| The lab-on-a-chip integrates biological and chemical synthesis or detection processes on a silicon or polymer chip,where the reaction is at the center of everything.The scale at which the micromixer is located gives it the characteristic of a high surface area to volume ratio,which provides good conditions for chemical reactions and some physical processes with high yield,stability,selectivity,low energy consumption,high sample consistency,low reaction volume,high throughput,improved detection sensitivity and other advantages,and is therefore widely used in drug preparation,organic synthesis,medical diagnostics and other fields.Currently,passive micromixers generally suffer from poor mixing efficiency at low Reynolds numbers and are not conducive to integration.At the same time,it is practically difficult to precisely achieve predetermined reaction conditions,such as reaction temperature,in a micromixer due to complex conditions such as contact,measurement,structure and materials.In order to integrate an efficient and widely adaptable mixing function into a small chip,this paper proposes a modular design approach and explores the general design rules of this design approach,through which a series of Splitting And Recombination(SAR)micromixers with a tesseract-like structure are designed.The optimized micromixers were selected for their low pressure loss and high performance,and their mixing performance and simulation were subsequently validated using experiments and simulations.A simulation of continuous injection of reagents into the microchannel of the chip under PCR temperature cycling conditions was also carried out,and the structural design of the chip and system under these conditions was discussed and analyzed.Based on this,the research methods and contents of this paper are as follows :(1)Based on existing national and international research,a strategy for designing micro-mixers by matching contact surfaces to increase the concentration difference is proposed based on Fick’s law and Einstein’s equation for Brownian motion.The Coanda effect is then extended to realize this strategy of matching contact surfaces,the direction of fluid flow on the channel surface is analyzed and four specific functions are abstracted from specific microchannel modules.A modular design approach is proposed with the four specific functions,selecting functionally explicit modules to intuitively and efficiently address different needs.(2)Four micromixers were designed using a modular design approach based on four functional modules,using the three-dimensional Navier-Stokes equation and the convective diffusion equation for mass transport,and numerical analysis was carried out in the Reynolds number range of 0.1 to 100 using COMSOL finite element analysis software to verify the response of different modules and design strategies to variations in Reynolds number and to explore the overall design rules.Convective heat transfer and heat conduction equations have also been used to analyse the temperature distribution and response of the chip when continuously supplied with reagents under temperature cycling conditions,providing a solid basis for implementing complex and accurate biochemical experiments under on-chip conditions.(3)The best performing micromixer chip was fabricated using soft lithography process,and a test system platform was built to experimentally test the mixing performance of the micromixer,to visually characterize the micromixer performance,and to qualitatively and quantitatively compare and analyse the results with the previous simulations to prove the correctness of the simulation results.(4)Experimental and simulation results show that the designed micromixer at3.3mm,i.e.22 times the length of the hydraulic diameter,consistently provides 94% to99% mixing efficiency over a wide range of Reynolds numbers.The results provide a significant advantage over previous studies at the equal hydraulic diameter,and the structure is easy to integrate on a chip. |
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