A team of scientists has discovered an exception to a scientific law that has been in force for more than 200 years which governs how heat diffuses through solid materials.
This law is called Fourier’s law. which works like this: as the molecules vibrate and the electrons move, heat diffuses from the hotter end to the colder end at a rate that is proportional to the temperature difference and the area through which it flows. heat flows.
Now, 200 years later, this group of researchers led by polymer physicist KaiKai Zheng of the University of Massachusetts has discovered that It is a model that does not work at the nanometer scaleas they point out from Science Alert.
To be exact, they have detected that, at a macroscopic level, Fourier’s law breaks down and no longer predicts how fast or slow heat will move through a solid material.
The discovery has come thanks to the fact that, being translucent, these materials allow some wavelengths of light to pass through.
This has led Zheng’s team to form the following hypothesis: in addition to heat diffusing through these solid materials, their translucency could also allow thermal energy to travel through the materials in the form of thermal radiation.
“This research started with a simple question,” explains Steve Granick, a materials scientist also at the University of Massachusetts. “What if heat could be transmitted [a través de sólidos] another path, not just the one that people had assumed?”
To test this question, the scientists put test materials inside a custom-made vacuum chamber to eliminate the possibility of heat dissipating from the materials through the air.
“Find violations [en la ley de Fourier] at macroscopic scales would be surprising, as this would go beyond standard textbook thinking,” the researchers write in their paper, reflecting on their thinking before the experiments.
Once in the chamber, they used 3 methods to heat the materials and see how the heat spread: a temperature sensor placed directly on the surface of the material; measuring the color change of a temperature sensitive coating painted on the sample; and an infrared camera.
“The data shows that warming [ocurrió] faster than can be attributed to diffusion”the researchers note, “indicating that radiation contributes significantly to heat flux during the early times after a heat pulse, although the relative contribution of radiation decreases as diffusion becomes dominant at later times.”
“It’s not that Fourier’s law is wrong,” Granick clarifies, “It just doesn’t explain everything we see when it comes to heat transmission.“
The team suggests that translucent materials radiate heat internally because structural imperfections act as heat absorbers and sources, allowing heat to spread from one point to another instead of slowly diffusing.
They add that their findings could help engineers design new strategies for heat management in translucent materialsnow that their study provides an expanded understanding of how heat spreads in solids, approximately 200 years after this phenomenon was first described in mathematical terms.