Thermal Waves and Heat Transfer Efficiency Enhancement in Harmonically Modulated Turbulent Thermal Convection

TL;DR

This study investigates how harmonic temperature modulation affects turbulent Rayleigh-Bénard convection, revealing thermal wave propagation and significant heat transfer efficiency improvements across a wide range of Rayleigh numbers.

Contribution

It experimentally confirms the enhancement of heat transfer due to harmonic modulation and explores its dependence on modulation parameters, building on recent numerical predictions.

Findings

Thermal waves propagate at modulation frequency within the flow.

Harmonic modulation significantly increases Nusselt number.

The enhancement depends on frequency and amplitude of temperature modulation.

Abstract

We study turbulent Rayleigh-B\'enard convection over four decades of Rayleigh numbers 4E8 < Ra < 2E12, while harmonically modulating the temperatures of the plates of our cylindrical cell. We probe the flow by temperature sensors placed in the cell interior and embedded in the highly conducting copper plates and detect thermal waves propagating at modulation frequency in the bulk of the convective flow. We confirm the recent numerical prediction [PRL 125, 154502 (2020)] of the significant enhancement of Nusselt number and report its dependence on the frequency and amplitude of the temperature modulation of plates.