The Chemicals of OC'n and Super Cooling - Coolants

By: Brian 9/16/02

Page 2

Biological Growths

Nobody wants things growing in their computer. Biological growths can cause the hoses to become clouded or even turn different colors. The best way to prevent the growths is a combination of methods. First, use distilled water to avoid adding algae and other life forms from the start. Then, add some biocide to prevent life from migrating in and finding a good spot to grow.

This problem has seen some of the most interesting additives put into computer cooling systems.  People have put mouthwash, dishwashing soap, pool chlorine, and many other strange substances into their computer coolants to kill existing growths or prevent future growths.  Unfortunately, a minty-fresh smelling coolant does not guarantee that it has no algae.

Most of the chlorine additives are effective at killing germs and algae, but chlorine quickly evaporates from water. So, bleach will work for a short time, but it is only temporary. Also, chlorine is a very reactive substance that causes gaskets and some types of tubing to become brittle.  Be wary of adding a cup of bleach to your coolant.  It may cause your pump to start leaking!  If you choose this route, add a teaspoon to your loop every month, and carefully monitor the pump and tubing for leaks.  Bleach may also be corrosive to metals in your system (it is a powerful oxidizer). Dishwasher detergent does contain some chlorine, which is probably why dishes come out so sparkling and clean. So, you could add detergent, but it also causes a problem with foaming (i.e. try something else).

Alcohol is similar to chlorine biocides but not as harsh.  For a given concentration, it kills less effectively than chlorine, but it is also easier on gasket materials (as far as I know). Unfortunately, it will also evaporate from the coolant although not as quickly as chlorine.  A good idea would be to add a teaspoon or two to your coolant and change the coolant every 3 to 6 months to refresh the biocide.

Neither Water Wetter™ nor antifreeze is a good biocide.  However, they do provide higher pH (base instead of acid) so that some growths do not form as readily.  The majority of bacteria prefer to live in a slightly acidic environment. Many people with closed loops run distilled water and Water Wetter™ for long periods of time without any biological problems.

As a last resort, adding humidifier additives or other common biocides such as silver or sodium azide can help.  Some people recommend biocides from your local pool supply store, but those are very powerful chemicals. In other words, be careful with any of these chemicals! Read the labels and add only the required amounts, because more is not necessarily better.

Precipitated Solids

Precipitated solids are a related effect to galvanic corrosion in that dissolved metal ions get dumped out of solution onto a ready surface. However, the most common precipitated solids arise from ions present in a poorly chosen coolant: calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃). Typically the problem starts when someone uses tap water instead of distilled or de-ionized water.

The composition of tap water is varied, but it will typically contain fairly high concentrations of Ca2+ and Mg₂+ (dissolved Calcium and Magnesium). Some tap water even contains copper and lead, which are not particularly good for your health. When these ions are placed into a cooling loop with dissolved CO2 and Water Wetter™, then eventually solid phases (CaCO₃ and/or MgCO₃) will start to precipitate out. Avoid tap water! Buying distilled water is well worth the investment of $0.79 for a gallon. Even a cheap Brita water filter removes the majority of these dangerous (for your coolant) ions.  A water block covered in Calcium Carbonate does not transfer heat nearly as well as a clean block, and when tubing clogs with solids water circulation will suffer.

Heat Movement

The whole point of using water is to increase the amount of heat moving away from your CPU, Northbridge or other hot component. All of the additives we have discussed actually move heat less efficiently than water. But, wait! I hear many people complaining already. Isn't Water Wetter™ good at helping the system work more efficiently?  What about Antifreeze?

Water Wetter™ appears to be mostly a surfactant with a pH alteration to help reduce corrosion.   The surfactant, as we all know, is designed to reduce surface tension. So, it reduces the size of the bubbles that form in a normal car or motorcycle engine as the water boils.  As a side effect, lowering surface tension improves heat transfer at lower temperatures by changing the surface tension and viscosity of water. This results in a more perfect wetting of the surface (contact angle close to 0) which helps the water move faster near the heat exchange surface.  We are mostly concerned about the side effect, as most of our chips do not exceed 212ºF/100ºC to cause water boiling, I hope!

However, pure Water Wetter™ is not particularly good at moving heat. So, if you add too much to your coolant, the total heat transfer efficiency drops. You only need as much Water Wetter™ as it takes to reduce the surface tension.  Any more, and you only dilute the excellent heat moving characteristics of water.  Redline Oil has a page specifically for the Water Wetter™ product, and it clearly shows how adding too much can decrease performance.

Please note that I am using Water Wetter™ as a specific example of many fine products which perform very similarly, such as Purple Ice. Technically, you could use some proportion of surfactant (e.g. soap or glycerin), soluble silicate, and a basic substance (e.g. sodium carbonate or some other substance to increase the pH level). However, it seems more trouble than it's worth unless you plan on using gallons and gallons of it.

I could bring up a table of the heat capacity and conductivity of the other additives, but this has been well discussed in other articles and forum threads. Simply put, pure water is the best at moving heat if you are measuring a static system. If you are using a chiller to go below ambient, consider methanol as an additive to reduce the freezing temperature not Antifreeze. Antifreeze is very thick at low temperatures.  At normal temperatures, the only performance known enhancement is a surfactant such as Water Wetter™ or soap.  However, remember that pure methanol is poisonous and flammable. Silicone tubing may allow methanol fumes to migrate out and reach unpleasant concentrations in a poorly ventilated room.

Conclusions

First, change your coolant regularly.  All additives reduce in effectiveness as they age   I recommend changing your coolant at least every year or two to prevent scale buildup, biological growths and corrosion problems.

Second, use the required amount of additives and no more!  Remember that more is not better. Adding too much of anything to your water will reduce the effectiveness of heat transfer and it might cause extra problems (e.g. too much bleach may corrode your gaskets).

Third, use distilled water as your base. Tap water has deposits that will clog up your system, cloud up your tubing and generally facilitate corrosion. It also has a healthy starter colony of life-forms waiting to grow in your system.

My recommendation for normal water cooling is to use a combination of Water Wetter™ (or one of its many clones such as Purple Ice) with distilled water (see the product for the recommended mixing ratio) and then change the coolant every 3-6 months. If you are concerned about biological growths, add some methanol or one of the biocides sold by humidifier companies.  If you hate the residue that Water Wetter™ leaves in your silicone tubing, you might try using antifreeze (realizing that you will have a minor performance hit).  If you run a chiller, change that to mixture to distilled water and methanol. Methanol has the lowest viscosity and thermal transfer characteristics of the additives to reduce freezing temperature.

If you have any comments or Questions please email me at Brian@ProCooling.com