One of the most demanding engineering issues in Inertial Fusion Energy (IFE) reactors is the design of a reaction chamber that can withstand the intense photons, neutrons and charged particles due to the fusion event. Rapid pulsed deposition of energy within thin surface layers of the fusion reactor components such as the first wall may cause severe surface erosion due to ablation. One particularly innovative concept for the protection of IFE reactor cavity first walls from the direct energy deposition associated with soft X-rays and target debris is the thin liquid film protection scheme. In this concept, a thin film of molten liquid lead is fed through a silicon carbide first wall to protect it from the incident irradiations. Numerous studies have been reported in the literature on the thermal response of the liquid film to the intermittent photon and ion irradiations, as well as on the fluid dynamics and stability of liquid films on vertical and upward-facing inclined surfaces. However, no investigation has heretofore been reported on the stability of thin liquid films on downward-facing solid surfaces with liquid injection through (i.e. normal to the surface of) the bounding wall. This flow models the injection of molten liquid lead over the upper end cap of the reactor chamber. The hydrodynamics of this flow can be interpreted as a variation of the Rayleigh-Taylor instability due to the effect of the bounding wall which is continuously fed with the heavier fluid. In order to gain additional insight into the thin liquid film protection scheme, experiments have been conducted to investigate the critical issues associated with this concept. To this end, an experimental test facility has been designed and constructed to simulate the hydrodynamics of thin liquid films injected normal to the surface of and through downward-facing flat walls. In this doctoral thesis, the effect of different design parameters (film thickness, liquid injection velocity, liquid properties and inclination angle) on liquid film stability has been examined. The results address the morphology of the film free surface, the frequency of droplet formation and detachment, the size and penetration depth of the detached droplets, and the interface wave number. These experimental data have been used to validate a novel mechanistic numerical code based on a level contour reconstruction front tracking method over a wide range of parameters. The results of this investigation will allow designers of IFE power plants to identify appropriate windows for successful operation of the thin liquid film protection concept for different coolants.

In all coating applications, a liquid film displaces air in contact with a dry solid substrate. At a low substrate speed a thin uniform wetting line is formed on the substrates surface, but at a high speed the wetting line becomes segmented and unsteady as air becomes entrained between the substrate and the liquid. These air bubbles affect the quality of the coated product and any means to postpone this at higher speeds without changing the specifications of the coating liquid is desirable. This research assesses the validity of a theoretically based concept developed by Blake and Rushack [1] and exploited by Cohu and Benkreira [2] for dip coating. The concept suggests that angling the wetting line by an angle ß would increase the speed at which air is entrained by a factor 1/cos ß. In practice, if achieved this is a significant increase that would result in more economical operation. This concept was tested in a fast coating operation that of curtain coating which is already enhanced by what is known as hydrodynamic assistance [2]. Here we are effectively checking an additional assistance to wetting. The work, performed on a purposed built curtain coater and a rotating die, with a range of fluids showed the concept to hold but provided the data are processed in a way that separate the effect of curtain impingement from the slanting of the wetting line.

With the use of grand canonical molecular dynamics, we studied the slow ompression(0.01m/s) of very thin liquid films made of equimolar mixtures of short and long alkane chains (hexane and hexadecane), and branched and unbranched alkanes (phytane and hexadecane). Besides comparing how these mixtures behave under constant speed compression, we will compare their properties with the behavior and structure of the pure systems undergoing the same type of slow compression. To understand the arrangement of the molecules inside the confinement, we present segmental and molecular density profiles, average length and orientation of the molecules inside well layered gaps. To observe the effects of the compression on the fluids, we present the number of confined molecules, the inlayer orientation, the solvation force and the inlayer diffusion coefficient, versus the thickness of the gap. We observe that pure hexadecane, although liquid at this temperature, starts presenting strong solid-like behavior when it is compressed to thicknesses under 3nm, while pure hexane and pure phytane continue to behave liquid-like except at 1.3nm when they show some weak solid-like features. When hexadecane is mixed with the short straight hexane, it remains liquid down to 2.8nm at which point this mixture behaves solid-like with an enhanced alignment of the long molecules not seen in its pure form; but when hexadecane is mixed with the branched phytane the system does not present the solid-like features seen when hexadecane is compressed pure.

Film flow of a suspension has been investigated both experimentally and theoretically. Gravity-driven free-surface inclined plane flow of a suspension of neutrally buoyant particles has been investigated using a stereoscopic particle imaging velocimetry technique. Particles have been shown to migrate away from the solid surface, and the film thickness has been shown to decrease as the fluid moves down the inclined plane. The free surface has been characterized using a light reflection technique, which shows that surface topography is affected by the inclination angle, and the particle concentration. This flow has been modeled based on a suspension normal stress approach. A boundary condition at the free surface has been examined, and model predictions have been compared with experimental results. The model predicts that the film thickness, relative to its initial value, will decrease with the bulk particle concentration. The thin film flow over the inner cylinder in partially filled Couette flow of a suspension has been experimentally investigated as well as modeled. Concentration bands have been shown to form under a variety of different fill fractions, bulk particle concentrations, inclination angles, ratio of inner to outer cylinder, and rotation rates of the inner cylinder. The banding phenomena ranges from a regime where bands are small, mobile and relatively similar in concentration to the bulk, to a regime where the concentration bands are larger, stationary, and where the space between them is completely devoid of particles. The role of the film thickness in the band formation process has been investigated, and has led to a model for the band formation process based on a difference in the rate that fluid can drain from height fluctuations relative to the particles.

An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness. A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters. Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.

Thin liquid layers have been proposed for heat extraction and protection of the solid surfaces of divertors in magnetic fusion reactors. A number of conceptual designs for plasma-facing components (PFC) use stationary and flowing liquid layers as a renewable first wall for reactor chambers to remove heat and shield solid surfaces from damaging radiation while maintaining acceptable plasma purity levels. Such liquid-protected PFC have the potential to make fusion more commercially attractive by increasing reactor lifetimes and decreasing failure rates. The results of this research will help identify the parameter ranges for successful operation of such protection schemes. This thesis investigates the thermocapillary behavior of axisymmetric horizontal liquid layers with initial heights from 0.27 to 3.0 mm. A negative radial temperature gradient is imposed at the bottom of the liquid layer. Experimental, numerical and asymptotic analyses were carried out for thin layers where buoyancy forces are negligible. A novel asymptotic solution for this axisymmetric geometry was derived from the previous two-dimensional long-wave analysis by Sen et al. (1982). A numerical simulation using the level contour reconstruction method was used to follow the evolution of the liquid-gas interface above an axisymmetric non-isothermal solid surface. Experimental validation of the theoretical and numerical studies was performed using silicone oils of various viscosities (μ = 0.48 × 10-2 9.6 × 10-2 N s/m2). Two measurement techniques, a needle contact method and laser-confocal displacement method, were employed to obtain height profiles for applied temperature differences up to 65°C. Finally, reflectance shadowgraphy was used to visualize free-surface deformation and classify flow regimes in thick layers, where the assumptions of negligible buoyancy and axisymmetric flow are no longer valid. The results of this investigation will allow designers to determine operating windows for successful implementation of liquid-protected PFC.

In electromagnetic launcher (EML) systems, the behavior of the materials and forces at the armature-rail interface involves fluid mechanics, electromagnetics, thermal effects, contact mechanics and deformation mechanics. These factors must interact successfully in order for a launch to be successful. A lubricant film either deposited on the rails prior to launch or injected from the armature during launch has been suggested as a means of improving the electrical conductivity of the rail-armature interface and of avoiding the occurrence of arcing. The fluid pressure generated by such film, together with the magnetic force, the contact force and the uneven temperature field in the armature, deforms the armature and changes the interface gap shape. An analytical model to study the interfacial behavior under these influences is necessary in order to predict the performance of a potential EML design and to provide optimization information. Studies of this interfacial behavior have been done by a number of researchers. However, many critical factors were not included, such as surface roughness, cavitation, injection, magnetic lateral force, interface deformation and thermal effects. The three models presented in this study investigate the influence of those factors on the EML interface problem. The magneto-hydrodynamic (MHD) model establishes a description of the lubrication process under electromagnetic stress but neglects interface deformation. The magneto-elastohydrodynamic (MEHD) model extends the MHD model by considering the lateral magnetic force, interface contact force and elastic deformation. Finally, the magneto-elastothermohydrodynamic (METHD) model adds the thermal effects to the deformation analysis. A coupled analysis of the interface behavior with the METHD model is developed and the history of a typical launch is studied. Detailed injection, lubrication and launch processes are revealed and the performance is predicted. A failed launch is simulated and the cause of failure is identified to be debris left on the rails. Several operation and design parameters, such as rail surface profile, electric current pattern, reservoir load, lubrication length, pocket size and geometry, injection conduit diameter, are analyzed and a recommended injection design procedure is developed. A scaling study is performed by doubling the dimensions to predict the scaling effects. In the end, the base case configuration and scaled configuration are optimized using the technique developed in this study.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2005. / Said I. Abdel-Khalik, Committee Chair ; Sheldon M. Jeter, Committee Member ; Minami Yoda, Committee Member. Includes bibliographical references.

Les films liquides tombants et cisaillés par un contre-écoulement de gaz jouent un rôle prépondérant dans de nombreux processus industriels. En effet, les ondes à l'interface gaz/liquide augmentent sensiblement les transferts de chaleur et de masse entre les deux phases. Nous avons cherché, dans un premier temps, à mieux comprendre la dynamique 2D et 3D d'un film liquide tombant sur un plan incliné grâce à des outils expérimentaux (visualisations par ombroscopie, mesures d'épaisseur) et numériques (modèles d'équations réduits, analyses de stabilité). Le point optimal de fonctionnement des procédés se situe proche de la limite d'engorgement caractérisée par un envahissement de l'espace disponible par la phase liquide. Notre objectif, dans un second temps, a été de mieux comprendre les mécanismes physiques à l'origine de l'engorgement grâce à la réalisation d'expériences en géométrie simplifiée (canal plan). Ces travaux s'inscrivent dans le cadre d'un contrat CIFRE entre le laboratoire FAST et la société Air Liquide afin d'appliquer les résultats au procédé de distillation de l'air. Deux dispositifs expérimentaux ont été mis en place : l'un à température ambiante (étude fondamentale), l'autre à température cryogénique (étude appliquée et confidentielle). / Falling liquid films with or without a gazeous counter-flow play a leading role in many industrial process. Indeed, the waves at the gas/liquid interface increase noticeably the heat and mass transfer between both phases. We have tried, as a first step, to better understand the 2D and 3D dynamics of a liquid film falling down an inclined plane using experimental (shadowgraphy visualisations, thickness measurements) and numerical (reduced equation models, stability analysis) tools. The optimal operating conditions are closed to the limit of flooding characterized by an invasion of the available space by the liquid phase. Our goal, as a second step, has been to better understand the physical mechanisms at the origin of flooding using simplified geometry experiments (plane channel). These works fall within a CIFRE contract between the FAST laboratory and the Air Liquide company in order to apply the results to the air distillation process. Two experimental set-ups have been built : one at room temperature (fundamental study), the other at cryogenic temperature (applied and confidential study).

Les mousses liquides soumises à du cisaillement présentent une très grande viscosité, mais l'origine locale de la dissipation se produisant pendant cette déformation est encore mal comprise. Dans le but d'apporter quelques éléments de réponses à cette importante question ouverte, notre travail décrit le comportement observé sur quelques films connectés lorsqu'une déformation leur est appliquée. Nous avons créé un montage permettant de fabriquer un pattern élémentaire de mousse, et de modifier la taille de chaque film en contrôlant la géométrie du cadre qui le supporte. Ce montage original, auquel s'ajoute une combinaison d'appareils optiques, nous permet de révéler les processus se produisant dans le film, notamment la compétition entre son allongement ou compression, et l'extraction d'un nouveau film depuis les ménisques raccordant les films. Nous montrons de plus que cette compétition dynamique dans un film donné est affectée par la déformation de ses premiers et seconds films voisins. La géométrie particulière du montage nous a également permis de découvrir et de décrire pour la première fois une instabilité gravitationnelle se produisant lorsqu'un film épais se situe au-dessus d'un film plus mince. Nous avons mesuré la longueur d'onde de l'instabilité et l'avons comparée à des prédictions théoriques en régime linéaire. Ces différents écoulements affectent la distribution d'épaisseur dans le film, et peuvent ainsi jouer un rôle important sur la viscosité ou sur la stabilité des mousses 3D. Finalement, le montage utilisé pourra s'avérer utile à l'avenir comme rhéomètre de films liquides. / Liquid foams under shearing exhibit a large effective viscosity, and the understanding of the local origin of the dissipation occurring during deformation is unknown. In the aim to contribute to this important open problem, we tried to describe the behavior of a few connected films under deformation. We created a setup allowing to make an elementary foam sample and to modify each film size by controlling the shape of the deformable frame supporting the films. This original setup together with a combination of optical devices allowed us to reveal processes happening in the film, and especially the competition between film stretch or compression, and extraction of a new film from the menisci connecting the films. Importantly, we show that this dynamical competition in a given film is affected by the deformation of its first and even second neighbors. The unique geometry of the setup gave us the opportunity to discover and describe for the first time a gravitational instability which takes place when a thicker film is on top of a thinner one. We measured the wavelength and compared it to theoretical predictions in the linear regime. These different flows affect the thickness distribution, and may thus play an important role in the viscosity or in the stability of 3D foams. As a perspective, the designed setup could prove to be useful as a liquid film rheometer.