Abstract
Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. We report a novel bi-functional heterogeneous surface structure that is capable of tuning bubble nucleation, growth and departure dynamics. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of heterogeneous surfaces with distinct wettability regions. Heterogeneous surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. Taking advantage of our fabrication method, a 6 inch wafer size heterogeneous surface was prepared. Pool boiling experiments were also performed to demonstrate a heat flux enhancement up to 3X at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface.
Highlights
The continuous increase in energy density for advanced energy and electronic systems such as concentrated photovoltaics, advanced lasers, radars, and power electronics resulted in a search for technologies to dissipate ultra-high heat fluxes[1]
The use of biphilic surfaces with mixed wettability offers the opportunity to design ideal boiling surfaces compared to homogeneously hydrophobic or hydrophilic surfaces[14,15,16,17,18,19]
There are many studies about boiling surfaces with mixed wettability, there has been no report with a focus on spatial control of bubble nucleation and tunable departure frequency using patterned, mixed wettability surfaces
Summary
Summary Inkjet printing set up for printed hydrophobic dot arrays. ® tured by printing fluorine-silane material. 1.2 mL of PFP was diluted with 2 mL of SU-8 developer This volume ratio was determined to sustain the printer cartridge as long as possible. A piezoelectric inkjet printer (Dimatix DMP-2831, Fujifilm) was used to deposit the polymer dot arrays. A hydrophilic treatment of the substrate was carried out with 1 M NaOH solution for 30 min, followed by a cleaning process with acetone, methanol, and deionized (D.I.) water. A ZnO seed layer was first formed on the SS 304 substrate (2 × 2 cm), the polymer dots were printed, followed by a curing process of 120 °C for 15 min. We employed a MAND process to form the seed layer and ZnO nanostructures as well. The growth of ZnO nanostructures on the printed PFP surface was completed after a 3 min. The growth of ZnO nanostructures on the printed PFP surface was completed after a 3 min. deposition period
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