A surface embossing technique to create micro-grooves on an aluminum fin stock for drainage enhancement

Abstract

Recent advances using a surface embossing technique allow us to inexpensively impart micro-scale surface features on heat exchanger construction material, which we exploit to reduce condensate retention. The retention of condensate is important to the performance of heat exchangers in a broad range of air-cooling and dehumidification applications. We report a study of wetting behavior and drainage performance on a series of embossed surfaces with different micro-groove dimensions. Static contact angles, critical sliding angles, droplet aspect ratios, etc, are reported with detailed surface topographical information. Our results show that unless the spacing between grooves is very large (>100 µm), the parallel-grooved surface feature normally increases the apparent contact angle of a droplet on the surface. The micro-groove structure causes anisotropic wetting behavior of the droplets, and apparent contact angles measured by viewing along with the micro-grooves (θ⊥) were found to be larger than those measured from the other direction (θ‖) (by viewing perpendicular to the grooves). A consistent reduction of a critical sliding angle was observed on surfaces after embossing (the micro-grooves are aligned to be parallel with gravity). This may be due to contact line discontinuities and contact-line pinning induced by a groove structure of the surface. Water droplets exhibit an elongated shape along the micro-grooves, which is in contrast to the nearly circular base contour observed on an isotropic surface. Smaller groove spacing, larger depth and steeper sidewalls are observed to be favorable for drainage enhancement and recommended as design guidelines in the future.

Anisotropic Wetting Surfaces with One‐Dimesional and Directional Structures: Fabrication Approaches, Wetting Properties and Potential Applications

“…In one study, Liu et al . used an embossing method on heat exchanger material to produce anisotropic wetting for potential management of condensation in air‐cooling applications 38. Here, hard rubber embossing plates were used to generate micrometer‐scale grooves with triangular or trapezoidal shapes on aluminum.…”

Grooves Accelerate Dew Shedding

“…Provided that large-scale and resilient micro-grooving can be made affordable, they open promising opportunities for considerably improving the collection of small volumes of condensates, such as natural dew water harvesting. In addition, this study may help us to understand how grooves can be used to accelerate drainage and passively direct water on heat exchange surfaces [33], fog collecting materials [34], and open microfluidic systems [35].…”

A nanoporous, ultrahydrophobic aluminum-coating process with exceptional dropwise condensation and shedding properties

“…[27]- [29]), which offer nanometer-level precision but require smooth, flat starting surfaces and multiple process steps, in some cases including energy-intensive plasma-based processing under vacuum. Alternatively, and more scalably, features with dimensions as small as ~30 µm have been mechanically embossed into aluminum alloy surfaces [30], [31].…”