Subcooling

The term subcooling (also called undercooling) refers to the intentional process of cooling a liquid below its normal <a href="/facts/Boiling_point/E2BK9QoS">boiling point</a>. For example, water boils at 373 K; at room temperature (293 K) liquid water is termed "subcooled". Subcooling is a common stage in refrigeration cycles and steam turbine cycles. Some rocket engines use subcooled propellants. 
In refrigeration systems, subcooling the refrigerant is necessary to ensure the completion of the remaining stages of the <a href="/facts/Refrigeration_cycle/yW0gnSvL">refrigeration cycle</a>. The subcooling stage provides certainty that the refrigerant is fully liquid before it reaches the next step on the cycle, the <a href="/facts/Thermal_expansion_valve/TTvjb0tf">thermal expansion valve</a>, where the presence of gas can be disruptive. Subcooling is often accomplished in <a href="/facts/Heat_exchanger/CUzlMnBG">heat exchangers</a>. 
Subcooling and <a href="/facts/Superheating/FVKFCdhg">superheating</a>, which are similar and inverse processes, are both important for the stability and well-functioning of a refrigeration system.

Subcooling open-in-new

Subcooling