Investigation of the starting modes of the low-temperature refrigerating machines working on the mixtures of refrigerants

The starting mode of a small low-temperature Joule–Thomson refrigerating machine is in focus of the experimental investigation reported here. The refrigerating machine operates by the Linde cycle. A mixture of hydrocarbons – isobutane/ethane/methane – is used as a refrigerant. The object of cooling is a small testing chamber to be cooled down and thermostabilized at the temperature level of (−70, …, −80) °C. The starting modes were studied under heavy-duty heat load on the system resulting from the initial thermal equilibrium between the whole system and ambience. The experimental data demonstrate a crucial effect of the low-boiling mixture components condensation in the refrigerant high-pressure flow on the machine starting performance. Excessive values of the discharge pressure, compression ratio and compressor input power have been observed during the start-up process which may last for tens of minutes affecting the refrigerating machine reliability. Some probable causes of the phenomena and countermeasures are pointed out.