Some studies in recent years indicated the possibility of extending the application temperature of the natural refrigerant carbon dioxide (CO2) beneath its triple point (approximately 0.52 MPa and -56°C) in a refrigeration cycle for low temperature cooling.

A small-scale cascade refrigeration system using CO2-Sublimation is introduced in this study. The upper stage is provided with a condensing unit and operates with R-452A. The lower stage is equipped with a rolling piston compressor, a capillary tube as throttling device and the sublimation unit including a visualization section.

An operation point below the triple point of CO2 is achieved in a laboratory test. Clogging effects in the system were observed and are discussed. Design improvements are considered in order to reduce and omit the risk of clogging.

It is shown that the CO2-Sublimation cycle can be realized by the presented demonstration unit. Further work should focus on long term reliability tests and the improvement of the system performance.