Enhanced heat transport by turbulent two-phase Rayleigh-B\'enard convection

TL;DR

This study demonstrates that turbulent heat transport in two-phase Rayleigh-Bénard convection is significantly enhanced by droplet condensation and nucleation, especially near the critical point, leading to a substantial increase in effective thermal conductivity.

Contribution

The paper introduces measurements of heat transport in turbulent two-phase convection with phase change, revealing a dramatic increase in effective conductivity near the critical point.

Findings

Effective conductivity increases linearly with decreasing top temperature.

Maximum effective conductivity exceeds single-phase value by an order of magnitude.

Near the critical point, effective conductivity increases dramatically despite vanishing latent heat.

Abstract

We report measurements of turbulent heat-transport in samples of ethane (C$_2$H$_6$) heated from below while the applied temperature difference $\Delta T$ straddled the liquid-vapor co-existance curve $T_\phi(P)$. When the sample top temperature $T_t$ decreased below $T_\phi$, droplet condensation occurred and the latent heat of vaporization $H$ provided an additional heat-transport mechanism.The effective conductivity $\lambda_{eff}$ increased linearly with decreasing $T_t$, and reached a maximum value $\lambda_{eff}^*$ that was an order of magnitude larger than the single-phase $\lambda_{eff}$. As $P$ approached the critical pressure, $\lambda_{eff}^*$ increased dramatically even though $H$ vanished. We attribute this phenomenon to an enhanced droplet-nucleation rate as the critical point is approached.