it works pretty well
i'm doing it with an heat exchanger in copper similar to the "volenti mini bong" (but really smaller) and with the tube closed. i keep that in a bath of water and i have 2 80 mm fans @ 7v blowing on it.
it keep my barton 2500 @2.4 Ghz under 35 C (even when the water bath is dry
, temps stay around 40 C)