Shakhawat Hossain

Mixing Analysis of Passive Micromixer with Unbalanced Three-Split Rhombic Sub-Channels

A micromixer with unbalanced three-split rhombic sub-channels was proposed, and analyses of the mixing and flow characteristics of this micromixer were performed in this work. Three-dimensional Navier-Stokes equations in combination with an advection-diffusion model with two working fluids (water and ethanol) were solved for the analysis. The mixing index and pressure drop were evaluated and compared to those of a two-split micromixer for a range of Reynolds numbers from 0.1–120. The results indicate that the proposed three-split micromixer is efficient in mixing for a range of Reynolds numbers from 30–80. A parametric study was performed to determine the effects of the rhombic angle and sub-channel width ratio on mixing and pressure drop. Except at the lowest Reynolds number, a rhombic angle of 90° gave the best mixing performance. The three-split micromixer with minimum minor sub-channel widths provided the best mixing performance.

Mixing Performance of a Serpentine Micromixer with Non-Aligned Inputs

In this study, a numerical investigation on mixing and flow structure in a serpentine microchannel with non-aligned input channels was performed. The non-aligned input channels generate a vortical flow, which is formed by incoming fluid streams through tangentially aligned channels. Mixing index was evaluated to measure the degree of mixing in the micromixer. Analyses of mixing and flow field were investigated for a Reynolds number range starting from 0.1 to 120. The vortical structure of the flow was analyzed to find its effect on the mixing performance. Mixing of two working fluids in the micromixer was evaluated by using three-dimensional Navier–Stokes equations. In order to compare the mixing performance between the serpentine micromixers with and without non-aligned inputs, the geometric parameters, such as cross-section areas of the input channels and main channel, height of the channel, axial length of the channel, and number of pitches, were kept constant. Pressure drops were also calculated with fixed axial length in both cases.

Optimization of Micromixer with Staggered Herringbone Grooves on Top and Bottom Walls

Abstract Multi-objective shape optimization of a micromixer with staggered herringbone grooves on the top and bottom walls has been performed through three-dimensional Navier–Stokes analysis, surrogate method and multi-objective evolutionary algorithm. Mixing index and friction factor are selected as objective functions, and four design variables, viz., number of grooves per half cycle (N), angle of groove (θ), groove depth to channel height ratio (d/h), and groove width to pitch ratio (Wd/pi) are chosen out of the various geometric parameters which affect the performance of the micromixer for the shape optimization. Numerical analysis has been performed with two working fluids, viz., water and ethanol at Reynolds number 1. The variance of the mass fraction at various nodes on a plane is used to quantify the mixing performance in the micromixer. The design space is explored through some preliminary calculations and a Latin hypercube sampling method is used as a design of experiments to exploit the design space. Response surface approximation model is constructed using numerical solutions at the designed-sites. The trade-off between the two competing objective functions has been found and discussed in the light of the distribution of Pareto-optimal solutions in the design space. It is observed that the Pareto-optimal solutions shift towards lower values of the design variables θ and wd/pi, and towards higher value of the design variable d/h whereas the design variable N remains insensitive along the Pareto-optimal front in the direction of higher mixing index.

Shape Optimization of a Three-Dimensional Serpentine Split-and-Recombine Micromixer

Optimization of a three-dimensional split-and-recombine micromixer with serpentine structure was performed using Navier–Stokes analysis and optimization techniques. The optimization study was performed at a fixed Reynolds number of 15, with four dimensionless design variables, viz. the ratio of the subchannel width to the main channel width, the ratio of the subchannel length to the pitch length, the ratio of the subchannel depth to the main channel depth, and the ratio of the recombination channel width to the main channel width. The design space was investigated by a parametric study, and the design points within the design space were selected by the Latin hypercube sampling method. Two different objective functions, viz. the mixing index at the micromixer exit and mixing effectiveness, were used alternately for the single-objective optimizations. Mixing effectiveness was defined as the ratio of the mixing index to the pressure drop. A surrogate modeling technique based on a radial basis neural network was used to approximate the objective functions. Optimum configurations of the micromixer were found through the mixing-index and mixing-effectiveness optimizations. The optimum design of the micromixer obtained by the mixing-index optimization confirmed 33.0% relative increase in the mixing index compared with the reference micromixer. The mixing index, 0.86, which was achieved by the optimization of the micromixer, is much higher than those of the other split-and-recombine micromixers at the same mixing length and Reynolds number, and the optimized micromixer could be integrated with microfluidic systems including lab on a chip and micro total analysis system.

Numerical study on mixing of two fluids with modified Tesla structure

In this study, a parametric investigation on mixing of two fluids in a modified Tesla microchannel, has been preformed. Modified Tesla micromixer applies both flow separation and vortices string principles to enhance the mixing. The fluid stream splits into two sub-streams and one of them mixes with the other again at the exit of the Tesla unit. Analyses of mixing and flow field have been carried out for a wide range of Reynolds number from 0.05 to 40. Mixing performance and pressure drop characteristics with two geometrical parameters, i.e, ratio of the diffuser gap to channel width (h/w) and ratio of the curved gap to the channel width (s/w), have been analyzed at six different Reynolds numbers. The vortical structure of the flow has been analyzed to explain mixing performance. The sensitivity analysis reveals that mixing is more sensitive s/w, than the h/w.Copyright