Experimental investigation of low-pressure refrigerant mixtures for micro cryogenic coolers.

Micro Cryogenic Coolers (MCCs) can achieve very small sizes and high efficiencies when operating with a refrigerant mixture, but micro-scale compressors have a limited pressure output. Four refrigerant mixtures were designed to operate between 0.4 MPa and 0.1 MPa, and tested in a MCC system both with and without pre-cooling. For comparison, two pure refrigerants were tested as well. Without pre-cooling, each mixture exhibited considerably lower cooling power than the design value. With pre-cooling, the mixtures exhibited unsteady cooling temperatures accompanied by flow pulsations after a period of time. The low cooling power, unsteady temperatures, and time required for the pulsations to occur are analyzed in terms of composition change due to liquid hold-up in the annular and intermittent flow regimes.