Cryogenic propellants are going to be the cornerstone for effective future human space exploration. These propellants need to be stored and maintained at really low temperatures for a long duration. Accurate phase change modeling is necessary for characterizing the thermal state of future cryogenic propellant tanks and for designing systems to alleviate the self pressurization problem. Better understanding about how to properly store and manage cryogenic propellants would help greatly with In-Situ Resource Utilization (ISRU) strategies for future missions to Mars and further. Predicting the fluid flow, heat transfer, and phase change mass transfer in long term cryogenic storage using CFD models is greatly affected by our understanding of the accommodation coefficient. The kinetically limited phase change model governed by the Hertz-Knudsen-Schrage equation is the model of choice for such calculations. The value of the accommodation coefficient required for the model is unknown for cryogenic propellants. Even in the case of water, the value of the accommodation coefficient has been found to vary over three orders of magnitude based on 80 years of measurements. Experiments specifically built to study accommodation coefficient are needed to estimate the value of the accommodation coefficient and understand some of the uncertainties surrounding these models. <div><br></div><div>Two phase change models, viz. the thermally limited and the kinetically limited phase change model are implemented in OpenFOAM. Different approaches to implement the Hertz-Knudsen-Schrage equation in a sharp interface conjugate heat transfer solver are studied. Evaporation and condensation calculations for a liquid hydrogen meniscus inside an aluminum container are compared with experimental measurements. The effect of accommodation coefficient on phase change is then studied with the kinetically limited model by comparing with the thermally limited model and the experimental measurements. The uncertainties associated with the temperature and pressure measurements in the experiment are quantified to show their effect on computational predictions. Since cryogenic propellants are perfectly wetting fluids, modeling the thin-film region close to the contact line leads to a multi-scale computational problem. However, the phase change contribution from the thin-film region is approximated in these computations to show the importance of modeling the contact line region accurately to adequately capture the small local thermodynamics in that region.</div>

No description available.

Un caloduc pulsé diphasique est un lien thermique composé d'un tube capillaire lisse sous forme de serpentin reliant un évaporateur à un condenseur, séparés par une partie adiabatique. Les conditions de température et de pression du fluide à l'intérieur du caloduc sont proches des conditions de changement de phase. De ce fait, et grâce aux dimensions capillaires du tube, le fluide se distribue en différentes parties liquide et vapeur distribuées de manière alternée. Les instabilités thermo-hydrauliques permanentes sont à l'origine d'un écoulement oscillant qui permet le transfert de chaleur de l'évaporateur jusqu'au condenseur.L'objectif du présent projet de recherche consiste à étudier le comportement thermo-hydraulique de trois caloducs cryogéniques pulsés diphasiques testés avec différents fluides cryogéniques (azote, néon et argon) pour le refroidissement d'aimants à haute température critique. De plus, un code numérique a été développé pour les futures simulations 2D des caloducs pulsés diphasiques.Au cours de ce projet de recherche, de nombreux tests expérimentaux ont été réalisés avec trois fluides cryogéniques différents: azote, néon et argon. Les résultats expérimentaux des tests avec une augmentation de puissance progressive dans l'évaporateur ont révélé des capacités de transfert thermiques très différentes en fonction du fluide, chaque fluide présentant un comportement thermo-hydraulique différent. L'état thermodynamique du fluide lors du fonctionnement stable du PHP et la phase d'assèchement (dry-out) ont été étudiés. Les différences dans le comportement des différents fluides ont été expliquées après l'analyse de leurs propriétés physiques. De plus, les taux de remplissage de fluide dans le PHP donnant les meilleures performances thermiques ont été définis. Ajouté à cela, de nombreux tests réalisés en configuration ouverte (avec le PHP connecté au volume tampon) et en configuration fermé (avec le PHP isolé du volume tampon) ont permis de conclure sur la capacité de régulation du volume tampon en cas de surpression dans le PHP. Aussi, les résultats expérimentaux des longs tests de stabilité ont permis de vérifier la stabilité du système PHP pendant des longues périodes de fonctionnement. Par ailleurs, des tests spécifiques ont été réalisés pour déterminer des conditions optimales de démarrage, l'influence de la température du condenseur dans les performances thermiques du système et l'influence du nombre de tubes en parallèle dans la capacité de transfert thermique du système. Finalement, une série de tests avec une forte puissance thermique imposée au niveau de l'évaporateur imitant une situation de quench dans un aimant supraconducteur ont données des précieuses informations sur les limites thermiques du système. Concernant les simulations numériques, un modèle a été développé avec le solveur Fluent pour des simulations dans une géométrie 2D axisymétrique en utilisant la méthode VOF. La dynamique du fluide dans un tube capillaire a été modélisée et les simulations thermiques ont permis de conclure que les instabilités thermodynamiques restent insuffisantes pour maintenir les oscillations du fluide. Ce modèle est présenté comme une nouvelle plateforme pour de futures modélisations 2D des caloducs pulsés diphasiques. / A pulsating (or oscillating) heat pipe (PHP or OHP) is a heat transfer device composed of a single capillary tube bent in many U-turns, connecting an evaporator to a condenser, separated by an adiabatic part. In the PHP, temperature and pressure conditions of the working fluid are close to phase-change conditions. Due to this and to the capillary dimensions of the tube, the fluid is distributed in alternating liquid slugs and vapor plugs. Permanent thermal instabilities in the PHP create the oscillating flow which allows the transfer of heat from one end (the evaporator) to the other (the condenser).The objective of the present work consists in characterizing the thermo-hydraulic behavior of the meter-scale horizontal cryogenic pulsating heat pipes as a cooling solution for space superconducting magnets. To this, several experiments have been conducted in a cryogenic facility containing three different horizontal pulsating heat pipes. In addition, a numerical 2D model has been proposed for future horizontal pulsating heat pipes simulations.During the research project, numerous tests have been performed using three different working fluids: nitrogen, neon and argon. From experimental results of progressive heat load tests it has been possible to compare the maximum heat load transfer capacity of the PHP with each fluid and the corresponding thermal performance. It has also been noticed that each fluid presents a specific behavior concerning the fluid oscillations. In addition, the thermodynamic state of the fluid in operating conditions and the dry-out process have been characterized. Differences between fluid's behaviors have been partly explained by analyzing the evolution of the fluid physical properties related to the movement and the heat transfer capacity. Furthermore, it has been possible to conclude about the relation between the liquid filling ratio in the PHP and its thermal performance, determining the filling ratios giving the highest thermal performances. Moreover, similar tests have been performed in open configuration (with the PHP connected to the buffer volume) and closed configuration (with the PHP isolated from the buffer volume). From this, it has been possible to conclude about the regulation made by the buffer volume in case of overpressure in the PHP. Also, experimental results from long stability tests have confirmed that these pulsating heat pipe are able to work in stable conditions during long periods as a reliable cooling system. In addition to that, specific tests have been done to determine the optimum start-tup conditions, the influence of the temperature of the condenser in the thermal performance and the influence of the number of turns in the global heat transfer capacity. A final series of tests have been achieved with a sudden extra heat load at the surface of the evaporator while the PHP is operating in stable conditions, simulating a quench event of a superconducting magnet. Experimental results gave us precious information about the transient thermal behavior and operating limits of this kind of device during transient heat loads like quench situations. Concerning the numerical part, a numerical model has been proposed for transient simulations with a pressure-based Fluent solver using the Volume of Fluid (VOF) method in a 2D axisymmetric geometry. Certain characteristics of fluid dynamics in capillary tubes have been confirmed. It has also been noticed that thermodynamic instabilities are not enough to generate the fluid oscillations in capillary tubes. Even if the 2D axisymmetric simulation is still at its early stages, several aspects of the models have been validated after analyzing the evolution of different parameters, suggesting that this kind of model can be considered as a new platform for future 2D pulsating heat pipes simulations.

No description available.

Ultra-sensitive photodetectors on-board space missions need very low temperatures to keep a good resolution. Cryo-coolers, such as pulse-tubes, help maintaining these conditions within a cryostat. In return however, they generate micro-vibrations. These micro-vibrations dissipate enough heat to cause temperature fluctuations at the detector's support, thus lowering the detector's resolution. The first objective is to establish a test bench almost from scratch. The test bench includes a dummy representing the detector's support. The next objectives is to verify that we can measure heat dissipation at the dummy, corresponding to very low values of power ; and finally, to find a link between mechanics and heat dissipation. The dummy consists of a mass suspended by Kevlar chords and is mounted on the cold plate of a cryostat. From the cryostat enclosure, we were able to generate micro-vibrations at the suspended mass and to carry out acceleration and temperature measurements. At 4 K, we were able to measure heat dissipation only around the suspended mass resonance modes. As a first quantitative result, we found that an acceleration of thousands µg (g is the gravitational acceleration) on the cold plate dissipates hundreds of nano-watts. However, these are preliminary results and we will need to improve the test bench for future measurement campaigns. / Ultrakänsliga fotodetektorer ombord rymduppdrag behover mycket låga temperaturer för att hålla en rätt upplösning. Kryokylare, såsom pulse-tubes, hjälper att upprätthålla dessa förhållanden i en kryostat. I gengäld genererar de dock mikrovibrationer. Dessa mikrovibrationer släpper ut tillräckligt med värme för att orsaka temperatursvängningar vid detektorns stöd, vilket sänker detektorns upplösning. Det första målet är att upprätta en testbänk från grunden. Testbänken innehåller en dummy som representerar detektorns stöd. Nästa mål är att kontrollera att vi kan mäta värmeavledning vid dummy, vilket motsvarar mycket låga effektvärden. Sista mål är att hitta en länk mellan mekanik och värmeavledning. Dummy består av en massa som är upphängd av Kevlar och är monterad på en kryostats kallplatta. Från kryostathöljet kunde vi generera mikrovibrationer vid den upphängda massan och genomföra accelerations- och temperaturmätningar. Vid 4 K kunde vi bara mäta värmeavledning runt upphängda massans resonanslägen. Som ett första kvantitativt resultat, upptäckte vi att en acceleration på tusentals µg (g är tyngdaccelerationen) på kylplattan försvinner hundratals nanowatt. Detta är dock preliminära resultat och vi kommer att behöva förbättra testbänken för framtida mätkampanjer.

No description available.

<p> </p> <p>Over the last few years, there has been a concerted effort to develop and validate models<br> aiding the development of cryogenic refueling technologies. This effort is focused on the goal<br> of one day being able to refuel and store cryogenic propellants in the low gravity environ-<br> ment of space. The purpose of this research is to leverage the capabilities of some of these<br> recently developed models to create new ones and model more phenomena related to the<br> space applications of cryogenics.<br> The modelling work presented here is focused in the areas of cryogenic tank chilldown<br> and tank pressure control during storage/transfer. These tools are meant to help inform<br> future experiments being performed at the Glenn Research Center and elsewhere.<br> The model focusing on cryogenic tank chilldown provides a transient approach using<br> the charge-hold-vent (CHV) methodology to calculate the mass and time required to chill<br> a tank down to a desired temperature. Building on the 1-g Universal No-Vent Fill model<br> developed by NASA, the model captures the flashing of pooling liquid during the rapid<br> de-pressurization caused during the vent stage of the chilldown process. The model is com-<br> pared against two different datasets and successfully predicts pressure response throughout<br> the process to within 22%.<br> The thermodynamic vent system (TVS) model has been designed to be seamlessly inte-<br> grated into the 1-g Universal No-Vent Fill model to predict condensation and heat transfer<br> provided by the TVS during a no-vent fill. The TVS coil is spatially discretized and the<br> axial temperature distribution solved for. The model is capable of adapting to a rapidly<br> lowering or rising fill level that can lower the overall heat removal provided by the TVS.<br> While the heat removal is of primary importance, by capturing secondary phenomena such<br> as two-phase pressure drop, the TVS model is also capable of informing design decisions for<br> future systems. The model is compared against three test cases and predicts heat removal<br> to within 2%.<br> <br> </p> <p> </p>

A way to obtain materials that show novel phenomena is to explore the interplay between geometry and interactions. When it is not geometrically possible to satisfy all the interactions by a given configuration, then to find the ground state becomes very complicated. This interplay between geometry and interactions defines geometrical frustration. One of the most popular examples of geometrical frustration in magnetism is spin ice. In this system, nearest neighbour ferromagnetic interactions between Ising spins in a pyrochlore structure emulate water ice by showing the same degree of frustration. This is manifested by the same ground state residual entropy. Although the clearest example of spin ice among magnets is shown by Dy₂Ti₂O₇, the behaviour of this material is richer than that of pure spin ice. The large magnetic moments of the rare earth Dy form a spin ice that also interacts via dipolar interactions. These long range interactions give rise to monopolar excitations which dramatically affect the dynamics of the system with respect to the pure spin ice case. In this thesis magnetisation experiments and numerical methods are used to explore the properties of the magnetic insulator Dy₂Ti₂O₇. We study its excitations at low temperature and describe the out-of-equilibrium characteristics of the magnetisation processes, below a temperature where the system freezes out. For temperatures above the freezing temperature, we describe and measure a 3D Kasteleyn transition and the concomitant Dirac strings associated to it, for the field in the [100] crystallographic direction. For temperatures below the freezing temperature, we find new out-of-equilibrium phenomena. Magnetic jumps are measured and their sweep rate dependence analysed. A deflagration theory is proposed and supported by simultaneous magnetisation and sample temperature measurements obtained by a new design of a Faraday magnetometer.

ALTO (Accélérateur Linéaire et Tandem d’Orsay) est une installation équipée de deux accélérateurs pour la recherche et les applications industrielles (un tandem de 15 MV et une accélérateur linéaire). Mon travail de thèse consiste à l’instrumentation pour la recherche fondamentale de la partie accélérateur linéaire d’ALTO qui fournir des faisceaux de noyaux radioactifs. Les faisceaux de noyaux radioactifs riches en neutrons sont produits par la technique de séparation isotopique en ligne (ISOL). Cette méthode de production permet trois types d’expérience : la mesure de masse, l’orientation nucléaire et les expériences de décroissances radioactives. Parmi ces trois types d’expériences, j’ai participé aux développements de deux nouvelles plateformes expérimentales dans le cadre du projet de l’instrumentation de l’installation ISOL d’ALTO. Le premier, BEDO (BEta Decay studies in Orsay) est un ensemble de détecteurs dédié à la spectroscopie β-γ des noyaux décroissants par désintégration β produits par ALTO. Je présente ici, la mise en fonctionnement de cette plateforme expérimentale, ses caractéristiques techniques et les développements d’outils permettant d’aboutir aux premiers résultats. Pour cette expérience un faisceau de la masse 82 a été produit, saisissant cette opportunité, une ré-investigation de la décroissance de ⁸²Ge vers ⁸²As a permis d’établir un nouveau schéma de niveaux pour ⁸²As et de donner les premières indications de la présence d’états issus de configurations intruses dans les isotones impair-impair N=49. Le second projet développé est POLAREX (POLARization of EXotic nuclei), il s’agit d’une plateforme expérimentale dédiée aux expériences d’orientation nucléaire. Mon travail traite ici de l’entière réhabilitation du cryostat à dilution ³He-⁴He (élément principal et le plus complexe de l’installation) et des développements techniques et R&D apportés à l’ensemble de la plateforme. L’ensemble de ces contributions a permis la validation du fonctionnement de l’installation avec les premières mesures physiques sur les noyaux de ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co créés par activation d’une feuille de Fer avec des deutons produits par le Tandem. / ALTO (Accélérateur Linéaire et Tandem d’Orsay) is a facility composed of two accelerators dedicated to research and industrial applications. There is a 15 MV tandem and a linear accelerator. My PhD work was to develop the instrumentation of the linear accelerator part of ALTO which provides radioactive beams for fundamental research. These radioactive beams are produced using the Isotope Separation On-Line method (ISOL). This technique allows three kinds of experiments: mass measurement, nuclear orientation and radioactivity experiments. Among those three types of experiments, I worked on the development of two new experimental platforms for the ALTO instrumentation. The first one, BEDO (BEta Decay studies in Orsay) is an ensemble of detectors dedicated to β-γ spectroscopy of β-decaying nuclei produced by ALTO. I present in this thesis, the commissioning of this new experimental set-up, its technical characteristics and the tools development leading to the first results. For this commissioning experiment a mass 82 radioactive beam was produced, taking this opportunity the ⁸²Ge vers ⁸²As decay was re-investigated allowing to establish a new level scheme for ⁸²As and giving the first evidences for the presence of intruder states in the N=49 odd-odd isotones. The second project, which is developed, is POLAREX (POLARization of EXotic nuclei), a new facility for nuclear orientation experiments. My thesis deals with the entire reconditioning of a ³He-⁴He dilution refrigerator (major and most complex element of the facility) and R&D and technical developments of the platform. These contributions allowed the successful commissioning of the new experimental platform with the first physical measurements on ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co created by activation of an iron foil with deuterons produced by the Tandem.

Este trabalho tem por objetivo avaliar a viabilidade técnica de processos de separação de gás carbônico em correntes de gases de combustão. Neste sentido, a separação por meio de membranas e por criogenia são avaliadas por meio de simulação de sistemas. As propostas envolvendo membranas avaliam arranjos de membranas em série, os quais são otimizados para condições de maior fluxo permeado e maior beneficio econômico. A corrente de alimentação é de 5 kmol/s e as respectivas frações molares de CO2 e N2 que compõem esta corrente são 0,15 e 0,85. Os resultados obtidos da otimização, para um arranjo de três membranas em série de polyimida de 9000 m² de área superficial, foram uma corrente de permeado de 443,1 mol/s de CO2 a 41,6%, correspondendo a aproximadamente 59% do CO2 da corrente de alimentação. Já com um arranjo de 6 membranas de 9000 m², onde a função objetivo é o maior lucro, foi selecionado o material kapton e a quantidade de CO2 separada é 161,12 mol/s, cuja concentração na mistura é de 79%, e a função objetivo tem um valor de 24.405,30 €/ano. Na outra parte do trabalho, propõe-se e avalia-se um ciclo para o aproveitamento da disponibilidade térmica na regasificação do gás natural líquido, para liquefação de CO2. Obtém-se como resultando em CO2 líquido com fração molar igual a 94%. Este processo consta de uma corrente proveniente da combustão completa de 1 mol/s de metano, contendo 1 mol/s de CO2 e 7,52 mol/s de N2. Esta corrente é comprimida e resfriada até atingir a pressão de 4000 kPa e 25 °C, posteriormente uma membrana enriquece a corrente de gases de combustão, que novamente é comprimida e resfriada até se obter a condensação e separação do CO2. Realiza-se o cálculo de equilíbrio líquido-vapor da mistura utilizando as equações de Peng-Robinson e a regra de mistura de Van der Waals no software VRTherm. A vazão molar do CO2 líquido obtida é de 0,3207 mol/s na concentração declarada. A intensidade energética do processo é de 1,135 kWh/kg de CO2 liquefeito. / The objective of this work is to evaluate the technical feasibility of carbon dioxide separation processes of flue gases streams. In this way, separation processes due membrane and cryogenics are evaluated by system simulation. The systems using membranes evaluates setup of those membranes in series, these setups are optimized for the largest permeate molar flow and the largest economic profit. The feed stream is a 5 kmol/s CO2 – N2 mixture, with molar fraction of 0.15 and 0.85 respectively. The result obtained from the optimization for a setup of three polyimide membranes of 9000 m² is a permeate stream of 443.1 mol/s with CO2 at 41.6%, corresponding to aproximadely 59% of the CO2 contained in the feed stream. When a setup of six 9000 m² membranes is analyzed using an objective function that results in the largest profit, kapton was selected as the material for the membranes. The quantity of CO2 captured is 161.12 mol/s, at 79% of concentration in the mixture, and the objective function has a value of 24,405.30 €/year. The second part of this work, proposes and evaluates a cycle that takes the thermal availability of the regasification of liquid natural gas in advantage for CO2 liquefaction. The product of the cycle is liquid CO2, with a molar fraction of 0.94. The process is fed with a stream that comes from the stoichiometric combustion of 1 mol/s of methane, that stream is composed by 1 mol/s of CO2 and 7.52 mol/s of N2. The stream is then compressed up to the pressure of 4000 kPa and cooled down to 25 °C. After that a membrane concentrates the CO2 in one stream, which is again compressed and cooled down until the condensation of CO2 is achieved. Calculations of liquid – vapor are performed with the Peng- Robinson’s equations and the Van der Waals mixture rule using the software VRTherm. The molar flow rate of liquid CO2 obtained is of 0.3207 mol/s in the concentration mentioned before. The energy intensity of the process is of 1.135 kWh/kg of liquid CO2.