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.

► We designed and tested four refrigerant mixtures for a high pressure of 0.4 MPa. ► Each mixture exhibited both steady and pulsating flows, and low cooling powers. ► Low cooling power is analyzed in terms of liquid hold-up. ► Pulsing flow is analyzed in terms of held-up liquid developing into slug flow.