Carrier-Fluid Screening for a Three-Phase Sublimation Refrigeration Cycle with CO₂ Using Reference Equations of State and COSMO-SAC

The recently proposed combination of the multifluid mixture model with g^E-models is used for investigating possible carrier-fluids for CO₂ for a new type of refrigeration cycle. According to the EU regulation No. 517/2014, placing refrigerants with a global warming potential greater than 2500 on the market is prohibited after January 1, 2020. Cooling applications designed to cool products below −50 °C, for which mostly the refrigerant R-23 with a global warming potential (GWP) of 14800 is used, are an exception. R-23 could be replaced by carbon dioxide (CO₂, GWP = 1) in a refrigeration cycle in which the CO₂ is expanded into the sublimation region. The CO₂ could be blended with a suitable carrier-fluid in order to prevent blockages due to enrichment of dry ice as well as to increase the heat transfer in the sublimator. A screening for a suitable carrier-fluid has been conducted using the most accurate equations of state available in the multifluid mixture model combined with a version of the predictive g^E-model COSMO-SAC that considers different strengths of donor–acceptor surface segment combinations. Some of the carrier-fluids lead to a significantly improved coefficient of performance compared to the process with pure CO₂.