Scientists have shown that a theory called thermodynamic transport theory (TTT) can compute how heat moves through fluids using only measurable properties, eliminating the need for trial‑and‑error fitting. No parameters are tweaked, and the formula stems directly from the underlying physics of energy fluctuations in small fluid cells.

TTT was tested against computer simulations of a Lennard‑Jones fluid, a common model for molecular interactions. At a reduced temperature T* = 1.36 and densities up to 0.8 ρ*, the average error of TTT relative to simulation data was 8.8 %. In contrast, the revised Enskog theory, another popular method, had an error of 29 %. These results demonstrate that TTT captures the density dependence of heat transport far more accurately than the older approach. The improved agreement holds across a range of temperatures, although the largest discrepancies appear near the fluid’s critical point, where higher‑order thermodynamic derivatives become important.

Because TTT relies solely on equilibrium measurements, it offers a practical way to estimate thermal conductivity for real fluids without costly experiments or expensive simulations. Its success in matching simulation data for a wide density range also suggests the theory could be extended to more complex fluids, provided careful attention is paid to behavior close to critical points.

The study’s key findings: 1. Thermal conductivity equals dilute‑gas value × a function of equilibrium properties with no adjustable parameters. 2. The function is built from specific heats and their temperature derivatives. 3. In Lennard‑Jones fluids at T* = 1.36, TTT’s error is 8.8 % versus 29 % for the revised Enskog theory. 4. Errors grow near the critical point due to sensitivity to higher‑order derivatives.

The visual below summarizes the error comparison for the Lennard‑Jones fluid.