Preparation Of Superhydrophobic Microchannels Via Hybrid Laser Ablation And Chemical Etching Process And Its Drag Reduction Performance

Stainless steel has good thermal conductivity,electrical conductivity and chemical stability,and has broad application prospects in heat transfer and corrosion resistant microchannels.At present,research on drag reduction in microchannels mainly be focused on non-metallic materials.The main ways to reduce friction between the fluid and the wall in non-metallic microchannels include introducing drag reducing polymer additives into the fluid,preparing micro groove structures or micro dents on the microchannel wall,using oscillating walls,and introducing microbubbles.There are still difficulties and challenges in achieving drag reduction in metal microchannels without adding polymer drag reducing agents.In this paper,the periodic microstructures were fabricated on the microchannel wall of 316L stainless steel by nanosecond laser ablation-chemical etching,to realize the superhydrophobicity and drag reduction.In addition,the effects of nanosecond pulsed laser average power,scanning speed,and scanning interval on the height and periodicity of microstructures,the mechanism and process of periodic microstructure formation,and the effects of laser processing parameters on surface roughness,composition,and hydrophobicity were revealed in the paper.The effects of microstructure height and periodicity on the drag reduction performance in microchannels were studied.Experiments show that this process is conducive to expanding the application of stainless steel in the microchannel field,improving the strength of the microchannel,and reducing the flow resistance in the microchannel.Firstly,periodic microstructures were prepared on the surface of 316L stainless steel by nanosecond laser ablation hybrid chemical etching(LACE)process.Ultrasonic assisted chemical etching is used to remove oxides and impurities from the surface of stainless steel samples ablated by nanosecond pulsed laser,and then the periodic microstructures in the subsurface layer are obtained.Exploring the mechanism and process of microstructure formation based on the thermal effect of nanosecond laser processing materials and the morphology of microstructures.By measuring the surface roughness,chemical composition,and height and period of periodic microstructures of the samples,the effect of nanosecond pulse laser processing parameters on the height and period of periodic microstructures is revealed.Secondly,evaluate and characterize the superhydrophobicity and drag reduction characteristics of the prepared periodic microstructures.The surface of the sample prepared by this process is superhydrophobic after being placed in air for 5 days.By measuring and analyzing the contact angle of water droplets on the surface prepared by different laser average power and scanning intervals,the effect of laser processing parameters on the surface superhydrophobicity can be explored.The water repellency of the surface prepared by this process was confirmed by the bouncing behavior of water droplets on the surface.The boundary slip analysis of superhydrophobic surfaces is performed using a rheometer to verify the potential application of superhydrophobic surfaces in the field of drag reduction.Finally,the nanosecond laser ablation hybrid chemical etching process was used to process the microstructures in the microgrooves of the stainless steel sample.PMMA double-sided adhesive was used to bond and package the acrylic cover plate with the stainless steel to prepare the microchannel.Taking pressure drop as the drag reduction index,the effect of microstructures with different heights and periods on drag reduction performance is tested and analyzed,and the optimal microstructures and nanosecond pulse laser processing parameters are selected.When the average laser power is 15 W,the scanning speed is 1 mm/s,and the scanning interval is 60 μm,the drag reduction rate can reach 29.83%.