Viscosity–turbulence mechanism for larger bubbles in hot water

Determine whether the reduced viscosity of hot water increases the turbulence intensity of the pouring jet and thereby generates larger entrained air bubbles than in cold water, validating or refuting this proposed mechanism with targeted experiments.

Background

The authors discuss potential fluid-dynamic drivers of bubble size differences and point to decreased viscosity at higher temperatures as a plausible cause via increased turbulence intensity producing rougher jets and larger bubbles.

They explicitly refer to this as a conjecture and suggest comparative experiments (e.g., hot sugar water with viscosity closer to cold water) while noting that a definitive conclusion requires further expert analysis.