Cette thèse porte sur l'amélioration de la modélisation des écoulements à bulles, et plus particulièrement des écoule- ments bouillants, dont la compréhension et la prédiction est essentielle pour de nombreuses applications industrielles. L'axe de recherche choisi ici est la prise en compte du caractère polydisperse de la population de bulles, autrement dit du fait que toutes les bulles n'aient ni la même taille, ni la même vitesse. Divers mécanismes peuvent être cités pour expliquer l'existence de la variété de tailles de bulles ; dans notre cas on peut principalement citer la coalescence et la fragmentation de bulles, la cinématique de changement de phase ou encore la compressibilité du gaz à l'intérieur des bulles. De cette polydispersion en taille découle également une polydispersion en vitesse, puisqu'il est bien connu que la vitesse de déplacement d'une bulle est fonction de sa taille. Un modèle moyenné spécialement adapté aux écoulements à phase dispersée est présenté dans ce manuscrit, modèle que l'on pourra caractériser de polydisperse puisque prenant en compte une fonction de distribution en taille et en vi- tesse des bulles. Deux lois mathématiques particulières, une loi quadratique et une loi cubique, sont proposées dans ce manuscrit pour modéliser la fonction de distribution en taille des bulles, son évolution spatio-temporelle étant obtenue à l'aide la méthode des moments. Ces deux lois ayant une expression mathématique relativement simple, les différents termes d'échanges entre phases ont pu être fermés dans un cadre polydisperse. Ce modèle moyenné polydisperse a été implanté dans le code de calcul NEPTUNE_CFD, puis testé en tentant de reproduire par la simulation l'expérience DEBORA du CEA Grenoble, expérience dédiée à l'étude des écoulements bouillants sous-saturés. / The objective of this work was to improve the modelling of boiling bubbly flows.We focused on the modelling of the polydisperse aspect of a bubble population, i.e. the fact that bubbles have different sizes and different velocities. The multi-size aspect of a bubble pupolation can originate from various mechanisms. For the bubbly flows we are interested in, bubble coalescence, bubble break-up, phase change kinematics and/or gas compressibility inside the bubbles can be mentionned. Since, bubble velocity depends on bubble size, the bubble size spectrum also leads to a bubble velocity spectrum. An averaged model especially dedicated to dispersed flows is introduced in this thesis. Closure of averaged inter- phase transfer terms are written in a polydisperse framework, i.e. using a distribution function of the bubble sizes and velocities. A quadratic law and a cubic law are here proposed for the modelling of the size distribution function, whose evolution in space and time is then obtained with the use of the moment method. Our averaged model has been implemented in the NEPTUNE_CFD computation code in order to simulate the DEBORA experiment. The ability of our model to deal with sub-cooled boiling flows has therefore been evaluated.

Resource degradation is a significant problem in the world, which is directly related to the textile and fashion industry. Efficient use of the material has been identified as an essential aspect to be addressed seriously. It is a critical topic that has attracted the attention of people and companies in recent years and has become a fundamental issue of sustainability. This research study was based on UN sustainable development goals number 12 and 8, which focuses on resource efficiency. The research is designed in considering fabric consumption, which has a significant impact on the textile and clothing industry to contribute to a brighter future and a more sustainable life. The purpose of this study is to reduce the fabric consumption through improving marker efficiency. The research focuses on investigating the behaviour of marker efficiency concerning usable fabric widths, markers with different sizes and marker with style combinations to reduce fabric consumption. The improvements of the existing markers lead to reduce fabric wastage during the cutting process while improving resource efficiency in consumption and production. In this study, the explanatory sequential design of mixed research method is employed with carrying out experiments to collect and analyze quantitative data, explained and elaborated with qualitative findings through expert interviews to get insights into the quantitative findings in a deductive approach. The marker efficiency significantly varies according to the combination of sizes and style and usable fabric width. The improvements of the marker efficiency, reduce the fabric consumption per garment and increase resource efficiency while preventing waste generation. A saving of 1% of a material which consumed millions of tons per year, significantly affect on reducing resource depletion and environmental pollution. This study is limited to five usable fabric widths, four size marker combinations and two style combinations. Moreover, it is focused on material efficiency, and cost efficiency is not considered. There are possibilities for clothing manufactures’ to improve resource efficiency by improving marker efficiency while planning the demand, considering multi-size and multi-style markers. They can concern usable fabric widths, which provide higher marker efficiencies during material purchasing.