Pulse Tube Cryocoolers (PTC) is widely used in aerospace and missile guiding systems where extreme reliability and ruggedness are crucial. PTCs, in particular, are a class of rugged refrigeration systems that are capable of maintaining temperatures as low as 4 K, without a moving part in their cold end. The operation of PTCs is based on complicated and poorly-understood solid-fluid interactions involving periodic flows of a cryogenic fluid in micro porous structures. Currently, PTCs is often modeled as one-dimensional flow fields using methods whose relevance to cryocoolers is at best questionable. Furthermore, recent CFD-based investigations have underscored the need for adequate closure relations representing periodic flows in anisotropic micro porous media, and have shown that multi-dimensional effects can be significant in PTCs. The objectives of this investigation were to experimentally measure and correlate the anisotropic hydrodynamic parameters for typical micro porous structures that are used in the regenerators of PTCs fillers; perform modeling and CFD-based simulations to elucidate the component and system-level thermo-fluidic processes in modern pulse tube cryocooler designs; and perform a preliminary CFD-based assessment of the effect of miniaturization on the thermal performance of a current PTC design. In the experiments, the measurement and correlation of the directional (axial and radial) permeabilities and Forchheimer s inertial coefficients of meshed screen, sintered mesh, foam metal, and stacked micro-machined plate regenerator fillers were of interest. Hydrodynamic parameters under steady-state conditions were addressed first. Pressure drops were measured for purely axial flow in cylindrical test sections and predominantly radial flows in annular test sections that contained regenerator fillers of interest, under steady-state conditions. The permeabilities and Forchheimer s inertial coefficients were then obtained in an iterative process where agreement between the data and the predictions of detailed CFD simulations addressing the entire test sections and their surroundings were sought. Periodic flows were then addressed. Using high frequency pressure transducers and hot wire anemometry, instantaneous pressures and mass fluxes are measured under periodic purely axial flow conditions. CFD simulations of the experiments were then performed, whereby permeabilities and Forchheimer coefficients that bring about agreement between data and simulation results were calculated.

Il est bien connu que les particules inertielles dans un écoulement périodique ont tendance à se focaliser sur des trajectoires privilégiées. Le but de ce travail de thèse est d'étudier l'influence de cette focalisation sur le transport et la sédimentation de particules dans une fracture plane à rugosité périodique. Tout d'abord, un écoulement monophasique dans une fracture est analysé asymptotiquement dans le cas de faible rugosité. Les résultats classiques de la théorie de la lubrification inertielle sont généralisés au cas de fractures avec des parois asymétriques. Les corrections non linéaires à la loi de Darcy sont calculées explicitement en fonction des facteurs géométriques de la fracture. Le transport de particules dans une fracture horizontal est étudié asymptotiquement dans le cas de particules de faible inertie. Les particules se focalisent sur une trajectoire attractrice, si le débit d'écoulement est assez fort par rapport à la gravité. Un diagramme complet de focalisation a été obtenu, qui prédit l'existence de l'attracteur en fonction du nombre de Froude et des facteurs géométriques de la fracture. Les paramètres quantitatifs du transport ont été calculés également. L'influence de la force de portance sur la migration de particules a été étudiée également. Dans un canal vertical, la portance (provoquée par la gravité) modifie le nombre d'attracteurs et leurs positions. En absence de gravité, la portance peut provoquer une dynamique chaotique des particules. En outre, le captage des particules par une paire de tourbillons a été étudié. Le diagramme d'accumulation obtenu démontre que toute paire de tourbillons peut être un piège à particules / It is well-known that inertial particles tend to focus on preferential trajectories in periodic flows. The goal of this thesis was to study the joint effect of particle focusing and sedimentation on their transport through a model 2D fracture with a periodic corrugation. First, single-phase flow though the fracture has been considered: the classical results of the inertial lubrication theory are revisited in order to include asymmetric fracture geometries. Cubic corrections to Darcy's law have been found analytically and expressed in terms of two geometric factors, describing channel geometry. For weakly-inertial particles in a horizontal channel it has been shown that, when inertia is strong enough to balance out the gravity forces, particles focus to some attracting trajectory inside the channel. The full trapping diagram is obtained, that predicts the existence of such attracting trajectory regime depending on the Froude number and on geometric factors. Numerical simulations confirm the asymptotic results for particles with small response times. The influence of the lift force on particle migration has also been studied. In a vertical channel the lift is induced by gravity and leads to complex trapping diagrams. In the absence of gravity the lift is caused by inertial lead/lag of particles and can lead to chaotic particle dynamics. Finally, for dust particles in a vortex pair it has been shown that particles can be trapped into one or two equilibrium points in a reference frame rotating with the vortices. A full trapping diagram has been obtained, showing that any pair of vortices can trap particles, independently of their strength ratio and the direction of rotation