CFD Simulation of Fluid Slip on Different Micro-nanostructured Surfaces

The study on the effect of micro-nanostructures on the slip length of fluid boundaries in microchannels plays a crucial role in the field of microfluidics. In microfluidics, there exists a close relationship between surface micro-nanostructures and boundary slip effects. The work aims to delve into the impact of micro-nanostructures with different parameters on the slip length of fluids in microchannels, providing a deeper understanding of flow behavior in microfluids. By utilizing the finite element method and simulation software, microchannel models with three different microstructure shapes (square, cylindrical, and triangular prisms) in Cassie state are established. Physical fields are selected, fluid material properties are defined, boundary conditions are set, meshes are generated, and geometric parameters are adjusted for each model with different micro-nanostructure shapes, sizes, and spacing. Integral calculation of channel flow rate is conducted by defining a two-dimensional cross-sectional area at the channel outlet. The variation in channel flow rate is then utilized to assess the magnitude of the slip length. Based on the basic condition of Navier slip, the relationship between pressure drop, volume flow rate, and slip length of two infinite parallel plates is determined to derive a theoretical model for slip length calculation. The simulated results and relevant parameters are incorporated into the model to ultimately obtain the slip length of fluid flow on channel surfaces with different micro-nanostructures. The simulated data, presented in two-dimensional and three-dimensional schematic diagrams, are analyzed. The simulated data indicate that under identical parameters, the slip length of fluid flow on the surfaces of square, cylindrical, and triangular prism microstructures is 22.7, 23.1, and 22.9 μm, respectively. The slip length of the three microstructure-shaped channels varies when the side length and spacing differ. When the spacing of the structures ranges from 1-12 μm, the effect of microstructure size on the slip length is minor and exhibits a negative correlation. However, when the microstructure spacing exceeds 12 μm, the slip length shows significant fluctuations with the increasing microstructure size. The value of the slip length remains stable as the channel side length changes at various channel heights. However, under constant channel side length, the slip length rapidly increases with the increasing channel height. Under the same parameters, the boundary slip length of the fluid on the surfaces of square, circular, and triangular prism microstructure channels fluctuates within the range of (22.7±0.1), (23.1±0.1), and (22.9±0.1) μm, respectively, with the increasing placement angles. There are significant differences in the slip length due to different microstructures and channel parameters. Particularly, at the same size, cylindrical microstructures exhibit the most pronounced slip phenomenon compared to square and triangular prisms, and they have a greater impact on fluid velocity and pressure distribution. The shape, spacing, and channel height of microstructures on microchannel surfaces have a more pronounced effect on the slip length. Specifically, the slip length increases with the increasing microstructure spacing and channel height, with cylindrical structures exhibiting the longest slip length, followed by triangular prisms, and squares had the shortest slip length. Furthermore, the effects of microstructure size, placement angle, channel side length, and driving pressure difference on the slip length are relatively minor. In conclusion, different microstructures and channel parameters significantly affect the slip length. Particularly, cylindrical microstructures exhibit the most prominent slip phenomenon at the same size, exerting the greatest impact on fluid velocity and pressure distribution. The shape, spacing, and channel height of microstructures on microchannel surfaces have a notable effect on the slip length. Future research can be conducted to explore the effects of micro-nanostructure size, angle, and driving pressure on the slip length to expand the understanding of microfluidic behavior and provide more accurate guidance for the application of microfluidic technology. © 2025 Chongqing Wujiu Periodicals Press. All rights reserved.