Performance of cascade cycles working with blends of CO2 + natural refrigerants

In this paper, an analysis on the performance of a cascade refrigeration cycle operated with blends of carbon dioxide (or R744) plus hydrocarbons (ethane or R170, propane or R290, ethylene or R1150, propylene or R1270) and dimethyl ether (or RE170) as the low-temperature working fluid was carried out. The properties of the investigated blends were used to simulate the behaviour of a cascade cycle using ammonia (or R717) as the high-temperature-circuit working fluid. The aim of this work was to study the possibility of using carbon dioxide mixtures in those applications where temperatures below its triple point (216.59 K) are needed. The analysis was carried out by developing a software based on the Carnahan-Starling-DeSantis (CSD) Equation of State (EoS) using binary interaction parameters derived from the experimental data in the literature. Results show that adding R744 to HCs and dimethyl ether reduces the cycle performance, even if acceptable values are always achieved for the COP. Main attractive of the R744 + natural refrigerant blends is connected with their GWP, ODP and flammability properties lower than those of pure fluids. (C) 2011 Elsevier Ltd and IIR. All rights reserved.