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A Temperature Instability in 4 K Cryocooler Regenerators Caused by Real Fluid Properties



Ryan Snodgrass, Vincent Y. Kotsubo, Joel Ullom, Scott Backhaus


We report temperature profile measurements from a densely instrumented, commercial pulse tube refrigerator. Azimuthal temperature differences of 15 K were measured across its 3 cm diameter regenerator which was operated at cold end temperatures below 10 K. These asymmetries may appear and disappear with just 0.1 K changes to the cold end temperature, suggesting a potential thermofluid instability. Experiments and analysis suggest that real fluid properties of helium at low temperatures may be the driving mechanism of the instability. We sketch the beginnings of a linear perturbation analysis and show that small changes to regenerator temperature profiles are reinforced by accompanying changes to the component of power flow due to real fluid properties, particularly at temperatures less than 9 K. Our measurements show that temperature asymmetries are specific to particular sections within the regenerator and negatively affect cooling power at the cold end.
Proceedings Title
Cryocoolers 21
Conference Dates
December 7-10, 2020
Conference Location
Virtual/online, CO, US
Conference Title
21st International Cryocooler Conference


Cryocooler, pulse tube refrigerator, real fluid effects, thermodynamics


Snodgrass, R. , Kotsubo, V. , Ullom, J. and Backhaus, S. (2021), A Temperature Instability in 4 K Cryocooler Regenerators Caused by Real Fluid Properties, Cryocoolers 21, Virtual/online, CO, US, [online], (Accessed May 30, 2024)


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Created April 1, 2021, Updated March 31, 2022