Circular Mixing Chamber Research Articles

Enhancing mixing efficiency of a circular electroosmotic micromixer with cross-reciprocal electrodes

Enhancing mixing efficiency in microscale processes for sensitive biomedical, pharmaceutical, and chemical applications is crucial, particularly when operating under low-velocity constraints. This study presents a comprehensive investigation into the impact of various factors on microfluidic mixing within a circular mixing chamber micromixer, utilizing electroosmotic principles. The governing equations are solved numerically using the finite element technique-based solver. This research examines the effects of microchamber diameter (D), inlet velocity (uo), alternating current (AC) voltage amplitude (ϕo), and AC frequency (f) on fluid mixing dynamics. Several key findings are noted from this study. The reduction of the circular microchamber diameter decreases the linear distance between cross-reciprocally placed microelectrodes, resulting in increased electroosmosis force and mixing efficiency. The voltage amplitude within the specified range shows increased mixing efficiency when fluid species are combined at appropriate velocity and AC frequency. The highest mixing efficiency of 98.84% is achieved with the following parameters: flow velocity (uo) of 150 μm/s, AC frequency of 4 Hz, voltage amplitude of 500 mV, and microchamber diameter of 20 μm. At a frequency of 12 Hz and voltage amplitude of 500 mV, the mixing efficiency exceeds 94.66% across a wide range of input velocities (100–200 μm/s), enabling versatile control in microfluidic devices. The nonlinear interaction between electroosmotic flow and microchamber geometry significantly contributes to this enhanced mixing efficiency. These results demonstrate the potential for optimizing microfluidic mixing processes through careful parameter tuning, particularly in applications requiring high efficiency at low flow rates. Thus, this study provides valuable insights for designing more effective microfluidic systems in various scientific and industrial fields.

Design optimization of micromixer with circular mixing chambers (M-CMC) using Taguchi-based grey relational analysis

Abstract The aim of the present study is to optimize the micromixer with circular mixing chambers (M-CMC) using Taguchi-based grey relational analysis approach. Simulations are performed to investigate the effect of design parameters viz. chamber diameter, transverse offset and width of constriction channel on performance characteristics for parameter sets corresponding to Orthogonal Array (OA) L9. Further, grey relational grade is used to identify the optimal set of design parameters. In depth study of flow and mixing dynamics are carried out to visualize the mixing mechanism for optimal and other two cases of proposed micromixer design configuration for Re in the range from 0.1 to 50. In order to assess the response of each design variable at each level, analysis of variance (ANOVA) is also performed to analyse influence of design parameters on mixing index and pressure drop.

An integrated microfluidic chip for formaldehyde analysis in Chinese herbs

Abstract A novel integrated microfluidic chip with a three-layer polymethyl methacrylate (PMMA) structure is proposed for formaldehyde concentration detection applications. In the proposed device, the sample and a fluorescence derivatization reagent (Fluoral-P) are mixed in a circular mixing chamber and then flow through a serpentine reaction channel heated to a temperature of 30 °C by an integrated hotplate. Following a reaction time of 4 min, the microchip is removed from the hotplate and placed in the microscope stage of a laser-induced fluorescence (LIF) detection system. The formaldehyde concentration of the sample is then inversely derived from the measured value of the fluorescence intensity. The validity of the proposed device is confirmed by comparing the detection results obtained for standard samples with known formaldehyde concentrations ranging from 1 to 50 ppm with those obtained using a traditional UV/VIS absorption spectrometry. The real-world applicability of the proposed device is then demonstrated by measuring the formaldehyde concentration in ten commercial Chinese herbs. It is shown that the measurement results deviate by no more than 3.7% from those results obtained using colorimetric method by CAAPIC. Overall, the results presented in this study show that the proposed microchip provides a rapid and reliable tool for formaldehyde concentration measurement purposes.

Mixing performance of a planar micromixer with circular chambers and crossing constriction channels

Abstract A planar micromixer design with circular mixing chambers and two constriction channels crossing each other to connect adjacent mixing chambers is proposed in this work. The mixing performance of this micromixer is analyzed numerically, and compared to three other planar micromixers (with circular chambers but with a single constriction channel). Analyses of flow fields and mixing are performed using three-dimensional Navier–Stokes equations for a wide range of Reynolds numbers from 0.1 to 100, with a fixed ratio of the width of the constriction channel to the diameter of the circular chamber (1/8). Mixing is evaluated by calculating a mixing index based on the variance of the mass fraction. The proposed micromixer shows excellent mixing performance in the low Reynolds number range in which diffusion dominates the mixing, but shows the worst performance for Reynolds numbers greater than 50 among the four micromixers tested in this work. The proposed micromixer shows a much lower pressure drop than the other micromixers, especially at higher Reynolds numbers. Thus, the proposed micromixer is recommended for use with Reynolds numbers of less than 10.

Microfluidic mixing using contactless dielectrophoresis

The first experimental evidence of mixing enhancement in a microfluidic system using contactless dielectrophoresis (cDEP) is presented in this work. Pressure-driven flow of deionized water containing 0.5 μm beads was mixed in various chamber geometries by imposing a dielectrophoresis (DEP) force on the beads. In cDEP the electrodes are not in direct contact with the fluid sample but are instead capacitively coupled to the mixing chamber through thin dielectric barriers, which eliminates many of the problems encountered with standard DEP. Four system designs with rectangular and circular mixing chambers were fabricated in PDMS. Mixing tests were conducted for flow rates from 0.005 to 1 mL/h subject to an alternating current signal range of 0-300 V at 100-600 kHz. When the time scales of the bulk fluid motion and the DEP motion were commensurate, rapid mixing was observed. The rectangular mixing chambers were found to be more efficient than the circular chambers. This approach shows potential for mixing low diffusivity biological samples, which is a very challenging problem in laminar flows at small scales.

A PDMS Self-Vortical Micromixer Without Obstructions

Microfluidic micromixers are extremely essential components of microfluidic systems for microliter to nanoliter fluid mixing. This paper proposes a new passive micromixer called the self-vortical micromixer with no obstructions, composed of three polydimethylsiloxane (PDMS) layers. Each PDMS layer is fabricated by a PDMS replication molding process with a 150-micron height dry-film photoresist replication mold, manufactured from an organic solvent-free process. The three PDMS layers are precisely bonded together by the PDMS alignment bonding process developed in this study. This paper presents the simulation results demonstrating the self-vortical mixing phenomenon of the self-vortical micromixer with swirly flow fields and self-vortical flow fields. As the mixing test results demonstrate the mixing performance of the micromixer, the injected food dyes are completely mixed in the downstream of the mixing channel by the swirly flow fields and the self-vortical flow fields in the circular mixing chamber of the self-vortical micromixer. At Re =200, effective mixing (mixing index 0.42) can be achieved..

Rapid glucose concentration detection utilizing disposable integrated microfluidic chip

A novel three-dimensional (3D) disposable glucose concentration detection chip is presented. The chip comprises a four-layer polymethyl methacrylate (PMMA) structure and is fabricated using a commercial CO2 laser and a hot-press bonding technique. In the proposed device, the glucose solution is injected into a double parallel connection micromixer (DPCM) and is mixed with DNS reagent by means of a self-rotation effect. An experimental platform has been created for multiple reaction process by integrating chip and micro-heater. The fluid streams exiting the two circular mixing chambers of the DPCM are then combined and mixed further at a T-type microchannel outlet before passing to a collection chamber. Numerical simulations are performed to analyze the vortex streamline distribution within the DPCM and to estimate the mixing performance. The numerical results show that a mixing efficiency as high as 92.5% can be obtained at low Reynolds numbers (Re = 12). It is found a good linear relation of R2 = 0.9953 from the chip detection method comparing to the traditional method of R2 = 0.9976 at DNS reagent and glucose solution volume ratio of 1:1. In addition, the experimental results show that the accuracy of the glucose concentration measurements obtained using the proposed microfluidic chip is comparable with that of the measurements obtained using a conventional large-scale detection method. Overall, the results presented in this study indicate that the DPCM chip provides a rapid and low-cost means of detecting the concentration of glucose solutions.

A numerical study of mixing in a microchannel with circular mixing chambers

AbstractThe mixing of fluids in a microchannel is numerically investigated using three‐dimensional Navier–Stokes equations. The microchannel has circular mixing chambers that are designed to create a self‐circulating flow that operates at low Reynolds numbers. The investigations have been performed on a design that comprises of four circular mixing chambers that are joined together with constriction channels. The study has been carried out in two parts. Firstly, the mixing and the flow field are analyzed for a wide range (1–250) of the Reynolds number. Secondly, the effects of two design parameters, namely, the ratio, w/d, of the width of the constriction channel to the diameter of the circular chamber, and the angle, θ, between the outer walls of the chamber and the connection channel, on the mixing and the flow field have been evaluated. The mixing has been evaluated using a parameter, called mixing index, which is based on the variance of the mass fraction. The mixing index at the end of the device increases rapidly with the Reynolds number. The presence of a flow recirculation zone in the circular chamber is found to be effective in enhancing mixing, especially for larger Reynolds numbers. The mixing performance improves with an increase in θ, and with a decrease in w/d. The characteristics of the pressure drop have also been investigated as a function of the Reynolds number and geometric parameters. © 2009 American Institute of Chemical Engineers AIChE J, 2009

A Study on Mixing Efficiency in a Two-Channel Circular Micromixer

AbstractThe mixing behavior of a two-channel micromixer with a circular mixing chamber at four different chamber depths and six different flow rates had been investigated. Experiments were implemented with the mixings of two fluids. An image inspection method using the variance of the image gray level contrast as the measurement parameter to determine the mixing efficiency distribution in these mixers. The steady, three-dimensional and laminar flow fields inside the micromixers were also simulated numerically with a finite volume discretization. Through the numerical integration over the chamber depth, the three-dimensional numerical prediction could be compressed into a two-dimensional result, which could be directly used to compare with the experimental measurements. Experimental results show that the measured mixing efficiency is raised with the increase of chamber depth. The numerical prediction of mixing efficiency agreed qualitatively with those obtained from the experimental measurements, while the ratio of the depth to diameter of the mixing chamber is big enough to eliminate the viscosity effect.

Rapid circular microfluidic mixer utilizing unbalanced driving force

This paper proposes a novel rapid circular microfluidic mixer for micro-total-analysis-systems (mu-TAS) applications in which an unbalanced driving force is used to mix fluids in a circular chamber at low Reynolds numbers (Re). The microfluidic mixer has a three-layered structure and is fabricated on low-cost glass slides using a simple and reliable fabrication process. Using hydrodynamic pumps, fluids are driven from two inlet ports into a circular mixing chamber. Each inlet port separates into two separate channels, which are then attached to opposite sides of the 3-dimensional (3-D) circular mixing chamber. The unequal lengths of these inlet channels generate an unbalanced driving force, which enhances the mixing effect in the mixing chamber. Numerical simulations are performed to predict the fluid phenomena in the mixing chamber and to estimate the mixing performance under various Reynolds number conditions. The numerical results are verified by performing flow visualization experiments. A good agreement is found between the two sets of results. The numerical and experimental results reveal that the mixing performance can reach 91% within a mixing chamber of 1 mm diameter at a Reynolds number of Re=3. Additionally, the results confirm that the unbalanced driving force produces a flow rotation in the circular mixer at low Reynolds numbers, which significantly enhances the mixing performance. The novel micromixing method presented in this study provides a simple solution for mixing problems in Lab-on-a-chip systems.

A rapid three-dimensional vortex micromixer utilizing self-rotation effects under low Reynolds number conditions

This paper proposes a novel three-dimensional (3D) vortex micromixer for micro-total-analysis-systems (μTAS) applications which utilizes self-rotation effects to mix fluids in a circular chamber at low Reynolds numbers (Re). The microfluidic mixer is fabricated in a three-layer glass structure for delivering fluid samples in parallel. The fluids are driven into the circular mixing chamber by means of hydrodynamic pumps from two fluid inlet ports. The two inlet channels divide into eight individual channels tangent to a 3D circular chamber for the purpose of mixing. Numerical simulation of the microfluidic dynamics is employed to predict the self-rotation phenomenon and to estimate the mixing performance under various Reynolds number conditions. Experimental flow visualization by mixing dye samples is performed in order to verify the numerical simulation results. A good agreement is found to exist between the two sets of results. The numerical results indicate that the mixing performance can be as high as 90% within a mixing chamber of 1 mm diameter when the Reynolds number is Re = 4. Additionally, the results confirm that self-rotation in the circular mixer enhances the mixing performance significantly, even at low Reynolds numbers. The novel micromixing method presented in this study provides a simple solution to mixing problems in the lab-chip system.

Design of passive mixers utilizing microfluidic self-circulation in the mixing chamber.

This paper proposes the design of a passive micromixer that utilizes the self-circulation of the fluid in the mixing chamber for applications in the Micro Total Analysis Systems (microTAS). The micromixer with a total volume of about 20 microL and consisting of an inlet port, a circular mixing chamber and an outlet port was designed. The device was actuated by a pneumatic pump to induce self-circulation of the fluid. The self-circulation phenomenon in the micromixer was predicted by the computational simulation of the microfluidic dynamics. Flow visualization with fluorescence tracer was used to verify the numerical simulations and indicated that the simulated and the experimental results were in good agreement. Besides, an index for quantifying the mixing performance was employed to compare different situations and to demonstrate the advantages of the self-circulation mixer. The mixing efficiencies in the mixer under different Reynolds numbers (Re) were evaluated numerically. The numerical results revealed that the mixing efficiency of the mixer with self-circulation was 1.7 to 2 times higher than that of the straight channel without a mixing chamber at Re= 150. When Re was as low as 50, the mixing efficiency of the mixer with self-circulation in the mixing chamber was improved approximately 30% higher than that in the straight channel. The results indicated that the self-circulation in the mixer could enhance the mixing even at low Re. The features of simple mixing method and fabrication process make this micromixer ideally suitable for microTAS applications.