What is the optimal gas for forced air cooling?

[Mike_In_Plano]

A friend and I got into a debate regarding the characteristics desired in a gas for forced air cooling.

Having worked with mass flow meters, I was well away of how hydrogen and helium had high thermal conductivity. However, as my friend pointed out, simply having high conductivity (i.e. a light molecule) wouldn't necessarily mean a gas was the best choice for forced air cooling. In that case, the specific heat would become important and perhaps a gas like SF6 would be more ideal.

Does anyone have any thoughts to offer?

Thanks

 

[SteamKing]

For safety, I would stay away from flammable gasses like hydrogen and oxygen. Ditto for poisonous or corrosive gasses like fluorine or chlorine (in fact, any halogen).

I guess the ideal gas for forced air cooling would be ... air. It's cheap, abundant, non-poisonous, and non-corrosive.

 

[Mike_In_Plano]

We are dealing with a closed, refrigerated system that operates at low temperatures (i.e. no moisture allowed). It is desirable to utilize existing fans and heat spreaders within this system, but the nature of the preferred atmosphere is in question.

Please avoid anecdotal references and stick purely with the science.

Thanks,

- Mike