[Paper Review] Tunable liquid-solid hybrid thermal metamaterials with a topology transition

Peng Jin, Jinrong Liu+5 more|arXiv (Cornell University)|Aug 29, 2022

Advanced Materials and Mechanics5 citations

TL;DR

This paper proposes a tunable liquid-solid hybrid thermal metamaterial that enables continuous switching between thermal cloaking and thermal concentration via external control of liquid flow. By breaking Onsager reciprocity through thermal convection, the system achieves a topology transition in virtual space, allowing dynamic, reversible heat manipulation beyond conventional conductive limits.

ABSTRACT

Thermal metamaterials provide rich control of heat transport which is becoming the foundations of cutting-edge applications ranging from chip cooling to biomedical. However, due to the fundamental laws of physics, the manipulation of heat is much constrained in conventional thermal metamaterials where effective heat conduction with Onsager reciprocity dominates. Here, through the inclusion of thermal convection and breaking the Onsager reciprocity, we unveil a regime in thermal metamaterials and transformation thermotics that goes beyond effective heat conduction. By designing a liquid-solid hybrid thermal metamaterial, we demonstrate a continuous switch from thermal cloaking to thermal concentration in one device with external tuning. Underlying such a switch is a topology transition in the virtual space of the thermotic transformation which is achieved by tuning the liquid flow via external control. These discoveries illustrate the extraordinary heat transport in complex multi-component thermal metamaterials and pave the way toward an unprecedented regime of heat manipulation.

Motivation & Objective

• To overcome the limitations of conventional thermal metamaterials dominated by effective heat conduction and Onsager reciprocity.
• To integrate thermal conduction in solids and thermal convection in liquids within a single metamaterial structure for enhanced heat control.
• To achieve on-demand, continuous tunability of thermal functions (e.g., cloaking to concentration) in one device.
• To experimentally demonstrate a topology transition in the virtual space of thermotic transformation via hydraulic tuning.
• To open a new regime in heat manipulation by exploiting the synergy between conduction and convection beyond classical constraints.

Proposed method

• Design of a liquid-solid hybrid thermal metamaterial with porous structures to independently control conductive and convective heat transport.
• Use of Darcy’s law (Q = σAΔP / ηL) to model and calculate effective permeability of porous units, with σ estimated from experimental flow rates and geometry.
• Finite-element simulations to model heat flux distribution and validate the effective thermal properties under varying hydraulic pressure.
• Implementation of type-I and type-II porous units: type-I for fluid flow (permeability ~2.68×10⁻⁹ m²), type-II as baffles (permeability 10⁻¹⁸ m²) to guide flow.
• Application of external hydraulic pressure (ΔP) to tune fluid velocity and thus control the heat flux amplification factor β.
• Use of fixed temperature boundaries in simulations and heat exchange conditions in experiments, with validation that discrepancies do not significantly affect β.

Experimental results

Research questions

• RQ1 Can thermal convection be harnessed in thermal metamaterials to break Onsager reciprocity and enable directional heat control?
• RQ2 Is it possible to design a single hybrid metamaterial that continuously switches between thermal cloaking and thermal concentration?
• RQ3 How does a topology transition in the virtual space of thermotic transformation manifest in a physical liquid-solid system?
• RQ4 To what extent can the effective thermal transport properties be tuned via external hydraulic control in a hybrid conduction-convection system?
• RQ5 Can experimental realization of such a system be achieved with measurable and controllable heat flux amplification?

Key findings

• The heat flux amplification factor β was experimentally tuned continuously from ~1.0 (thermal cloaking) to ~2.5 (thermal concentration) by adjusting external hydraulic pressure.
• Finite-element simulations confirmed that β increases monotonically with ΔP, with the total heat flux in the core region rising proportionally to the applied pressure difference.
• The effective permeability of type-I units was experimentally calculated as 2.68×10⁻⁹ m², matching simulation results (2.26×10⁻⁹ and 1.02×10⁻⁹ m² for metashell components).
• Reynolds number of ~45 confirmed laminar, steady-state flow, validating the use of Darcy’s law and neglecting inertial effects.
• The system demonstrated a topology transition in virtual space corresponding to the functional switch between cloaking and concentration, confirmed via simulation and experimental validation.
• Despite minor boundary condition differences (fixed vs. heat exchange), the heat flux amplification factor β remained robust and unaffected by experimental thermal contact variations.