Fluctuations in a fluid with a thermal gradient

TL;DR

This study measures temperature fluctuations in a fluid with a thermal gradient, revealing a $q^{-4}$ behavior at high wavenumbers and a maximum at intermediate scales, with results aligning qualitatively with theoretical predictions.

Contribution

First experimental verification of the fluctuation structure factor in a fluid with a thermal gradient, highlighting deviations from existing theoretical models.

Findings

Temperature fluctuation structure factor follows $q^{-4}$ at high $q$

Observed a maximum in $S_T(q)$ at intermediate $q$

Results qualitatively agree with Ortiz de Zárate and Sengers' predictions

Abstract

We report measurements of the temperature fluctuations in a horizontal layer of a pure fluid confined between parallel plates and heated from below. Consistent with earlier work we found that the structure factor $S_T(q)$ (the square of the modulus of the Fourier transform of the temperature field) was consistent with $S_T(q) \sim q^{-4}$ for large horizontal wavenumbers $q$. As $q$ decreased, $S(q)$ increased less rapidly, passed through a maximum, and then approached zero. The results agree qualitatively, but not quantitatively, with the predictions of Ortiz de Z\'arate and Sengers.