Donald Bernard Bivens

Role of refrigerant mixtures as alternatives to CFCs

Abstract Refrigerant mixtures may provide some solutions to the problem of the very limited number of fluids which have suitable properties to provide alternatives to CFCs. Mixing of refrigerants allows the adjustment or tuning of the most desirable properties of the mixture by varying the molar fraction of the components. There are three categories of mixtures which can be used as working fluids: azeotropes, near-azeotropes and zeotropes. Azeotropes are usually binary and have long been used in the refrigeration industry; it is unlikely that new combinations will now be found. Near-azeotropes have a much greater potential for development, but under leakage conditions may alter their composition and properties. Near-azeotropes have the most potential as drop-in alternatives to CFCs. Zeotropes have potential for improvements in energy efficiency and capacity modulation, but, as they require hardware design changes can only be considered in new system designs. However, with the long-term concerns about global warming, energy efficiency, and therefore the use of zeotropes, will probably have a great influence on the refrigeration industry.

Fluoroethers and other next generation fluids

Hydrofluorocarbons (HFCs) have been predominantly chosen as the zero ozone depletion potential (ODP) alternatives for chlorofluorocarbon (CFC) refrigerants. Since there might be other types of zero ODP compounds more preferable than HFCs as working fluids, several organizations have investigated fluorinated ethers, alcohols, amines, silicon, and sulfur compounds. Evaluation criteria included toxicity, nonflammability, stability, atmospheric lifetime, refrigeration performance, and manufacturing feasibility/cost. Although a few of the compounds have predicted refrigeration performance close to HFCs, at this stage of the evaluations none appear to have a balance of refrigerant fluid requirements to challenge HFCs.