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Title Periodic flow physics in porous media of regenerative cryocoolers
URL
Publication Date
Date Accessioned
Degree PhD
Discipline/Department Mechanical Engineering
Degree Level doctoral
University/Publisher Georgia Tech
Abstract 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 123 K. PTCs are particularly suitable for applications in space, guiding systems, cryosurgery, medicine preservation, superconducting electronics, magnetic resonance imaging, weather observation, and liquefaction of gases. Applications of these cryocoolers span across many industries including defense, aerospace, biomedical, energy, and high tech. Among the challenges facing the PTC research community is the improvement of 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 hydrodynamic and heat transfer parameters. These hydrodynamic resistances parameters were found to be significantly different for steady and oscillatory flows.
Subjects/Keywords Regenerator; ErPr; Nusselt; Porous media; Pore level; Periodic flow; Oscillatory flow; Darcy permeability; Forchheimer; Hydrodynamic; Thermal dispersion; Conjugate; Heat transfer; CFD; Pulse tube; Cryocooler; Cryogenics; Physics; Rare-Earth; Steady flow; Low temperature engineering; Materials at low temperatures; Porous materials Thermal properties; Porous materials
Contributors Ghiaasiaan, S. Mostafa (advisor); Desai, Prateen (committee member); Walker, Mitchell (committee member); Wilhite, Alan (committee member); Haynes, Comas (committee member); Radebaugh, Ray (committee member)
Language en
Country of Publication us
Record ID handle:1853/49056
Repository gatech
Date Indexed 2020-05-13
Issued Date 2013-05-23 00:00:00
Note [degree] Ph.D.;

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…Figure 2.12: Sample grid system [44]. 44 Figure 2.13: Forchheimer term as a function of Reynolds number for the steady flow [44]. 47 Figure 2.14: Variation of the instantaneous Forchheimer coefficients for different porosities […

…permeability and Forchheimer inertial terms. 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…

…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…

…domains. Detailed numerical data were obtained for frequencies of 0 ~ 60 Hz and low and high flow amplitudes, for a 75% porous domain. Pore-scale volumeaverage Darcy permeability, Forchheimer coefficient, and Nusselt number associated with the standard…

Flow in Porous Media 35 2.2.4 Periodic Flow in Porous Media 40 2.3 Regenerators 56 2.3.1 General Remarks 57 2.3.2 Regenerator and System-Level Studies 58 2.3.3 Experimental Studies 63 viii 3 4 5 6 EXPERIMENTAL METHODOLOGY 73 3.1…

…Regenerator Characteristics 73 3.2 Apparatus and Test Matrix for Steady Flow 76 3.3 Apparatus and Text Matrix for Periodic Flow 80 3.4 Determination of Hydrodynamic Closure Parameters 83 3.5 Uncertainty in Experiments 85 MODELING AND SOLUTION METHODS…

…87 4.1 Computational Fluid Dynamics (CFD) Modeling and Governing Equations 87 4.2 Exact Solutions for Steady Flow in Anisotropic Porous Medium 91 4.3 Computational Fluid Dynamics (CFD) Models 92 4.3.1 Pore-Level Study 92…

…4.3.2 Regenerator Filler Study 98 RESULTS AND DISCUSSION 104 5.1 Steady Flow Experiments 104 5.2 Periodic Flow Experiments 109 5.3 Correlations for Experimental Data 124 5.4 Pore-Level Phenomena 128 CONCLUSIONS AND RECOMMENDATIONS 145 6.1…

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