Analysis of mixing and heat transfer intensification mechanisms by combining passive methods in tubular internal flows : application continuous chemical reactors and solar collectors

The energy efficiency of thermal components and systems, as well as the improvement and development of new technologies, are major challenges today. In this general context, the work of this thesis is aimed at improving the thermal performance and mixing of multifunctional heat exchanger-reactors, which are more than ever key components. To achieve this goal, a passive intensification technique has been explored, involving the application of two types of macro-wall deformations on the walls of a laminar flow annular tube. The study initially focused on characterizing the secondary flows created by each of the deformations applied separately in order to enhance heat transfer.Subsequently, a combination of successive and alternating radial deformations on the outer wall, coupled with a geometry that induces swirl motion on the inner wall, significantly increased mixing by promoting chaotic advection within the flow. The understanding of the underlying physical mechanisms relied on numerical analysis of local thermal and hydraulic fields, identification of vortical structures, Poincaré sections, as well as the determination of thermo-hydraulic and mixing performance at both global and local levels. An experimental evaluation of hydraulic behavior was also conducted using the residence time distribution method, partially validating the chosen numerical model in this study. Finally, the last part of the study was dedicated to the application of the intensification concepts studied to the case of a concentrated solar thermal collector.