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

Abstract

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.

Endoscopic Visualization of Contact Line Dynamics during Pool Boiling on Capillary‐Activated Copper Microchannels

“…Since the theoretical concept of local evaporation near the three‐phase contact line was first introduced, [ 11 ] both experimental and numerical investigations on the effects of contact line dynamics on boiling performance have been performed. [ 4,12,13 ] Microstructures, [ 14–16 ] nanostructures, [ 17 ] and the hierarchical micro/nanostructures [ 18,19 ] have been used to alter wettability, [ 20 ] wickability [ 21–24 ] and roughness [ 25–28 ] to increase contact line length and enhance microlayer evaporation, thereby enhancing critical heat flux (CHF) and heat transfer coefficient (HTC). Among these various surface structures, the microchannel has received widespread interest and use to study the effects of surface structure on boiling performance due to its regular periodic shape which is easy to fabricate and model.…”

Temperature-dependent mechanical behavior of three-dimensionally ordered macroporous tungsten

“…Moreover, the densities of 3DOM materials can be reduced into the single-digit percentages relative to those of the bulk material [11]. Additional flexibility exists to produce nanoporous thin films and to employ a wide variety of materials (e.g., 3DOM materials have been generated from C [12], V 2 O 5 [13], SiO 2 [14,15], W and W-Mo [16,17,18], TiO 2 [11,19], Ni [20,21], Cu [22,23]). These geometries and chemistries are not all readily produced with electrochemical dealloying processes.…”

“…Some of the materials that have been synthesized in the 3DOM structure do not typically deform via thermally activated mechanisms. These include face-centered cubic (FCC) metals [20,21,22,23], which deform by dislocationmediated processes on close-packed planes and directions, and ceramics [11,14,15,19], which demonstrate limited plasticity at experimentally accessible temperatures. In contrast, body-centered cubic (BCC) metals are known to possess highly temperature-dependent mechanical properties due to increasing numbers of active slip systems ({110},{112}, and {123}) at increasing temperatures [24].…”

Coupling droplets/bubbles with a liquid film for enhancing phase-change heat transfer

“…The dynamic behaviors of the bubbles, e.g. , nucleation, growth, escape, and bursting, can frequently disturb liquid film that is confined within the wicking structure, increasing convection heat transfer through the liquid film ( Ćoso et al., 2012 ; Palko et al., 2015 ; Sudhakar et al., 2020 ; Weibel et al., 2010 ; Zhang et al., 2018 ). The bubbles formed in the wicking structure can also increase additional liquid-vapor interfaces for liquid vaporization near the tri-phase contact line of the bubbles and carry heat away directly from the heated substrate by bubble growth, motion, and bursting.…”