13. Air-Condition and Refrigeration

Lubricating oil is essential in vapor compression systems to reduce the friction and wear on moving parts of the compressor components for its proper functioning and longevity. However, during the system operation eventually, some of the lubricant oil escaped from the compressor casing and oil separator and carried along with the refrigerant through the system. Naturally, not all of the oil is returned to the compressor, some of it can get trapped in various system components, such as the evaporator, condenser, or piping. Notably, oil transport properties such as viscosity, surface tension, thermal conductivity, and Prandtl number differ from refrigerant transport properties in several orders and magnitude. As a result performance of each component either augmented or deteriorated depends on the mass fraction of oil circulated and accumulated on each component. Moreover, Montreal Protocols to Kigali amendments, refrigerants have gone through a continuous transition phase from chlorofluorocarbons (CFCs) to hydrofluoroolefin (HFOs) thereby lubricating oil from mineral oils to synthetic oils. Overall, managing oil transport is critical for the reliable and efficient operation of refrigeration and air conditioning systems. Hence, the present study presents an overview of the influence of the oil transport phenomenon on the design and performance of refrigeration and air conditioning systems focused on low GWP refrigerants. In addition, compatibility of lubricant oils with low GWP refrigerant in terms of transport properties, miscibility, solubility, oil retention, coefficient of performance, heat transfer, pressure drop, and energy consumption is also addressed.