Scientists have discovered a game-changing phenomenon, a challenge to the 200-year-old Fourier Law. This law, like the law of the physical world, has always governed the way heat is transferred in solid materials. Fourier's law, with its profound insight, describes how heat is transmitted through solid materials: molecular vibrations, electrons shuttle, so that heat flows from the warm end of the object to the cold end, and its velocity is closely related to the temperature difference and the heat flow area.
However, the boundaries of science are always being challenged. Studies in recent decades have revealed that at the microscopic nanoscale, this classical diffusion model fails. Fourier's law, which is unable to move heat in a solid state at the nanoscale, is like tearing a hole in the solid foundation of the physical world.
Polymer physicist Kaikai Zheng and his team at the University of Massachusetts Amherst are not satisfied with the status quo and are eager to explore whether such an exception to Fourier's law exists on a larger scale in transparent materials such as translucent polymers and inorganic glass. These materials, although translucent, allow certain wavelengths of light to pass through, and the light is scattered in them, from the impurities in the structure of the material**, like a meteor in the night sky, although short but bright.
This scattering phenomenon led Zheng and his team to a bold hypothesis: in addition to diffusion through solid materials, does the translucency of these materials also allow thermal energy to pass through in the form of thermal radiation? Radiant heat, like electromagnetic waves in the air, especially infrared radiation, silently transmits heat, such as the warmth of the sun that we feel.
Senior author Steve Granick, who is also a materials scientist at the University of Massachusetts Amherst, is curious: "What if heat could travel in another way, not just the one that people think?" This question, like a seed, was planted deep in the hearts of the research team.
So, they began the painstaking experiment. They clamped the test strips and hung them one by one in a custom-made vacuum chamber, which eliminated the possibility of dissipating heat from the material through the air. They emit instantaneous laser pulses at the materials to heat them up and use three methods to measure how the heat travels through each material: a temperature sensor placed directly on the surface of the material, a temperature sensor that measures the color change of the temperature-sensitive coating applied to the sample, and an infrared camera.
The experimental results show that the rate of heating exceeds the rate of diffusion, suggesting that the contribution of radiation to the heat flux is very large in the early stages after the heat pulse. Although the relative contribution of radiation decreases as the later stages of diffusion dominate, its presence cannot be ignored.
"It's not that Fourier's Law is wrong, it's that it doesn't explain everything we see in terms of heat transfer," Granick clarified. "This discovery, like a ray of light, illuminates our understanding of the mechanism of heat transfer. Translucent materials radiate heat internally, as structural defects act as heat absorbers and heat sources, allowing heat to travel quickly from one point to another, rather than spreading slowly.
Their findings not only have a profound impact on scientific theories, but may also provide engineers with new design ideas. Their research has provided us with a deeper understanding of how heat travels in solids, some 200 years after the phenomenon was first described in mathematical terms. This is a milestone in the development of science that is constantly challenging itself and exploring the boundaries of the unknown.