This paper compares the performance of an existing Sunpower M77 free-piston Stirling cryocooler with the simulated performance of a proposed pulse-tube cryocooler that uses the same linear compressor. Sunpower has built and delivered numerous M77 free-piston Stirling cryocoolers. These cryocoolers lift 5 W at 77K with 100 W of electrical input power. These coolers are state of the art both in thermodynamic performance and in mechanical design. The mechanical design includes a high efficiency permanent magnet linear motor; piston and displacer supported by gas bearings; mechanical compliance to reduce manufacturing costs; and effective folded fin heat exchangers. While the M77 is a successful design that is reliable and able to be manufactured cost effectively, it is not as mechanically simple as a pulse tube cryocooler might be. A pulse tube design would eliminate the moving displacer and replace it with a tuned volume connected to the expansion space. However, the expansion space work would be lost, unlike in the moving displacer design. To assist in understanding which arrangement would have the best cost and performance trade-offs, a preliminary pulse tube cryocooler design, using the linear motor/piston combination (linear compressor) of the M77, is presented. Simulated performance is compared with test results for the M77.
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