Originally Posted by
peterb
Eityher you haven't read the previous posts properly - or you don't understand the concepts of thermal management and heat transfer...
The CPU generates heat which in a normal set up, pases to a heat sink. If that heat sink was in a vacuum, it would soon reach the same temperature as the CPU. However we use absorb the heat and remove it either by convextion of forced cooling, so that the hot air is blown to the outside of the case, and cold air drawn in.
With water cooling, the heatsink is cooled by water, which has a greater specific heat capacity than air (it can absorb more heat without increasing its temperature). The hot (or warm) water is pumped to the outside of the case where it is cooled by air - the point being that there is a heat flow from hotter to cooler, eirther in one stage (air) or two stages - water and air.
A Peltier device is a semiconductor device. If it connected to a powersupply in frre space, one side will get hot, the other one cold - in other words a temperature difference, and this is what some car coolboxes use, and some of those little beer can fridges. If you look at those car cool boxes, there is a big heatsink on the outside which dissapates the heat the the peltier device is effectively pumping out (in fact you can think of it as a heat pump) The heat energy out will be the sum of the heat energy absorbed (on the cold side) plus a bit because it isn't 100% efficient. If the peltier decvice was put in a closed (insulted) box and power applied, eventually the two sides would get to the same temperature (or the device would destroy itself) because there is nowhere for the heat to go.
Peltier devices are quite thin - so if you fitted it to the top of the CPU (a small area) then the hot side of the device is still going to be in the case, and you still need something to remove the heat from it, otherwise it will lose efficiency or destryoy itself. You can remove that with a heatsink - fan cooled - or a water block - water cooled.
Alternatively, you could use a conventional heatsink, and remove the fan and put a peltier device on that. It will still be putting the heat into the case, so it has to be removed with the case fanss, otherwise the heatsink will start absorbing the heat back from the air round it, and the temperatures will just rise. The only way you could do it would be if the hot side of the peltier device was mounted on the side of the case, the CPU bonded directly to the cold side while plugged into the mobo. This would use the case as the heatsink (ultimateky still air cooled) but would require a completely bespoke case, and would pose problems connecting othe bits to the mobo.
I hope that explains why Peltier devices are not quite as good as you might have thought. Ultimately the CPU is propducing heat - and that heat has to be removed to the outside of the case - removing it just from the CPU is not enough.