Lubrication in Refrigeration Systems: Performance of Journal Bearings Lubricated with Oil and Refrigerant Mixtures

摘要

The phasing out of chlorofluorocarbon refrigerants (CFCs) from refrigeration systems for environmental reasons has stimulated the study of oil and refrigerant mixtures, as different oils are required to work with the replacement refrigerants, especially hydrofluorocarbons (HFCs). Considering lubrication of the compressor present in most refrigeration systems, several experimental studies have investigated aspects such as film-forming capability and wear performance presented by oils working in pressurised refrigerant environments. However, there is little published research on how lubricant properties are affected by the solubility of refrigerant in rich oil-phase mixtures and their application to the design of components. In this context, this work studies lubrication with an oil and refrigerant mixture as the lubricant. Initially, a steadily loaded partial journal bearing is analysed, where the lubricant is characterised through correlations for solubility, density and viscosity. The methodology presented eliminates the use of intermediate boundary conditions in determining cavitation. Alternatively, the release of refrigerant gas from the lubricant mixture when saturation pressure is reached in the divergent region of the bearing is considered directly, with a two-phase flow thereafter. Results comparing this alternative treatment of cavitation with the Reynolds condition are presented and discussed. Furthermore, the differences in the performance of the bearing lubricated with the oil-refrigerant mixture instead of pure oil are analysed. It is observed that, under the same operating conditions, a reduction in the load carrying capacity occurs for the lubricant mixture due to its lower viscosity.