Low-GWP halocarbon refrigerants: a review of thermophysical properties.

Following the Montreal Protocol (1987), the refrigeration industry has undertaken a process to reduce the negative environmental impacts of working fluids. In a first step, chlorinated compounds (CFCs and HCFCs) were substituted by fluorinated hydrocarbons (HFCs) and natural fluids (e.g., ammonia, carbon dioxide, hydrocarbons) to solve the problem of stratospheric ozone depletion. In a second step following the Kyoto Protocol (1997), a process was begun and still underway, to limit and control the emissions of HFCs that contribute to global warming and climate change. The process of reducing the emissions of high GWP refrigerants is increasing as more and more regulations are being negotiated and implemented (see, e.g., EU Regulation No. 517/214).
Several groups of chemicals have been analyzed in the publicly available literature to identify possible substitutes for high GWP HFCs in HVAC&R and organic Rankine cycle applications. Taking into account various critieria (particularly low toxicity, flammability, and GWP, and high energy efficiency), only a few compounds are suitable for many applications. In particular, in addition to natural fluids, studies have shown that there are a few HFCs and a dozen or so HFOs, i.e. fluorinated olefins characterized by the presence of a C=C double bond in the molecule, that are potentially appropriate for a number of applications. In this paper, a review of the present knowledge of scientifically-determined thermophysical properties of a number of working fluids is presented, with emphasis given to saturation and critical properties, vapour phase PVT data, liquid density, thermal conductivity, viscosity, and surface tension.