Common organic modification of metal superhydrophobic surface has these problems such as serious environmental pollution, high thermal resistance, low processing efficiency, and easy to fall off. A chemical-free direct laser selective texturing technology is proposed to enhance condensation heat transfer performance on stainless steel surface. A micro-textured steel plate was processed by nanosecond pulsed laser to obtain a superhydrophilic surface of a square grid groove-convex structure. After heat treatment, the superhydrophilic surface changed to be superhydrophobic. The superhydrophobic surface was then laser selective textured to get a wedge-shaped superhydrophilic-superhydrophobic surface. Surface morphology, chemical composition and three-dimensional profile were analyzed. By comparing the superhydrophobic and superhydrophilic surfaces, the back-surface temperature and the average detached diameter of the condensed droplets was measured. Furthermore, the surface condensation heat transfer coefficient of samples was calculated according to the relevant condensing heat transfer theory. At the same time, samples with different area ratios of laser textured superhydrophilic-superhydrophobic were designed for heat transfer analysis. Condensation results showed that the heat transfer coefficient of the selective-textured surfaces was enhanced compared to the full laser textured superhydrophobic surface. After the condensed droplet grew to the superhydrophobic boundary of the laser selected area, it was restricted to grow and merge quickly and then was removed by self-transport in the wedge-shaped superhydrophilic area. The laser textured patterns showed a smaller detachment diameter than the fully superhydrophobic surface and had enhanced condensation heat transfer coefficient, as laser textured superhydrophilic-superhydrophobic areas are equal.
Based on the beam propagation method, a compact 1 × 16 polymeric optical splitter with center wavelength ∼1550 nm is designed for electro-optical printed circuit board (EOPCB). The length of the optical splitter is 20,000 μm. Spacing between each output port is 127 μm. The cross section of the optical splitter is 10 μm × 10 μm. The silicon glass is chosen as a substrate material of the optical splitter, the cladding material of the optical splitter is air, and the core material of the optical splitter is SU8 polymer. It is fabricated for a 1 × 16 chip-to-chips optical interconnect by femtosecond laser. The testing results show that average insertion loss per channel for the optical splitter is IL ≤ 20 dB and the uniformity for the optical splitter is Cu ≈ 1.42 dB. It is very suitable for the optical interconnection of EOPCB.
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