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Pressurized water reactor nuclear plants, currently under construction, have been designed with passive containment cooling systems. Turbulent, natural-convective condensation, with high non-condensable mass fraction, on the walls of the containment vessel is a primary heat transfer mechanism in these new plant designs. A number of studies have been completed over the past two decades to justify use of the heat and mass transfer analogy for this scenario. A majority of these studies are founded upon natural-convective heat transfer correlations and apply a diffusion layer model to couple heat and mass transfer. Reasonable success in predicting experimental trends for vertical surfaces has been achieved when correction factors are applied. The corrections are attributed to mass transfer suction, film waviness or mist formation, even though little experimental evidence exists to justify these claims. This work examines the influence of film waves and mass transfer suction on the turbulent, natural-convective condensing flow with non-condensable gas present. Testing was conducted using 0.457 m x 2.13 m and a 0.914 m x 2.13 m condensing surfaces suspended in a large pressure vessel. The test surfaces could be rotated from vertical to horizontal to examine the inclination angle effect. The test facility implements relatively high accuracy calorimetric and condensate mass flow measurements to validate the measured heat and mass transfer rates. Test results show that application of the Bayley (1955) and Al-Arabi and Sakr (1988) heat transfer correlations using the heat and mass transfer analogy is appropriate for conditions in which the liquid film remains laminar. For transitional and wavy film flows, a clear augmentation in heat transfer was observed due to disruption of the gas layer by film waves. This result has implications for the scalability of existing correlations. A new correlation is proposed and results compared to several other datasets.

Dans ce travail, on s'intéresse à l'étude mathématique des phénomènes de charge des satellites dans les orbites basses (Low Earth Orbit, LEO).Aprės un rappel du contexte physique, nous dérivons un modėle de type bi-fluide pour le plasma entourant le satellite. En effet, en orbite LEO, le plasma peut être considéré fortement collisionnel comparativement au cas par exemple des orbites polaires ( Polar Earth Orbit, PEO). Le modėle utilisé est composé des équations d'Euler pour la conservation de la masse, de la quantité de mouvement et de l'énergie ainsi que de l'équation de Poisson pour le potentiel électrostatique et est obtenu dans le cas tri-dimensionnel.Pour l'étude mathématique du modėle nous nous concentrons sur le cas uni-dimensionnel afin de mettre en évidence les principales difficultés.Nous considérons d'abord les équations d'Euler stationnaires couplées à l'équation de Poisson. La dynamique de charge du satellite est alors contenue dans les conditions limites qui font apparaître la dérivée en temps du potentiel. Nous donnons des résultats d'existence et d'unicité de solution ainsi que des simulations numériques. Ici nous utilisons uniquement des conditions limites de Dirichlet pour les quantités macroscopiques. Elles peuvent être loin de celles qui sont physiquement intéressantes et que nous ne connaissons qu'au niveau microscopique.C'est pourquoi, nous proposons ensuite une solution numérique permettant d'utiliser dans la simulation des équations évolutives d'Euler des conditions limites venant d'une modélisation microscopique au travers d'un régime où le libre parcours moyen est petit. La condition limite vient d'une analyse de couche limite qui s'explique par le fait que le flux cinétique peut être loin de l'équilibre thermodynamique. / In this work we are concerned with a mathematical study of the spacecraft charging phenomena of Low Earth Orbit (LEO).After recalling the physical context, we derive a two-fluid type model for the plasma around the spacecraft. Indeed in LEO, the plasma can be considered highly colisional compared with the case for example of Polar Earth Orbit (PEO). The model used here consist in the Euler equations for the conservation of mass, momentum and energy plus a Poisson equation for the electrostatic potentiel and is derived in the three dimensionnal case.For the mathematical study of the model, we concentrate our attention on the one dimensionnal case to point out the main difficulties.We first consider the stationnary Euler equations coupled to the Poisson equation. The charging dynamics is then embodied into the boundary conditions where the time derivative of the potentiel appears. We present rigourous existence and unicity results together with numerical simulations. Here we only use some Dirichlet boundary conditions for the macroscopic quantities. They can be far from the ones of physical interest wich we only know at a kinetic level.That's why we next propose a numerical solution to incorporate in the simulation of the evolutive Euler equations boundary condition that come from a microscopic modeling in the small mean free path regime. THe boundary condition relies on the analysis of boundary layers formation that accounts from the fact that the incoming kinetic flux might be far from the equilibrium.

My thesis, Condensation, is centered on seeing and the limits of our perceptions. I’m interested in the psychological and emotional effects of visual phenomena and am exploring this area through glass’s ability to reflect and obscure. I’m also experimenting with photography because it’s simply documentation of reflection. The solidity of reflection whether on glass, photography, or water is something that I’m questioning. The viewer assumes its physicality, but what we accept as conclusive is at times a construct. The palpability of reflection then disintegrates into the residue of sight. I’ve been contemplating our eyes perceptual limits and what our mind sees in relation to what’s shown. The act of seeing works as a catalyst to initiate doubt in our perceptions and reminds us of our eyes ability to reveal and conceal information. Visual shifting has led me to question the idea of boundaries in both physical and mental spheres.

M.Ing. / Since the promulgation of the Montreal Protocol many refrigerants needed to be phased out. R-22, which is a widely used refrigerant in refrigeration systems, was one of these. Many replacements have been found throughout the years but very few have the same refrigeration capacity without being penalised by an increase in pressure drop. R-407C is one of the refrigerants having the potential to replace R-22 as it has the same theoretical coefficient of performance and has a lower global warming potential. However, due to its zeotropic characteristics there is a degradation in heat transfer during evaporation and condensation attributed to mass transfer resistance. Thus, augmentation techniques are needed not only to increase the heat capacity, but also to achieve an increase without incurring an excessive pressure drop. One approach to cope with this problem is to make use of the recently developed herringbone micro-fin tubes. Unfortunately very little data exists for refrigerants undergoing condensation inside herringbone micro-fin tubes. There is also little pressure drop information available for this type of tube. An experimental set-up was designed to determine the characteristics of this type of tube due to the scarcity of information. With the aid of current literature, various techniques were used to determine the pressure drops inside the herringbone micro-fin tube. One of these techniques was the use of the Kattan-Thome-Favrat flow regime map which helped to identify the flow patterns inside the tube. Knowledge of the type of flow occurring inside the tube helped to clarify the behaviour of the pressure drop relationships. The type of refrigerant being used also affected the behaviour of the pressure drop curves. A low-pressure refrigerant had a higher pressure drop due to the high vapour velocities achieved. Another cause for excessive pressure drop is the friction created by the high velocity vapour and condensate inside the tube. Many relationships for the friction factor exist and these are used to analyse the experimental data.The experimental facility comprised of a vapour compression loop and a water loop. The vapour compression loop consisted of a hermetically sealed compressor with a cooling capacity of 9.6 kW, a manually operated expansion valve and an evaporator. Three condensers were tested, namely a smooth tube, a helical micro-fin tube, and a herringbone micro-fin tube. The condensers were of the tube-in-tube type with the refrigerant flowing in the inner tube and the water in counter flow in the annulus. The hot water loop was used as a source for the evaporator and a cold loop as a heat sink for the condenser. Three refrigerants were tested, namely R-22, R-134a, and R-407C, all operating at a nominal saturation temperature of 40°C and at mass fluxes between 300 and 800 kg/m 2s. Accurate sensors and transducers were used to measure the temperatures, pressures, and mass flows at predefined points. Video cameras were attached to sight glasses to aid in the identification of the type of flow regime. Data were captured using a computerised data acquisition programme designed specifically for use with the experimental study. The experimental results showed that transition between the annular and intermittent flow regimes occurred at around 25% vapour quality for the herringbone micro-fin tube, as opposed to 30% for the helical micro-fin tube and 50% for the smooth tube. Pressure drops for the herringbone micro-fin tube were higher than those for the smooth tube but slightly lower than those for the helical micro-fin tube when using refrigerants R-22 and R-134a. The correlation of Liebenberg was modified for the pressure drops inside the herringbone micro-fin tube and gave a mean deviation of 12%. The efficiency ratio for the herringbone tube using R-22 was 1.85 and 1.69 when compared with the helical micro-fin and smooth tube respectively. For R-134 the efficiency ratio was 2.02 and 2.13 when compared with the helical micro-fin and smooth tube respectively, while for R-407C it was 1.58 and 1.26 for the two respectively. It was also concluded that R-407C could be used as a replacement refrigerant for R-22when used with a herringbone micro-fin tube.

M.Ing. / The Montreal Protocol led to the phasing-out of ozone layer depleting refrigerants and replacing them with more environmentally friendly refrigerants, which in many cases caused heat transfer degradation in heat exchanger equipment. To make up for the heat transfer degradation, there was a need for the application of heat transfer enhancement techniques. One such technique is the use of micro-fin tubes as opposed to traditional smooth tubes. The purpose of this study is to develop a flow regime map for the condensation of R-22, R-407C and R-134a in a herringbone micro-fin tube. It was perceived that with the knowledge of flow patterns inside the tube and especially the annular-to-intermittent transition, it is possible to perform improved analyses of the heat transfer and pressure drop characteristics. Experimental and analytical work was performed to investigate the flow regimes during condensation of the refrigerants in smooth, helical micro-fin and herringbone micro-fin tubes at an average saturation temperature of 40oC, with mass fluxes ranging from 300 to 800 kg/m2s. Condensation occurred in tube-in-tube type condensers with cooling water flowing in the annulus and the refrigerant in the inner tubes. The condensers consisted of eight sub-sections to allow for the acquisition of sectional heat transfer and pressure data. Various criteria were considered in order to generate flow regime maps. The Thome flow regime transition criterion was used and complemented with visually-observed and photographic imaging, as well as the objective power spectral density distributions of the pressure signals of the condensing refrigerants. The observed flow regimes were mainly annular flow and intermittent flow. Stratified-wavy flow was observed at low mass fluxes and low vapour qualities. There were notable similarities in the flow pattern between the smooth and micro-fin tubes. However, the experimental results show that the transition from annular to intermittent flow regimes occurred at average vapour quality values of 0.26, 0.29 and 0.48 for the herringbone micro-fin, the helical micro-fin and smooth tubes respectively. The combined analyses assisted in adapting the helical micro-fin tube condensing flow pattern map, to ensure its application in accurately predicting herringbone micro-fin tube condensation. The new transition criterion effectively predicts the delay in transition from annular to intermittent flow for all three refrigerants, condensing in the herringbone micro-fin tube.

Cette thèse présente une description nouvelle et les conséquences physiques de la seconde transition pour les gaz parfait de Bose dans des milieux fortement anisotropes. Nous développons ainsi dans le chapitre 1 une approche dite d'échelle qui permet de revisiter les différents concepts autour de la condensation de Bose-Einstein : la condensation généralisée (M.van den Berg, J.Lewis, J.Pulé, 1986), les cycles infinis (R.Feynmann, 1953) et les corrélation à longue portée (O.Penrose, L. Onsager, 1956). Cette nouvelle approche nous permet, dans un premier temps, de montrer l'équivalence entre ces critères de condensation et entre les différentes classifications de condensats. Ensuite, dans les chapitres 2 et 3, nous caractérisons, via notre méthode, les effets physiques (nouvelle température critique, modification des fractions condensées, localisations énergétiques et longueurs de cohérence) pour les gaz de Bose dans des boîtes quasi-2D (Ch2) et des pièges harmoniques quasi-1D (Ch3) exponentiellement anisotropes. Dans le chapitre 4, nous discutons principalement l'analogie entre cycles et polymère à la P.-G de Gennes que fourni notre description des cycles via notre méthode d'échelle / This thesis presents a description and new physical results about the second transition for the Bose ideal gas i n strongly anisotropes systems. Thus, we develop in Chapter 1 an approach of scale that allowq us to revisit the concepts around the Bose-Einstein condensation : generalised condesation (M. van den Berg, J. Lewis, J. Pule, 1986), infinite cycles (R. Feynman, 1953) and off-diagonal-long-range order (O. Penrose, L. Osager, 1956). This new approach allows us, initially, to show equivalence between these criteria are condensation between different classifications of condensates. The, in Chapter 2 and 3, we characterize using our method, the physical (new critical temperature, changing fractions condensed localization energy and coherence lenghts) for the Bose gas cans in quasi-2D (Ch2) and of quasi-1D harmonic traps (Ch3) exponentially anisotropic. In Chapter 4, we discuss mainly the analogy between cycles and the polymer (P.-G de Gennes description), using our scaling argument for cycles.