How to Water Cool a Computer

Author: Dave Melchiore

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Water Cooling
So you’ve decided to water cool your computer. Perhaps you’ve reached the limit of your overclock on air, and you want even more speed. Or, perhaps your computer and its 15 fans are too noisy for you to bear any longer. Either way, once you’ve made the decision to water cool, you may not know how to turn the idea into reality. Luckily, you’ve come to the right place. This article will help you turn your water cooling aspirations into your own water cooled beast of a machine.

Why Water Cool?
Water cooling has many advantages over air cooling. Let’s start with the basics. First of all, water has a thermal conductivity of 0.6062 W/ (m*K) whereas the thermal conductivity of air is only 0.0262. This means heat can be drawn away from components more efficiently with water. Water also has a much higher specific heat capacity than air (1.0 J/ (kg*K) versus 0.24), which allows the water cooling system to absorb a lot more energy before heating up. Using liquid to cool components allows the heat to be carried to a remote location, usually a radiator where the heat can be dissipated more effectively than with a heat sink. A water cooling radiator works identically to the radiator in your car: coolant is pumped through an array of tubes and fins, and air is blown across this array to remove heat. Because the radiator is mounted remotely, it can be larger than a chip-mounted heat sink, and therefore will be able to cool more effectively. Because all major components in the computer will be cooled by the same system, there will be fewer fans, and therefore less noise.

It is important to know all of the components in a water cooling system and their functions. In the following paragraphs, I will discuss water blocks, tubing, radiators, reservoirs, pumps, fluid type, and packaging.


Water Cooling Blocks, Radiators & Pumps
First off are the water blocks. A water block is a hunk of thermally conductive metal (usually copper or aluminum) which interfaces with the chip being cooled. Copper is generally regarded as a superior cooling material, with a thermal conductivity of 401 W/ (m*K) versus 237 for aluminum, but it is also more expensive. Different water block manufacturers use different water block designs; the goal is to create maximum surface area inside the block for heat to transfer from the metal to the water. Therefore, water blocks are filled with a maze of channels designed to maximize surface area and create turbulence in the water, which will help avoid “hot spots”. Water blocks can be used on the CPU, GPU, and Northbridge; although a water cooling system does not need to cool all those components.

Next, the question of how large of a radiator and what fans will be used to cool said radiator must be addressed. A great choice for a radiator is a heater core from an automobile, because they are excellent performers and very inexpensive. A few popular heater cores are those from ’86 Chevelles and ’89 Camaros, because they are just the right size for a water cooling system. If using an automotive heater core, be sure to either solder barbs on or buy one with barbs already in place. Radiator cooling is usually accomplished via 120mm fans blowing through the radiator. This is because 120mm fans have the best airflow to noise ratio. Using a large 120mm fan and radiator will also allow the water to come in contact with more surface area of the radiator. After the water has been cooled by the radiator, it is usually returned to a reservoir (or “res” for short). A water cooling reservoir should be used unless there is insufficient space. There are many advantages to using a reservoir. Reservoirs are not mandatory, but are useful in that they increase the fluid capacity, and therefore the thermal capacity, of the system. They also allow for convenient filling and bleeding (removing excess air) of the system. Without a reservoir, a fillport must be used to fill and bleed the system. A fillport is basically just a barb with a screw-type cap on it which allows the user to gain access to the coolant inside the system.

To move water through the system, a water cooling pump must be used. Many water cooling setups use submerged pumps which sit inside the reservoir. Generally speaking, a pump with 100-300 g/h should be sufficient; although that will depend on what components you have in the rest of your system. A pump should be just powerful enough to move water through the system without allowing it to sit inside a water block for an extended time. If the water moves too slowly, it will not be able to effectively whisk heat away from the chip. If the water moves too quickly, it won’t have adequate time to soak up the heat from the water block.


Compatability
Now that you understand the basic components of a water cooling system, you have some choices to make. First, you must make sure that the water blocks you purchase are compatible with the CPU, GPU, and northbridge in your computer. Current CPU compatibilities are generally related to the manufacturer of the CPU: AMD or Intel. On the AMD front, common sockets include A, 754, 939, and 940. On the Intel front, the two common ones are socket 478 and LGA775 (also known as Socket T). GPU compatibilities follow a similar trend: ATI and NVIDIA are competing companies with their own chipset designs. Most CPU and GPU water blocks are universal these days; simply check to make sure that the water block you are purchasing lists your video card / CPU in the compatibility list.


Water Cooling Tubing
There is a debate within the water cooling community about what size tubing is superior. A 1/2" inner diameter system will offer higher possible flow rates than a 3/8" system, but higher flow isn’t necessarily desirable. As long as water is moving in the system, it will spend the same amount of time in the radiator regardless of how fast it’s moving. (If this sounds weird, imagine a car going around a racetrack. The car will spend the same amount of time in a given section of track regardless of how fast the car is moving, because if the car moves more quickly, it will spend less time traveling through the section per lap but make more laps.) Just make sure all the components you purchase are compatible with whatever inner-diameter tubing you choose to go with. Another tubing decision which needs to be made is material. There are three main choices. Tygon is the most resistant to kinks, but it is expensive at around $3.00 per foot. ClearFlex 60 is about half the price of Tygon, but not quite as kink-resistant. The cheapest tubing is good old vinyl, but vinyl tubing is not very kink resistant.


Installation
Where should you mount everything? The water blocks are self-explanatory, but everything else will demand a bit of creativity, depending on your case setup and space availability. The reservoir is usually mounted in the front of the case in the drive bay area. The radiator can be mounted in a number of locations, including the drive bay area, the top of the case (if the case is equipped with a top-mounted blowhole), or the rear of the case by the exhaust fans (most common). Sometimes, an external radiator and even an external reservoir are preferable. There are integrated radiator/reservoir systems on the market, such as the Zalman Reserator, which allow the user to water cool their computer when case space is at a premium.


Water Cooling Liquid
A final yet important consideration to make is water cooling coolant type. Theoretically, you could fill your water cooling system with anything, but some fluids work much better than others. First of all, do not use tap water. Tap water has minerals, bacteria, and algae in it which will corrode and cloud your water cooling system, possibly causing a catastrophic failure. Another alternative is de-ionized water. De-ionized or non-conductive water may seem desirable initially, because it is a poor electrical conductor, and therefore will not cause much damage if a leak occurs. However, water is an excellent solvent, and so if de-ionized water is put into a water cooling system, it will corrode the water blocks to get its ions back. Therefore, de-ionized water is not something we recommend, either.

A good choice is distilled water, because it is relatively cheap yet pure enough to use in a water cooling system. Distilled water will not deposit harmful minerals in your system, nor will it cause algal blooms because there are no living organisms present. It will not, however, corrode your water blocks because it is not de-ionized. There are various additives which may be added to the coolant in your system. Water wetter is great for increasing the cooling capacity of your system by altering the properties of water and making it even more thermally capacitive. Water wetter will also help reduce corrosion in your water cooling system. Other additives, such as UV-reactive dyes, may be added for aesthetic reasons.


Water Cooling Testing
After your water cooling system has been designed, ordered, and assembled, it must be filled, bled, and tested for leaks. The water cooling system should be filled OUTSIDE of the computer. A small funnel will come in handy. Just fill up the reservoir, turn the pump on, and continue adding water until the reservoir fluid level has reached an adequate height. After the system is filled, slowly tilt and move the components (without spilling, of course) to put the reservoir at the top of the system. This will allow air trapped in the components to escape through the reservoir. Finally, the system should be run for a few hours on a bed of paper to check for leaks. Only after all these steps are completed should the system be installed in the case. When installing the system in the case, make sure to mind all existing components inside your computer, and pay special attention to water block mounting. Make sure that the water blocks are adequately mounted, and be extra careful not to put uneven pressure on a core; doing so may crack the core and end up forcing you to buy a new chip. Once everything is installed, boot up your machine and immediately go into the BIOS to check your temps. Make sure that everything seems to be within expected ranges; unexpected temperatures could be indicative of improper water flow, inadequate radiator performance, or improper water block mounting. If everything seems to be within expected tolerances, congratulations!


Conclusion
As you can see, the choices, and therefore the possibilities, are endless. This is part of the fun of building a water cooling system; every custom job is unique and incorporates some creativity from the builder. If all these choices are overwhelming, it is probably best to purchase a ready-made water cooling kit, because it will contain everything you need right in the box. Happy overclocking!