Short Mixing Length Research Articles

Optimization of passive micromixers: effects of pillar configuration and gaps on mixing efficiency

Chemical bioreactions play a significant role in many of the microfluidic devices, and their applications in biomedical science have seen substantial growth. Given that effective mixing is vital for initiating biochemical reactions in many applications, micromixers have become increasingly prevalent for high-throughput assays. In this research, a numerical study using the finite element method was conducted to examine the fluid flow and mass transfer characteristics in novel micromixers featuring an array of pillars. The study utilized two-dimensional geometries. The impact of pillar configuration on mixing performance was evaluated using concentration distribution and mixing index as key metrics. The study explores the effects of pillar array design on mixing performance and pressure drop, drawing from principles such as contraction–expansion and split-recombine. Two configurations of pillar arrays, slanted and arrowhead, are introduced, each undergoing investigation regarding parameters such as pillar diameter, gap size between pillar groups, distance between pillars, and vertical shift in pillar groups. Subsequently, optimal micromixers are identified, exhibiting mixing efficiency exceeding 99.7% at moderate Reynolds number (Re = 1), a level typically challenging for micromixers to attain high mixing efficiency. Notably, the pressure drop remains low at 1102 Pa. Furthermore, the variations in mixing index over time and across different positions along the channel are examined. Both configurations demonstrate short mixing lengths and times. At a distance of 4300 μm from the inlet, the slanted and arrowhead configurations yielded mixing indices of 97.2% and 98.9%, respectively. The micromixers could provide a mixing index of 99.5% at the channel’s end within 8 s. Additionally, both configurations exceeded 90% mixing indices by the 3 s. The combination of rapid mixing, low pressure drop, and short mixing length positions the novel micromixers as highly promising for microfluidic applications.

Orthogonal Pattern Louver Mixer for Two-Dimensional Air Mixing in HVAC Applications: Performance and Design Optimization

This article focuses on the investigation of the mixing and hydraulic performance of an orthogonal pattern louver mixer in a square duct. The investigation includes various configurations, including the following parameters: mixer spacing and louver pattern orientation for a pair of mixers, as well as louver angle and louver array size were for both a single and a pair of mixers. Additionally, operational parameters such as mixing length, total flow rate, and flow rate ratio between cold and warm air were considered. Experimental testing was conducted to assess the performance of the orthogonal pattern louver mixer across various parameter combinations. Additionally, a numerical model was developed to enhance understanding of the mixing pattern and flow behavior. Numerical results highlighted that the two-dimensional mixing flow, characterized by multiple vortices generated through the unique louver design, significantly contributed to rapid and robust mixing, effectively reducing maldistribution within a short mixing length. The performance of the orthogonal pattern louver mixer from the experimental results was compared to other mixer types, such as orifice type mixers and ASHRAE Standard 41.2-based “cheese grater” baseline louver mixers. The orthogonal pattern louver mixer was found to be outstanding, with a maximum mixing effectiveness of 88 % for a mixing length of 2.0 Dh. Although it caused a higher static pressure drop than the baseline louver mixers, it was still acceptable for industrial use. The findings indicate that the orthogonal pattern louver mixer is a promising option due to its simple design, easy fabrication, high mixing performance with low pressure drop, and two-dimensional mixing. The orthogonal pattern louver mixer was also less sensitive to flow rate and velocity maldistribution than orifice-type mixers. This article provides useful guidelines for designing and selecting the best mixer type for HVAC applications, considering factors such as cost-effectiveness, mixing performance, pressure drop, and sensitivity to flow rate and velocity maldistribution. In addition, the article offers valuable insights into the performance characteristics of single or dual-use orthogonal pattern louver mixers, as well as the importance of carefully selecting the louver angle and array size when configuring the mixer.

Numerical and experimental investigation on a planar passive micromixer embedded with omega-shaped obstacles for rapid fluid mixing

An efficient fluid mixing performance is achieved by a Tesla/hexagon-shaped passive micromixer in a wide range of Reynolds numbers with short mixing length (4.2 mm/1.15 mm from the origin). The passive micromixers are composed of Tesla/hexagonal chambers and Ω-shaped obstacles or combined with straight-shaped obstacles that induce the generation of vortex, contraction and expansion process, the changes of the flow direction, and even the split and recombination of streams. The mixing process of two fluids (water and ferrofluid) is numerically investigated using computational fluid dynamics. For the Tesla-shaped micromixer embedded with Ω-shaped obstacles, a sufficient mixing is obtained as the obstacles are in contact with the internal walls of Tesla chambers. In the hexagon-shaped micromixer, the combination of straight- and omega-shaped obstacles greatly enhance the performance of micromixer in particular at moderate flow rate (1<Re<10). Moreover, reasonable increasing the curvature radius of the omega-shaped obstacles can further improve its mixing performance. The designed passive micromixers were also fabricated, tested and compared with the numerical results through the soft-lithography processes, and the good agreement between the experimental and numerical results identifies our predictions. The good performance of the designed micromixers provides a new direction in designing micromixer with high-throughput and short mixing length.

Flow regime and Reynolds number variation effects on the mixing behavior of parallel flows

The hydraulic single-phase mixing of three parallel rectangular channels is experimentally investigated at various Reynolds numbers (Re) and flow regime combinations. Particle Image Velocimetry results for seven mixing cases are presented and discussed with varying Re combinations ranging from 1,824 to 20,844. While all cases result in the same Re ratio of ∼0.69 between the inner and outer flows, two cases represent multi-regime mixing with the inner-outer regime pair of laminar-transitional and transitional-turbulent, while the other 5 cases are all characteristic of turbulent mixing with varying levels of turbulence. The outer channels initially share characteristics with a backward facing step. The center channel is found to initially behave like a slot jet, but then sees a significant increase in velocity decay. This inner flow velocity decay increased dramatically in the laminar-transitional mixing case, whose centerline velocity decay was ∼6 times larger than the decay in the turbulent mixing cases. Second order statistics revealed a consistent mixing layer thickness of ∼0.1 hydraulic diameters for all the cases but showed more intense shearing in the multi-regime mixing cases. The combined point and thereby the mixing layer length is determined using centerline velocity decay profiles, which show a much more aggressive mixing in multi-regime flows. Multi-regime mixing demonstrated superior characteristics relative to turbulent mixing due to a more dramatic velocity decay in the inner flow and a shorter mixing length. The contributions of this work include communicating the benefits of multi-regime mixing and providing detailed characterization efforts that can serve future efforts for validating computational models. This research also lays the groundwork for future studies aimed at achieving high levels of mixing without a severe penalty in pressure drop.

Investigation of efficient mixing enhancement in planar micromixers with short mixing length

Achieving rapid mixing of different liquids in a short distance is important for biochemical applications. Here, a new type of micromixers consisting of double symmetrical V-shaped baffles (MMA and MMB mixers) and double asymmetrical V-shaped baffles (MMC and MMD mixers) is proposed. Numerical simulations are performed to evaluate their mixing performance when the Reynolds number (Re) ranges from 0.1 to 50. Meanwhile, the visualization of vortex formation is conducted to analyze the mixing mechanism. The results show that the mixing efficiency of all mixers approaches 0.8 for all Re at the short distance of 3500 μm. At relatively low Re=0.5, the MMA and MMB perform better than MMC and MMD due to more adequate molecular diffusion; whereas the unbalanced lateral flows and multidirectional vortices in the MMC and MMD induce stronger chaotic convection at high Re=50, leading to a higher performance. Moreover, the disturbance created by the vortex on the mass transfer surface is not only relying on its vorticity but also correlates with the position of vortex/vortex leg. Lastly, all micromixers are fabricated, tested and compared with the simulation results and both of them show a good agreement.

Effect of Geometry Design on Mixing Performance of Newtonian Fluids using Helical Overlapped Mixer Elements in Kenics Static Mixer

The laminar flow pattern and mixing behavior of incompressible Newtonian fluids in different modified mixer ‎configurations were numerically investigated using Computational Fluid Dynamics (CFD) simulations in the range of ‎Re=0.15-100. The governing equations were solved by ANSYS Fluent 14 using the second-order finite volume method ‎‎(FVM) and the SIMPLE algorithm scheme. The computational model is assessed by comparing the predicted pressure ‎drop results to empirical correlations in the literature. The effects of incorporated helical overlapped mixer elements and ‎the diameter aspect ratio (C) on the mixing efficiency for different mixer geometries were examined and evaluated by ‎characteristics measures of Intensity of Segregation (IOS), pressure drop, extensional efficiency, and G-factor. The ‎performance of new modified mixers is evaluated via comparison with the standard industrial Kenics static mixer. The ‎static mixers with modified internal geometry achieved fast mixing and better mixing quality than the Kenics mixer. ‎Besides, an increase in diameter aspect ratio C benefited from a decrease in pressure drop within the static. The ‎modified mixer: C=1.5 was found to have the highest mixing efficiency, concerning short mixing length with marginally ‎higher pressure drop than the other mixers. In contrast, the mixer: C=2 is the most efficient based on low pressure drop ‎and energy requirement with slightly greater mixing length‎‎.

LES study on the effect of cavity configuration on combustion characteristics of a scramjet combustor with air-throttling

Three-dimensional Large Eddy Simulation (LES) is performed to numerically investigate the implication of air throttling on the combustion performance of ethylene fueled dual-cavity scramjet combustor. The augmentation of combustion performance with the conjunction of throttling and dual cavity being established, the effects of L/D ratio and interspacing distance between the cavities is discussed. Our results indicate that combustion efficiency is enhanced owing to the pre-combustion shock train generated because of the introduction of air throttling for different configurations of cavity. Further, the combination of air-throttling with dual cavity improves combustion performance in comparison with dual cavity without air throttling. Also, dual cavity with L/D = 7 and spacing S = 12 mm displays intense and larger recirculation zones in comparison with other configurations being considered. It is found that for dual cavity with L/D = 7 and S = 12 mm, shorter mixing length and higher penetration height is attained.

Efficient mixing enhancement by orthogonal injection of shear-thinning fluids in a micro serpentine channel at low Reynolds numbers

Viscoelastic fluids have been recently proposed to promote mixing effect in microfluidic systems, where limited success has been obtained. However, the flow and mixing mechanism of a viscoelastic fluid is still poorly understood, particularly regarding the roles of injection on mixing at low Reynolds numbers. In this work, an efficient mixer by orthogonal injection into a primary flow is proposed. The mixing behaviors of shear-thinning fluids in a serpentine channel with an orthogonal injection are investigated experimentally. Dye visualization and concomitant statistical analysis are conducted to quantitatively characterize the mixing performance and to reveal the flow kinematics. Enhanced mixing is achieved just over a short effective mixing length. The probability distribution functions (PDFs) analysis shows that the mixing efficiency, defined by the normalized concentration of dye intensity (Gan et al., 2007), can be significantly improved from 22% for the Newtonian fluids to 69% and 76% by using a shear-thinning fluid with polymer concentrations of 25 and 50 ppm, respectively. The decay exponents of shear-thinning fluids plateau at −3.4 indicates the occurrence of elastic instability. The relative-change-ratio fluctuations illustrates that the observation area can generate sufficient elastic stress to induce flow instabilities, resulting in effective mixing in the channel.

Hydrodynamics and Local Turbulent Mixing of Submerged, Parallel Liquid Jets: Experiments and CFD Simulations

The hydrodynamics and local turbulent mixing of parallel multiple liquid jets, submerged in liquid, were investigated by means of experiments and computational fluid dynamics (CFD). A renormalization group (RNG) k-ε turbulence model was used to simulate the flow field. The model was validated experimentally by particle image velocimetry (PIV) measurements. In the converging region adjacent to the nozzle exits, the recirculation region disappears, and there is only ambient fluid entrainment. Different jet arrays were compared to evaluate the effects of the jet spatial arrangement on the hydrodynamics and mixing performance. A shorter mixing length in the merging region suggests that mixing is more efficient in the triple-jet system than in other jet systems. Compared with the jet Reynolds number, the jet spacing plays a more significant role in determining the critical mixing regions, while the linear relationship between them is more sensitive than that for multiple parallel plane jets.

On the computational analysis of short mixing length planar split and recombine micromixers for microfluidic applications

ABSTRACT Micromixers are one of the prominent devices in applications like Lab-On-A-Chip (LOC), micro-total analysis system (µTAS), etc. The performance of micromixer is governed by geometry of micromixer, type of obstructions like baffles, obstacles introduced in the fluid flow. In this paper, the mixing performance for three types of baffle-based split and recombination planar passive micromixers is analysed using numerical simulation. The three design configurations, namely, square baffle-based split and recombination (SB-SAR), circular baffle-based split and recombination (CB-SAR) and triangular baffle-based split and recombination (TB-SAR) micromixers are considered. In-depth flow physics analysis was carried out to assess and affirm the quantitative results of the mixing quality at Reynolds number in the range of 0.1–60. The mixing index is found to be 1.0 at Re = 0.1 for SB-SAR micromixer and 0.80 at Re ≥ 10 for all the micromixer design configurations. Micromixers showed diffusion-dominated mixing mechanism at Re = 0.1, and chaotic advection dominated mixing mechanism at Re ≥ 30. The advantages of rapid mixing, simple geometry and shortest mixing length make these micromixers more encouraging in chemical, biochemical and medical applications.

Burner geometry effect on coherent structures and acoustics of a confined swirling partially premixed methane flame

The effect of the mixing tube length and fuel nozzle geometry on coherent structures and acoustics’ characteristics of partially premixed swirling methane flame is experimentally studied. Particle image velocimetry (PIV) is used to document the flowfield inside the transparent confinement tube. Proper orthogonal decomposition along with phase averaging are used to capture coherent structures. High-speed imaging is carried out to shed light on the flame front dynamics within the outer shear layer (OSL). The acoustic waves are measured using a Bruel & Kjaer type 4189 microphone. A radial-type swirl generator with a swirl number (S) of 1.15 is adopted. Two different lengths of the mixing tube and two different geometries of the fuel nozzle with a similar equivalent diameter are tested. The swirling airflow and fuel flowrates are kept constant. The results showed a significant difference in the energy of coherent structures between the two central nozzle geometries with the same mixing length. Both, the mixing length and central nozzle geometry, are found to alter the integral length scale and the central recirculation zone (CRZ). The mixing length is found to alter the amplitude of the acoustics modes when using the same central nozzle geometry. However, keeping the same mixing tube and varying the central nozzle geometry has the same effect. The flame front dynamics within the outer recirculation zone (ORZ) is found to depend on both the central nozzle geometry and mixing tube length (i.e., level of mixing). High amplitude coherent structures are found to contribute to flame roll-up within the outer shear layer. The results showed that the mixing length is not the only parameter to mitigate combustion instabilities. That is, combustion stability can be improved using a single-orifice nozzle with a long mixing length or a multi-orifice nozzle with a short mixing length.

Mixing improvement induced by the combination of a micro-ramp with an air porthole in the transverse gaseous injection flow field

A new injection strategy combined with a micro-ramp and an air porthole is proposed in this paper, and the properties of the transverse gaseous injection flow field with such injection strategy have been investigated simultaneously. The numerical approach employed in the current study has been validated against the two-dimensional and three-dimensional experimental data in the open literature, and it can be used with confidence to investigate the influence of the air porthole aspect ratio and the distance between the air porthole and the fuel orifice on the transverse injection flow field with the combination of a micro-ramp and an air porthole. The obtained results predicted by the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model show that the mixing performances of the transverse gaseous injection flow fields vary under different conditions, and a transverse injection flow field with short mixing length, low stagnation pressure loss and ideal fuel penetration depth has been achieved by adding the combination of an optimized micro-ramp with a proper air porthole, i.e. Case 6–8, and its mixing length decreases considerably by 14.26 mm on the basis of Case c, even shorter than the mixing length of Case a by 2.86 mm. However, its total pressure loss increases when compared with Case c, and its stagnation pressure loss is 2.7 percent smaller than Case a. Further, the hydrogen distribution on the flat plate of Case 6–8 is much less than that of Case a and Case b. Additionally, it is found that the mixing enhancement mechanism of the air jet is different from that of the micro-ramp. The micro-ramp enhances the mixing process between the fuel and air by inducing large-scale vortices, while the air porthole enhances the mixing process by seeding lots of air into the fuel boundary layer, as well as fuel plume.

Frequency-Controlled Wireless Passive Thermopneumatic Micromixer

This paper reports a novel wireless control of a thermopneumatic zigzag micromixer achieved by selectively activating two passive wireless heaters enabled by an external radiofrequency magnetic field. The two heaters, which are designed to have different resonant frequency (f r ) values of 100 and 130 MHz, are selectively activated by modulating the field frequency to their corresponding f r values. Each heater is responsible for heating an air-heating chamber that is connected to a loading reservoir through a microdiffuser element, while the solutions pumped from each reservoir are mixed in a zigzag micromixing element that ends with an outlet hole. Mixing is achieved in a relatively short mixing length of a 2 mm, and was investigated over a low range of Reynold's number (Re) ≤ 10 that is suitable various biomedical applications. The numerically simulated and measured results of the proposed micromixer have shown mixing efficiencies values higher than 82% for the whole range of Re. The optimal activation switching time of the heaters is 10 s, at which the micromixer achieves a steady value of the maximum mixing efficiency after ~65 s. The micromixer provides mixing-ratio controllability with a maximum flow rate and pressure drop of ~3.4 μL/min and ~385.22 Pa, respectively.

High efficiency micromixing technique using periodic induced charge electroosmotic flow: A numerical study

Micromixers due to their prominence in Lab-On-a-Chip (LOC), biomanufacturing and chemical engineering applications are of great significances and emphases. In this paper, a 3D transient single phase solver has been developed in the open source code package, OpenFOAM, to investigate mixing efficiency and mixing length of a T-junction micromixer based on AC electroosmotic flow for both Newtonian and non-Newtonian fluids. The mathematical model and the developed solver are validated with existing data in the literature and the effects of substantial parameters such as AC amplitude, period of oscillation and conducting edges are investigated and the optimum range of each parameter are proposed to obtain simultaneously a high mixing efficiency and a relatively short mixing length. Present study shows that by using conducting edges, due to their capability of creating strong vortices, a high mixing efficiency and a short mixing length is achievable.Results show that via implementation of AC electric field as well as conducting edges, the mixing efficiency of 99% in a considerably short mixing length i.e. 20μm even in relatively high flow rates is obtainable. Since the mixing length is depended on the height of microchannel, in order to attain the capability of comparing achieved mixing length with findings of previous studies, a dimensionless parameter, Lm*, is proposed. Comparing of the value of this parameter for the present work and previous studies revealed that the presented micromixer can reduce the dimensionless mixing length up to 60%.

Numerical simulation of a non-equilibrium electrokinetic micro/nano fluidic mixer

In this study we numerically simulate a novel micromixer that utilizes vortex generation from the non-equilibrium electrokinetics near the micro/nanochannels interface. After mixing in combined pressure-driven and electroosmotic flows was compared with mixing in a pure pressure-driven flow, the superior mixing performance of the former was evident: for a specific case study, 90% mixing of two fluid streams for a short mixing length was achieved. The results of our numerical study were very similar to those of previously reported experiments. In this paper we explain the phenomenon occurring adjacent to the nano-junctions by plotting the electrical field components, the velocity contours and the concentration distribution in the micromixer. The vortices at the micro/nanochannel interface were obviously indicators of non-equilibrium behaviour in these regions. At the end, the mixing performance was evaluated by the investigation of different applied voltages, Reynolds numbers and surface charge densities using the mixing index parameter, and the results showed that more efficient mixing occurred when the applied voltage and surface charge density magnitude were increased and the Reynolds number was decreased.

Numerical and experimental analyses of planar micromixer with gaps and baffles based on field synergy principle

The characteristics of fluid flow and mass transfer in a novel micromixer with gaps and baffles are studied numerically and experimentally. Based on the principles of multiple vortices, abrupt contraction/expansion and twice split/recombine, the effects of gaps and baffles are investigated considering both mixing performance and pressure drop at Reynolds numbers ranging from 0.1 to 60. The mixing efficiency of the novel micromixer is found to be as high as over 94% at extremely low (Re=0.1) or high Reynolds number (Re≥40). The mechanism of mass transfer enhancement in the novel micromixer is analyzed by the field synergy principle. It is found that the novel micromixer is helpful to mass transfer enhancement which can be attributed to a good synergy between the velocity field and the concentration field. It is shown that the field synergy principle provides an alternative way to evaluate the performance of micromixers. In addition, the influence of the different locations of gaps and baffles on the mixing performance is analyzed. The comprehensive performance of micromixers is investigated by the field synergy principle and the ratio of the mixing index to the pressure drop (MI/PD). The merits of rapid mixing, low energy consumption and short mixing length make the novel micromixer more promising in microfluidic application.

Mixing enhancement in a passive micromixer with convergent–divergent sinusoidal microchannels and different ratio of amplitude to wave length

Experimental investigations and computational fluid dynamic on the characteristics of mixing inside the fabricated micromixers have been conducted. In order to study the mixing, several micromixer made by CO2 laser ablation process with sinusoidal convergent–divergent cross section including the T-shape inlet have been employed. The fluid mixing is clearly observed using a digital microscope imaging system. Beside, computational fluid dynamics via finite element method is used for 3D modeling of single phase flow in a microchannel. Experimental results demonstrated the reasonable agreement with those obtained by CFD. The main purpose of this modeling is to extend the previous knowledge related to the Dean and separation vortices forming inside the convergent–divergent sinusoidal microchannels. Moreover, effects of designing parameters such as aspect ratio of cross section and ratio of amplitude to wave length (A/ʎ) and operational condition such as Reynolds number on pressure-drop and mixing index are also investigated. Therefore, based on the obtained results, best mixing condition at short mixing length is introduced and a new micromixer is suggested that may be considered as a proper case due to higher mixer index and ease of fabrication in comparison with previous ones used in biomedical and biochemical analysis.

Investigation into the cause of high multi-mode combustion instability of H2/CO/CH4 syngas in a partially premixed gas turbine model combustor

In this paper, the fuel composition effects of H2/CO/CH4 syngas (0–100% for each component gas) on the self-excited high multi-mode (mainly the 3rd and 4th with their harmonics) combustion instability (CI) characteristics have been studied in a partially premixed swirl-stabilized gas turbine model combustor by investigating phase-resolved high-speed OH∗ planar laser induced fluorescence (OH-PLIF) and OH∗ chemiluminescence at a rate of 12.5kHz and analyzing the proper orthogonal decomposition (POD), spatio-temporal Rayleigh index (RI), and time-lag. Phase-synchronized OH-PLIF images suggested critical clues of CI driving mechanisms, including the periodic alternation of flame attachment/detachment and vortex coupling with everlasting flames at the outer recirculation zone due to high hydrogen fuels’ high reactivity. These PLIF results also demonstrated that the relatively short mixing length and highly fuel-dependent flame length are the root causes of a high instability-mode and sensible mode-shift. Thus, PLIF images were used to calculate the flame length by obtaining the intensity-weighted centroid for the more precise time-lag analysis. The spatio-temporal RI results indicated that the fuel composition affects the location and intensity of CI driving/damping, RI frequency, and instability mode and frequency. POD analysis from high-speed OH∗ images showed that the distinct coherent structures and large roll-up of flames are responsible for generating flame oscillations for each mode. High cross-correlation between the POD modes showed the convection of these coherent structures and axially-alternative swirl-like flame motions. At some particular compositions of H2/CH4/CO, high multi-mode CI was observed (e.g., the 3rd, 4th, and 6th modes appear simultaneously) and the original time-lag model could not be applicable, since the acoustic pressure wave is not simply sinusoidal but largely distorted. Thus, a new time-lag model using skewness time (τskew) was proposed to reflect the distortion from multi-mode CI and the accuracy of this model was verified using the experimental data.

Simulation and fabrication of a branch-channel rhombic micromixer for low pressure drop and short mixing length

The planar micromixers merit easy integration with the microsystem but encounter the problems of high pressure drop and long mixing length for high mixing efficiency over 90 %. In this article, an advanced branched rhombic micromixer (BRM) have been designed and investigated by 3D numerical simulations and experiments. Polydimethylsiloxane (PDMS) molding process was used for chip fabrication of the experiment. The CFD-ACE+ software was applied for modeling simulations. Simulation results showed that this optimum geometry design of four-mixing-unit BRM with the branch position at 700 μm high and 100 μm wide can effectively improve the mixing efficiency over 95 % at Reynolds number (Re) 120 with a rather low pressure drop about 9,000 Pa and a short mixing length of 5.5 mm as well. The high mixing efficiency at low pressure drop is attributed to the greatly increased contact interface area and chaotic-convection vortices as well as the low flow resistance with branched channels. The mixing verification is performed by the flow visualization system via the popular rhodamine B dye (10 mM) added DI method for PDMS BRM chips.

Simulation and experimental investigation of planar micromixers with short-mixing-length

Mixing laminar flows in short lengths is an important issue in chemical, biochemical and medical reactions. This work presents a numerical and experimental investigation on planar micromixers for obtaining an optimum micromixer with short mixing length. The numerical investigation of eight planar micromixers with two different chambers and four obstacle geometries is carried out by using three dimensional (3D) Navier–Stokes equations at the range of 0.1–40 of the Reynolds (Re) number. In total, 40 simulations (eight micromixers at five Re numbers) were done and the optimum micromixer was obtained by the analysis of the simulation data. The optimum micromixer has 0.89 and 0.99 mixing efficiency at Re=0.1 and 40 respectively at the short distance of 1.18mm from the origin. In addition, the effect of the chamber and obstacle geometry on mixing efficiency and pressure drop at the range of 0.1–40 of Re have been investigated. The results show that the chamber geometry manifests itself at a low Re number and obstacle geometry is significant at a high Re for mixing efficiency and pressure drop. The optimum micromixer was fabricated, tested and compared with the simulation results and both of them show a similar behavior in the mixing process.