Controlling turbulent heat transfer by manipulating cohesive structures

This topic has been reviewed by Professor Ke-Qing Xia (Southern University of Science and Technology, Shenzhen, China) and his collaborators, based on their research over the past 10 years.

As the last unsolved problem in classical physics, fluid turbulence has attracted a lot of attention from the academic and engineering communities. In contrast to fully turbulent systems, one of the defining features of turbulent flows is the presence of coherent structures that are spatially and temporally linked across a range of scales.

It has long been known that these cohesive structures are the primary carriers for the transfer of mass, momentum, and heat in turbulence. However, due to the inherent properties of turbulent flows, such as strong nonlinearity and strong dissipation, how to deal with coherent structures to control turbulent transport has been a long-standing issue.

In the past decade, Professor Xia’s team has made great progress on this issue. By conducting a series of studies in a canonical thermal turbulence regime, i.e., Rayleigh-Bénard turbulent convection, they discovered a new mechanism for tuning turbulent heat transfer by manipulating the coherent structure through simple geometric confinement.

Under this mechanism, the heat transfer efficiency is controlled by the coherence of the thermal structures (which are characterized by their geometrical characteristics), rather than by the intensity of the disorder.

As a result, the heat transfer efficiency can be greatly improved even as the resulting flow is much slower. Importantly, this mechanism is fundamentally different from the dominant heat management approach based on the classical view of wall-bounded turbulence, which typically focuses on modifying the diffusion-dominant boundary layer to enhance or prevent turbulent heat transfer.

In the review article, Professor Xia and his collaborators present and detail the physical picture behind this newly discovered mechanism, and discuss its potential applications in passive thermal management (eg cooling of electronics).

Moreover, by providing additional examples of thermal perturbation regimes that undergo various dynamic processes (including rotation, double diffusion, magnetic field, tilting, modulation by polymer additive etc.), they also demonstrate how a cohesive structure manipulation framework can Generalization to understand heat transfer behaviors in apparently different disordered systems in a uniform way. This GM is expected to materialize in other types of turbulent flows.

This review article also covers other important developments in this research topic and outlines some future directions. These not only provide a new understanding of the turbulence and heat transfer research communities, but also enhance the design and development of engineered systems with tunable transfer efficiencies.

The work was published in National Science Review.