Design and optimization of well-ordered microporous copper structure for high heat flux cooling applications

Abstract Capillary-driven boiling enables promising passive cooling structures and devices, and the use of highly-ordered microporous media promises efficient heat transfer at low superheat. Here we leverage the structural regularity of copper inverse opals (IO) to develop capillary structures with unprecedented fidelity, enabling a detailed study of the impacts of architectural design variables on boiling critical heat flux (CHF) as well as liquid and vapor transport properties. Fabrication of IO using a template-assisted electrodeposition method allows fine control of the microstructure and bulk geometry, producing structures with varying pore diameters (3.2 - 10.2 µm), heated area lateral dimensions (0.2 - 5.5 mm2), and structural thicknesses (10 - 40 µm). We demonstrate capillary fed copper IO structures capable of dissipating over 1 kW cm−2 in boiling with water as the working fluid. We identify two distinct transport regimes, namely, a capillary-limited regime where CHF increases as IO lateral dimension decreases, and a boiling-limited regime where further decrease in IO areal footprint does not significantly improve CHF. This yields an optimal length scale of porous media area and structural thickness that maximize the CHF of capillary-driven boiling due to hydrodynamic competition between capillary wicking of liquid replenishment and the viscous forces on vapor. This work makes progress both on the fundamentals of two-phase flow physics in porous media while providing fabrication and optimization details for practical capillary structures that will support the device design for applications ranging from energy conversion to electronics cooling.