Do you still remember a PC with a passively cooled CPU? No I'm not talking about those new VIA CPU's which have the calculation power of your average cellular phone, I'm referring to those old Pentium I and 486 machines which only needed a small piece of aluminum on the CPU to keep it running cool.
How times have changed, in order to passively cool your CPU today you need to have massive heatsinks with meters of heat pipes running through them, and in the end you end up with a very hot, not highly clocked CPU.
Speaking about clocking, adding OVERclocking to the equation increases heat output tenfold, especially when increasing both the CPU's operation Mhz and the amount of voltage running though the core. The final heat output easily saturates any heatsink not up to the job, and the high temperature decreases the overclocking potential of your CPU. How lower you can get the CPU temperature, the higher you are able to push it.
In general there are 3 different upgrades somebody can do to permanently increase the overclock of their CPU, each one being more expensive and offering more impressive results. First up you can upgrade your air cooling solution, slapping a high end heatsink on the CPU combined with an extremely fast spinning FAN will give you an increase in OC headroom close to water cooling at the expensive of your hearing.
Next up is water cooling; depending on the components used in the system you will obtain average to very good results.
Choice two and a half is adding a Peltier element to your water cooling setup, this can give you CPU temperatures below ambient if you are lucky, however installation can be a challenge, a considerable amount of power is blasted through the Peltier element to keep it running optimal, and the more power you provide, the more power loss you have, to add things up, you need a separate power supply which can provide the needed voltage and ampere to the unit;
The most effective step is going with phase change cooling or also referred to as vapor compression cooling. In the test labs today I have a Phase Change Cooling Unit from asetek for review; the VapoChill Xtreme Edition II is the latest revision of their popular VapoChill product line which incorporates the Phase Change Unit and a Case into one.
How does Vapor Change work? ZENNZZO from Pimprig has written a clear and comprehensive explanation, one of the best I've come across which describes the whole phase change process.
This describes the basic layout of a single stage Phase change cooling system.
Image from this forum thread at Pimprig; corrected with info provided by Jort thanks!
It starts with the compressor
. As the name states this is what compresses the refrigerant. At this point it is a gas and that's what it is designed to pump.
From here it pumps to the condenser
, the top side of the condenser to be exact. By cooling the gas and compressing it, it will turn into the liquid needed to create the Phase-change. Out of the bottom of the condenser and into a filter is where the flow goes next. Out of the filter there is a small diameter copper line called the capillary tube
or capline. This is where the tuning of the system is done. The length and diameter is critical for the temperature of the evaporator.The Evaporator
is the equivalent to the CPU block in a water cooling system. It is what is mounted to the CPU or GPU. There are many different designs and it acts similar to its H20 counterpart, to more surface area that can be exposed to the refrigerant the better.
This is also where the Phase-Change occurs. Liquid refrigerant makes its way to a larger volume of space and changes its phase from a liquid to a vapor
, or boils off. Refrigerant boils at a very low temperate and that is the main difference between the dozens of types of refrigerants (R134/R404A/R504/etc). During this change it sucks up the heat and releases its cold.
The return line or suction line as it is referred to, has negative pressure in it. It is caused by the compressor pressurizing the high side, creating a low side in the return line, because the system is sealed. The refrigerant is now back in a gas form and is cycled again through the system.
In case of the VapoChill the cycle can also be drawn out like this:
Illustration showing old-style CPU-kit
While the first edition of the VapoChill XE used R404A the new one is equipped with R507 gas, both have similar properties but the difference lies in the temperature obtained on the evaporator at same Heat Load (Watt). While looking for differences between these two gasses, I came across interesting thread at Over-Clock.com
While the R404A could give you a higher maximum Heat Load, this does not necessarily translate into better overclocking results, both the XE and XE II are rated at ~180W maximum Heat Load, but the XE II keeps lower temperatures:
Graph from asetek
let's check up on the specs of the VapoChill XE 2 ->