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The study of flow and mixing dynamics for conventional micromixers as well as micromixers with split and recombine (SAR) units has been carried out using laminar and transport diluted physics modules. Initially, a pilot numerical analysis was done for the basic Y-shaped curved, rectangular and triangular serpentine micromixers. Later, SAR units have been added to these basic designs and the effect of SAR units on the performance characteristics viz., mixing index, pressure drop, performance index and pumping power has been studied. In-depth qualitative analysis was also carried out to visualize the flow and mixing dynamics for the Reynolds number in the range from 0.1–50. The study results revealed that the square shaped chambers and circular obstacle based rectangular serpentine micromixer (SCCO-RSM) demonstrated better performance as compared to the other designs. The proposed micromixer is the better candidate for microfluidics applications such as Lab-On-a-Chip (LOC), Micro-Total-Analysis-Systems (µTAS) and Point of Care Testing (POCT), etc. [ABSTRACT FROM AUTHOR]

Microfluidic devices/systems, including Micro-Total-Analysis-System (µTAS), Point of Care Testing (POCT) and Lab-On-a-Chip (LOC) are used in many chemical and biological assays applications. Among the vital tasks that these microfluidic devices must achieve essentially include a high degree of mixing and accordingly, micromixers are being used for the same purpose. The design depends on the yield required in particular application. In the proposed study, the four kinds of heart-shaped micromixers with different obstacles have been studied through simulations. The influence of the shape and size of different obstacles viz., circular shape, diamond shape, teardrop shape, and heart shape obstacles on the performance characteristics has been studied. The performance characteristics namely, the mixing index and pressure drop have been used. In accordance with the study, a heart-shaped micromixer with heart shape obstacles (HSM-HSO) has come out to be the most efficient micromixer due to the significant chaotic convection effect. The heart-shaped micromixer with heart shape obstacles (HSM-HSO) of size 0.350 µm × 0.350 µm has shown better performance for a wider range of Reynolds number (Re), i.e., mixing index of Re > 0.99, for Re of 0.1 and Re in the range of 15–45. [ABSTRACT FROM AUTHOR]

Three-dimensional CFD simulations carried to evaluate mixing performance of two designs of micromixers namely RB-TSAR and EB-TSAR. The results of flow physics analysis indicate that the interfacial area between the two flow fluids can be enhanced by creating a flow in transverse direction with the help of split and recombination of fluid streams by placing baffles in diffuser shaped mixing elements along the axial direction. Further, the simulation results indicate that at inlet Reynolds number below 1, the molecular diffusion is the most dominant mechanism of mixing, and the mixing index is almost the same for all cases. However at Re > 5, the secondary flow influencing the mixing process dramatically and thus mixing index is increased. The results also reveal that baffles can break the fluid streams, produce fluid convection and increase the contact area of the fluid by folding and deflecting which in turn helps to improve the mixing index. The split and recombination of the fluid streams and separation vortices play vital role in enhancing the mixing performance. The design configurations studied here showed mixing index higher than 0.85 for the Re in the range from 10 to 50. [ABSTRACT FROM AUTHOR]

An eye shaped split and collision micromixer having low-pressure drop is proposed, which works on the concept of unbalanced splits and cross-collisions of fluid streams. The 3-D Navier–Stokes equations in combination with an advection–diffusion model were solved for the analysis with water and ethanol as working fluids. The in-depth analysis of the flow features and the mixing performance parameters viz. mixing index and pressure drop of the micromixer has been carried out. The micromixer model is composed of two sub-channels of equal/unequal widths which repeatedly undergo splitting and collision of fluid streams along the flow direction. The numerical study has been carried out on the micromixer at Reynolds numbers ranging from 0.1 to 45. The difference between the mass flow rates in the two sub-channels creates an unbalanced collision of the two fluid streams. Mixing enhancement is mainly due to the effect of unbalanced collisions of the fluid streams. The micromixers show exciting flow features for different ratios of the widths of the sub-channels. The ratios of a width of subchannels viz. 1, 1.4 and 2 are considered. The highest mixing performance has been observed for the width ratio of 2, whereas poor mixing performance has been observed for the width ratio of 1. [ABSTRACT FROM AUTHOR]

The performance analysis of wavy micromixers with split and recombine (SAR) elements has been carried out. The two types of SAR elements viz. circular split and recombine elements and elliptical split and recombine elements are used to get benefit of SAR mechanism. The main concept in the proposed design is to enhance the interfacial area between the two fluids by creating a transverse flow and split and recombination of fluid flow streams with the help of SAR elements. The effects of balanced split and unbalanced split of SAR elements and operational parameter Reynolds number on the mixing index and pressure drop are evaluated. The COMSOL Multiphysics 5.0 is used for computational fluid dynamics analysis of micromixers. The analysis is carried out for balanced and unbalanced split of the mixing elements at various Reynolds numbers in the range of 0.1-75. The computation interfacial patterns on the planes perpendicular to the direction of fluid flow, mixing index and pressure drop are studied in depth. The results indicate that at inlet Reynolds number below 5, the mixing performance is diffusion dominated. However at Reynolds number greater than 5, the mixing index increases intensely due secondary flow and separation vortices, as well as SAR effect. [ABSTRACT FROM AUTHOR]

Design optimization of a rectangular wave passive micromixer is performed using numerical analysis, and Taguchi based grey relational analysis. Optimization study is carried out at a constant Reynolds number of 25. The three design variables viz. the height of the channel, the width of the wavy channel in the y-direction, and the wavy amplitude are considered. The parametric study has been conducted based on the Taguchi’s orthogonal array, L27. The significant performance characteristics viz. mixing index and pressure drop are considered for multi-objective optimization. A grey relational grade is used as a performance index to find out an optimal set of design parameters. The experimental validation for micromixer with optimal design configuration and other three micromixer design configurations has been carried out. The optimized micromixer could be integrated with microfluidic systems including lab on a chip, micro total analysis system, and in the biomedical and biochemical analysis. [ABSTRACT FROM AUTHOR]

In this paper, passive planar micromixers based on circular and square mixing chambers spaced at equidistant along the length of micromixer are proposed to operate in the laminar flow regime for high mixing index. Numerical simulations are conducted to evaluate the performance of proposed micromixers by solving the Navier-Stokes equation and convection-diffusion equation. A COMSOL Multiphysics 5.0 is used for computational fluid dynamics. Numerical simulation of mixing of fluids in a micromixer with circular and square chambers in a laminar flow regime has been carried out. Four performance parameters namely, mixing index, pressure drop, pumping power, and performance index are used to evaluate different design configurations of micromixers. Analysis of mixing index based on the standard deviation of the mass fraction is carried with different constriction channel width such as 200, 250, and 300 µm for a range of Reynolds number from 0.1 to 75. The both micromixers show over 95% mixing at the exit for the range 15-75 of Reynolds number at constriction width of 200 µm. Especially, about 99% mixing is achieved at Reynolds number less than one i.e. at 0.1. The effect of Reynolds number on the pressure drop is also investigated. Thus, the proposed micromixers can be used in microfluidic systems which require fast mixing at Re less than 1 and greater than 15. [ABSTRACT FROM AUTHOR]