An initial non-equilibrium porous-media model for CFD simulation of stirling regenerators

Roy Tew, Terry Simon, David Gedeon, Mounir Ibrahim, Wei Rong

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Scopus citations

Abstract

The objective of this paper is to define empirical parameters (or closure models) for an initial thermal non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two CFD codes currently being used at Glenn Research Center (GRC) for Stirling engine modeling are Fluent and CFB-ACE. The porous-media models available in each of these codes are equilibrium models, which assume that the solid matrix and the fluid are in thermal equilibrium at each spatial location within the porous medium. This is believed to be a poor assumption for the oscillating-flow environment within Stirling regenerators; Stirling 1-D regenerator models, used in Stirling design, use non-equilibrium regenerator models and suggest regenerator matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle. A NASA regenerator research grant has been providing experimental and computational results to support definition of various empirical coefficients needed in defining a non-equilibrium, macroscopic, porous-media model (i.e., to define "closure" relations). The grant effort is being led by Cleveland State University, with subcontractor assistance from the University of Minnesota, Gedeon Associates, and Sunpower, Inc. Friction-factor and heat-transfer correlations based on data taken with the NASA/Sunpower oscillating-flow test rig also provide experimentally based correlations that are useful in defining parameters for the porous-media model; these correlations are documented in Gedeon Associates' Sage Stirling-Code Manuals. These sources of experimentally based information were used to define the following terms and parameters needed in the non-equilibrium porous-media model: hydrodynamic dispersion, permeability, inertial coefficient, fluid effective thermal conductivity (including thermal dispersion and estimate of tortuosity effects), and fluid-solid heat transfer coefficient. Solid effective thermal conductivity (including the effect of tortuosity) was also estimated. Determination of the porous-media model parameters was based on planned use in a CFD model of Infinia's Stirling Technology Demonstration Converter (TDC), which uses a random-fiber regenerator matrix. The non-equilibrium porous-media model presented is considered to be an initial, or "draft," model for possible incorporation in commercial CFD codes, with the expectation that the empirical parameters will likely need to be updated once resulting Stirling CFD model regenerator and engine results have been analyzed. The emphasis of the paper is on use of available data to define empirical parameters (and closure models) needed in a thermal non-equilibrium porous-media model for Stirling regenerator simulation. Such a model has not yet been implemented by the authors or their associates. However, it is anticipated that a thermal non-equilibrium model such as that presented here, when incorporated in the CFD codes, will improve our ability to accurately model Stirling regenerators with CFD relative to current thermal-equilibrium porous-media models.

Original languageEnglish (US)
Title of host publicationCollection of Technical Papers - 4th International Energy Conversion Engineering Conference
PublisherAmerican Institute of Aeronautics and Astronautics Inc.
Pages65-77
Number of pages13
ISBN (Print)156347817X, 9781563478178
DOIs
StatePublished - 2006
Event4th International Energy Conversion Engineering Conference - San Diego, CA, United States
Duration: Jun 26 2006Jun 29 2006

Publication series

NameCollection of Technical Papers - 4th International Energy Conversion Engineering Conference
Volume1

Other

Other4th International Energy Conversion Engineering Conference
Country/TerritoryUnited States
CitySan Diego, CA
Period6/26/066/29/06

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