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 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 thermal electric cooler. An optimized five-component mixed refrigerant was calculated to provide a minimum isothennal enthalpy difference of 1.35 kJlmol 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 ,umol/s. A transient temperature of 76 K was observed.
Pub Type: Journals
cryogenic cooler, Joule-Thomson, micro cryogenic cooler, mixed refrigerants