Fabrication and Thermal Characterization of Composite Cu-CNT Micropillars for Capillary-driven Phase-Change Cooling Devices

Abstract

This paper presents the fabrication, testing, and modeling of an array of composite copper-carbon nanotubes (Cu-CNT) micropillars as a wick structure for potential application in passive phasechange cooling systems. This novel wick structure has a larger spacing at the base of the micropillars to provide a higher liquid permeability and mushroom-like structures on the top surface of the micropillars with a smaller spacing to provide a greater capillary pressure. The composite Cu-CNT micropillars were fabricated by an electrochemical deposition method on a patterned copper template. Cauliflower-like nanostructures were then grown on the top surface of the micropillars using chronoamperometry technique to improve the capillary pressure and thermal performance of the wick structure. After successful fabrication of the micropillars, a series of tests were conducted to quantify the thermal performance of the wick structures. The results demonstrate superior thermal and corrosion performances for composite Cu-CNT micropillars compared to those of copper micropillars. Additionally, a thermal resistance network analysis was conducted to model the thermal performance of the fabricated mushroom-shaped micropillar array. Model predictions were compared with the experimental results and good agreement was observed.

Biomimetic Micropillar Wick for Enhanced Thin-Film Evaporation

“…Such wicks consist of an array of micropillars, and their performance has been investigated both experimentally and numerically for thin-film evaporation applications. Some of the well-defined micropillar geometries that have been explored in the past for evaporative cooling are as follows: (a) cylindrical: ,,− one of the most common and optimized micropillar geometry due to their ease of fabrication, provides better thermal performance at low to mid heat flux conditions; (b) pyramidal: provides high capillary pumping at lower contact angles and better thin-film area available for evaporation; (c) conical: low dryout heat flux and effective heat transfer coefficient compared to cylinders due to less curvature of meniscus; (d) pies: shows marginal enhancement of effective heat transfer coefficient as a result of increase in thin-film region; (e) rectangular ribs: , maximum capillary pressure generated is lower than cylinder but has comparable thin-film area fraction; (f) mushroom-shaped: provides lower overall thermal resistance as result of thinner thin-film region; (g) catenoidal: re-pinning of meniscus led to higher maximum effective heat transfer coefficient than cylinder but has comparable capillary performance; (h) gradient cuboid: generates high capillary pumping pressure and at the same time has better effective heat flux throughout the meniscus than cuboidal micropillar. Additionally, wicks with nonuniform micropillar distribution and segmented arrangement of micropillars have also been reported to simultaneously maximize dryout heat flux and minimize thermal resistance.…”

“…8 Such wicks consist of an array of micropillars, and their performance has been investigated both experimentally and numerically for thin-film evaporation applications. Some of the well-defined micropillar geometries that have been explored in the past for evaporative cooling are as follows: (a) cylindrical: 5,6,8−13 one of the most common and optimized micropillar geometry due to their ease of fabrication, provides better thermal performance at low to mid heat flux conditions; (b) pyramidal: 14 provides high capillary pumping at lower contact angles and better thin-film area available for evaporation; (c) conical: 15 low dryout heat flux and effective heat transfer coefficient compared to cylinders due to less curvature of meniscus; (d) pies: 16 shows marginal enhancement of effective heat transfer coefficient as a result of increase in thin-film region; (e) rectangular ribs: 17,18 maximum capillary pressure generated is lower than cylinder but has comparable thin-film area fraction; (f) mushroom-shaped: 19 provides lower overall thermal resistance as result of thinner thin-film region;…”