Moto Guzzi Concept Heat Pipes
By Kevin Ash - 24/10/2010
The cool-looking finned heat sinks on either side of the Guzzi concept bikes' headstocks are there for more than just the style: they use what's known as heat pipe technology to take excess heat away from the motor, improving emissions and allowing a higher power output.
In the image you can see a plastic-covered flexible tube running from the hottest region of the cylinder head around the exhaust valve up to the heat sink - this is the heat pipe, and inside is a mechanism for transporting heat around four times as effectively as if a plain copper pipe was used.
The important principle here is the large amount of energy involved in the phase change of a material, in other words the transition from liquid to gas, solid to liquid and so on. This usually involves much larger amounts of energy than simply raising the temperature of a substance. Water for example requires 4.2 joules to heat one gramme up by one degree centigrade. This is called its specific heat. But to turn one gramme of water at 100 degrees C into one gramme of steam at 100 degrees C - no temperature rise, just a phase change from liquid to gas -takes 2300 joules.
This means that a much larger amount energy can be transported from one place to another if a phase change is involved as well as a temperature rise, and that‘s what happens inside a heat pipe. Guzzi doesn‘t say which liquid is used in this case - no doubt that‘s still to be determined according to cost, efficiency and safety criteria - but the process will be the same regardless.
The liquid absorbs heat at the engine end until it evaporates. The hot vapour then flows up the tube to the heat sink, carrying a large amount of heat with it, where it condenses and loses a lot of energy that in turn is dispersed by air cooling the heat sink‘s fins. Once it‘s liquid again it flows back down the pipe to the cylinder head to be heated up and vapourised once more.
It‘s a continuous flow process, enhanced by either a wicking matrix inside the tube or possibly grooves in an internal structure, while the liquid must be something with a boiling point at a suitable temperature. This can be altered by changing the pressure inside the tubes. Terblanche talked about using sodium for the best efficiency, which would work only in a vacuum conditions as it usually boils at nearly 900 degrees C, but it‘s also a dangerous substance which explodes on contact with water, so something more bike-friendly would have to be considered.
The point of this is that it increases the cooling capacity of the engine only when it gets hot, as the heat tube only works properly when the temperature of the head rises above a certain level, so engine warm up time is unaffected. Then because the engine is capable of losing more heat than a conventional design, it‘s possible to increase the power output. Both peak power and exhaust emissions benefit.
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