Study of mixed refrigerant undergoing pulsating flow in micro coolers with pre-cooling

•We study micro coolers with mixed refrigerant pulsating flow.•Mixture component distribution, flow patterns, and cooling power are measured.•Pulses are due to liquid forming in mini channels then moving to micro channels.•A cooling power model for pulsating flow is derived and verified.

Micro cryogenic coolers can provide low temperatures with a smaller volumetric footprint and smaller power draw than their conventional-scale counterparts. However, they can exhibit lower-than-desired cooling power. We measure the specific cooling power of a refrigerant expanding from a high pressure of 0.6 MPa to a low pressure of 0.1 MPa, while undergoing pulsating flow in a micro cryogenic cooler with pre-cooling. We further observe that the pulses in the flow-rate occur due to a volume of liquid forming in the high-pressure coupling mini-channel. The composition of the flowing refrigerant is analyzed with gas chromatography and thermal conductivity detection (GC/TCD), showing that there is no overall composition change in the refrigerant after it enters the pre-cooling lines. A model of the cooling power under such a pulsating flow regime is developed with good agreement to measured values. An improved refrigerant mixture is designed with this model, and subsequently tested, showing increased specific cooling power.