In an operating evaporator, oil stays on the top of which refrigerant?

In an operating evaporator, the behavior of oil in relation to refrigerants is influenced by their physical properties and solubility. In this context, carbon dioxide (R-744) is unique because, unlike many other refrigerants, oil typically does not mix well with it. This limited solubility leads to the oil remaining on the top with carbon dioxide since it is not absorbed into the refrigerant, allowing for operational efficiency where the oil helps lubricate the compressor without being carried along with the refrigerant in the vapor phase.

In comparison to other refrigerants, ammonia (R-717), Freon (R-12), and propylene (R-290) tend to have higher solubility levels with oils, meaning that under normal operating conditions, oil can mix into the refrigerant, thus not allowing it to stay at the top. This characteristic of carbon dioxide is crucial for the design and maintenance of systems using this refrigerant, ensuring proper lubrication and preventing the oil from adversely affecting the heat exchange properties in the evaporator. Therefore, the behavior of oil remaining on top, as seen with carbon dioxide, is a distinct aspect of its operational dynamics.