Mixed Refrigerants for a Glass Capillary Micro Cryogenic Cooler
COLORADO UNIV AT BOULDER DARPA CENTER FOR INTEGRATED MICRO/NANO ELECTROMECHANICAL TRANSDUCERS
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Optimized mixed refrigerants are applied in Joule-Thomson JT micro cryogenic coolers MCC to enhance efficiency. Mixed refrigerants deliver equivalent refrigeration power with much lower pressure ratio and flow rate compared to pure nitrogen refrigerant. To determine the behavior of mixtures in MCCs, the normal boiling points of the components, mixture solubility, and refrigeration loss due to pressure drop on the low-pressure side of the heat exchanger are evaluated. The MCC discussed here was designed to operate at 77 K with the heat exchanger warm end precooled to 240 K by a thermo-electric cooler. An optimized five-component mixed refrigerant was calculated to provide a minimum isothermal enthalpy difference of 1.35 kJmol between 77 K and 240 K with a high pressure of 1.6 MPa and a low pressure of 0.1 MPa. Experimentally, a stable temperature of 140 K was achieved with a flow rate of 11 lmols. A transient temperature of 76 K was observed.
- Lubricants and Hydraulic Fluids