Enhanced heat transport in thermal convection with suspensions of rod-like expandable particles

TL;DR

This study experimentally demonstrates that suspensions of rod-like, thermally expandable particles can enhance heat transport in thermal convection at high Rayleigh numbers by acting as active mixers within boundary layers.

Contribution

It introduces a novel experimental investigation of how rod-like, thermally expandable particles influence heat transfer in Rayleigh-Bénard convection, highlighting their role as active flow mixers.

Findings

Heat transport is enhanced at high Rayleigh numbers.

Particles act as active mixers in boundary layers.

Thermal expansion contrast influences particle buoyancy and flow interactions.

Abstract

Thermal convection of fluid is a more efficient way than diffusion to carry heat from hot sources to cold places. Here, we experimentally study the Rayleigh-B\'enard convection of aqueous glycerol solution in a cubic cell with suspensions of rod-like particles made of polydimethylsiloxane (PDMS). The particles are inertial due to their large thermal expansion coefficient and finite sizes. The thermal expansion coefficient of the particles is three times larger than that of the background fluid. This contrast makes the suspended particles lighter than the local fluid in hot regions and heavier in cold regions. The heat transport is enhanced at relatively large Rayleigh number ($Ra$) but reduced at small $Ra$. We demonstrate that the increase of Nusselt number arises from the particle-boundary layer interactions: the particles act as ``active'' mixers of the flow and temperature fields across the boundary layers.