Enhancing Heat Transport in Multiphase Rayleigh-B\'enard Turbulence by Changing the Plate-Liquid Contact Angles

TL;DR

This study demonstrates that using oleophilic walls in multiphase Rayleigh-Bénard turbulence significantly enhances heat transport by promoting plume detachment and oil phase transport, with potential applications in optimizing turbulent heat transfer.

Contribution

It introduces a simple method of using oleophilic walls to greatly improve heat transport in turbulent multiphase flows, supported by numerical simulations.

Findings

Over 100% heat transport enhancement with 10% oil volume fraction

Oleophilic walls promote plume detachment and oil transport

Oil-water interface prevents mixing, maintaining turbulence structure

Abstract

This numerical study presents a simple but extremely effective way to considerably enhance heat transport in turbulent multiphase flows, namely by using oleophilic walls. As a model system, we pick the Rayleigh-B\'enard setup, filled with an oil-water mixture. For oleophilic walls, e.g. using only $10\%$ volume fraction of oil in water, we observe a remarkable heat transport enhancement of more than $100\%$ as compared to the pure water case. In contrast, for oleophobic walls, the enhancement is then only about $20\%$ as compared to pure water. The physical explanation of the highly-efficient heat transport for oleophilic walls is that thermal plumes detach from the oil-rich boundary layer and are transported together with the oil phase. In the bulk, the oil-water interface prevents the plumes to mix with the turbulent water bulk. To confirm this physical picture, we show that the minimum amount of oil to achieve the maximum heat transport is set by the volume fraction of the thermal plumes. Our findings provide guidelines of how to optimize heat transport in thermal turbulence. Moreover, the physical insight of how coherent structures are coupled with one phase of a two-phase system has very general applicability for controlling transport properties in other turbulent multiphase flows.