Melting dynamics of large ice balls in a turbulent swirling flow

TL;DR

This study investigates how large ice balls melt in turbulent flows, revealing that turbulence significantly enhances heat transfer and leads to an ultimate heat transfer regime independent of particle size.

Contribution

It provides new insights into the melting dynamics of large particles in turbulence and characterizes the heat transfer regimes based on flow conditions.

Findings

Heat transfer is much stronger in turbulence than in laminar flows.

Nusselt number scales as a power law of Reynolds number with exponent 0.8 for fixed particles.

For freely advected particles, Nusselt number is proportional to Reynolds number.

Abstract

We study the melting dynamics of large ice balls in a turbulent von Karman flow at very high Reynolds number. Using an optical shadowgraphy setup, we record the time evolution of particle sizes. We study the heat transfer as a function of the particle scale Reynolds number for three cases: fixed ice balls melting in a region of strong turbulence with zero mean flow, fixed ice balls melting under the action of a strong mean flow with lower fluctuations, and ice balls freely advected in the whole flow. For the fixed particles cases, heat transfer is observed to be much stronger than in laminar flows, the Nusselt number behaving as a power law of the Reynolds number of exponent 0.8. For freely advected ice balls, the turbulent transfer is further enhanced and the Nusselt number is proportional to the Reynolds number. The surface heat flux is then independent of the particles size, leading to an ultimate regime of heat transfer reached when the thermal boundary layer is fully turbulent.