An involute-foil regenerator was designed, microfabricated, and tested in an oscillating-flow test rig. The concept consists of stacked involute-foil nickel disks (see figure) microfabricated via a lithographic process. Test results yielded a performance of about twice that of the 90-percent random-fiber currently used in small Stirling converters.

Micrographs of Regenerator Disks are shown during the final steps of fabrication: (a) micrograph of features with remaining PMMA removed and (b) picture of nickel ribs after removal from substrate.
The segmented nature of the involute-foil in both the axial and radial directions increases the strength of the structure relative to wrapped foils. In addition, relative to random-fiber regenerators, the involute-foil has a reduced pressure drop, and is expected to be less susceptible to the release of metal fragments into the working space, thus increasing reliability. The prototype nickel involute-foil regenerator was adequate for testing in an engine with a 650 °C hot-end temperature. This is lower than that required by larger engines, and high-temperature alloys are not suited for the lithographic microfabrication approach.

This work was done by Mounir Ibrahim and Daniel Danila of Cleveland State University; Terrence Simon, Susan Mantell, and Liyong Sun of the University of Minnesota; David Gedeon of Gedeon Associates; Songgang Qiu of Infinia Corp.; Gary Wood of Sunpower Inc.; and Kevin Kelly and Jeffrey McLean of International Mezzo Technologies for Glenn Research Center. For more information, download the Technical Support Package (free white paper) at under the Manufacturing & Prototyping category.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-18431-1.