Aluminium Evaporator coil for Ammonia

[skhan855]

Hi

This has been discussed before, but I don't know results obtained in end.
http://www.refrigeration-engineer.com/forums/showthread.php?21863-Aluminum-coil-evaporator-for-NH3

Question is same: Is it good idea to build Aluminium Evaporator for ammonia operation.

Some technicians says that Aluminium is more corrosive when gas pass from Aluminium pipes.

Has someone installed it? What's the experience.

Regards
Salman

[Brian_UK]

The thread that you have quoted has given good answers and has covered the question.

[skhan855]

Hi

It was 2009, quite old now..
Can someone share new experiences?

[RANGER1]

Hi

It was 2009, quite old now..
Can someone share new experiences?

Nothing has changed since then, Ammonia is safe with aluminium, nothing left to say.
Believe it to have very good heat transfer, next to using copper.

[skhan855]

Hi

Just to reconfirm, are we speaking about aluminium Pipes + Aluminium fins or just aluminium fins?

My evaporator supplier is insisting that carbon steel pipes will have more life compare to ammonia,

[RANGER1]

Hi

Just to reconfirm, are we speaking about aluminium Pipes + Aluminium fins or just aluminium fins?

My evaporator supplier is insisting that carbon steel pipes will have more life compare to ammonia,

That might be true, externally as stated in old post about pitting on outside of tube.
Aluminium is fine with ammonia fins & tubes in direct contact with it.

[RANGER1]

This is one of a number of articles on aluminium & ammonia

http://www.advancedfreezer.com/listings/files/73_1.pdf

[sterl]

All aluminum evaporators have been in use at least 40 years. They last very well in cold storage duty, for controlled atmosphere and similar storage, for plenty of dock operations and in process operations where they operate 24-7. Aluminum evaps lighter for same construction and nominally smaller because of the improved heat transfer: thus often save on structural. Some form of dielectric separation required between coil and (steel) pipe and aluminum much more active chemically than steel so refrigerant needs to be maintained in near-pure condition. They are more delicate than Galv Steel and there is no bridge in terms of contributed material between tube and fin so in "wet coil" duty the air cannot contain soluble corrosives or the fins will loose contact with the tube; this also true of Aluminum fins on Stainless tubes though the collection of reactives are different. Stainless fins on Stainless tubes tend not to do this but the heat transfer is worse and adding any profile to the fins is more difficult so ST-ST tends to become a large heavy coil with flat fin plates.
Basically the selection is application driven by the nature of the space. Protein and dairy processors should be careful with aluminum in spaces involving washdown or otherwise chemical exposures.
There are also some horror stories with internal chemical soups attacking aluminum from the inside but that was the result of some pretty odd refrigerant contamination conditions.