Thermal and chemical stability

Refrigerants are tested for thermal and chemical stability and by this for applicability in usual refrigerant circuits at the conditions expected there.

Refrigerant will be charged into a refrigeration installation that is designed for this refrigerant. The thermodynamic design assumes a pure fluid resp. the pure fluids in a defined mixture of a blend. If the refrigerant would change during operation due to thermal or chemical effects, or maybe even break down, the fluid properties of the circulated fluid do not any longer match the design.

Controllers for superheat or evaporation temperature will work incorrectly if the vapour pressure does not match the original calculation, as an example.

If the chemical compound called refrigerant breaks down, reactive break down products can be expected. This can lead to acid formation in oil, corrosion of pipes, chemical attack on the very smooth bearing surfaces and creation of different chemical substances, maybe also to chemical transport of material in the system. Also non condensable gases can be created, increasing the pressure and decreasing the efficiency, like air in the system does.

As long as the amount of reactive substances and acids is very small, filter driers mostly absorb them. With increasing amounts, the system will be damaged.

In former times, so called copper plating was observed in systems with high humidity and chlorine containing refrigerant: copper ions were removed from the inner pipe surface and disposed at other places, mostly in the discharge side of the compressor. With some refrigerants, depending on the system cleanliness, creation of laquer like layers can be observed, formed by polymerisation of oil, maybe refrigerant breakdown parts and so on. Things like this can have impact on the working valves of reciprocating compressors or the lifetime of the roller bearings on the discharge side of screw compressors.

Basically, uncontrolled removal and disposal inside the circuit is of disadvantage for the reliability and safety.

Formation of acids in the oil can damage sealings and gaskets and thus lead to leakage. Acid can also attack electrically isolating materials and lead to motor failure.