Exotic Cooling Fluids

This content was originally featured on Amdmb.com and has been converted to PC Perspective’s website. Some color changes and flaws may appear.

I’m not generally one for throwing around disclaimers, but one is warranted here. Virtually all of the fluids I’ll mention for use in extreme cooling solutions have hazards associated with them. These hazards range from minor such as being chemically incompatible with one or more of your components to major, such as being harmful or fatal if handled improperly. Extreme cooling is a venture not to be taken lightly. This article is purely intended to introduce you to some of the options that exist. Prior to beginning any extreme cooling project, I’d encourage you to fully research the fluid you intend to use so that you have the complete understanding necessary for safe handling and operation.

It is not easy to locate solid (pun intended) data on fluids that retain low viscosity and good heat transfer characteristics at extremely low temperatures while still remaining stable at room temperature. One forum member in particular has done more research in this department than any one else I know. Scott Gamble (r0ckstarbob) has devoted countless hours to comparing and compiling data on a variety of low temperature fluids. Along the way, he’s probably learned more than most engineering students about the topic and certainly has more information than I could ever find time to gather.

I’m going to reproduce a chart of his, showing the properties of a few available heat transfer fluids. All data listed at 20°C. Viscosity is highly temperature dependent and roughly doubles for every 20°C drop in temperature.

Freezing Point (°C)Specific Heat (kJ/kg-°C)Conductivity
Dynamic Viscosity(n-s/m^2)*10^4
Water 1000
“50/50 Anti-freeze”
1050 -293.5.4113.1
Glycol 1114 -582.4.2517.3
Isopropyl 780 -883.275.79
Methanol 810 -982.55.255.97
33:67 ratio
937 -383.64.497.93
Ethanol 800 -1142.45.1611.9
Hydrogen Peroxide/Water
50:50 ratio
1200 -473.35.3375.97

All of the alternatives to pure water tolerate temperatures well below 0°C. What differentiates among them is their performance at low temperatures and their “friendliness” with common materials in cooling systems. Anti-freeze is an excellent fluid when temperatures vary over a very wide range. Its low-temperature performance, however, is less than stellar. This is mainly due to its higher viscosity, which drops total flow rate, and the impact this has on convection efficiency. Pure isopropyl and methanol along with a blend of hydrogen peroxide and water all have respectable performance, but are also relatively hazardous materials. Flammability of the first two and material incompatibility of the final one make them unsuitable for normal usage.

A 33:67 blend of methanol and water is commonly known as windshield washer fluid. This combination nearly matches the performance of pure water while permitting operation well below water’s freezing point. If you intend to run a chiller or peltier system with fluid temperatures below °C, you’ll want to check out a methanol and water mix. If you buy windshield washer fluid, try to avoid those with additives. Most additives are there to help clean bugs off your windshield and to keep your spray nozzles clean. These additives are of no benefit to a cooling system.

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