Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Refrigerants to replace chlorofluorocarbons and hydrochlorofluorocarbons

Attempts to identify suitable substitutes for chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) have met with mixed success. Some CFCs can be readily replaced by appropriate HFCs. However, other proposed substitutes have toxicity problems or are chemically unsuitable. An alternative could be the use of a mixture of refrigerants, but the properties of such mixtures are not yet well known. More work is needed to understand the thermodynamic properties of these mixtures and their lubrication requirements. Flammable refrigerants such as propane and butane can also be considered as alternatives to HFCs, but the problem associated with flammability needs to be addressed.

This study was carried out by a team of 13 from large and small industries, fluorocarbon manufacturers, universities and research organizations. Extensive investigations were made into the properties and applications of new refrigerants. The technical properties involved in their use as replacements for refrigerant R22, which is to be phased out, were investigated. The results are being used extensively by the refrigerant industry to develop new products.

A number of pure fluids and mixtures were identified as meeting the criteria of flammability, compatibility and environmental acceptability, and their thermodynamic properties were established. For flammable refrigerants, extensive operating experience was gained with a range of systems, lubricant problems were noted and safety aspects identified using a hazard and operability analysis. Compressor lubricants and their properties were investigated in various models to describe their solubility in refrigerants. The effects of the interactions between the refrigerant and the oil on system performance were assessed. Finally, performance evaluations on the use of compact heat exchangers and new refrigerants were carried out.

Equations of state for working fluids and mixtures were developed. Other equations described the physical properties, viscosities, and thermal conductivities. These equations can be used in engineering design for new refrigeration systems, together with their methods for calculating entropy and enthalpy. Studies into flammable refrigerants identified accident scenarios and presented risk calculations. These showed that maintenance is the most dangerous period, and suggested that thorough training for installers should be considered of prime importance. A new generation of synthetic oils was developed for use as compressor lubricants together with theoretical models on general compatibility between refrigerant mixtures and compatible lubricants.

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John MCMULLAN
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