ExxonMobil’s Gilles Delafargue, Field Engineering Support Advisor looks into how synthetic lubricants respond to the changes and trends in today’s refrigeration and help improve energy efficiency of refrigeration systems.
Evolution of the market
The Kyoto Protocol (1997) established commitments for the reduction of greenhouse gases. It is likely to impact some ozone-friendly HydroFluoroCarbons (HFCs) refrigerants as some of them have high Global Warming Potential (GWP), and drive the use of HydroFluoroOlefins (HFOs). Together, these protocols indirectly promoted the re-birth of ammonia (0 ODP/0 GWP) and carbon dioxide CO2 (low ODP/GWP) as refrigerant options.
The environmental legislation has created a growing trend towards natural refrigerants, such as ammonia, CO2 and, to some extent, Hydrocarbons (HCs). HCs are likely to stay in domestic appliances, but advocates of HCs are continuing to promote their use in larger equipment, with commercial ice machines as well as reach-in/walk-in freezers and coolers possibly next in line .
HFCs still have an important presence, however their replacement with Low ODP/Low GWP HFOs is expected to grow. Both CO2 and HFO-1234yf are being promoted in Europe for car air conditioning systems. In 2012, one of the world’s biggest drinks companies announced that it will have completed phasing out the use of HFCs in new equipment by 2015. We have also started to see HFC-free supermarkets.
Miscibility and viscosity for proper lubrication
The lubricant’s miscibility with the refrigerant at the evaporator temperature is crucial in miscible applications (systems not equipped with oil separators). The refrigerant fluid/lubricant blend must not separate after expansion in the evaporator to travel through to the compressor. If they separate due to inappropriate miscibility, fluid is likely to get trapped in the evaporator and seriously affect the efficiency of the refrigeration unit or the smooth running of the compressor.
At compressor level, both high pressure and temperature will cause a decrease in oil viscosity (linked to the solubility of the refrigerant in the lubricant), which would affect wear protection if viscosity at application was not high enough. The effects of the viscosity decrease can be mitigated by selection of the appropriate lubricant technology and viscosity
Large refrigerant systems using ammonia (non- or low-miscible with HCs) as a refrigerant are equipped with oil separators so it is desirable to use a lubricant that is quite immiscible with the refrigerant fluid, and has low vapour pressure to avoid or minimize oil carry over in circuit.
Future for cold
Rcently two European firms have announced plans for commercial and domestic launches of products based on magnetic refrigeration within the next two years and some specialists say that magnetic refrigeration can cover 80 per cent of the vapour compressor market today. However the classic compression units, together with the evolution towards Low ODP/Low GWP refrigerant fluids, are expected to stay for a while in the market.
ExxonMobil has endeavoured to respond to these demands and trends with a wide range of globally available products and continues to develop its portfolio to meet the challenges of tomorrow, while providing guidelines and expert technical assistance to customers.