Research Papers

Performance Analysis of an Integrated Micro Cryogenic Cooler and Miniature Compressor for Cooling to 200 K

[+] Author and Article Information
Jill Cooper, Y. C. Lee

University of Colorado at Boulder,
Boulder, CO 80309

Marcia Huber

National Institute of Standards and Technology,
Boulder, CO 80305

Certain trade names and company products are mentioned to specify adequately the experimental apparatus and procedures. In no case does such identification imply endorsement by the National Institute of Standards and Technology, nor does it imply that the products are necessarily the best available for the purpose.

Manuscript received February 17, 2012; final manuscript received August 23, 2012; published online June 24, 2013. Assoc. Editor: Mark North.

J. Thermal Sci. Eng. Appl 5(3), 031003 (Jun 24, 2013) (6 pages) Paper No: TSEA-12-1031; doi: 10.1115/1.4023307 History: Received February 17, 2012; Revised August 23, 2012

Joule-Thomson (J-T) based micro cryogenic coolers (MCCs) are attractive because they can provide the cryogenic temperatures needed for small electronic devices while having a low cost and small volumetric footprint. A compressor is a major part of a cryogenic system, but so far J-T based MCCs have not used miniature or microscale compressors. This work demonstrates a J-T based MCC coupled with a miniature compressor for cooling to 200 K, with precooling of 273 K, using a custom hydrocarbon mixture as refrigerant. The compressor is formed by coupling a miniature piston oscillator built for stirling coolers with a micromachined check valve assembly. The MCC is formed by glass fibers within a capillary forming a counter flow heat exchanger, and a silicon and glass chip forming a J-T valve. Minimum temperatures of 166 K have been observed in transient, and stable temperatures of 200 ±1 K have been observed for >1 h. Some insight is given into the unstable performance in terms of intermittent liquid accumulation. The coefficient of performance is analyzed for the system, and it is found that most of the inefficiencies arise at the compressor.

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Fig. 1

Microcryogenic cooler: (a) the CFHX and J-T valve; (b) cross section of J-T valve, showing path of warm high-pressure refrigerant (red/not bold arrows) as it expands to a lower pressure and cools (blue/bold arrows); (c) MCC in macrocoupler; and (d) cross sectional schematic of macrocoupler.

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Fig. 2

The miniature compressor composed of a miniature piston oscillator and micromachined check valve assembly

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Fig. 3

Microvalve assembly: (a) schematic cross-section showing polyimide film, stainless steel substrate, and sealing ring; (b) photograph of valve and zoom into L-tether and sealing ring

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Fig. 4

Schematic of test setup

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Fig. 5

Curve of isothermal enthalpy difference for the mixture with a high pressure of 4 bar and a low pressure of 1 bar. The minimum isothermal enthalpy difference is 4.09 kJ/mol in the temperature range 300 K – 200 K.

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Fig. 6

The pressure ratio and efficiency as a function of flow-rate. Note that the maximum efficiency occurs at a flow-rate of 270 sccm.

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Fig. 7

(a) control volume used to analyze compressor performance with respect to valves and piston leakages. (b) pressure ratio, and (c) efficiency as a function of flow-rate.

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Fig. 8

(a) the temperature profile and (b) flow rate as the MCC cools down. There is a 30 min initial period where the flow rate builds up, followed by rapid cooling which accompanies instabilities in the flow rate.

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Fig. 9

200 s of flow rate data collected while visualizing the cold-tip. Darker regions in the J-T valve are liquid, and lighter regions are vapor. The cold-tip fills with liquid during the periodic jumps in flow rate.

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Fig. 10

Stabilized temperatures showing (a) spikes of 6 K; (b) stability to ±1 °C, with rapid cooling from 275 to 200 K in 62 s; and (c) a device with high flow-rates preventing cooling below 210 K. No heat is applied for the third device.

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Fig. 11

Curves of an ideal J-T cooler COP, cooler COP, and system COP: (a) COPs as a function of pressure, at 200 K; (b) COPs as a function of temperature, with high pressure of 0.72 MPa and low pressure of 0.15 MPa. Enthalpy and Gibb's free energy values were calculated with REFPROP [11].




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