Numerical Study Of Fluids Mixing Reinforement In Microchannels

Micromixer and micro fluid mixing have been the most important part of microfluidic systems. Many fields such as biochemicals, control chemistry, medical analysis, micro/nano particle preparation, and chemical reaction require high efficiency of fluids mixing. Focusing on the reinforcement of fluids mixing, this research carried out the numerical study of fluids mixing under single and two phase flow. The main content are as following:Computational Fluid Dynamics (CFD) was carried out on the investigation of mixing performance in three types of T-shaped wavy micro-channels with rectangular barriers embedded. Velocity field along with mixing snapshot was obtained, and then fluid mixing degree was analyzed quantitatively, as to examine the effects of barrier parameters on fluid mixing performance on the reinforcement of mixing performance. The Mass Transportation Model was applied to simulate the mixing process, and the degree of chaotic mixing was characterized by both the averaged fluid line stretching and Lyapunov exponents. Analysis results indicated that chaos was generated by periodic velocity field in the micro-mixers due to the corporate contribution of V-shaped grooves on the wall of micro-mixer and barriers in the micro-channel. By setting the barriers aslant or adding barriers in the micro-channels, chaos could be further strengthened, which would reinforce the mixing degree of fluids more effectively. Finally, the mixing performance of each mixer under different Peclet number (Pe) was examined, and the relationship between dimensionless mixing length and Pe was mathematically developed.The Volume Of Fluid (VOF) method was carried out to analyze the operation parameters, fluids physical parameters and the structure of microchannel on the formation, development and travelling of microdroplets in the microchannels, and compared the pressure in the straight and winding channels. The results show that the length of the microdroplets grows with the viscosity of dispersion phase, the water rate and Capilar Number(Ca), and also it becomes longer under the gravity effect. The formula of droplet legth and prameters was developed, which indcated that the water fraction, oil fraction and the ratio of viscosity of dispersion phase and continuous phaseIn order to both qualitative and quantitative evaluation of micro-droplets of fluid mixed performance in the previous step using VOF method based on liquid-liquid two-phase flow, the dispersed phase by adding tracer, concentration changes to reflect fluid mixing process were investigated micro-direct channel and two slightly curved channel mixing performance of fluid droplets. According to Hagen-Poisseulli equation, micro-droplets will be generated within the circulation flow channel on the direct mixing of fluid droplets have a major impact:When the desire within the mixed fluid in the droplet into place about when the role of the inner loop had said little to promote mixed effect; when fluid around the place, then the inner loop of the mixing process to promote a better role. Micro-channel entrance on the droplet distribution within the fluid, the role of weight, so in the appropriate operating conditions, such as direct-channel, total flow rate of 50mm/s,εd=0.30, you can create a suitable vortex effect, after intending to put into the mixed fluid, and to strengthen the process of droplets within the fluid mixing (mixing degree above 93.8%).In order to determine the cross effect of bending of the microchannel and the entrance twirling on the mixing reinforcement, the T-type inlet microchnnel were carried out. The results show that the concave bending microchannel plus the desirable twirling effect of entrance is the optimal one for reinforcing the fluid mixing in droplets.