Butane/Propane when used as a coolant is used as a non-contact refrigerant much like R134a air-con refrigerant and is typically passed through a compressor into a heat exchanger. It is not used as a direct contact coolant like with immersion cooling.
Good point. I am not sure if it would be possible with hydro miners but i guess the pressure might be too hight for them.
Btw: do you know some good hydro cooled overclocking PSU for hydro miner?!
@notfuzzywarm: i don't think 2-phase immersion cooling is the best solution. Regarding heat flow only it might be the best solution but regarding the economics they are not. as far as i know the 2-phase coolants are much more expensive than other coolants and not nessecary with current heat flux density. In Addition to that the 2-phase coolants i know are mostly harmful to the climate and therefore not easy to get in europe.