Poorly water-soluble and insoluble chemical agents are routinely investigated in the pharmaceutical industry for pharmacological activity, but many of these are never commercialized due to inadequate dissolution and subsequent low oral bioavailability following oral administration. The bioavailability of many hydrophobic active pharmaceutical ingredients (APIs) can be increased by enhancing their aqueous dissolution. Spray-Freezing into Liquid (SFL) is a novel particle engineering technology that has been demonstrated in the following studies to significantly enhance the dissolution of insoluble APIs. The ultimate goal throughout the studies was to produce micronized SFL powders where the inherently insoluble API would be completely dissolved in aqueous dissolution media within a minimal amount of time (less than ca. 10 minutes). The SFL particle engineering technology is a novel process that was developed, investigated and optimized in order to broaden its applications in pharmaceutical drug delivery systems. Micronized SFL powders were compared head-to-head with powders produced from milling, co-grinding with excipients and slow freezing of liquids containing dissolved API and excipients followed by lyophilization. To strengthen the applicability of the SFL particle engineering technology, studies were conducted where micronized SFL powders were exposed to various stability storage conditions, and characterized to determine the influences of the exposure conditions and time on the physicochemical properties of the powder containing the API. The utility of the SFL process was further enhanced by developing an atmospheric freeze-drying (ATMFD) technique to obtain dry micronized SFL powders. Micronized SFL powders dried by ATMFD were compared to micronized SFL powders dried by vacuum-freeze drying to determine any changes in physicochemical properties or dissolution profiles as a function of the drying technique utilized. The usefulness of the SFL particle engineering technology was broadened when it was found that highly concentrated emulsions could be processed by SFL to produce micronized powders that rapidly wetted and dissolved in dissolution media. Micronized SFL powders produced from emulsion were investigated and compared to slowly frozen agglomerates from emulsion and a micronized SFL powder from solution. As a result of the following studies, the enabling examples using the SFL platform were designed to illustrate applications of the SFL technology as a tool to enhance the aqueous dissolution of poorly water-soluble and insoluble APIs. Therefore, it was demonstrated that this novel particle engineering technology is a feasible method that may be used in the pharmaceutical industry to solve the ever-present solubility and dissolution problems associated with poorly water-soluble or insoluble APIs, or chemical agents being investigated for pharmacological activity as future APIs / text

This thesis presents results from the application of cryogenic cooling on multiple-pass friction stir processing and the subsequent orthogonal machining on friction stir processed and as-received Mg AZ31B-O disks, and shows their combined effects on microstructure and microhardness values. A simple friction stir tool, a specially designed fixture and liquid nitrogen are used to perform multiple-pass friction stir processing experiments on Mg AZ31B-O alloy. The friction stir processed and as-received sheets are then made into disks for the orthogonal machining experiments. This study analyzes the microhardness, microstructure changes by cryogenic friction stir processing and the effect of machining conditions such as dry, MQL and cryogenic and cutting parameters on the Mg AZ31B-O alloy. Four different speeds and three different feed rates are used for the orthogonal machining experiments. The effects of stirring parameters such as the translational feed, rotational speed, cooling conditions and the machining parameters are studied. The resulting microstructure and microhardness from these processes hold a key to the mechanical properties of the alloy. This analysis would help to understand and evaluate the specific aspects of grain size and microhardness that influence the fatigue life of a component.

Realization of spectral responsivity scale was studied in three stages. Firstly, absolute optical power measurements using Electrical Substitution Cryogenic Radiometer (ESCR) was studied. The absolute measurements were done at discrete laser wavelengths of tunable Ar+ (488 nm and 514.5 nm), Nd:YAG (532 nm) and fixed He-Ne (632.8 nm) laser sources. To increase measurement accuracy the method used for the stabilization of laser beams, transmittance measurements of optical windows, and minimization of scattered beams were discussed. Secondly, realization of absolute responsivity scale between 350- 850 nm ranges was studied. The scale based on reflection type trap detectors consisting of three silicon photodiodes. Various measurement systems were established in order to make optical characterization of trap detectors like non-linearity, surface non-homogeneity, polarization dependency, reflectance, and internal quantum efficiency. The absolute responsivity was linked to the absolute optical power by measuring the current response of trap detectors to the absolute power measured by ESCR system at laser wavelengths. Using models for the trap detector&rsquo / s, reflectance and internal quantum efficiency the scale between 350- 850 nm ranges was realized with an uncertainty of 0.05 %. Finally, the spectral responsivity scale in ultraviolet (UV) and near-infrared (NIR) regions was realized using Electrically Calibrated Pyroelectric Radiometer (ECPR). Optically characterizing the spatial non-uniformity of pyroelectric detector and its surface reflectance, the spectral responsivity scale was established with uncertainties &plusmn / 0.5-1.0 % between 250 nm and 350 nm and &plusmn / 0.5-1.5 % between 850 and 2500 nm.

The 2010 National Space Policy of the United State of America introduced by President Obama directed NASA to set far reaching exploration milestones that included a crewed mission to a Near Earth Asteroid by 2025 and a crewed mission to Martian orbit by the mid-2030s. The policy was directly influenced by the recommendations of the 2009 Review of United States Human Space Flight Plans Committee, which called for an evolutionary approach to human space exploration and emphasized the criticality of budgetary, programmatic, and program sustainability. One potential method of improving the sustainability of exploration architectures is the utilization of orbital propellant depots with commercial launch services. In any exploration architecture, upwards of seventy percent of the mass required in orbit is propellant. A propellant depot based architecture allows propellant to be delivered in small increments using existing commercial launch vehicles, but will require three to five times the number of launches as compared to the using the NASA planned 70 to 130 metric ton heavy lift launch system. Past studies have shown that the utilization of propellant depots in exploration architectures have the potential of providing the sustainability that the Review of United States Human Space Flight Plans Committee emphasized. However, there is a lack of comprehensive analysis to determine the feasibility of propellant depots within the framework of human space exploration. The objective of this research is to measure the feasibility of a propellant depot and commercial launch based exploration architecture by stochastic assessment of technical, reliability, and economic risks. A propellant depot thermal model was developed to analyze the effectiveness of various thermal management systems, determine their optimal configuration, quantify the uncertainties in the system models, and stochastically compute the performance feasibility of the propellant depot system. Probabilistic cost analysis captured the uncertainty in the development cost of propellant depots and the fluctuation of commercial launch prices, and, along with the cost of launch failures, provided a metric for determining economic feasibility. Probabilistic reliability assessments using the launch schedule, launch reliability, and architecture requirements of each phase of the mission established launch success feasibility. Finally, an integrated stochastic optimization was performed to determine the feasibility of the exploration architecture. The final product of this research is an evaluation of propellant depots and commercial launch services as a practical method to achieving economic sustainability for human space exploration. A method for architecture feasibility assessment is demonstrated using stochastic system metrics and applied in the evaluation of technical, economic, and reliability feasibility of orbital propellant depots and commercial launch based exploration architectures. The results of the analysis showed the propellant depots based architectures to be technically feasible using current commercial launch vehicles, economically feasible for having a program budget less than $4 billion per year, and have launch reliability approaching the best single launch vehicle, Delta IV, with the use of redundant vehicles. These results serve to provide recommendations on the use of propellant depots in exploration architectures to the Moon, Near Earth Objects, Mars, and beyond.The 2010 National Space Policy of the United State of America introduced by President Obama directed NASA to set far reaching exploration milestones that included a crewed mission to a Near Earth Asteroid by 2025 and a crewed mission to Martian orbit by the mid-2030s. The policy was directly influenced by the recommendations of the 2009 Review of United States Human Space Flight Plans Committee, which called for an evolutionary approach to human space exploration and emphasized the criticality of budgetary, programmatic, and program sustainability. One potential method of improving the sustainability of exploration architectures is the utilization of orbital propellant depots with commercial launch services. In any exploration architecture, upwards of seventy percent of the mass required in orbit is propellant. A propellant depot based architecture allows propellant to be delivered in small increments using existing commercial launch vehicles, but will require three to five times the number of launches as compared to the using the NASA planned 70 to 130 metric ton heavy lift launch system. Past studies have shown that the utilization of propellant depots in exploration architectures have the potential of providing the sustainability that the Review of United States Human Space Flight Plans Committee emphasized. However, there is a lack of comprehensive analysis to determine the feasibility of propellant depots within the framework of human space exploration. The objective of this research is to measure the feasibility of a propellant depot and commercial launch based exploration architecture by stochastic assessment of technical, reliability, and economic risks. A propellant depot thermal model was developed to analyze the effectiveness of various thermal management systems, determine their optimal configuration, quantify the uncertainties in the system models, and stochastically compute the performance feasibility of the propellant depot system. Probabilistic cost analysis captured the uncertainty in the development cost of propellant depots and the fluctuation of commercial launch prices, and, along with the cost of launch failures, provided a metric for determining economic feasibility. Probabilistic reliability assessments using the launch schedule, launch reliability, and architecture requirements of each phase of the mission established launch success feasibility. Finally, an integrated stochastic optimization was performed to determine the feasibility of the exploration architecture. The final product of this research is an evaluation of propellant depots and commercial launch services as a practical method to achieving economic sustainability for human space exploration. A method for architecture feasibility assessment is demonstrated using stochastic system metrics and applied in the evaluation of technical, economic, and reliability feasibility of orbital propellant depots and commercial launch based exploration architectures. The results of the analysis showed the propellant depots based architectures to be technically feasible using current commercial launch vehicles, economically feasible for having a program budget less than $4 billion per year, and have launch reliability approaching the best single launch vehicle, Delta IV, with the use of redundant vehicles. These results serve to provide recommendations on the use of propellant depots in exploration architectures to the Moon, Near Earth Objects, Mars, and beyond.

L’échange d’énergie par rayonnement est proportionnel à l’émissivité. Ce facteur dépend de la température et de la longueur d’onde mais aussi de l’état de surface, de la composition et de la phase. Sa mesure précise est donc toujours un défi à cause des influences connues ou inconnues. Par rapport à d’autres travaux, le but de ce travail est de l’étudier dans des conditions extrêmes, des températures cryogéniques aux hautes températures : Nous avons ainsi étudié à 80K l’absorption d’un diélectrique pour la protection thermique d’un satellite et celles de surfaces en or de différentes rugosités. A la température ambiante nous avons déterminé par une méthode en réflexion, l’émission de vitrages dans le but de la recherche d‘économie d’énergie. Nous avons aussi étudié la variation de l’émissivité pendant le changement de phase solidus-liquidus et α-β de second ordre. Autour de 100°C le soufre devient plus émissif lorsqu’il passe du solide au liquide mais par contre il n’y a pas de différence sur l’émissivité pour ses deux variétés allotropiques principales. A une beaucoup plus haute température, le silicium liquide se comporte comme un métal avec une émissivité très faible et un saut net a été constaté à son passage au point de fusion. Une variation marquée de l’émissivité pour les deux phases solides du SiC a été observée entre 8-11μm dans notre étude. Contrairement aux résultats de la littérature, les sommets d’émissivité diminuent progressivement avec l’augmentation de la température. Enfin trois points X, longueur d’onde où l’émissivité ne dépend pas de la température, ont été observés pour chaque phase. / Heat transferred by radiation is proportional to the emissivity. This coefficient depends not only on the wavelength and the temperature, but also on the surfaceroughness, the chemical composition and the phase. A precise measurement is always a challenge because of the known and unknown factors. Compared with others, this thesis aims at the studies in extreme conditions, from cryogenic temperature to very high temperature: The absorptivity of a dielectric applied to the thermal protector for the satellite and the emissivity of gold surfaces with different roughness have been measured at 80K. The emissivity of different windows has been determined by the reflection method at room temperature for the research of energy saving. We have also studied the variation of the emissivity during the solid to liquid and α-β phase transition. The sulfur becomes more emissive when it changes from solid to liquid around 100°C, but there is no difference on the emissivity between its two major allotropies. The liquid silicon behaves like a metal with a very low emissivity and an obvious bound has been measured when it crosses its melting point. A marked variation of the emissivity of SiC for its two solid-state phases has been observed between 8-11μm. Contrary to other results, the peak values of the emissivity attenuate with the increase of temperature. Finally, three X points at which the emissivity doesn’t depend on the temperature have been measured for each phase.

Ce travail de thèse, porte sur le développement d’une technique originale de traitement de surface par jet d’azote cryogénique. Ce procédé a été initialement développé pour le décapage et le nettoyage des surfaces. Il est ici utilisé pour obtenir un durcissement superficiel sans altération ou endommagement de la surface du matériau traité. Sous certaines conditions, dans un premier temps, nous avons appliqué la technique jet d’azote en conditions statiques de traitement afin de cartographier les domaines d’utilisation du jet en fonction des paramètres de procédé (distance de tir et temps d’exposition). On montre, un durcissement superficiel sans endommagement de la surface du matériau cible (acier austénitique AISI 316L). L’influence de la distance à laquelle la surface est traitée (distance de tir) et le temps d’exposition du jet sur l’évolution de la microstructure, le durcissement et l’endommagement en surface de l’acier AISI 316L a été étudiée. Des analyses par microscopie électronique à balayage, des analyses d’images ainsi que des mesures de microdureté ont été effectuées sur les microstructures des surfaces traitées pour quantifier les effets de traitement par jet d’azote. Le durcissement en surface, du essentiellement à la transformation martensitique, est ainsi quantifié selon les conditions d’essai. Dans un second temps, un traitement en conditions cinématiques a été réalisé en vue d’obtenir un durcissement superficiel sans endommagement de matière. Les essais de traitement en conditions cinématiques ont été essentiellement réalisés sur les surfaces d’aciers austénitiques instables, l’AISI 316L et l’AISI 304L et, ponctuellement sur l’acier stable, l’AISI 310s. L’influence de la vitesse d’avance du jet et la pression de consigne sur l’évolution de la microstructure, les fractions de martensites formées et le niveau de durcissement en surface d’aciers AISI 316L et AISI 304L ont été étudiées. Les analyses EBSD, MEB ainsi que les mesures de microdureté réalisées sur les surfaces traitées ont permis de mettre en évidence le lien entre le niveau de durcissement et la quantité de martensite induite. Le durcissement de la surface de l’acier AISI 310s, qui reste très faible comparé à celui d’aciers instables, est le résultat de l’écrouissage de sa phase austénitique. Il a été également montré qu’un traitement avec un double passage du jet conduit à l’amélioration de la microdureté en surface des trois aciers traités / This work focuses on the study of an original surface treatment technique that uses supercritical cryogenic nitrogen jet. This process was initially designed for environmentally friendly surface cleaning, where indeed such gas recycles in the air after operation. In the present work, this technique is implemented for surface hardening use without damage of the surface to be treated. Two types of operation cases are studied: static jet tool impingement, cinematic using jet tool scanning on the top surface. In fact, these two static and cinematic treatment cases can be used in industrial operations. In the first stage, the treatment was performed under static conditions in order to map the domains of use of the process. Variation of the experimental parameters (standoff distance and dwell time - treatment time-) made possible to define several uses of the nitrogen jet. In particular the hardening without any damage of the surface of the material to be treated such as AISI 316L stainless steel. Thus, the influence of the standoff distance and the dwell time on the evolution of surface microstructure and damage and hardening was studied. To quantify the effects of nitrogen jet on the microstructure, SEM (Scaning Electrons Microscope) observations and micro hardness measurements were carried out on the treated surfaces. As a result, for different conditions of treatment, the relationship between hardness and martensite rate during surface transformation process, is shown and plotted. Secondly, we focus on hardening without surface damage. The treatments were essentially carried out on both AISI 316L and AISI 304L metastable stainless steels. The influence of both torch velocity and jet static pressure on the variation of microstructure, martensite fractions and hardening level, was also studied and discussed. Thanks to both SEM/EBSD analysis and micro hardness measurements, the relationship between martensite rate and increase of hardness, is highlighted. It is also established that the treatment using several passes allows to increase the surface micro hardness without damage. Finally, it is found that, for some particular working parameters, the nitrogen jet process can also be used for surface hardening without martensitic transformation

In this thesis, I have developed a range of theoretical and numerical techniques for modelling the behaviour of partially coherent optical systems and multi-mode detectors. The numerical simulations were carried out for the ultra-low-noise Transition Edge Sensors (TESs) being proposed for use on the SAFARI instrument on the cooled aperture infrared space telescope SPICA (34 - 210 μm). The optical behaviour of the SAFARI system is described in terms of the optical modes of the telescope, as distinct from the optical modes of the detector. The performance of the TESs were assessed in terms of signal power, background power and photon noise. To establish a method for precisely characterising and calibrating ultra-low-noise TESs, a cryogenic test system was designed and engineered to measure the optical efficiencies of the SAFARI TESs. The multi-mode, partially coherent illumination conditions of the measurement system were engineered to be precisely the same as those of the telescope. A major difference between the test system and the telescope’s optics is that the telescope will have focusing elements, but the test system was designed to avoid focusing elements in order to keep the optical path as clean as possible. The theoretical formalism and numerical models were adapted accordingly to address this difference. The numerical simulations show that the test system could provide near identical optical performance as that of the telescope system even though the focusing elements were absent. I also performed experimental measurements to investigate the optical efficiencies of the multi-mode TESs. The detectors worked exceedingly well in all respects with satisfactory optical efficiencies. In addition, it has been shown that the optical model provides a good description of the optical behaviour of the test system and detectors. Further modal analysis was developed to study losses in the multi-mode horns. The optical behaviour of the waveguide-mounted thin absorbing films in the far-infrared was modelled using a mode-matching method.

Made available in DSpace on 2015-03-26T13:53:23Z (GMT). No. of bitstreams: 1 texto completo.pdf: 3804010 bytes, checksum: a7e6fd6b0be4482ad931d87955437622 (MD5) Previous issue date: 2012-02-16 / Periglacial environments constitute one of the most important components of the global landscape, especially with regards to regulatory processes of water, temperature and carbon. Weathering processes related to ice action and the presence of permafrost are peculiar characteristics of these environments, which include regions of high altitude and/or latitude around the globe. Among the general processes of weathering and soil formation common to free ice areas of Antarctica, it is observed that some of these processes take major or minor importance when they are observed in details for the formation of specific landscapes. The Seymour Island (Marambio) is located in the Northern portion of the Weddell Sea and it is composed of sediments dating from the Late Cretaceous to the Lower Tertiary, cut by basaltic dikes. These sediments are constituted of glauconitic sands, bituminous silts, sulfides and carbonates coming from fossil. The main factors which influence the pedogenesis are the arid and cold climates favoring the presence of soluble salts in abundance, the occurrence of sediments rich in sulfides and the bird activity leading to the formation of ornithogenic soils. Thus, this work aimed at describing properties of soils developed on polar semi desert of Seymour Island, identifying and analyzing pedogenic factors and processes in different pedological systems of the island; and, finally, classifying such soils according to Soil Taxonomy and WRB (FAO) classification systems. It was described profiles of representative soils from different pedoambientes and collected samples of pedogenic horizons. In samples of fine ground dried on air, it was promoted a pretreatment to remove soluble salts. It was also promoted chemical and physical routines as soil pH, potential acidity (H + Al), extraction and determination of exchangeable bases; the total organic carbon, electrical conductivity, particle size and dry soil color. The profiles were classified according to the Soil Taxonomy and the World Reference Base for Soil Resources classification systems. Most of the soils showed permafrost inside the control section and, consequently, they were classified as Gelisols and Cryosols by the Soil Taxonomy and WRB/FAO, respectively. In general, they presented little cryoturbation, which is explained by the low humidity of the system (dry permafrost). The physical weathering is less active than those observed in the Antarctic Maritime due to the decreased cryoclastic. Similarly, the soils indicate lower chemical weathering compared to more humid regions of Antarctica, since the high aridity is a limiting factor for triggering chemical reactions in general. It was emphasized the salinisation, phosphate and sulfurization as the main processes of soil formation on the island. The soils are mostly saline, nátric, eutrophic, alkaline, and contain high CTC. According to the interpretation of the morphological, physical, chemical, mineralogical characteristics, classification and specific environmental conditions, the soils from the Seymour Island were divided into three groups. They are: immature alkaline soils on sandstones and siltstones; sulfate and ornithogenic soils. It was observed that the definition of the different pedological systems on the island is closely connected to the difference of the relief, which is decisive for the presence of permafrost dried or coated by ice. Another important factor is the constitution of the original material with lower or higher content of sulfides, carbonates and other minerals. Several features of the landscape suggest a more humid paleoenvironmental condition. Both phosphate and sulfurization are important sources of acidity for this alkaline system. The Soil Taxonomy and WRB/FAO systems do not have adequate classification criteria to classify all the soils developed in areas of climate transitions that are affected by salts, phosphate and sulphidesoxidise. / Os ambientes periglaciais constituem um dos mais importantes componentes da paisagem global, principalmente no que diz respeito a processos regulatórios de água, temperatura e carbono. Processos intempéricos relacionados à ação do gelo e presença de permafrost são características peculiares desses ambientes, que englobam regiões de elevada altitude e/ou latitude por todo o planeta. Dentre os processos gerais de intemperismo e de formação de solo comuns às áreas livres de gelo da Antártica, observa-se que alguns desses processos tomam maior ou menor importância quando observados em detalhe para a formação de paisagens específicas. A ilha Seymour (Marambio) encontra-se na porção setentrional do Mar de Weddell e é formada por sedimentos originados desde o Cretáceo Superior até o Terciário Inferior, cortados por diques basálticos. Esses sedimentos são compostos por areias glauconíticas, siltes betuminosos, sulfetos e carbonatos advindos de fósseis. Os principais fatores que influenciam a pedogênese são: o clima árido e frio, favorecendo a presença de sais solúveis em abundância, a ocorrência de sedimentos ricos em sulfetos e a atividade da avifauna levando à formação de solos ornitogênicos. Nesse sentido, os objetivos desse trabalho foram descrever propriedades de solos desenvolvidos em semideserto polar da Ilha Seymour; identificar e analisar fatores e processos pedogenéticos nos diferentes pedoambientes da ilha; e classificar tais solos nos sistemas de classificação Soil Taxonomy e WRB (FAO). Foram descritos perfis de solos representativos de diferentes pedoambientes e coletados amostras dos horizontes pedogenéticos. Em amostras de terra fina seca ao ar, promoveu-se o pré-tratamento para remoção de sais solúveis; rotinas químicas e físicas como pH em água, acidez potencial (H + Al), extração e determinação de bases trocáveis; carbono orgânico total, condutividade elétrica, granulometria e cor do solo seco. Os perfis foram classificados segundo a Soil Taxonomy e pelo sistema de classificação da World Reference Base for Soil Resources. A maioria dos solos apresentaram permafrost dentro da seção de controle, sendo, portanto, enquadrados como Gelisols e Cryosols pela Soil Taxonomy e WRB/FAO, respectivamente. De forma geral, apresentaram pouca crioturbação, explicada pela pouca umidade do sistema (permafrost seco). O intemperismo físico é menos atuante do que se observa na Antártica Marítima devido à diminuição da crioclastia. Da mesma forma, os solos indicam menor intemperismo químico em relação a regiões mais úmidas da Antártica, uma vez que a elevada aridez é fator limitante para o desencadeamento de reações químicas em geral. Destacamos a salinização, a fosfatização e a sulfurização como principais processos de formação de solos na ilha. Os solos são em sua maioria salinos, nátricos, eutróficos, alcalinos e com elevada CTC. De acordo com interpretação das características morfológicas, físicas, químicas, mineralógicas, classificação e condições ambientais específicas, os solos da Ilha Seymour foram agrupados em três grupos: solos alcalinos pouco evoluídos sobre arenitos e siltitos; solos sulfatados e solos ornitogênicos. Observou-se que a definição dos diferentes pedoambientes na ilha está intimamente ligada à diferenciação do relevo sendo este, determinante para a presença de permafrost seco ou cimentado por gelo. Outro fator determinante é a constituição do material de origem, com menor ou maior conteúdo de sulfetos, carbonatos e outros minerais. Diversos traços da paisagem sugerem uma condição paleoambiental mais úmida. Tanto a fosfatização, quanto a sulfurização são importantes fontes de acidez para esse sistema generalizadamente alcalino. Os sistemas Soil Taxonomy e WRB/FAO não possuem critérios de classificação adequados para classificar todos os solos desenvolvidos em áreas de transição climática que sejam afetados por sais, fosfatização e sulfidização.

This work is concerned with the design, development and performance evaluation of an inertance Pulse Tube Cryocooler (PTC). The main components of a PTC are the compressor, regenerator, pulse tube and inertance tube coupled to a reservoir. The inertance tube is a key component that affects the pressure and mass flow and phase shift between them and hence the performance. In conjunction with the compressor, it also plays a strong role in determining the frequency of operation. The PTC is designed based on system level numerical models (SAGE and DeltaE), component level thermo-acoustic models (DeltaE) of inertance tube and regenerator and experimental data of earlier fabricated Stirling coolers. As a starting point, an inertance tube with a diameter of 3 mm and 3.1 m long was chosen through component level analysis that provides phase shift of around 50 degrees at a pressure ratio of 1.1 for an acoustic power of about 4 W (in order to achieve 1 W of net cooling at 80 K) at 25 bar mean pressure and 60 Hz. From this inertance tube geometry, an estimate of the mass flow rate at the cold heat exchanger is obtained. Based on this mass flow rate, the initial dimensions of the pulse tube and regenerator are arrived at. A parametric study using system level model is carried out to obtain the maximum COP by varying inertance tube length and regenerator diameter. A flexure bearing compressor consisting of moving coil linear motor coupled to a piston is designed for the above cold head. Based on the above design considerations, the PTC compressor and cold head are fabricated and assembled. The PTC is charged with helium at mean pressure of 25 bar and instrumented with pressure and position transducers, temperature sensors and a skin-bonded heater for simulating the heat load on the cold head. Experimental data for the PTC were obtained with two different inertance tube lengths for different frequencies of operation. The cold head temperature exhibited a minimum with respect to the frequency. This optimum frequency shifts towards lower frequency with increased length of the inertance tube. The experimental data clearly shows that with different inertance tube lengths the optimum frequency locates itself for obtaining zero phase shift at the middle of the regenerator. It is observed that the optimum frequency is closely linked to the natural frequency of the pressure wave in the inertance tube suggesting a standing wave within the inertance tube with the pressure node at the reservoir. Thus the inertance tube is found to be analogous to a quarter wave resonator in a thermo-acoustic device. It may thus be possible to pre-fix an operating frequency for a given PTC cold head by choosing an inertance tube length close to quarter wave resonator length. This study has given insights on the phase shift between pressure and mass flow rate governed by the inertance tube and the connection between the optimum and natural frequencies which can be used for better design of PTCs.

Cette thèse de doctorat à été réalisée au sein du Laboratoire des Écoulements Géophysiques et Industriels (LEGI) et du Service des Basses Températures du CEA de Grenoble. Ce travail expérimental a porté sur l'étude comparative de la turbulence classique et quantique à très grand nombre de Reynolds d'un écoulement turbulent de jet d'hélium liquide normal (HeI) et superfluide (HeII) entre 2.3K et 1.78K. Le travail s’est en premier lieu concentré sur le développement des moyens d'essais (une soufflerie cryogénique à boucle fermée pressurisée et régulée en température) et sur l'adaptation de la technique de l'anémomètrie à fil chaud aux basses températures. L’étude s’est poursuivie par l'analyse statistique du champ de vitesse en He I et, plus particulièrement, des incréments spatiaux de vitesse en fluide normal montrant un bon accord avec la littérature et fournissant un véritable point de départ pour la mise en évidence de comportements différents en HeII. Les résultats obtenus en superfluide montrent d'une part un comportement classique à grande échelle et, d’autre part, des écarts aux petites échelles qui dépendent de la température du fluide (i.e. de la fraction variable de superfluide). L'effet le plus évident se manifeste par un changement du signe de la fonction de structure d'ordre 3 des incréments de vitesse. / This experimental work is focused on the the statistical study of the high Reynolds number turbulent velocity field in an inertially driven liquid helium axis-symmetric round jet at temperatures above and below the lambda transition (between 2.3 K and 1.78 K) in a cryogenic wind tunnel. The possibility to finely tune the fluid temperature allows us to perform a comparative study of the quantum HeII turbulence within the classical framework of the Kolmogorov turbulent cascade in order to have a better understanding of the energy cascade process in a superfluid. In particular we focused our attention on the intermittency phenomena, in both He I and He II phases, by measuring the high order statistics of the longitudinal velocity increments by means of the flatness and the skewness statistical estimators.A first phase consisted in developing the cryogenic facility, a closed loop pressurized and temperature regulated wind tunnel, and adapting the classic hot-wire anemometry technique in order to be able to work in such a challenging low temperature environment. A detailed calibration procedure of the fully developed turbulent flow was the carried out at 2.3 K at Reynolds numbers based on the Taylor length scale up to 2600 in order to qualify our testing set-up and to identify possible facility-related spurious phenomena. This procedure showed that the statistical properties of the longitudinal velocity increments are in good agreement with respect to previous results.By further reducing the temperature of the working fluid (at a constant pressure) below the lambda point down to 1.78K local velocity measurements were performed at different superfluid density fractions. The results show a classic behaviour of the He II energy cascade at large scales while, at smaller scales, a deviation has been observed. The occurence of this phenomenon, which requires further investigation and modelling, is highlighted by the observed changing sign of the third order structure function of the longitudinal velocity increments. The intermittency phenomena is also observed and a quantitative analysis is carried out by measuring the scaling behaviour of the velocity increments flatness which is consistent with results obtained in Navier-Stokes fluids. This Ph.D. thesis has been carried out at the LEGI (Laboratoire des Écoulement Géophysiques et Industriels) laboratory in Grenoble and at the CEA Low Temperature Department (SBT) in Grenoble.