Dissertations / Theses on the topic 'Matrix cooling'

<p>A first part of a ”Heat Transfer Handbook” about correlations for internal cooling of gas turbine vanes and blades has been created. The work is based on the cooling of vanes and blades 1 and 2 on different Siemens Gas Turbines. The cooling methods increase the heat transfer in the cooling channels by increasing the heat transfer coefficient and/or increasing the heat transfer surface area. The penalty paid for the increased heat transfer is higher pressure losses.</p><p>Three cooling methods, called rib turbulated cooling, matrix cooling and impingement cooling were investigated. Rib turbulated cooling and impingement cooling are typically used in the leading edge or mid region of the airfoil and matrix cooling is mostly applied in the trailing edge region.</p><p>Literature studies for each cooling method, covering both open literature and internal reports, were carried out in order to find correlations developed from tests. The correlations were compared and analyzed with focus on suitability for use in turbine conditions. The analysis resulted in recommendations about what correlations to use for each cooling method.</p><p>For rib turbulated cooling in square or rectangular ducts, four correlations developed by Han and his co-workers [3.5], [3.8], [3.9] and [3.6] are recommended, each valid for different channel and rib geometries. For U-shaped channels, correlations of Nagoga [3.4] are recommended.</p><p>Matrix cooling is relatively unknown in west, but has been used for many years in the former Soviet Union. Therefore available information in open literature is limited. Only one source of correlations was found. The correlations were developed by Nagoga [4.2] and are valid for closed matrixes. Siemens Gas Turbines are cooled with open matrixes, why further work with developing correlations is needed.</p><p>For impingement cooling on a flat target plate, a correlation of Florschuetz et al. [5.7] is recommended for inline impingement arrays. For staggered arrays, both the correlations of Florschuetz et al. [5.7] and Höglund [5.8] are suitable. The correlations for impingement on curved target plate gave very different results. The correlation of Nagoga is recommended, but it is also advised to consult the other correlations when calculating heat transfer for a specific case.</p><p>Another part of the work has been to investigate the codes of two heat transfer programs named Q3D and Multipass, used in the Siemens offices in Finspång and Lincoln, respectively. Certain changes in the code are recommended.</p>

Modern gas turbine blades and vanes are operated at temperatures above their material’s melting point. Active external and internal cooling are therefore necessary to reach acceptable lifetimes. One possible internal cooling method is called matrix cooling, where a matrix of intersecting cooling air channels is integrated into a blade or vane. To further increase the efficiency of gas turbines, the amount of cooling air must be reduced. Therefore it is necessary that heat transfer inside a cooling matrix is well understood. In the first part of the thesis, a methodology for estimating heat transfer in the flow of matrix cooling channels was established using Computational Fluid Dynamics. Two four-equation RANS turbulence models based on the k-ε turbulence model showed a good correlation with experimental results, while the k-ω SST model underpredicted the heat transfer significantly. For all turbulence models, the heat transfer showed high sensitivity towards changes in the numerical setup. For the k-ω SST turbulence model, the mesh requirements were deemed too computationally expensive and it was excluded from further investigations. As the second part of the thesis, a parameter study was conducted investigating the influence of several geometric parameters on the heat transfer in a cooling matrix. The matrix was simplified as a channel flow interacting with multiple crossing flows. The highest enhancement in heat transfer was seen with changes in taper ratio, aspect ratio and matrix angle. Compared to smooth pipe flow, an increase in heat transfer of up to 60% was observed. Rounded edges of the cooling channels showed a significant influence on the heat transfer as well. In contrast, no influence of the wall thickness on the heat transfer was observed. While no direct validation is possible, the base case and the parameter sweeps show a good correlation with similar cases found in the literature.

This work investigates three-dimensional power loop layout for application to a SiC based matrix converter, providing a symmetric, low-inductance solution. The thesis presents various layout types to achieve this design target, and details the implementation of a hybrid layout to the matrix converter phase-leg. This layout is more easily achievable with a surface-mount device package, which also offers benefits such as ease in manufacturing, and a compact package. In order to implement a surface-mount device, a PCB thermal management strategy should be utilized. An evaluation of these methods is also presented in the work. The final power loop solution that implements an aluminum nitride inlay is evaluated through simulated parasitic extraction and experimental double pulse tests. The layout achieves small, symmetric loop inductances. Finally, the full power, three-phase matrix converter demonstrates the successful implementation of this power loop layout.<br>Master of Science<br>In the United States, 40% primary energy consumption comes from electricity generation, which is the fastest growing form of end-use energy. Industries such as commercial airlines are increasing their use of electric energy, while phasing out the mechanical and pneumatic aircraft components, as they offer better performance and lower cost. Thus, implementation of high efficiency, electrical system can reduce energy consumption, fuel consumption and carbon emissions [1]. As more systems rely on this electric power, the conversion from one level of power (voltage and current) to another, is critical. In the quest to develop high efficiency power converters, wide bandgap semiconductor devices are being turned to. These devices, specifically Silicon Carbide (SiC) devices, offer high temperature and high voltage operation that a traditional Silicon (Si) device cannot. Coupled with fast switching transients, these metal oxide semiconductors field effect transistors (MOSFETs), could provide higher levels of efficiency and power density. This work investigates the benefits of a three-dimensional (3D) printed circuit board (PCB) layout. With this type of layout, a critical parasitic – inductance – can be minimized. As the SiC device can operate at high switching speeds, they incur higher di/dt, and dv/dt slew rates. If trace inductance is not minimal, overshoots and ringing will occur. This can be addressed by stacking PCB traces on top of one another, the induced magnetic field can be reduced. In turn, the system inductance is lowered as well. The reduction of this parameter in the system, reduces the overshoot and ringing. This particular work applies this technique to a 15kW matrix converter. This converter poses a particular design challenge as there are a large number of devices, which can lead to longer, higher inductance PCB traces. The goal of this work is to minimize the parasitic inductance in this converter for high efficiency, high power density operation.

This thesis deals with the design of LED matrix array contains 150 LEDs. In the first part, the thesis identifies source of light like OLED and LED and provide an overview of their lifetime, reliability and basic principle of design systems with LEDs. The thesis then describe design of LED matrix array, deals with power supply of this LED array and with cooling of LED. Finally the thesis describes a software for contol of LED matrix array.

Le domaine du refroidissement est en constante expansion, le système actuel est basé sur la compression/décompression des fluides. Face aux problèmes environnementaux et économiques que ce système présente (natures des fluides frigorigènes et leurs recyclages, nuisances sonores et vibratoires, réglementations contraignantes), de nouvelles solutions techniques alternatives émergent. Ainsi ce travail de thèse porte sur de nouveaux systèmes de refroidissement basés sur les effets électrocalorique et magnétocalorique, respectivement présents dans des films minces de polymère fluoré et dans des composites à matrice polymère et à charges magnétocaloriques. A travers des caractérisations physico-chimiques, électriques, électrocaloriques et magnétocaloriques ces travaux se proposent d’identifier l’origine de l’effet électrocalorique dans des films minces de terpolymère P(VDF-TrFE-CTFE) ferroélectrique relaxeur, mais également d’étudier l’influence de la dispersion des particules magnétocaloriques La(Fe,Si)H dans une matrice polymère de poly(propylène) sur le phénomène magnétocalorique. De plus, dans le cadre de cette thèse, un appareil de mesure directe de l’effet électrocalorique a été développé avec le Dr. Basso de l’INRIM de Turin. La comparaison avec la méthode de mesure indirecte permet d’aborder ce phénomène d’un point de vue thermodynamique afin de faire le point sur la validité des hypothèses thermodynamiques utilisées dans le cas d’un polymère ferroélectrique relaxeur<br>The cooling sector is in constant expansion, the current system is based on the compression/decompression of fluids. In front of environmental and economic problems of this system (nature of frigorigen fluids and their recycling, noise and vibration issues, restrictive regulations), new alternative technological solutions emerge. Thus this thesis provides new cooling systems based on the magnetocaloric and electrocaloric effects respectively present in thin films of fluoropolymer and composites with polymer matrix and magnetocaloric loads. Through physicochemical, electrical, electrocaloric and magnetocaloric characterizations, this work intends to identify the origin of electrocaloric effect in thin terpolymer films P(VDF-TrFE-CTFE) which is a ferroelectric relaxor, but also to study the influence of the magnetocaloric particles La(Fe,Si)H dispersion in a polymer matrix of poly(propylene) on the magnetocaloric phenomenon. In addition, as part of this thesis, a direct measurement device of the electrocaloric effect was developed with Dr. Basso from the INRIM of Turin. The comparison with the indirect measurement method comes up with this phenomenon from a thermodynamic point of view to take stock of the validity of thermodynamic assumptions used in the case of a ferroelectric polymer relaxor

Particles in granular systems collide inelasticly and kinetic energy is dissipated in the granular system. Granular temperature measures the unordered relative motion of the particles. As a result of the inelastic collisions granular temperature decreases, this process is called collisional cooling. In most cases granular particles are charged. This thesis studies the influence of electrical charges on the collisional cooling by using computer simulations and kinetic theory. It is shown, that electrical charge modifies the dissipation rate by a Boltzmann-factor. The energy barrier of the Boltzmann-factor is given by the electrostatic interaction of two colliding particles. In dense systems this energy barrier is reduced due to the interactions with the particles, that do not take part in the collision. A quantitative expression is given for the effective reduction of the energy barrier. The results found for homogeneous systems is expanded for the local description of inhomogeneous systems.

This thesis deals with the study and design of composite materials based on silica matrix suitable for extreme conditions, eg. for the repair of concrete structures with anticipated increased risk of fire. The theoretical part summarizes basic knowledge concerning the fire resistance of structures and the behavior of the composite system during extreme conditions. Theoretically oriented section also contains information on alkali-activated materials and their use in high temperature environments. Based on the evaluation of the theoretical part of the experiment were designed and tested different types of composite materials with increased content of raw materials from alternative sources. Laboratory research has been based on testing of basic physico-mechanical parameters including phase composition and microstructure of the proposed formulations before and after thermal exposure of 1200 ° C. Also considered was the effect of different cooling conditions.

Nel presente lavoro di tesi sono state affrontate le problematiche della realizzazione di canali di raffreddamento conformi per le matrici di estrusione di profilati in alluminio. In ambito tecnologico il problema termico è molto sentito nel settore, perché nei processi di estrusione a caldo le temperature in gioco e i gradienti termici influenzano sia la riuscita della lavorazione in termini di fattibilità e produttività, sia la durata stessa degli utensili. L’obiettivo di maggiore interesse è di ottenere un raffreddamento mirato delle matrici di estrusione, permettendo di asportare il calore dove serve, senza l’effetto controproducente sulla billetta in deformazione. La novità in ambito tecnologico arriva dalla possibilità di sfruttare le tecniche di additive manufacturing per la costruzione dei canali di raffreddamento, grazie ai suoi punti di forza in termini di possibilità realizzative di geometrie molto complesse e in sottosquadro. Lo studio degli effetti del raffreddamento delle matrici nel processo di estrusione è stato seguito con un'analisi numerica con un software multi-fisico che permette di effettuare simulazioni termo-strutturali accoppiate. Si sono visti i benefici del raffreddamento, ottenendo da un lato un’asportazione del calore mirata dell’inserto, dall’altro una diminuzione di temperatura della billetta all’uscita del profilo, senza causare eccessivi aumenti della forza di processo. Quindi è possibile ottimizzare i parametri per ottenere un aumento della velocità d’estrusione e quindi di produttività senza avere i difetti sul profilato tipici di eccessive temperature raggiunte. Sviluppi futuri del lavoro saranno la validazione del modello presentato con un’attenta campagna sperimentale. Sarà così possibile migliorare la precisione previsionale dell’analisi simulativa, ottenendo un efficace strumento di supporto alla progettazione delle matrici.

O efeito magnetocalórico, i.e., o aquecimento e/ou resfriamento de um material magnético sob variação do campo magnético aplicado é a base da refrigeração magnética.O efeito magnetocalórico é caracterizado pela variação da entropia em um processo isotérmico (O efeito magnetocalórico, i.e., o aquecimento e/ou resfriamento de um material magnético sob variação do campo magnético aplicado é a base da refrigeração magnética. O efeito magnetocalórico é caracterizado pela variação da entropia em um processo isotérmico (&#916;Siso) e pela variação da temperatura em um processo adiabático &#916;Tad.Apesar dos inúmeros trabalhos experimentais e teóricos publicados nessa área, muitos aspectos desse efeito ainda não são bem compreendidos.Nesse trabalho discutimos os efeitos da anisotropia sobre as propriedades magnetocalóricas de um sistema de momentos magnéticos localizados. Para essa finalidade, utilizamos um modelo de spins interagentes com um termo de anisotropia uniaxial do tipo DS2 z , onde D é um parâmetro. Nesse modelo, em que o eixo z é a direção de fácil magnetização, a magnitude do parâmetro de anisotropia e a direção do campo magnético aplicado têm um papel fundamental no comportamento das grandezas magnetocalóricas &#916;Siso e &#916;Tad. Realizamos um estudo sistemático para um sistema com J = 1 aplicando o campo magnético em diferentes direções. Os resultados mostram que, quando o campo magnético é aplicado ao longo da direção z, as grandezas magnetocalóricas apresentam o comportamento normal (valores positivos de &#916;Tad e valores negativos de &#916;Siso para &#916;B > 0). Quando o campo magnético é aplicado em uma direção diferente do eixo z, as grandezas magnetocalóricas podem apresentar o comportamento inverso (valores negativos de &#916;Tad e valores positivos de &#916;Siso para &#916;B > 0) ou o comportamento anômalo (troca de sinal nas curvas de &#916;Tad e &#916;Siso). Resultados equivalentes também foram obtidos para um sistema com J = 7=2.<br>The magnetocaloric effect, i.e., heating and/or cooling of a magnetic material subjected to magnetic field variation is the basis of magnetic refrigeration. The magnetocaloric effect is caracterized by the entropy change in an isothermic process (&#916;Siso) and by the temperature change in an adiabatic process (&#916;Tad). Despite the large number of experimental and theoretical works published in this area, there are many aspects of the magnetoccaloric effect which are not yet completely understood.In this work we discuss the effects of anisotropy on the magnetocaloric properties of a system of localized magnetic moments. In order to do that, we used a model of interacting spins with a uniaxial anisotropy term DS2 z , where D is a parameter. In this model, where the z axis is the easy magnetization direction, the magnitude of the anisotropy parameter and the direction of the applied magnetic field have an important role in the behavior of the magnetocaloric quantities &#916;Siso and &#916;Tad. We perform a systematic study for a system with J = 1 by applying the magnetic field in different directions. The results show that, when the magnetic field is applied in the z direction, the magnetocaloric quantities have the normal behavior (positive values of &#916;Tad and negative values of &#916;Siso with &#916;B > 0). When the magnetic field is applied in a direction different from the z axis, the magnetocaloric quantities can show the inverse behavior (negative values of &#916;Tad and positive values of &#916;Siso with &#916;B > 0) or the anomalous behavior (change of sign in the curves of &#916;Tad and &#916;Siso). Similar results have also been obtained for a system with J = 7=2.

This theoretical doctoral thesis investigates the collective effects that emerge in cold atomic systems caused by light-scattering in free space. Two specific cases are investigated: the collective atomic recoil laser (CARL) effect in a cold gas, without optical cavity, and a novel cooperative cooling effect via optical binding (OB) with cold atoms. As a main objective, this theoretical project investigates the spatial grating structures and the backward radiation that appears in a cold atomic cloud when it is irradiated by a single far-detuned laser beam, also known as CARL effect. While this effect has traditionally been described using a ring cavity, the study is performed here in free space, in the absence of such a cavity. Both 2D and 3D clouds show a transition from single-atom isotropic scattering to collective directional scattering. The effect is shown by the derivation and numerical solution of a set of multi-particle motion equations coupled by a self-consistent optical field, which is inspected with both a scalar model and a vectorial model. New original approaches are used to address the numerical study of the dynamics of the atomic system, such as molecular dynamics (MD) algorithms. A second system emerged, from the attempt to understand the main objective, where a few atoms rearrange themselves into crystalline atomic structures, with a periodicity between particles close to the optical wavelength. The atomic system is initially confined into a 2D plane (or 1D string) using two (or four) counter-propagating laser beams. Due to the multiple scattering experienced by all the particles in the system, a dipole-dipole force arises among them, generating a non-trivial dynamical trapping potential landscape that compels the atoms, to self-organize at distances multiple of the light wavelength. When atoms are rearranged into an atomic crystal, the force acting on each particle depends on the position of the others, thus allowing to study the stability of such optically bound structures. In addition, it turns out that a non-conservative force is generated from the dipole-dipole interaction, allowing the system to be cooled by controlling the value of certain parameters. This new phenomenon arises as a direct consequence of the use of cold atoms instead of dielectric nanoparticles in an OB system. Therefore, besides the atomic external motion, internal degrees of freedom (DOF) of the atoms are considered by treating each atom as a dipole. This latter aspect is investigated using the coupled dipole equations. When multiple atoms are set in line, the cooling mechanism is collectively enhanced, generating a novel cooperative cooling effect.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>SOUSA, Vinícius da Silva Ramos de. O efeito magnetocalórico anisotrópico nos compostos RAl2 (R = Dy, Er, Ho, Nd e Tb). 2008. 99f. Dissertação (Mestrado em Física) - Instituto de Física Armando Dias Tavares, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, 2008. O efeito magnetocalórico é a base da refrigeração magnética. O potencial magnetocalórico é caracterizado por duas quantidades termodinâmicas: a variação isotérmica da entropia (&#916;Siso) e a variação adiabática da temperatura (&#916;Tad), as quais são calculadas sob uma variação na intensidade do campo magnético aplicado ao sistema. Em sistemas magnéticos que apresentam uma anisotropia magnética é observada uma mudança no efeito magnetocalórico, isto porque este potencial torna-se fortemente dependente da direção de aplicação do campo magnético. A anisotropia em sistemas magnéticos pode levar a um efeito magnetocalórico inverso, assim como à definição de um efeito magnetocalórico anisotrópico, o qual por definição é calculado para um campo cuja intensidade é mantida constante e cuja orientação variamos de uma direção difícil de magnetização para a direção fácil de magnetização. O efeito magnetocalórico anisotrópico foi estudado para os compostos intermetálicos de terras raras do tipo RAl2 considerando-se um modelo microscópico que leva em conta as interações de troca (na aproximação de campo médio), de Zeeman e a interação de campo elétrico cristalino, que é a responsável pela anisotropia nos compostos RAl2. O efeito magnetocalórico anisotrópico foi investigado para a série RAl2 e comparado com o efeito magnetocalórico usual.<br>The magnetic refrigeration is based on the magnetocaloric effect. The magnetocaloric potential is characterized by the two thermodynamics quantities: the isothermal entropy change (&#916;Siso) and the adiabatic temperature change (&#916;Tad), which are calculated upon a change in the intensity of the applied magnetic field. In anisotropic magnetic systems it is observed a change in the magnetocaloric effect, since this potential becomes strongly dependent on the direction in which the external magnetic field is applied. The anisotropy in such magnetic systems can lead to an inverse magnetocaloric effect, as well as to the definition of an anisotropic magnetocaloric effect, that by definition is calculated upon a magnetic field which intensity is kept fixed and which orientation is changed from a hard direction of magnetization to the easy direction of magnetization. This anisotropic magnetocaloric effect was performed for the RAl2 intermetallic compounds considering a microscopic model Hamiltonian that includes the Zeeman interaction, the exchange interaction (taken in the mean field approximation) and the crystalline electrical field, that is responsible for the anisotropy in the RAl2 compounds. The anisotropic magnetocaloric was fully investigated for the serie RAl2 and compared with the usual magnetocaloric effect and several curves of (&#916;Siso) and (&#916;Tad) were obtained.

The physics of ultracold quantum gases has been the subject of a long-lasting and intense research activity, which started almost a century ago with purely theoretical studies and had a fluorishing experimental development after the implementation of laser and evaporative cooling techniques that led to the first realization of a Bose Einstein condensate (BEC) over 25 years ago. In recent years, a great interest in ultracold atoms has developed for their use as platforms for quantum technologies, given the high degree of control and tunability offered by ultracold atom systems. These features make ultracold atoms an ideal test bench for simulating and studying experimentally, in a controlled environment, physical phenomena analogous to those occurring in other, more complicated, or even inaccessible systems, which is the idea at the heart of quantum simulation. In the rapidly developing field of quantum technologies, it is highly important to acquire an in-depth understanding of the state of the quantum many-body system that is used, and of the processes needed to reach the desired state. The preparation of the system in a given target state often involves the crossing of second order phase transitions, bringing the system strongly out-of-equilibrium. A better understanding of the out-of-equilibrium processes occurring in the vicinity of the transition, and of the relaxation dynamics towards the final equilibrium condition, is crucial in order to produce well-controlled quantum states in an efficient way. In this thesis I present the results of the research activity that I performed during my PhD at the BEC1 laboratory of the BEC center, working on ultracold gases of 23Na atoms in an elongated harmonic trap. This work had two main goals: the accurate determination of the equilibrium properties of a Bose gas at finite temperature, by the measurement of its equation of state, and the investigation of the out-of-equilibrium dynamics occurring when a Bose Einstein condensate is prepared by cooling a thermal cloud at a finite rate across the BEC phase transition.To study the equilibrium physics of a trapped atomic cloud, it is crucial to be able to observe its density distribution in situ. This requires a high optical resolution to accurately obtain the density profile of the atomic distribution, from which thermodynamic quantities can then be extracted. In particular, in a partially condensed atomic cloud at finite temperature, it is challenging to resolve well also the boundaries of the BEC, where the condensate fraction rapidly drops in a narrow spatial region. This required an upgrade of the experimental apparatus in order to obtain a high enough resolution. I designed, tested and implemented in the experimental setup new imaging systems for all main directions of view. Particular attention was paid for the vertical imaging system, which was designed to image the condensates in trap with a resolution below 2 μm, with about a factor 4 improvement compared to the previous setup. The implementation of the new imaging systems involved a partial rebuilding of the experimental apparatus used for cooling the atoms. This created the occasion for an optimization of the whole system to obtain more stable working conditions. Concurrently I also realized and included in the experiment an optical setup for the use of a Digital Micromirror Device (DMD) to project time-dependent arbitrary light patterns on the atoms, creating optical potentials that can be controlled at will. The use of this device opens up exciting future scenarios where it will be possible to locally modify the trapping potential and to create well-controlled barriers moving through the atomic cloud. Another challenge in imaging the density distribution in situ is determined by the fact that the maximum optical density (OD) of the BEC, in the trap center, exceeds the low OD of the thermal tails by several orders of magnitude. In order to obtain an accurate image of the whole density profile, we developed a minimally destructive, multi-shot imaging technique, based on the partial transfer of a fraction of atoms to an auxiliary state, which is then probed. Taking multiple images at different extraction fractions, we are able to reconstruct the whole density profile of the atomic cloud avoiding saturation and maintaining a good signal to noise ratio. This technique, together with the improvements in the imaging resolution, has allowed us to accurately obtain the optical density profile of the Bose gas in trap, from which the 3D density profile was then calculated applying an inverse Abel transform, taking advantage of the symmetry of the trap. From images of the same cloud after a time-of-flight expansion, we measured the temperature of the gas. From these quantities we could find the pressure as a function of the density and temperature, determining the canonical equation of state of the weakly interacting Bose gas in equilibrium at finite temperature. These measurements also allowed us to clearly observe the non-monotonic temperature behavior of the chemical potential near the critical point for the phase transition, a feature that characterizes also other superfluid systems, but that had never been observed before in weakly interacting Bose gases. The second part of this thesis work is devoted to the study of the dynamical processes that occur during the formation of the BEC order parameter within a thermal cloud. The cooling at finite rate across the Bose-Einstein condensation transition brings the system in a strongly out-of-equilibrium state, which is worth investigating, together with the subsequent relaxation towards an equilibrium state. This is of interest also in view of achieving a better understanding of second order phase transitions in general, since such phenomena are ubiquitous in nature and relevant also in other platforms for quantum technologies. A milestone result in the study of second order phase transitions is given by the Kibble-Zurek mechanism, which provides a simple model capturing important aspects of the evolution of a system that crosses a second-order phase transition at finite rate. It is based on the principle that in an extended system the symmetry breaking associated with a continuous phase transition can take place only locally. This causes the formation of causally disconnected domains of the order parameter, at the boundaries of which topological defects can form, whose number and size scale with the rate at which the transition is crossed, following a universal power law. It was originally developed in the context of cosmology, but was later successfully tested in a variety of systems, including superfluid helium, superconductors, trapped ions and ultracold atoms. The BEC phase transition represents in this context a paradigmatic test-bench, given the high degree of control at which this second-order phase transition can be crossed by means of cooling ramps at different rates. Already early experiments investigated the formation of the BEC order parameter within a thermal cloud, after quasi-instantaneous temperature quenches or very slow evaporative cooling. In the framework of directly testing the Kibble-Zurek mechanism, further experiments were performed, both in 2D and 3D systems, focusing on the emergence of coherence and on the statistics of the spontaneously generated topological defects as a function of the cooling rate. The Kibble-Zurek mechanism, however, does not fully describe the out-of-equilibrium dynamics of the system at the transition, nor the post-quench interaction mechanisms between domains that lead to coarse-graining. Most theoretical models are based on a direct linear variation of a single control parameter, e.g. the temperature, across the transition. In real experiments, the cooling process is controlled by the tuning of other experimental parameters and a global temperature might not even be well defined, in a thermodynamic sense, during the whole process. Moreover, the temperature variation is usually accompanied by the variation of other quantities, such as the number of atoms and the collisional rate, making it difficult to accurately describe the system and predict the post-quench properties. Recent works included effects going beyond the Kibble-Zurek mechanism, such as the inhomogeneity introduced by the trapping potential, the role of atom number losses, and the saturation of the number of defects for high cooling rates. These works motivate further studies, in particular of the dynamics taking place at early times, close to the crossing of the critical point. The aim of the work presented in this thesis is to further investigate the timescales associated to the formation and evolution of the BEC order parameter and its spatial fluctuations, as a function of the rate at which the transition point is crossed. We performed experiments producing BECs by means of cooling protocols that are commonly used in cold-atom laboratories, involving evaporative cooling in a magnetic trap. We explored a wide range of cooling rates across the transition and found a universal scaling for the growth of the BEC order parameter with the cooling rate and a finite delay in its formation. The latter was already observed in earlier works, but for a much more limited range of cooling rates. The evolution of the fluctuations of the order parameter was also investigated, with an analysis of the timescale of their decay during the relaxation of the system, from an initial strongly out-of-equilibrium condition to a final equilibrium state. This thesis is structured as follows: The first chapter presents the theoretical background, starting with a brief introduction to the concept of Bose Einstein condensation and a presentation of different models describing the thermodynamics of an equilibrium Bose gas. The second part of this chapter then deals with the out-of-equilibrium dynamics that is inevitably involved in the crossing of a second-order phase transition such as the one for Bose-Einstein condensation. The Kibble-Zurek mechanism is briefly reviewed and beyond KZ effects are pointed out, motivating a more detailed investigation of the timescales involved in the BEC formation. In the second chapter, I describe the experimental apparatus that we use to cool and confine the atoms. Particular detail is dedicated to the parts that have been upgraded during my PhD, such as the imaging system. In the third chapter I show our experimental results on the measurement of the equation of state of the weakly interacting uniform Bose gas at finite temperature. In the fourth chapter I present our results on the out-of-equilibrium dynamics in the formation of the condensate order parameter and its spatial fluctuations, as a function of different cooling rates.

Gas turbines are extensively in use for aircraft propulsion, land-based power generations, and various industrial applications. Thermal efficiency and the power output of a gas turbine increases with increase in turbine rotor inlet temperature (RIT). The current RIT level in many advanced gas turbines is far above the melting point of the used blade material. Therefore, along with development in high temperature material, a more sophisticated cooling scheme must be developed for continuing the safe operation of gas turbines with high performances. Gas turbine blades can be cooled internally as well as externally. This paper is focused on the internal cooling of turbine blades and vanes of a gas turbine. Internal cooling can be achieved by passing coolant through various enhanced serpentine passages inside the blade and extracting heat from outside of the blades. Jet impingement, matrix cooling, rib turbulator, dimple and pin fin cooling are utilized as the methods of internal cooling, which are presented in various articles. Due to the different enhancement in heat transfer and in pressure drop, they are being used in specific part of the blades and the vanes on a gas turbine. The matrix cooling, also known as lattice-work or vortex cooling provides a good strength to blades by the layers of ribs which intersect each other from the opposite wall. A significant increase in the heat transfer is obtained due to an increase in heat transfer area, impinging and in swirling flows (which helps to promote turbulence), induced by the geometry of the matrix cooling channels.

In questa tesi sono riportati i risultati sperimentali di varie campagne di misura eseguite sia in condizioni statiche che rotanti su diverse geometrie di tipo matrix per il raffreddamento interno di palettature di turbina a gas. Sono stati quantificati gli effetti della variazione di parametri geometrici caratteristici, numero di Reynolds e Rotation number sulle distribuzioni del coefficiente di scambio termico e del fattore di attrito. A partire dai dati sperimentali sono state ricavate delle correlazioni di design. Queste correlazioni sono state applicate ad un caso reale su un trailing edge di una pala, adottando le dimensioni e le proprietà del refrigerante in condizioni macchina. Dal confronto dei risultati ottenuti con le prestazioni di sistemi attualmente impiegati è stata dimostrata la bontà dei sistemi matrix in termini di incremento del guadagno di scambio termico e riduzione delle perdite di carico.

Ko Ka Lung.<br>Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.<br>Includes bibliographical references.<br>Abstracts in English and Chinese.<br>Title page --- p.i<br>Abstract (English) --- p.ii<br>Abstract (Chinese) --- p.iii<br>Acknowledgement --- p.iv<br>Declaration --- p.v<br>Table of Content --- p.vi<br>List of Figure --- p.viii<br>Chapter 1. --- INTRODUCTION --- p.1<br>Chapter 1.1 --- Matrix-assisted Laser Desorption / Ionization (MALDI) --- p.2<br>Chapter 1.1.1 --- Evolution of Matrix-assisted laser desorption / ionization (MALDI) --- p.2<br>Chapter 1.1.1.1 --- Lasers --- p.3<br>Chapter 1.1.1.2 --- Matrices --- p.3<br>Chapter 1.1.1.3 --- Sample preparation --- p.4<br>Chapter 1.1.1.4 --- Desorption --- p.6<br>Chapter 1.1.1.5 --- Ionization --- p.7<br>Chapter 1.2 --- Fourier Transform Ion Cyclotron Resonance Mass Spectrometry with MALDI (FTICR-MS) --- p.9<br>Chapter 1.2.1 --- History of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry --- p.9<br>Chapter 1.2.2 --- Basics of FTICR-MS --- p.11<br>Chapter 1.2.3 --- FTICR couple with external ionization source --- p.15<br>Chapter 1.2.4 --- Coupling of MALDI to FTICR --- p.16<br>Chapter 1.3 --- Problems encountered on the coupling of MALDI to FTICR-MS --- p.17<br>Chapter 1.4 --- Outline of present work --- p.19<br>Chapter 2 --- SIMULATION METHOD --- p.20<br>Chapter 2.1 --- Overview of the ion optics simulation --- p.21<br>Chapter 2.2 --- History of SIMION Program --- p.22<br>Chapter 2.3 --- Basics and theory of SIMION version 6.0 --- p.24<br>Chapter 2.4 --- Simulation method --- p.26<br>Chapter 2.4.1 --- Creating potential array --- p.27<br>Chapter 2.4.2 --- User program --- p.29<br>Chapter 2.4.3 --- Ion definition parameter --- p.31<br>Chapter 2.4.4 --- Trajectories quality panel --- p.33<br>Chapter 2.4.5 --- Data recording --- p.36<br>Chapter 3 --- OPTIMIZATION OF RF-ONLY HEXAPOLE UNDER PULSE GAS CONDITION --- p.37<br>Chapter 3.1 --- Introduction --- p.38<br>Chapter 3.2 --- Simulation conditions --- p.39<br>Chapter 3.3 --- Results and discussion --- p.40<br>Chapter 3.3.1 --- rf-frequency (w) --- p.41<br>Chapter 3.3.2 --- rf voltage (Vo-p) --- p.44<br>Chapter 3.3.3 --- Pulse gas pressure(po) --- p.47<br>Chapter 3.3.4 --- Trapping potential (VT) --- p.49<br>Chapter 3.3.5 --- Effect of space charge --- p.53<br>Chapter 3.4 --- Conclusions --- p.60<br>Chapter 4 --- OPTIMIZATION OF DIFFERENT HEXAPOLE-BASED INTERFACES FOR PRE-TRAPPING COOLING --- p.61<br>Chapter 4.1 --- Introduction --- p.62<br>Chapter 4.2 --- Simulation conditions --- p.63<br>Chapter 4.3 --- Results and discussion --- p.66<br>Chapter 4.3.1 --- Static medium pressure interface --- p.66<br>Chapter 4.3.1.1 --- Effect of pressure --- p.66<br>Chapter 4.3.1.2 --- Effect of space charge --- p.70<br>Chapter 4.3.2 --- Differential pressure model (Skimmer-based) --- p.73<br>Chapter 4.3.2.1 --- Effect of pressure --- p.73<br>Chapter 4.3.2.2 --- Effect of space charge --- p.76<br>Chapter 4.3.3 --- A comparison of the optimal operating conditions for the three proposed interfaces --- p.81<br>Chapter 4.3.4 --- Comparison of the theoretical results amd the experimental results --- p.83<br>Chapter 4.4 --- Conclusion --- p.84<br>Chapter 5 --- CONCLUSIONS --- p.85<br>Chapter 5.1 --- Conclusions --- p.86<br>REFERENCES --- p.R1<br>APPENDIX --- p.A1