Urban Transport

Space technology cools Paris commute

Space technology cools Paris c...
French transportation company Alstom is running the capillary cooling system experiment on the Parisian Metro line (Photo: ESA/Alstom Transport/P. Sautelet
French transportation company Alstom is running the capillary cooling system experiment on the Parisian Metro line (Photo: ESA/Alstom Transport/P. Sautelet
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An advanced cooling system without moving parts is used on spacecraft, such as the Alphasat telecommunications satellite (Image: ESA/J. Huart)
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An advanced cooling system without moving parts is used on spacecraft, such as the Alphasat telecommunications satellite (Image: ESA/J. Huart)
The capillary cooling system for trains (Image: ESA/Calyos SA/M. Bries, Mandragore)
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The capillary cooling system for trains (Image: ESA/Calyos SA/M. Bries, Mandragore)
Loop Heat Pipe technology principle for trains (Image: ESA/Calyos SA)
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Loop Heat Pipe technology principle for trains (Image: ESA/Calyos SA)
French transportation company Alstom is running the capillary cooling system experiment on the Parisian Metro line (Photo: ESA/Alstom Transport/P. Sautelet
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French transportation company Alstom is running the capillary cooling system experiment on the Parisian Metro line (Photo: ESA/Alstom Transport/P. Sautelet
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The Paris Metro is one of the world's great underground railways and not the sort of place you'd expect to find cutting edge satellite technology at work. But for the last year and a half a cooling system developed by the European Space Agency (ESA) for its satellites has been making Trains on Metro Line One more comfortable. The new cooling system works without moving parts and frees up more space to be enjoyed by passengers while saving costs.

If you've ever been caught in an underground train during a power failure, you may have noticed that the situation soon becomes not only extremely frustrating, but also very hot. That's because an underground train is filled with all sort of heat-generating machinery in addition to the passengers, who each put out as much heat as a 100 watt incandescent bulb. In a cylinder like an underground rail tunnel, there isn't any place for this heat to go, so when the cooling system on a train conks out, things can get very unpleasant very quickly.

The trouble is that the machinery that controls this heat is bulky, noisy, expensive to run, prone to breakdowns, and takes up a lot of space on the train. So, when French transportation company Alstom decided to do away with the large fans that currently cool most of the trains, it turned to ESA and its space technology spin-off program.

Loop Heat Pipe technology principle for trains (Image: ESA/Calyos SA)
Loop Heat Pipe technology principle for trains (Image: ESA/Calyos SA)

Subject to the constant glare of the Sun and without the shielding benefit of the Earth's atmosphere, satellites need to stay cool, too, if their electronics aren't to end up frying. On Earth, large devices like computers are kept cool by using fans to blow air across the circuit boards to carry away the heat while smaller ones, like tablets, use air convection to cool off. But with no air in space, neither of these are an option. Also, fans use moving parts and motors, which don't do very well in a space environment.

ESA's solution was an advanced cooling system without moving parts that uses heat pipes to carry away waste heat. These copper, stainless steel, or plastic tubes are filled with liquid that runs in a closed loop between hot spots and cold spots on the satellite, such as between the sunward and leeward sides.

The liquid circulates; using the temperature differential between the two spots to cool the satellite. That is, it has a very low boiling point and turns into vapor on the warm side of the spacecraft. When it reaches the cool side, the vapor condenses and the cycle starts over again.

An advanced cooling system without moving parts is used on spacecraft, such as the Alphasat telecommunications satellite (Image: ESA/J. Huart)
An advanced cooling system without moving parts is used on spacecraft, such as the Alphasat telecommunications satellite (Image: ESA/J. Huart)

According to ESA, the tricky bit is to get the liquid circulating through the system without using pumps. The space agency engineers managed this by relying on capillary action. It's the same force that pulls sap up tree trunks, spilled drinks into paper towels, and coffee into sugar cubes.

"Picture dipping the tip of a sugar cube in coffee," says Michel Ganseman, CEO at Euro Heat Pipes. "The coffee is quickly drawn up into the sugar, through the pores, because of what s known as capillary action."

By using this capillary action combined with an air heat exchanger, the heat-pipe technology replaces the conventional mechanical fans on the Metro trains, though ESA says that the technology can also work with everything from computer chips to pigsties. In the meantime, the hope is to expand the cooling system to other trains in French rail transport.

"Currently, we have one experiment on the Parisian Metro line," says Alstom’s Sebastian Nicolau. "But potentially, we can propose this solution for all different trains, from tramways to metros, suburban trains, and high speed trains like the TGV."

Source: ESA

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4 comments
splatman
Heat pipes were invented before ESA had even been thought of.
richs
To all to Splatman's comment, heat pipes heat pipes using gravity were invented in the steam age. The concept of using capillary action to move the liquid in heat pipes was first proposed in the 1940s, and a patent issued 50 years ago which suggested their use in space. Their use in personal computers dates back over 20 years. Come on, Szondy, do some basic research before writing!
StillWind
In addition to what has already been mentioned, the Earth's atmosphere doesn't keep things cool. In fact, it is the atmosphere that keeps things here, warm. Although air does help move heat around on Earth, in space where it is a frosty 14 degrees above absolute zero, there is no air, so heat has to be radiated away in a different manner. Using closed "heat tubes" supplies the mechanical means of heat transference from the warm side to the cold side. As mentioned, this is not new technology.
Gadgeteer
If you have a PC or laptop, chances are you have heat pipes in your home or office. They've been used for quite some time now to transfer heat away from hot CPUs.