Alternatives to Air Cooling
Before we get further into our analysis and start dissecting the H2C cooling system, we thought it would make sense to take a look at several of the different alternatives to air cooling currently available, so we can better understand Dell's decisions when they designed the H2C.
In recent times, we've seen the average heat output of processors balloon out of control. The notoriously hot Intel Extreme Edition Presler core reached thermal envelopes of 130 watts. Clearly the trend towards higher frequencies has stalled due to thermal complications. The next logical solution and processor evolution was multiple cores and multi-threaded applications. While performance doesn't increase as linearly as simply increasing the frequency, adding more cores instead of increasing frequency allowed processor manufacturers to keep ramping up processor performance without needing to bundle an exotic cooling kit with every processor.
The current king-of-the-heap in both number of cores per physical processor and overall performance, is Intel's quad-core Core 2 Extreme QX6700 chip. With four cores churning away at 2.66 GHz each, this chip is a monster, and a hot one at that, with a thermal envelop matching the hottest Intel Presler core back in the day, at 130 watts. Now Dell wants to take one of these beasts and overclock it by 540 MHz. At that speed, the quad-cored processor will be producing more heat than most air cooling systems can handle effectively.
To get truly break-out cooling efficiency, you're going to have to leave air cooling behind and venture into a world of water, peltiers, refrigeration and cryogenics. The image below shows various cooling technologies, ordered with respect to their relative cooling abilities. Natural convection cooling through a heatsink (least effective) is at the top while liquid nitrogen (most effective) is at the bottom. As is clear from the diagram, traditional heatsink and heatsink/fan methods aren't nearly as effective.
Unfortunately, the more potent alternative methods of system cooling don't come without catches and drawbacks. Cryogenics, in the form of liquid nitrogen, is the most extreme and also the most effective method. However it has the nasty tendency to quickly turn whatever you're trying to cool into a non-functional frozen brick. There is also the problem of maintaining a steady supply of the stuff. Next comes phase change cooling, more commonly known as refrigeration. It too has its drawbacks. In order to be effective, phase change cooling systems require a number of components which renders them too bulky to fit into a standard computer case. Just like your refrigerator, these components are also quite power hungry. Additionally, both cryogenics and phase change cooling are a bit too effective, causing the cooling area to become so cold that condensation occurs. We don't think we need to explain why water + electronics = bad.
Thermoelectric Cooler (TEC) Cross-section
Then there's thermoelectric cooling (TEC), also known as the Peltier effect, named after the French physicist who discovered the phenomenon. A TEC device is essentially a heat pump that is made of two different metals (n-type and p-type) that are connected together at two junctions. A current is passed through the junction, causing heat transfer from one side of the junction to the other. This results in one side of the device becoming very hot while the other side becomes very cold. However, TECs only shift heat around, they don't remove heat from themselves so a secondary cooling solution is necessary to remove heat from the hot side of the TEC. TECs also draw a lot of power, often requiring over 100 watts and they are prone to suffering from condensation problems as well.
ThermalTake Bigwater 745 Water Cooling Kit
Water cooling has risen as the most popular of the air cooling alternatives and it is slowly creeping into the mainstream. It is now common to see water cooling kits being sold in computer shops and most boutique computer manufacturers have also adopted water cooling in their feature products. In concept, water cooling is actually closely related to air cooling. Like conventional air cooling, water cooling works by drawing heat away from the device being cooled with a primary medium (heatsink in air cooling) then a secondary medium is used to remove heat from the primary medium (air). Water cooling differs from air cooling in its use of a water-block as the primary medium and water, fed to the water block via tubes, as the secondary medium. A pump carries the water, which has been warmed up by the heat from the water block, to a radiator where it is cooled by a third medium, air. The cooled water is then pumped back to the water block where the process begins anew.
We know what you're thinking, "but didn't we just establish that water + electronics = bad a couple of paragraphs ago"? That is a genuine concern, but a well constructed water cooling system is quite safe. In fact, you should be more worried about the pump failing, or the water in the system evaporating than a leak in a well designed system. Unfortunately, most water cooling systems are "some/all assembly required" and this is the root of most problems. Water cooling also requires more maintenance than an air cooling setup. Over time, the water in the system will often evaporate and the system will need to be refilled. Many people also use some kind of coolant in their systems which needs to be periodically changed. These may both be very involved processes, depending on how the system is setup, certainly more involved than the near-zero maintenance required for an air cooling setup, where the only thing you need to worry about is blowing off some dust if it ever gets clogged up.