Ultra-kalte atomare Gase werden in zahlreichen Laboren weltweit untersucht und finden unter anderem Anwendung in Atomuhren und in Atominterferometer. Die Einsatzgebiete erstrecken sich von der Geodäsie über die Metrologie bis hin zu wichtigen Fragestellungen der Fundamentalphysik, wie z.B. Tests des Äquivalenzprinzips. Doch die beispiellose Messgenauigkeit ist durch die irdische Gravitation eingeschränkt. Zum einen verzerrt die Schwerkraft das Fallenpotential und macht damit die Reduktion der atomaren Energie unter einem bestimmten Limit unmöglich. Zum anderen werden die aus einer Falle frei gelassenen Teilchen durch die Erdanziehung beschleunigt und so ist deren Beobachtungszeit begrenzt. Im Rahmen dieser Arbeit werden die Ergebnisse des Projektes QUANTUS (Quantengase Unter Schwerelosigkeit) dargestellt. Auf dem Weg zur Implementierung eines Quantengasexperimentes im Weltraum wurde innerhalb einer deutschlandweiten Zusammenarbeit eine kompakte, portable und mechanisch stabile Apparatur zur Erzeugung und Untersuchung eines Bose-Einstein-Kondensats (BEC) unter Schwerelosigkeit im Fallturm Bremen entwickelt. Sowohl die Abbremsbeschleunigung von bis zu 50 g als auch das begrenzte Volumen der Fallkapsel stellen hohe Ansprüche an die mechanische Stabilität und die Miniaturisierung von optischen und elektronischen Komponenten. Der Aufbau besteht aus einer im ultra-hoch Vakuum geschlossenen magnetischen Mikrofalle (Atomchip) und einem kompakten auf DFB-Dioden basierenden Lasersystem. Mit diesem Aufbau ließ sich das erste BEC unter Schwerelosigkeit realisieren und nach 1 Sekunde freier Expansion zu beobachten. Weder die schwache Krümmung des Fallenpotentials noch die lange Beobachtungszeit würden in einem erdgebundenen Experiment realisierbar. Die erfolgreiche Umsetzung des Projektes eröffnet ein innovatives Forschungsgebiet - degenerierte Quantengase bei ultratiefen Temperaturen im pK-Bereich, mit großen freien Evolutions- und Beobachtungszeiten von mehreren Sekunden. / Recently, cooling, trapping and manipulation of neutral atoms and ions has become an especially active field of quantum physics. The main motivation for the cooling is to reduce motional effects in high precision measurements including spectroscopy, atomic clocks and matter interferometry. The spectrum of applications of these quantum devices cover a broad area from geodesy, through metrology up to addressing the fundamental questions in physics, as for instance testing the Einstein’s equivalence principle. However, the unprecedented precision of the quantum sensors is limited in terrestial laboratories. Freezing atomic motion can be nowadays put to the limit at which gravity becomes a major perturbation in a system. Gravity can significantly affect and disturb the trapping potential. This limits the use of ultra-shallow traps for low energetic particles. Moreover, free particles are accelerated by gravitational force, which substantially limits the observation time. Targeting the long-term goal of studying cold quantum gases on a space platform, we currently focus on the implementation of a Bose-Einstein condensate (BEC) experiment under microgravity conditions at the drop tower in Bremen. Special challenges in the construction of the experimental setup are posed by a low volume of the drop capsule as well as critical decelerations up to 50g during recapture at the bottom of the tower. All mechanical and electronic components were thus been designed with stringent demands on miniaturization and mechanical stability. This work reports on the observation of a BEC released from an ultra-shallow magnetic potential and freely expanding for one second. Both, the low trapping frequency and long expansion time are not achievable in any earthbound laboratory. This unprecedented time of free evolution leads to new possibilities for the study of BEC-coherence. It can also be applied to enhance the sensitivity of inertial quantum sensors based on ultra-cold matter waves.

This manuscript has been realized in the frame of SELENE experiment research activities. SELENE is the ac-ronym of Self-rewetting fluids for ENErgy management and consists of a space project aiming to investigate heat and mass transfer phenomena in mono-groove configuration with self-rewetting fluids (SRFs). Self-rewetting fluids are mixture showing an anomalous trend of surface tension with temperature, an inversion of the surface tension slope after certain temperature. As consequence, when the minimum in surface ten-sion is crossed, surface tension gradient at the meniscus interface pulls the liquid towards the warmest region, preventing hot spots. This mechanism is completely spontaneous and has an interesting potential when applied to heat transfer applications as heat pipes (HPs). In HPs heat is removed by the liquid at the warmest region (the evaporator) and transported at the coldest zone (the condenser) by phase change; here, heat is removed by the pipe and dissipated outside through a radiator. To operate correctly, liquid is supplied to the evaporator by capillarity and the liquid vapour is allowed to flow back to condenser from a dedicated pipe region where liquid is not allowed. Vapour condensation releases at the condenser the heat to be dissipated. When SRFs are replacing working fluid in HP applications and temperatures are higher than the characteristic minimum in surface tension, capillary force is assisted by inverse Marangoni flow at the vapour-liquid interface.Since heat pipe performances are related to liquid supplied at the evaporator, in order to compare SRFs and not SRFs working fluids, it is needed to split the contribution of Marangoni and capillary force in the liquid flow. Marangoni effect is related to surface tension gradient that, in a mixture as SRF, is dependent on temperature and local composition at the liquid interface. For all these reasons, SELENE is designed to be the link between scientific research on HPs and heat transfer applications using SRFs. SELENE consists of a mono-groove with trapezoidal section that can be considered as a “clump” of an Inner Grooved Heat Pipe (IGHP) and, in order to split capillary and Marangoni contribution, it is integrated dedicated tools providing the required data in terms of concentration and liquid meniscus shape. Experimental data are used to build a simplified thermo-soluto-fluido dynamic model describing the thermo-mechanic mechanisms between the liquid bulk and the vapour flow. In the manuscript here presented it has been carried on a technology development of the required diag-nostics for the SELENE space project. The diagnostics have been designed to work in microgravity condi-tions even if they are tested on ground. As concentration diagnostic, in the text are proposed several tech-niques and more interest is spent on the adaptation of I-VED (In vivo Embolic Detection) technology meas-uring fluid AC impedance to retrieve composition information; the technology is not yet mature to be inte-grated in SELENE but it presents interesting features to be investigated in microgravity conditions. As me-niscus reconstruction technique it is proposed a new and innovative technology developed in the frame of the presented thesis and it consists of a non-intrusive optical technique aiming to retrieve liquid meniscus shape (and so curvature) from a single visualization window mounted at the top of the SELENE breadboard.An analytical approach aiming to retrieve a simplified mathematical model of the transfer mechanisms is also provided in the text. The analytical analysis clearly shows the relations between the experimental measured data and the velocity profiles in the liquid and vapour regions. In addition, since in SELENE exper-iment the heat conduction across the groove itself is not negligible, in the text it is provided a semi-empirical thermal model based on the Multi Lumped Model (MLM) theory and able to retrieve local heat exchanged information along the pipe length. The model is used to compare experiments with different working fluids at different operational regimes. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

"The present work is a study of the low inertia spreading dynamics of initially spherical viscous droplets on a planar interface. The droplets are affected by gravity, surface tension and viscous forces and are modeled as two-dimensional axisymmetric bodies. The main focus of this study is the examination of the dependence of droplet stability, equilibrium shape and fluid motion within the drop on the relative magnitude of these forces. The dynamics are modeled using the unsteady, non-linear Navier-Stokes equations for an incompressible fluid. The spreading of a droplet on a solid surface is modeled with both a no-slip and a partial-slip boundary condition. In addition, the spreading of a droplet on another identical drop (two-drop problem) is modeled to study the problem without the contact point singularity. The governing equations are solved numerically using the Mixed Galerkin Finite Element formulation, augmented by the use of the Newton-Raphson iteration scheme to effectively treat the non-linearities of the problem. The Generalized Eulerian Lagrangian formulation is adopted for the treatment of the moving free surface of the droplet. Computations are performed for capillary numbers ranging from 0.01 to 100 and for Reynolds numbers from 0.005 to 50, where the velocity scale is based on the droplet radius and the gravitational acceleration. For the droplet spreading on a solid surface, three distinct behaviors are observed~: for low Reynolds numbers and sufficiently high capillary numbers, droplets deform to a stable, equilibrium shape; for higher Reynolds numbers, an oscillatory droplet behavior occurs; at still higher Reynolds numbers, the droplets shatter. Very often, a recirculation is induced near the contact point just before the droplet shatters, which is also observed for the case of stable oscillating droplets. When a partial-slip boundary condition is applied, it is observed that the stability of the droplet and the rate at which the droplet attains the static contact angle depend strongly on the velocity of slip of the droplet with respect to the solid surface at the contact point. For the two-drop problem, only two distinct behaviors are observed: for low Reynolds numbers and high capillary numbers, the droplet retains a near-spherical shape and remains stable; while for higher Reynolds numbers, the droplet deforms to a high extent and becomes unstable."

La gravité est un facteur environnemental majeur. C’est cette force qui a façonné la vie et le fonctionnement de notre organisme est intimement lié à la gravité. Pour rester en bonne santé, nous devons bénéficier de l’influence quotidienne de la gravité et d’un apport alimentaire adapté à notre activité physique. L’objectif de ce travail de thèse est d’étudier le remodelage vasculaire et la dysfonction endothéliale dans des modèles de sédentarité et de troubles métaboliques ainsi que d’explorer des moyens de contre mesures. Un alitement de 60 jours chez des sujets sains masculins induit un remodelage de la macrocirculation au niveau de l’artère fémorale ainsi qu’une dysfonction endothéliale au niveau de la microcirculation. La prise quotidienne d’extraits végétaux complexes issus de la médecine traditionnelle chinoise (Taikong Yangxin) a permis de prévenir l’atteinte endothéliale.Dans un modèle de rat diabétique avec atteinte vasculaire (rats GK),nous avons testé le salidroside, important composé issus du Taikong Yangxin. Bien qu’il n’ait pas d’effets sur le diabète, cecomposé a montré un effet bénéfique sur la vasodilatation endothéliale -dépendante et -indépendante. Dans une dernière partie nous avons étudié chez la souris l’implication du récepteur de type 2 à l’angiotensine et des récepteurs aux estrogènes dans les dysfonctions cardiovasculaires induite par une alimentation hypercalorique. L’inactivité physique induit un remodelage morphologique et fonctionnel au niveau de l’arbre vasculaire ce qui en fait un facteur de risque majeur et indépendant des maladies cardio-vasculaires. Des extraits végétaux simples ou complexes ont des effets bénéfiques sur les fonctions endothéliales. Le récepteur de type 2 à l’angiotensine et ses interactions possibles avec le récepteur aux oestrogènes pourrait être une cible pharmacologique comme contre mesure des atteintes vasculaires liées à l’environnement. / Gravity is a major environmental factor. This force that shaped the life and the functioning of our body is closely related to gravity. To remain healthy, we should benefit from the daily influence of gravity and a food intake adapted to our physical activity. The objective of this thesis is to study vascular remodeling and endothelial dysfunction in sedentary models and metabolic disorders and to explore ways of countermeasures. 60 days of head down bed rest in healthy male induce a macrocirculation remodeling at the femoral artery and an endothelial dysfunction at the microcirculation level. Daily intake of complex plant extracts from traditional Chinese medicine (Taikong Yangxin) helped to prevent endothelial dysfunction. In a diabetic rat model with vascular dysfunction (GK rats), we tested the salidroside, an important compound from the Taikong Yangxin. Although it has no effect on diabetes, this compound showed a beneficial effect on endothelial -dependent and -independent vasodilation. In the last part of our work, we studied the involvement of type 2 angiotensin receptor and estrogen receptor in cardiovascular dysfunction induced by a high calorie diet in mice. Physical inactivity induces morphological and functional remodeling in the vascular tree, making it a major risk factor independent of cardiovascular diseases. Simple or complex plant extracts have beneficial effects on endothelial function. Angiotensin type 2 receptor and its interaction with the estrogen receptor could be a pharmacological target as a countermeasure against vascular damage related to the environment.

The initial stage of liquid phase sintering, involving liquid penetration, agglomerate separation, particle spreading and growth has been investigated in experiments using tungsten heavy alloys. The particle composites used were produced by hot isostatic pressing (HIP) of pure powder mixtures of W-Ni-Fe-(Co). By using different HIP temperatures, volume fractions of tungsten, alloying elements like Cobalt and Sulphur or excluding Iron from the matrix, liquid penetration, agglomerate separation and particle growth conditions were affected. The investigations were performed mainly under microgravity (sounding rockets or parabolic trajectories by airplanes) but at high tungsten particle fractions, short sintering times or at infiltration of solid pure tungsten, they were performed at normal gravity. The liquid penetration of the tungsten agglomerates is explained by initial wetting under non-equilibrium conditions, due to the reaction between the liquid matrix and the particles, and a decrease of interfacial energy. The dissolving of tungsten gives a pressure drop in the penetrating liquid and a driving force for the liquid movement by a suggested parabolic penetration model. For cold worked tungsten, a penetration theory was proposed, where an internal stress release in the penetrated tungsten grains creates space for the advancing liquid. The spreading of the tungsten agglomerates is explained by an interagglomerate melt swelling due to a Kirkendall effect. The liquid matrix undergoes a volume increase since the diffusion rates of Ni-Fe are higher than for W and initial concentration gradients of W and Ni, Fe exists. The suggested model by Kirkendall are also used for an analysis of the interaction behaviour between solid particles and a solidification front and inclusion behaviour in iron base alloys during teeming and deoxidation. The average tungsten particles size decrease initially since part of the tungsten particles is dissolved when the non-equilibrium matrix phase is melting. When equilibrium is reached, the tungsten particles grow in accordance with the Ostwald ripening process by an approximately 1/3 power law. Larger particle fraction of particles showed a higher growth rate, due to shorter diffusion distances between the particles. Cobalt, Sulphur and absence of iron in the matrix were found to increase the growth rate of the tungsten particles due to a higher surface tension between the solid tungsten particles and the matrix melt. / QC 20100528

This document presents a methodology that (using tunable finite element models) allow validating during the development phase of the project, the behavior that equipment and mechanical systems will have once they are installed in microgravity. To achieve this purpose, a general methodology is developed initially. It can be applied to any space system or equipment necessary to know the behavior of any engineering parameter in case this parameter is affected by the particular space conditions. Later, the general methodology in applied over the VIF System. Thus, a concrete methodology for a mechanical system (VIF System) is developed in order to analyze a set of mechanical parameters that allow predicting on ground the mechanical behavior of this system once it is in microgravity. Once defined the mechanical parameters that are required to be analyzed and characterized form the VIF System (forces, moments, velocities, accelerations, etc), then the test phase started. In this phase, test equipment is developed and the VIF System is installed on. The VIF System is externally excited and it is acquired the VIF System behavior, for different levels of excitement, using the appropriate sensors (accelerometers, strain gauges, position sensors, etc). In this way, it is obtained the characterization of VIF System on ground. Once the VIF system has been already characterized on ground, a finite element model (FEM) of the VIF System is performed. This model is properly characterized to achieve the same behavior that the VIF System showed during previous tests. Finally, the FEM model is modified applying a zero gravity condition. This allows getting the VIF System behavior under these particular microgravity conditions. / El present treball planteja una metodologia que, basant-se fonamentalment en models d’elements finits caracteritzables, permet analitzar, a la fase de desenvolupament del projecte, el comportament que equips i sistemes mecànics tindran un cop es trobin instal•lats en condicions de microgravetat. Per aconseguir aquest propòsit, inicialment es desenvolupa una metodologia general que permet ser aplicada a qualsevol equip o sistema espacial on sigui necessari conèixer el comportament de qualsevol paràmetre d’enginyeria que es trobi afectat per les particulars condicions de l’espai. Posteriorment, la teoria general es particularitza pel cas concret d’un sistema mecànic, el Sistema VIF, plantejant així una metodologia particular que permet predir a terra el comportament que tindran un seguit de paràmetres mecànics quan el Sistema VIF es trobi en condicions de microgravetat. Un cop definits els paràmetres mecànics que es volen analitzar i caracteritzar del Sistema VIF (forces, moments, velocitats, acceleracions, etc), s’inicia la fase de test. En aquesta fase es desenvolupa un equip de test on s’hi instal•la el Sistema VIF. L’excitació externa que s’efectua sobre el Sistema VIF permet recollir, usant els sensors adients (acceleròmetres, galgues extensomètriques, sensors de posició, etc), el comportament del Sistema VIF per diferents nivells d’excitació. D’aquesta manera, s’obté la caracterització del Sistema VIF a terra. Una vegada es disposa del Sistema VIF ja caracteritzat a terra, cal realitzat un model d’elements finits (FEM) del Sistema VIF. Aquest model es caracteritza adequadament per tal que assoleixi el mateix comportament que mostrava el Sistema VIF durant la fase de tests. Finalment, s’aplica sobre el model FEM la condició d’ingravidesa imposant un valor de gravetat nul•la. D’aquesta manera, s’obté el comportament del Sistema VIF en aquestes particulars condicions de microgravetat que proporciona l’espai.

Ce travail de thèse porte sur l’étude, numérique et expérimentale, des mécanismes physiques intervenant lors de l’ébullition nucléée. L’étude numérique a été conduite avec un code de simulation numérique directe utilisant une méthode "level set". Cette méthode a été évaluée à travers la simulation de la croissance de bulles dans un liquide surchauffé et de bons accords ont été observés entre nos simulations et les résultats théoriques. Puis, des modèles ont été intégrés à l’outil numérique, afin de simuler la dynamique de la ligne de contact sans changement de phase. Par la suite, ces modèles ont été validés lors de la simulation de cas tests d’étalement de gouttes sur une plaque. Enfin, des simulations de croissance de bulles sur paroi ont été réalisées en considérant le flux provenant de la micro-couche. Parallèlement, une étude sur l’ébullition nucléée, en l’absence de gaz incondensables, a été conduite en microgravité, à l’aide d’une expérience en fusée sonde : SOURCE 2. Une analyse comparative a été menée sur les échanges thermiques obtenus en 1G et en 0G. Puis, l’influence de la configuration de l’ébullition sur les transferts thermiques, en microgravité, a été étudiée. Enfin, l’outil numérique a été utilisé afin de simuler un cas test défini à partir d’une séquence de l’expérience menée en microgravité. Nous avons simulé le remplissage et la pressurisation de la cellule d’essai et un bon accord a été obtenu entre les résultats numériques et les données expérimentales. / In this work, we study different phenomena that occur during nucleate boiling. Firstly, we numerically investigate nucleate boiling by using two phase flow direct numerical simulation based on a level set / Ghost Fluid method. Nucleate boiling on a plate is not only a thermal issue, but also involves multiphase dynamics issues at different scales and at different stages of bubble growth. As a consequence, we divide the whole problem and investigate separately the different phenomena considering their nature and the scale at which they occur. First we analyse the boiling of a static bubble immersed in an overheated liquid. Then, we implement a method that makes it possible to take into account the contact angle hysteresis model. Finally, considering the evaporation of the micro-layer, we perform simulations of bubble growth on a plate. Besides, an experimental study has been performed in the framework of a sounding rocket experiment : SOURCE 2, driven by ESA (European Spatial Agency) in which several partners are involved. For SOURCE 2, a single species configuration is used. No desorption and no thermo-capillary convection occur, the change in the bubble size is only due to vaporisation. Using this device, a comparison between heat transfer on ground and heat transfer in microgravity was performed and the influence of boiling configuration on heat transfer was studied. Finally a sequence of the experiment on the sounding rocket has been numerically simulated. It concerns the filling and the pressurisation of a small reservoir in microgravity. A good agreement was obtained between the simulations and the experimental results.

L’impact de la micropesanteur sur le comportement moteur humain représente une question fondamentale alors même que ce contexte environnemental constitue le quotidien d’hommes et de femmes astronautes durant leurs missions spatiales. En compensant le poids du corps (condition de flottabilité neutre), des méthodes d’entraînement en environnement subaquatique tentent de simuler les conditions d’allégement vécues par ces astronautes. Cependant, du point de vue du contrôle moteur, ces méthodes d’entraînement ne bénéficient d’aucune validité scientifique. Ce travail de thèse a pour objectif d’identifier et de comprendre les stratégies de contrôle du mouvement humain mises en oeuvre en micropesanteur réelle et simulée afin d’assurer une interaction désirée avec l’environnement. Nous avons réalisé trois expérimentations visant à étudier la réalisation de geste d’atteinte à la fois en environnement subaquatique (Exp.1) et lors de deux campagnes de vols paraboliques (Exp.2 et 3). Globalement, nos travaux mettent en exergue le fait qu’un contrôle fin de la flottabilité neutre en immersion améliore la qualité de la simulation de la micropesanteur en environnement subaquatique, optimisant ainsi l’entraînement des astronautes avant leurs missions spatiales. Plus intéressant encore, nos études en micropesanteur réelle suggèrent que l’Homme est capable d’anticiper les effets de l’absence de la gravité sur ses segments corporels lui permettant de gérer avec succès les contraintes spatiotemporelles de ses mouvements volontaires tout en conservant une flexibilité sensorimotrice adéquate dans cet environnement inhabituel. / The impact of microgravity on human motor behavior represents a fundamental issue while this environmental context constitutes the daily life of men and women astronauts during their space missions. By compensating the body weight (neutral buoyancy condition), underwater training methods attempt to simulate weightlessness as experienced by astronauts in space. However, in the field of motor control, these training methods have not been scientifically validated. This doctoral dissertation aims at identifying and understanding the human motor control strategies in real and simulated microgravity to ensure a desired interaction with the environment. We performed three experiments aiming at investigating reaching movements both underwater (Exp.1) and during two parabolic flight campaigns (Exp.2 and 3). Overall, our results highlight that a fine control of neutral buoyancy underwater may improve the quality of the simulation of microgravity environments, thus optimizing astronauts’ training before their space missions. More interestingly, our studies in real microgravity suggest that humans are able to anticipate the effects of gravity release on their moving limbs allowing them to successfully manage spatiotemporal constraints of voluntary movements while preserving sensorimotor flexibility in this unusual environment.

L'évaporation d'une goutte reposant sur un support plat semble être un système relativement simple à étudier et a fait l'objet d'études scientifiques depuis plus d'un siècle. Cependant, l'étude de l'évaporation de gouttes sessiles est toujours d'actualité aujourd'hui avec l'essor de nouvelles techniques de visualisation ou de l'apparition de nouveaux types de fluides complexes.Cette étude expérimentale sera focalisée sur deux aspects distincts :- L'étude sur l'évaporation de fluides purs permettra d'étudier la dynamique d'évaporation et les ondes hydrothermales qui apparaissent dans les gouttes de fluides volatils lors du changement de phase. L'influence du type de fluide (différents alcools et alcanes) et du niveau de gravité (terrestre, lunaire et martienne) seront étudiés. De plus, l'utilisation de différents niveaux de gravité permet de développer un modèle empirique afin de prendre en compte dans le modèle quasi-stationnaire limité par diffusion de la vapeur la convection naturelle qui augmente fortement le débit d'évaporation.- Si les fluides complexes présentent une dynamique de séchage similaire à celle des fluides purs, d'autres mécanismes entrent en jeux, comme la gélification, l'organisation des particules et l'apparition de craquelures (voir Figure 2). Le mouillage et les différents groupes fonctionnels graphés sur les particules seront étudiés en regard du motif final de craquelures. / Sessile droplets are widely found in day to day life: it might be a coffee spilt, rain onto a waterproof raincoat or again, water falling onto a cooking plate. However, despite the vast number of studies devoted to droplets for almost half a century, the fundamental phenomenon of the evaporation of sessile droplets is still a field that attracts a high level of interest due to its wide applicability and the development of new visualisation techniques or new types of complex fluids. This experimental study is focused two distinct aspects:- The evaporation of pure fluids has allow to study hydrothermal waves that appear in the droplets of volatile fluids during phase change. The influence of the type of fluid ---different alcohols and alkanes--- and the gravity levels ---Terrestrial, Lunar and Martian--- is investigated to have a better understanding of the flow motion inside droplet. Moreover, the use of different gravity levels allows to experimentally evidence the contribution of the atmospheric convective transport to sessile droplet evaporation. This investigation has allowed to develop an empirical model to take account of natural convection which greatly increases the evaporation rate in the quasi-steady diffusion-controlled evaporation model.- If complex fluids exhibit an evaporation dynamic similar to pure fluid, other mechanisms come into play, such as gelation, particles organisation and cracks formation. Wetting and different functional groups on the particles graphs will be studied in relation to the final pattern of cracks.

It is well known that surface tension of a liquid has a decisive role in flow dynamics and the eventual equilibrium state, especially in confined flows under low gravity conditions and also in free surface flows. One such instance of a combination of these two cases where surface tension plays an important role is in the microgravity environment of a spacecraft propellant tank. In this specific case both propellant acquisition and residual propellant estimation are critical to the mission objectives particularly in the end-of-life phase. While there have been a few studies pertaining to the equilibrium state in given geometric configurations, the transient flow leading to final state from an initial arbitrary distribution of propellant is rarely described. The present study is aimed at analysing the dynamic behaviour of the liquids under reduced gravity through numerical simulation and also addresses the specific case of propellant flow transient in a cone-in-a-sphere type of tank configuration proposed by Lal and Raghunandan which is likely to result in both improved acquisition and life time estimation of spacecraft. While addressing this specific problem, the present work aims to study the transient nature of such surface tension driven flows in a general form as applicable to other similar problems also. Volume of Fluid (VOF) method for multiphase model in ANSYS FLUENT was adapted with suitable changes for generating numerical solutions to this problem. Simulations were run for three different cone angles of 17o, 21o & 28o with a flat liquid surface for full scale models to measure the rise height and time of rise. Two scaled models of ½ and 1/10th of the original dimensions with the same liquid configuration of the 28o cone angle case were simulated to see if the time scales involved would come down for experimental feasibility. A third simulation of the 1/10th scale model was run with the liquid spread in the tank to imitate the general conditions found in the propellant tank in microgravity. To understand the behaviour of liquids in the microgravity state to changing physical parameters, a set of simulations was run using liquid phases as water and hydrazine with different physical parameters of temperature and surface tension. The theory put forward by Lal and Raghunandan was found to stand firm. In the case of the cone angle of 28o it was observed that in the final equilibrium state the liquid collected towards the apex of the cone with the larger volume fraction of liquid accumulating inside the cone. An addition of a cylindrical section at the bottom of the cone seems to help although not uniformly for all case. The equilibrium settling times for all the three cone angle cases were in the order of 300 to 600 seconds for simulations on a spherical tank of diameter two metres which was close to the actual tank dimension used on spacecraft. Scaled down simulations of 1/10th and ½ the tank geometry with both flat liquid surfaces and spread out liquid volumes showed that the smaller models had equilibrium settling times which were considerably lower (in the order of tens of seconds) than the full scale models. Although smaller, these time scales are larger than the maximum time scales available in drop tower tests which provide a maximum free fall time of around 9 to 10 seconds. Validation of the proposed configuration by flying an aircraft in a parabolic flight path is a possibility that could be explored for the scaled down models since the zero-g duration for these flights is on an average between 15-20 seconds.