Which refrigerant is known to be least miscible in oil?

The refrigerant known to be least miscible in oil is carbon dioxide (CO2). This characteristic is significant because miscibility between a refrigerant and oil can greatly influence the efficiency and performance of refrigeration systems.

In systems where the refrigerant is not well mixed with oil, the oil may not circulate effectively through the system. This can lead to lubrication issues, increased wear on the compressor, and even system failure over time. Carbon dioxide's low miscibility in oil means that it can lead to better separation between the refrigerant and lubricating oil, which can be advantageous in certain refrigeration applications.

The other refrigerants mentioned, R-12, R-40, and R-141, tend to have higher levels of miscibility in oil, which can affect lubrication and efficiency in different ways, often increasing the risk of oil returning to the compressor. Thus, CO2's distinct characteristic of being least miscible makes it particularly interesting in the context of design and application of refrigeration systems.