Enhanced Capillary‐Fed Boiling in Copper Inverse Opals via Template Sintering

Capillary‐fed boiling of water from microporous metal surfaces is promising for low thermal resistance vapor chamber heat spreaders for hot spot management. Vapor transport through the void spaces in porous metals enables high heat fluxes at low evaporator superheat. In this work, the critical heat fluxes of capillary‐fed boiling in copper inverse opal (IO) wicks that consist of uniform pores with 3D periodicity is investigated. Template sintering is used to enlarge the “necks”, or hydraulic vias, that bridge adjacent IO pores of diameters from 0.6 to 2.1 µm. The enhanced neck size increases the hydraulic permeability for vapor extraction by an order of magnitude, and subsequently the CHF from 100 to 1100 W cm−2. Modeling of the boiling limit accounts for the vapor pressure drop through an IO wick using Darcy's law at a given bubble departure rate. This work links the effect of wick structure design on the boiling crises phenomenon in microporous surfaces and demonstrates material capabilities for ultrathin and low superheat thermal management solutions for high‐power‐density electronic devices. Capillary‐driven boiling in ultrathin copper inverse opal structures can sustain heat fluxes over 1 kW cm−2 at low superheat owing to an order of magnitude enhancement of hydraulic permeability through template sintering. Modeling of the critical heat flux links the effect of wick structure design on the boiling crises phenomenon of porous surfaces.