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Sci Tech
Heat flows in all directions
IT'S A cardinal rule that heat flows from the hot end of an object to the cold, no matter which end you heat.
But according to a report in New Scientist, researchers now have suggested a way to build a device that conducts heat in only one direction.
Heat makes molecules vibrate, and the jostling of molecules by their hot neighbours is what makes heat flow. This usually happens in any direction but now researchers of Ecole Normale Superieure in Lyon have shown how to make it one way.
Molecules of most materials vibrate at the same `characteristic' frequencies regardless of temperature. As they get hotter, only the amplitude increases. But in a few `non-linear' materials, such as DNA, the frequency decreases as they get hotter.
The researchers suggest building a device with particles that vibrate at high frequency on the left and particles with a low frequency on the right. Sandwiched in the middle are non-linear particles.
If the left end is heated, the particles vibrate rapidly and start to transfer heat towards the centre. As heat passes into particles of the non-linear material, their rate of vibration slows.
The sets up a frequency mismatch that makes the transmission of energy inefficient.
But heat the right side, and the particles vibrate slowly, so the neighbouring non-linear particles conduct heat ever more efficiently as they start to heat up. Such a device would do for heat what diodes do for electricity.
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