These scientists didn’t break a law of physics, but it appeared so at first. The second law of thermodynamics, one of the fundamental rules of this universe, says that heat can flow by itself only from a warmer to a colder object.
Now, however, in the strangest claim I’ve found for this Sunday morning, researchers at the physics department in Zurich used a Peltier element to cool a nine-gram piece of copper from over 100°C to significantly below room temperature without an external power supply.
Heat will not leave a cold object for a warmer one (to further cool the colder object) without help.
Heat is, fundamentally, the temperature dependent motion of electrons, atomic nuclei, and molecules. The 2nd law of thermodynamics says that at an atomic scale molecules in one area moving faster than those another nearby area will bump into slower molecules and will thus speed them up while losing some of their own momentum in the process. Heat transfer, in this way, flows from higher to lower energy states. So far so good. But …
Physicists at the University of Zurich have developed an amazingly simple device that allows heat to flow temporarily from a cold to a warm object without an external power supply. Intriguingly, the process initially appears to contradict the fundamental laws of physics. …
The results of a recent experiment carried out by the research group of Prof. Andreas Schilling in the Department of Physics at the University of Zurich (UZH) appear at first sight to challenge the second law of thermodynamics. The researchers managed to cool a nine-gram piece of copper from over 100°C to significantly below room temperature without an external power supply. “Theoretically, this experimental device could turn boiling water to ice, without using any energy,” says Schilling.
… elements can transform electric currents into temperature differences. The researchers had already used this type of element in previous experiments, in connection with an electric inductor, to create an oscillating heat current in which the flow of heat between two bodies perpetually changed direction. In this scenario, heat also temporarily flows from a colder to a warmer object so that the colder object is cooled down further. This kind of “thermal oscillating circuit” in effect contains a “thermal inductor.”
It functions in the same way as an electrical oscillating circuit, in which the voltage oscillates with a constantly changing sign.
Laws of physics remain intact
Until now, Schilling’s team had only operated these thermal oscillating circuits using an energy source. The researchers have now shown for the first time that this kind of thermal oscillating circuit can also be operated “passively,” i.e. with no external power supply.
Thermal oscillations still occurred and, after a while, heat flowed directly from the colder copper to a warmer heat bath with a temperature of 22°C, without being temporarily transformed into another form of energy. Despite this, the authors were also able to show that the process does not actually contradict any laws of physics. To prove it, they considered the change in entropy of the whole system and showed that it increased with time — fully in accordance with the second law of thermodynamics. …
Read more: SciDaily
* Updated after further reading.*
Here is a functional, though not a physics explanation of a Peltier element:
Thermoelectric coolers operate by the Peltier effect (which also goes by the more general name thermoelectric effect). The device has two sides, and when a DC electric current flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter.
How does the Peltier element actually work?
When the current flows through the junctions of the two conductors, heat is removed at one junction and cooling occurs. Heat is deposited at the other junction. … In every case, a DC voltage is required.
That just says what it does. Why does it work that way?
Two unique semiconductors, one n-type and one p-type, are used because they need to have different electron densities.
That’s a good clue, different electron densities are needed. Why? Here’s another clue:
The thermoelectric (Peltier) effect of a module is completely reversible. If the direction of the current through a module is reversed the heat flow through the hot and cold sides will also reverse. Thus, what was the cold side will now become the hot side, and what was the hot side will now become the cold side. …
Okay, I get the N-type side in the animation above. Elections hitting the heat conductor will bump into those atoms and transfer heat through the energy of their motion.
But for the P-type semi-conductor, what are holes flowing?
I believe the “holes” are net positive atoms jostling upward to bump the thermal conductor as the electrons flow down and around the circuit.
For the N-type, electron moment is part of what defines heat, so electron flow that transfers heat.
If the module has a red and a black wire, locating the positive wire is simple—the red wire is the positive lead. Positive current flowing into this wire will cause heat to flow from the cold side of the module into the hot side of the module.
I can visualize this part of the cooling system. It would reverse if the current reversed.
Since heat is also the motion of jostling atoms, I can imagine the P-type semi-conductor transferring heat (molecular jostling energy) upward in that way.
The p-type has less dense electrons, so the net flow of heat will be in the direction opposite the electron flow.
Follow so far?
I’m not a physicist or an electrical engineer, so corrections are welcome. This is just me trying to make sense of it from what I know. Now…
Still, the claim about powerless cooling requires a Peltier element, which by definition, uses an electric current. The current is the electric inductor of heat transfer (bumping electrons bump the atoms in the thermal conductor) but the claim seems to be that with no external push, a simple system composed of an inductance coil connected to a Peltier element will spontaneously start heat oscillating.
The title of this paper is:
Heat flowing from cold to hot without external intervention by using a “thermal inductor” A. Schilling*, X. Zhang and O. Bossen
What is a thermal inductor of heat transfer?
Thermal inductance refers to the phenomenon wherein a thermal change of an object surrounded by a fluid will induce a change in convection currents within that fluid, thus inducing a change in the kinetic energy of the fluid.￼ It is considered the thermal analogue to electrical inductance …
Re-reading the news coverage on this, the Independent says:
… thanks to a piece of equipment more commonly deployed in hotel minibars, known as a Peltier element, the Swiss team has shown for the first time an object can be cooled significantly below room temperature without any external power.
From reading the abstract, I’m now of the view that the direct current flowing through the system at the start due to heat provides power to start cooling element and start the system oscillating. The system dips below room temperature before it would eventually all return to room temperature.