Nanoscale and Macroscale Effects of Mineral Deposition During Water Evaporation on Nanoporous Surfaces

Abstract

Recent studies have indicated that droplet evaporation heat transfer can be substantially enhanced by fabricating a thin nanoporous superhydrophilic layer on a metal substrate. Such surfaces have immense potential to improve spray cooling processes, however, little durability testing of the surface has been performed. In spray cooling applications, as water evaporates any impurities in the water will be deposited onto the surface. Primarily, this investigation serves to demonstrate how minerals in hard water deposit on the surface and interact with the ZnO nanopillars of the superhydrophilic surface. Quantifying the effects of mineral scale on droplet spreading and vaporization heat transfer on the surface is important in determining implementation requirements to advance the surface into industry applications. Micrographs of the surface demonstrate minerals deposit nonuniformly and quickly fill the nanostructure. Despite a reduction in the extent of droplet spreading due to the mineral deposition, scaled surfaces still demonstrated improved thermal performance compared to an uncoated, smooth copper surface. Scale tended to build up on previously deposited scale, leaving largely uncoated areas where droplets chose to preferentially spread and resulting in a continued low contact angle. Maintaining these uncoated areas and reducing the contaminants present in the water will extend the life and performance of the nanostructured surface.

Fast Capillary Wicking on Hierarchical Copper Nanowired Surfaces with Interconnected V-Grooves: Implications for Thermal Management

“…Liquid wicking on micro/nanostructured surfaces driven by the capillary pressure has attracted significant attention due to its numerous promising applications in industrial systems such as thermal management, − water harvesting, , and microfluidic − and biomedical devices . The better thermal management in industrial applications, including electronics, aeronautics, and nuclear power, would result in a more efficient and safe design .…”

Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

“…Challenges arise due to the dynamic and transient nature of interaction between the thin-film menisci present within the structures with the continuously changing droplet’s interfacial curvature as well as decreasing droplet volume. Consequently, wicking experiments to study droplet evaporation dynamics on heated structured surfaces at temperatures below nucleation have been sparsely conducted, ,− as structures are open to the environment resulting in small wicking distances. In order to optimize structure/liquid supply design and maximize heat flux removal, estimations of heat flux in micro/nanostructures as well as at the surface, along with dryout limits, are important.…”

Extending Lifetime of Water Droplets Using Mirror‐Nanoporous Surfaces

“…There remain some features of the system which are not trivial to infer a priori (including the behavior of the nanoporous infiltration at the confined space) that would require an analysis more complex than the simple model presented here; for example, it is known that vapor condensation also plays a role in the waternanopore interaction. [15] These additional aspects may provide further opportunities for system design with better performance, e.g., by optimizing water-nanopore interplay, one could further extend the droplet useful life. In that respect, it is noteworthy that nanopore properties and network morphology can be readily controlled by tuning synthesis parameters [31] or by means of pore functionalization.…”

“…the other hand, it is known that sessile droplets supported on nanoporous thin films create a wet annulus of infiltrated material surrounding the droplet (see Figure 1). [12][13][14][15] Furthermore, we have recently shown how this wet annulus leads to an enhanced evaporation rate of sessile droplets which are placed on nanoporous surfaces. [16] Paradoxically, this phenomenon would also provide a good scenario to embed droplets into a selfgenerated microclimate of enriched humidity, which eventually could be engineered to minimize the overall droplet evaporation rate.…”