Scientists have made a breakthrough discovery regarding an exception to a 200-year-old scientific law governing the universality of the Fourier law which describes thermal conductivity in solid bodies. A study conducted by specialists from the University of Massachusetts in Amherst, showed that heat can be transmitted not only due to temperature differences and cross-sectional areas as suggested by the Fourier law, but also through other mechanisms.
The ancient law states that the heat transmitted through an object depends on the temperature gradient and the region perpendicular to this gradient. This is why a hot drink slowly warms our hands through the solid wall of a mug. Despite known exceptions to this rule at the nanoscale, scientists have now demonstrated that the law does not always hold true at the macro level.
“This does not mean that the Fourier law is incorrect,” says Professor Steve Granik, who led the study. “It simply does not account for all aspects of heat transfer that we encounter. Our fundamental research broadens our understanding of heat transfer processes, providing engineers with new design strategies for heat circuits.”
The researchers focused on transparent polymers and inorganic glasses through which heat can diffuse. Due to their transparency, it was believed that energy could also be radiated through these materials. Experiments revealed that energy within these materials interacts with small structural imperfections, leading to secondary heat sources.
“This was previously unexplored territory,” says lead author Kaikai Jen. “Unexpected phenomena occur in transparent polymers.” To test their hypothesis, samples of transparent materials were placed in a vacuum to eliminate the influence of air. Heating was done using a laser in one experiment, while only one side of the sample was heated in another. Infrared imaging allowed researchers to observe what happened in each sample, with results consistently showing exceptions to the Fourier law.
“Sometimes, to be innovative, you have to set the textbook aside,” emphasizes Granik. This discovery not only challenges the current understanding of heat transfer processes but also paves the way for advancements in material science and engineering technologies.