SUBJECT: Ph.D. Dissertation Defense
BY: Mihir Pathak
TIME: Thursday, May 16, 2013, 2:00 p.m.
PLACE: Love Building, 210
TITLE: Periodic Flow Physics in Porous Media of Regenerative Cryocoolers
COMMITTEE: Dr. S. Mostafa Ghiaasiaan, Chair (ME)
Dr. Prateen Desai (ME)
Dr. Comas Haynes (ME)
Dr. Mitchel Walker (AE)
Dr. Alan Wilhite (AE)
Dr. Ray Radebaugh (NIST)


Pulse tube cryocoolers (PTC) are a class of rugged and high-endurance refrigeration systems that operate without moving parts at their low temperature ends, and are capable of reaching temperatures down to and below 120 K. Among the challenges facing the PTC research community is the improvement system efficiency, which is a direct function of the regenerator component performance. A PTC implements the theory of oscillatory compression and expansion of the gas within a closed volume to achieve desired refrigeration. An important deficiency with respect to the state of art models dealing with PTCs is the limited understanding of the hydrodynamic and thermal transport parameters associated with periodic flow of a cryogenic fluid in micro-porous structures. In view of the above, the goals of this investigation include: 1) experimentally measuring and correlating the steady and periodic flow Darcy permeability and Forchheimer’s inertial hydrodynamic parameters for available rare-Earth ErPr regenerator filler; 2) employing a CFD-assisted methodology for the unambiguous quantification of the Darcy permeability and Forchheimer’s inertial hydrodynamic parameters, based on experimentally-measured steady and periodic flow pressure drops in porous structures representing recently-developed regenerator fillers; and 3) performing a direct numerical pore-level investigation for steady and periodic flows in a generic porous medium in order to elucidate the flow and transport processes, and quantify the solid-fluid the hydrodynamic and heat transfer parameters.