torsdag 21 juli 2022

Similarity Between Fluid Turbulence and Radiative Energy Transfer

In the TNT Radio interview in the previous post I suggest a similarity between fluid turbulence and radiative heat transfer connecting to a phenomenon of high frequency "cut-off".  

Fluid motion transfers large scale ordered kinetic motion/energy over a cascade of successively smaller and smaller scales into a smallest scale depending on viscosity of unordered kinetic motion/energy as turbulence perceived as heat energy with the smallest scale representing the cut-off. The total energy transfer from large to smallest scale shows to depend mainly on the largest scales with thus little dependence on the smallest scales set by viscosity, thus with little dependence on viscosity once small enough. This is Kolmogorovs law of finite rate of turbulent dissipation.

Computational BlackBody Radiation describes radiative heat transfer between two bodies/oscillators $B1$ and $B2$ of temperature $T1$ and $T2$ with $T1>T2$ as an ordered resonance phenomenon with a frequency "cut off" increasing with temperature with energy balance for frequencies below the lower cut-off for $B2$, while frequencies above and below cut-off for $B1$ are absorbed by $B2$ in the form of unordered high-frequency oscillations perceived as heat energy by $B2$. The result is transfer of energy from the warmer body to the colder body. 

In both cases there is thus a split between ordered large scale motion and unordered small scale motion beyond cut-off perceived as heat energy. In both cases the small scale unordered motion perceived as heat energy is the consequence of an impossibility of sustained ordered motion: In fluid motion an impossibility of transferring energy to smaller scales in ordered fashion, and in radiative transfer an impossibility to balance frequencies above cut-off for the colder body, as an effect of finite precision

There is a connection to the 2nd law of thermodynamics with the transformation of large scale motion into heat energy as small scale unordered motion, is irreversible. In radiation it means that heat energy transfer is one-way from warm to cold.

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