I have done similar experiments with chill tanks and also inline chill blocks to charge the water passing thru with even two peltiers.
Whilst in a small loop without running thru the cpu as a test I could get my water temp as low as 8degc.However when run in a full circuit thru the cpu block the system does not yield any fantastic results.The effect is soon lost over the distance of the tubing and fighting the hot water created from the chip.
I did all this because I was reluctant to mount my peltier over the chip.
In the end I decided to give the peltier a go over the chip with my cold block etc.
My peltier is well mounted with s\s screws between the block and cold plate.I'm only running a 72w peltier cooling a pIII 1gig @ around 1200 but the temps are way better than before.Idle is around 6degc and max load 23 degc.
So after all the effort really the most simple and effective way was mounting the peltier over the chip which is very easy to do.
I'm not trying to dent your ability in taking on a challenge,but I thought I would pass on some of my previous experience of doing the same.
cheers stevo
