Hydrodynamic parameters for ErPr cryocooler regenerator fillers under steady and periodic flow conditions

Abstract

The regenerator, typically a microporous structure that is subject to periodic flow of a cryogenic fluid, is the most critical component of Pulse Tube or Stirling cryocoolers, which are widely used for high-demand defense and aerospace applications. Despite the critical impact of hydrodynamic irreversibilities in the regenerator on the overall cycle efficiency, the impact of the parameters that influence these losses are poorly understood.In this investigation, experiments were conducted in which steady and oscillatory flows of helium were imposed on Er50Pr50 rare-earth regenerator filler material and mass flow and pressure drop data were recorded under ambient temperature conditions. A filler material composed of 63–75μm diameter Er50Pr50 spheres was selected based on current commercially available particle geometries. The flow parameters in the experiments were in the laminar flow range. A computational fluid dynamic (CFD)-assisted method was applied for the analysis and interpretation of the experimental data, with sinusoidal time variations of inlet and exit boundary conditions for the periodic flow case. The permeability and inertial coefficients that led to agreement between the experimental data and computational simulations were iteratively obtained. The resulting Darcy permeability and Forchheimer inertial coefficients are reported herein. A constant Darcy permeability value for all steady and periodic flow tests was found to correlate well to experimental data. The Forchheimer inertial coefficients were correlated and found to be functions of the system charge pressure and the pore-based Reynolds number. The results also show that the periodic flow inertial coefficients are different than the steady flow parameters typically used.