Heat transport in boiling turbulent Rayleigh-B\'{e}nard convection

TL;DR

This study numerically investigates how bubble-induced buoyancy enhances heat transfer in boiling turbulent Rayleigh-Bénard convection, revealing increased circulation and plume activity, consistent with recent experimental findings.

Contribution

It provides a detailed numerical analysis of bubble buoyancy effects on heat transfer in boiling convection, focusing on the enhancement mechanisms without modeling bubble nucleation.

Findings

Significant heat transfer enhancement due to bubbles.

Increased plume activity and circulation strength.

Agreement with recent experimental results.

Abstract

Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to several mechanisms many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubbles compounds with that of the liquid to give rise to a much enhanced natural convection. In this paper we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-B\'enard convection process. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. We consider a cylindrical cell with a diameter equal to its height. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping the temperature difference constant and changing the liquid pressure we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between $2\times10^6$ and $5\times10^9$. We find a considerable enhancement of the heat transfer and study its dependence on the bubble number, the degree of superheat of the hot cell bottom and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the hot cell bottom and, as a consequence, the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experimental results of Zhong et al., Phys. Rev. Lett. {\bf 102}, 124501 (2009) for boiling Rayleigh-B\'enard convection.