SUBJECT: Ph.D. Dissertation Defense
BY: Matthew Perrella
TIME: Wednesday, August 23, 2017, 2:00 p.m.
PLACE: MRDC Building, 4211
TITLE: Periodic Flow Hydrodynamic Resistance Parameters for Various Regenerator Filler Materials at Cryogenic Temperatures
COMMITTEE: Dr. Mostafa Ghiaasiaan, Chair (ME)
Dr. Zhuomin Zhang (ME)
Dr. Devesh Ranjan (ME)
Dr. Mitchell Walker II (AE)
Dr. Ali Kashani (Atlas Scientific)


The regenerator is a critical component of all Stirling and Pulse Tube cryocoolers. It generally consists of a microporous metallic or rare-earth filler material contained within a cylindrical shell. The accurate modeling of the hydrodynamic and thermal behavior of different regenerator materials is crucial to the successful design of cryogenic systems, specifically Stirling and pulse-tube cryocoolers. Previous investigations have used experimental measurements at steady and periodic flow conditions in conjunction with pore-level CFD analysis to determine the pertinent hydrodynamic parameters, namely the Darcy permeability and Forchheimer coefficients. Due to the difficulty associated with experimental measurement at cryogenic temperatures, past investigations where performed at ambient conditions. These results are assumed to be accurate for cryogenic temperatures since, for fully-developed flow, the Darcy and Forchheimer coefficients should depend only on the geometry of the porous medium. There is, however, a pressing need in the literature to determine the hydrodynamic parameters for several regenerator materials under prototypical conditions and verify the validity of the foregoing assumption. In this analysis, regenerators filled with several common materials including spherical Er50Pr50 powder, #400SS mesh, and #325SS mesh were assembled and tested under periodic helium flow at cryogenic temperatures. The mass flow and pressure drop data was correlated with a porous media CFD model to determine the Darcy Permeability and Forchheimer coefficients. These results are compared to the previous investigations at ambient temperature conditions, and the relevance of room-temperature models and correlations to cryogenic temperatures is critically assessed.