If you say a refrigerant is sub-cooled, what phase is it in?

When a refrigerant is described as sub-cooled, it specifically refers to the state of the refrigerant being in a liquid phase that is at a temperature lower than its saturation temperature for a given pressure. This condition occurs after the refrigerant has been condensed into a liquid but is cooled further below its boiling point at that pressure.

In a refrigeration cycle, sub-cooling is essential for increasing the efficiency of the system. By ensuring that only liquid enters the evaporator, it prevents any unintended boiling, which could result in less efficient heat exchange. This means that the refrigerant, while it may still reflect characteristics of its surroundings, is strictly in the liquid state and enhanced for optimal performance in the refrigeration or air-conditioning process.

The other options are not applicable because they refer to other phases or combinations of phases, rather than stating the refrigerant in a pure liquid form at a temperature below its corresponding saturation point.