Large scale generation of micro-droplet array by vapor condensation on mesh screen piece

Abstract

We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more “hydrophilic” than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization.

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…In principle, any sub-microscale structures with a small feature size (tip size and interspace) and a certain height (or depth) can become effective candidates for creating CMDSP surfaces. In fact, except for arrays of closely packed nanotips, including nanocones, [22,27,50,69,70] nanoneedles, [21,28,31,66,71] nanopencils, [23] and tip-like nanotubes, [72,73] other architectures such as nano wires, [24,74] nanosheet arrays, [20,29,62,75] nanorod-capped nano pores, [68,76] the porous structure of nanoparticles, [67] nanoparticle aggregates, [73,[77][78][79][80] and two-tier structures [25,57,63,[81][82][83][84][85][86][87][88][89] have all been verified to be effective in endowing material surfaces with the desired CMDSP functionality as long as they follow these basic construction rules.…”

Capillary-Assisted Enhanced Condensation Heat Transfer for Low Surface Tension Liquids

“…hydrophilic. This surface gradient resulted in the microdroplets condensing only on the region 4 areas, thereby creating a controlled microdroplet condensation array as shown in Figure 1.9 [84]. Nam et al [85] also made a detailed comparative study to understand the effect of varying levels copper oxidation on their wettability behavior.…”

“…Chemically homogeneous micropillar array (left) and microdroplets controlled on the tips of these pillars (right) Copyright of Mandsberg et al[83]). A novel cost effective method to spatially control a condensing microdroplet array was experimented by Xie et al[84]. They fabricated a surface by sintering a copper mesh on to a copper block.…”

“…Commercially available mesh screens of varying pore sizes provided an easy and economical way to control the spacing and dimensions. After subjecting the meshed substrate to oxidization, they found that various parts of the mesh were subjected to varying levels of oxidization due to the non-uniform distribution of stresses in the mesh, as shown inFigure 1.8[84]. On the same weft wires itself, region 3(Figure 1.8 -(b), (e)) achieved a dense population of nano-rods/grass making it hydrophobic whereas region 4 (Figure 1.8 -(b), (f)) was over-oxidized and resulted in micropits making it…”

“…Physical model of the mesh structure, droplet growth and thermal analysis (Copyright of Xie et al[84]). …”