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A Microfabricated Involute-Foil Regenerator for Stirling EnginesA segmented involute-foil regenerator has been designed, microfabricated and tested in an oscillating-flow rig with excellent results. During the Phase I effort, several approximations of parallel-plate regenerator geometry were chosen as potential candidates for a new microfabrication concept. Potential manufacturers and processes were surveyed. The selected concept consisted of stacked segmented-involute-foil disks (or annular portions of disks), originally to be microfabricated from stainless-steel via the LiGA (lithography, electroplating, and molding) process and EDM. During Phase II, re-planning of the effort led to test plans based on nickel disks, microfabricated via the LiGA process, only. A stack of nickel segmented-involute-foil disks was tested in an oscillating-flow test rig. These test results yielded a performance figure of merit (roughly the ratio of heat transfer to pressure drop) of about twice that of the 90 percent random fiber currently used in small approx.100 W Stirling space-power convertors-in the Reynolds Number range of interest (50 to 100). A Phase III effort is now underway to fabricate and test a segmented-involute-foil regenerator in a Stirling convertor. Though funding limitations prevent optimization of the Stirling engine geometry for use with this regenerator, the Sage computer code will be used to help evaluate the engine test results. Previous Sage Stirling model projections have indicated that a segmented-involute-foil regenerator is capable of improving the performance of an optimized involute-foil engine by 6 to 9 percent; it is also anticipated that such involute-foil geometries will be more reliable and easier to manufacture with tight-tolerance characteristics, than random-fiber or wire-screen regenerators. Beyond the near-term Phase III regenerator fabrication and engine testing, other goals are (1) fabrication from a material suitable for high temperature Stirling operation (up to 850 C for current engines; up to 1200 C for a potential engine-cooler for a Venus mission), and (2) reduction of the cost of the fabrication process to make it more suitable for terrestrial applications of segmented involute foils. Past attempts have been made to use wrapped foils to approximate the large theoretical figures of merit projected for parallel plates. Such metal wrapped foils have never proved very successful, apparently due to the difficulties of fabricating wrapped-foils with uniform gaps and maintaining the gaps under the stress of time-varying temperature gradients during start-up and shut-down, and relatively-steady temperature gradients during normal operation. In contrast, stacks of involute-foil disks, with each disk consisting of multiple involute-foil segments held between concentric circular ribs, have relatively robust structures. The oscillating-flow rig tests of the segmented-involute-foil regenerator have demonstrated a shift in regenerator performance strongly in the direction of the theoretical performance of ideal parallel-plate regenerators.
Document ID
Document Type
Technical Memorandum (TM)
Tew, Roy
(NASA Glenn Research Center Cleveland, OH, United States)
Ibrahim, Mounir
(Cleveland State Univ. Cleveland, OH, United States)
Danila, Daniel
(Cleveland State Univ. Cleveland, OH, United States)
Simon, Terrence
(Minnesota Univ. Minneapolis, MN, United States)
Mantell, Susan
(Minnesota Univ. Minneapolis, MN, United States)
Sun, Liyong
(Minnesota Univ. Minneapolis, MN, United States)
Gedeon, David
(Gedeon Associates Athens, OH, United States)
Kelly, Kevin
(Mezzo Systems, Inc. Baton Rouge, LA, United States)
McLean, Jeffrey
(Mezzo Systems, Inc. Baton Rouge, LA, United States)
Qiu, Songgang
(Infinia Corp. Kennewick, WA, United States)
Date Acquired
August 24, 2013
Publication Date
October 1, 2007
Subject Category
Spacecraft Propulsion And Power
Report/Patent Number
AIAA Paper-2007-4739
Meeting Information
Fifth International Energy Conversion Engineering Conference and Exhibit (IECEC)(St. Louis, MO)
Funding Number(s)
WBS: WBS 138494.04.01.01
Distribution Limits
Public Use Permitted.
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