NDLI: Effects of Nanofluids on Droplet Evaporation and Wetting on Nanoporous Superhydrophobic Surfaces

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Leeladhar, Rajesh Xu, Wei Choi, Chang-Hwan
Copyright Year	2009
Abstract	In this paper, nanofluid droplets (fluid containing metal nanoparticles) were subjected to evaporation on a nanoporous superhydrophobic surface to study the effects of nanoparticles on evaporation kinetics, wetting dynamics, and dry-out patterns. Metal nanoparticles (gold chloride) of three different sizes (10, 100, and 250 nm) at three different concentrations (0.001, 0.01, and 0.1% wt) were tested as nanofluids, uniformly dispersed in deionized water. Anodized alumina membranes (200 nm in pore diameter) were tested as nanoporous superhydrophobic surfaces, coated with a self assembled monolayer (SAM). During the course of evaporation in a room condition, the change of a contact angle, contact diameter, height, and volume was measured by a goniometer and compared with that of the base fluid (water) taken as a control. The initial equilibrium contact angle of the nanofluids was significantly affected by the nanoparticle sizes and concentrations. During evaporation, the evaporation behavior for the nanofluids exhibited a complete different mode from that of the base fluid. In terms of a contact angle, nanofluids showed slower decrease rate than base fluid. Nanofluid contact diameter remained almost a constant throughout evaporation with a slight change only at the very end of evaporation stage, whereas the base fluid showed a sequence of constant, increase, and mixed states of increase/decrease behavior. The nanofluids also showed a clear distinction in the evaporation rates, resulting in slower rate than base fluid. The variation of the nanoparticle sizes and concentrations did not make significant difference in the evaporation rate within the tested conditions. No abrupt change in a contact angle and diameter was observed during the evaporation, suggesting that no remarkable wetting transition from Cassie (de-wetting) to Wenzel (wetting) state occurred. The scanning electron microscope (SEM) images of the deposited nanoparticles after complete evaporation of solvent showed unique dry-out patterns depending on nanoparticle sizes and concentrations, e.g., a thick ring-like pattern with larger particle sizes while a uniformly distributed pattern with smaller particles at higher concentrations.
Sponsorship	Nanotechnology Institute
Starting Page	725
Ending Page	733
Page Count	9
File Format	PDF
ISBN	9780791843901
DOI	10.1115/MNHMT2009-18551
e-ISBN	9780791838648
Volume Number	ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2
Conference Proceedings	ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer
Language	English
Publisher Date	2009-12-18
Publisher Place	Shanghai, China
Access Restriction	Subscribed
Subject Keyword	Superhydrophobic Evaporation Droplet Nanoporous Nanofluids Wetting Drops
Content Type	Text
Resource Type	Article

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