topological structure and technology of the semiconductor elements used in the input stage of the power harvesting system. The non regulated power supply model under variable current demand is also presented.

Transport and mixing enhancement in fluid-thermal microsystems

En esta tesis se investiga de forma experimental el transporte pasivo de magnitudes f��sicas en micro-sistemas con car��cter de inmediata aplicaci��n industrial, usando m��todos innovadores para mejorar la eficiencia de los mismos optimizando par��metros cr��ticos del dise��o o encontrar nuevos destinos de posible aplicaci��n. Parte de los resultados obtenidos en estos experimentos han sido publicados en revistas con un ��ndice de impacto tal que pertenecen al primer cuarto del JCR. Primero de todo se ha analizado el efecto que produce en un intercambiador de calor basado en micro-canales el hecho de dejar un espacio entre canales y tapa superior para la interconexi��n de los mismos. Esto genera efectos tridimensionales que mejoran la exracci��n de calor del intercambiador y reducen la ca��da de presi��n que aparece por el transcurso del fluido a trav��s de los micro-canales, lo que tiene un gran impacto en la potencia que ha de suministrar la bomba de refrigerante. Se ha analizado tambi��n la mejora producida en t��rminos de calor disipado de un micro-procesador refrigerado con un ampliamente usado plato de aletas al implementar en ��ste una c��mara de vapor que almacena un fluido bif��sico. Se ha desarrollado de forma paralela un modelo num��rico para optimizar las nuevas dimensiones del plato de aletas modificado compatibles con una serie de requerimientos de dise��o en el que tanto las dimensiones como el peso juegan un papel esencial. Por otro lado, se han estudiado los fenomenos fluido-din��micos que aparecen aguas abajo de un cuerpo romo en el seno de un fluido fluyendo por un canal con una alta relaci��n de bloqueo. Los resultados de este estudio confirman, de forma experimental, la existencia de un r��gimen intermedio, caracterizado por el desarrollo de una burbuja de recirculaci��n oscilante entre los reg��menes, bien diferenciados, de burbuja de recirculaci��n estacionaria y calle de torbellinos de Karman, como funci��n del n��mero de Reynolds del flujo incidente. Para la obtenci��n, an��lisis y post-proceso de los datos, se ha contado con la ayuda de un sistema de Velocimetr��a por Im��genes de Part��culas (PIV). Finalmente y como adici��n a este ��ltimo punto, se ha estudiado las vibraciones de un cuerpo romo producidas por el desprendimiento de torbellinos en un canal de alta relaci��n de bloqueo con la base obtenida del estudio anterior. El prisma se mueve con un movimiento arm��nico simple para un intervalo de n��meros de Reynolds y este movimiento se transforma en vibraci��n alrededor de su eje a partir de un ciero n��mero de Reynolds. En relaci��n al fluido, el r��gimen de desprendimiento de torbellinos se alcanza a menores n��meros de Reynolds que en el caso de tener el cuerpo romo fijo. Uniendo estos dos registros de movimientos y variando la relaci��n de masas entre prisma y fluido se obtiene un mapa con diferentes estados globales del sistema. Esto no solo tiene aplicaci��n como m��todo para promover el mezclado sino tambi��n como m��todo para obtener energ��a a partir del movimiento del cuerpo en el seno del fluido. Abstract In this thesis, experimental research focused on passive scalar transport is performed in micro-systems with marked sense of industrial application, using innovative methods in order to obtain better performances optimizing critical design parameters or finding new utilities. Part of the results obtained in these experiments have been published into high impact factor journals belonged to the first quarter of the Journal Citation Reports (JCR). First of all the effect of tip clearance in a micro-channel based heat sink is analyzed. Leaving a gap between channels and top cover, letting the channels communicate each other causes three-dimensional effects which improve the heat transfer between fluid and heat sink and also reducing the pressure drop caused by the fluid passing through the micro-channels which has a great impact on the total cooling pumping power needed. It is also analyzed the enhancement produced in terms of dissipated heat in a micro-processor cooling system by improving the predominantly used fin plate with a vapour chamber based heat spreader which contains a two-phase fluid inside. It has also been developed at the same time a numerical model to optimize the new fin plate dimensions compatible with a series of design requirements in which both size and wight plays a very restrictive role. On the other hand, fluid-dynamics phenomena that appears downstream of a bluff body in the bosom of a fluid flow with high blockage ratio has been studied. This research experimentally confirms the existence of an intermediate regime characterized by an oscillating closed recirculation bubble intermediate regime between the steady closed recirculation bubble regime and the vortex shedding regime (Karman street like regime) as a function of the incoming flow Reynolds number. A particle image velocimetry technique (PIV) has been used in order to obtain, analyze and post-process the fluid-dynamic data. Finally and as an addition to the last point, a study on the vortexinduced vibrations (VIV) of a bluff body inside a high blockage ratio channel has been carried out taking advantage of the results obtained with the fixed square prism. The prism moves with simple harmonic motion for a Reynolds number interval and this movement becomes vibrational around its axial axis after overcoming at definite Reynolds number. Regarding the fluid, vortex shedding regime is reached at Reynolds numbers lower than the previous critical ones. Merging both movement spectra and varying the square prism to fluid mass ratio, a map with different global states is reached. This is not only applicable as a mixing enhancement technique but as an energy harvesting method.

Extracting energy from Vortex-Induced Vibrations: A parametric study

Here, Vortex-Induced Vibrations (VIVs) of a circular cylinder are analyzed as a potential source for energy harvesting. To this end, VIV is described by a one-degree-of-freedom model where fluid forces are introduced from experimental data from forced vibration tests. The influence of some influencing parameters, like the mass ratio m��� or the mechanical damping �� in the energy conversion factor is investigated. The analysis reveals that: (i) the maximum efficiency ��M is principally influenced by the mass-damping parameter m����� and there is an optimum value of m����� where ��M presents a maximum; (ii) the range of reduced velocities with significant efficiency is mainly governed by m���, and (iii) it seems that encouraging high efficiency values can be achieved for high Reynolds numbers.

Assessing the potential of hybrid fossil���solar thermal plants for energy policy making: Brayton cycles

This paper proposes a first study in-depth of solar-fossil hybridization from a general perspective. It develops a set of useful parameters for analyzing and comparing hybrid plants, it studies the case of hybridizing Brayton cycles with current solar technologies and shows a tentative extrapolation of the results to integrated combined cycle systems (ISCSS). In particular, three points have been analyzed: the technical requirements for solar technologies to be hybridized with Brayton cycles, the temperatures and pressures at which hybridization would produce maximum power per unit of fossil fuel, and their mapping to current solar technologies and Brayton cycles. Major conclusions are that a hybrid plant works in optimum conditions which are not equal to those of the solar or power blocks considered independently, and that hybridizing at the Brayton cycle of a combined cycle could be energetically advantageous.