Optimization of AC Electrokinetic Mixing by Nanocomposite Monolayer

2014 ◽  
Author(s):  
Nazmul Islam
Keyword(s):  
Hydrophobic Surface ◽  
Clinical Diagnostics ◽  
Mixing Efficiency ◽  
Promising Technique ◽  
Ac Electroosmosis ◽  
Mixing Rate ◽  
Microfluidic Mixing ◽  
High Throughput Drug Screening ◽  
Conductivity Range ◽  
Short Diffusion Distance

The mixing of fluids using AC Electrokinetic is presented in this paper. Both AC electrothermal (ACET) and AC electroosmosis (ACEO) techniques are investigated for mixing operation. AC electrokinetic mixing utilizes the characteristics of short diffusion distance and large specific interface area, and the characteristics of laminar flow and multiphase flow in a microchannel. The proposed mixer will have advantages of easy implementation and compatibility with microchip fabrication. Furthermore low and high conductive fluid has been experimented for mixing operation. In this research, the ACET and ACEO mixing will be optimized by surface modification using a biocompatible hydrophobic nanocomposite monolayer. This coating will modify the mixer surface to a hydrophobic surface and improve the friction losses at the interface, and eventually increase the mixing rate. Both ACEO and ACET flow is a promising technique in microfluidic mixing toward laboratory automation applications, such as clinical diagnostics and high-throughput drug screening. But the mixing efficiency and type of AC electrokinetic usage depends on the conductivity range of the fluids. These mixers can be integrated with the lab-on-a-chip and can provide inexpensive disposable devices.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

scholarly journals The influence of far field stratification on shear-induced turbulent mixing

2021 ◽  
Vol 928 ◽  
Author(s):  
S.F. Lewin ◽  
C.P. Caulfield
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Richardson Number ◽  
Scaling Laws ◽  
Mixing Efficiency ◽  
Far Field ◽  
Mixing Rate ◽  
Gradient Richardson Number ◽  
Background Density ◽  
Secondary Instabilities

We compare the properties of the turbulence induced by the breakdown of Kelvin–Helmholtz instability (KHI) at high Reynolds number in two classes of stratified shear flows where the background density profile is given by either a linear function or a hyperbolic tangent function, at different values of the minimum initial gradient Richardson number ${{Ri}}_0$ . Considering global and local measures of mixing defined in terms of either the irreversible mixing rate $\mathscr {M}$ associated with the time evolution of the background potential energy, or an appropriately defined density variance dissipation rate $\chi$ , we find that the proliferation of secondary instabilities strongly affects the efficiency of mixing early in the flow evolution, and also that these secondary instabilities are highly sensitive to flow perturbations that are added at the point of maximal (two-dimensional) billow amplitude. Nevertheless, mixing efficiency does not appear to depend strongly on the far field density structure, a feature supported by the evolution of local horizontally averaged values of the buoyancy Reynolds number ${Re}_b$ and gradient Richardson number ${Ri}_g$ . We investigate the applicability of various proposed scaling laws for flux coefficients $\varGamma$ in terms of characteristic length scales, in particular discussing the relevance of the overturning ‘Thorpe scale’ in stratified turbulent flows. Finally, we compare a variety of empirical model parameterizations used to compute diapycnal diffusivity in an oceanographic context, arguing that for transient flows such as KHI-induced turbulence, simple models that relate the ‘age’ of a turbulent event to its mixing efficiency can produce reasonably robust mixing estimates.

scholarly journals Numerical Simulation of Mixing Process in a Splitting-and-Recombination Microreactor

2022 ◽  
Vol 3 ◽  
Author(s):  
Lifang Yan ◽  
Shiteng Wang ◽  
Yi Cheng
Keyword(s):  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Horizontal Distance ◽  
Mixing Process ◽  
Mixing Rate ◽  
Navier Stokes Equation ◽  
Vertical Distance ◽  
Wide Range ◽  
Spacing Distance ◽  
Comb Tooth

The mixing process between miscible fluids in a splitting-and-recombination microreactor is analyzed numerically by solving the Navier–Stokes equation and species transfer equation. The commercial microreactor combines rectangular channels with comb-shaped inserts to achieve the splitting-and-recombination effect. The results show that the microreactor with three-layer standard inserts have the highest mixing rate as well as good mixing efficiency within a wide range of Reynolds numbers from 0.1 to 160. The size parameters of the inserts, both the ratio of the width of comb tooth (marked as l) and the spacing distance (marked as s) between two comb teeth, and the ratio of the vertical distance (marked as V) of comb teeth and the horizontal distance (marked as H) are essential for influencing the liquid–liquid mixing process at low Reynolds numbers (e.g., Re ≤ 2). With the increase of s/l from 1 to 4, the mixing efficiency drops from 0.99 to 0.45 at Re = 0.2. Similarly, the increase in V/H is not beneficial to promote the mixing between fluids. When the ratio of V/H changes from 10:10 to 10:4, the splitting and recombination cycles reduce so that the uniform mixing between different fluids can be hardly achieved. The width of comb tooth (marked as l) is 1 mm and the spacing distance (marked as s) between two comb teeth is 2 mm. The vertical distance (marked as V) of comb teeth and the horizontal distance (marked as H) are both 10 mm.

Optimizing Biased AC Electroosmosis Micropump by Hydrophobic Nanoparticle Monolayer

2010 ◽  
Author(s):  
Nazmul Islam ◽  
Davood Askari
Keyword(s):  
Applied Voltage ◽  
Research Work ◽  
Hydrophobic Surface ◽  
Ac Electroosmosis ◽  
Frequency Channel ◽  
Nano Composite ◽  
Pumping Rate ◽  
Channel Thickness ◽  
Voltage Frequency ◽  
Hydrophobic Nature

This paper describes the optimization of bidirectional micropump velocity by a deposition of hydrophobic nanoparticle (NP) monolayer. A nano-composite polymer coating contains a homogeneous mixture of Silicon NP in polydimithylsiloxane (PDMS) which will modify the micropump surface to a hydrophobic surface. For hydrophobic nature of PDMS, the monolayer coating will modify the hydrophilic surface of biased AC electroosmotic micropump to a hydrophobic surface. Based on the results obtained from our previous research work for the biased AC electroosmotic micropump, the pumping velocity was 300 micron/sec in 100μm channel thickness for applied voltage of 4.4V at 1 KHz frequency [1]. In that research, we had optimized the applied AC voltage, frequency, channel dimension, and electrode width. The main objective of this research is to investigate the micropump velocity through a surface modification process. Adding a thin monolayer will separate the electrode from the pumping liquid; thus eliminating the reaction on the electrode for applied voltage. In such case, we can apply high voltage to achieve high pumping rate.

Numerical investigation on implication of innovative hydrogen strut injector on performance and combustion characteristics in a scramjet combustor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sribhashyam Krishna Kireeti ◽  
Gadepalli Ravikiran Sastry ◽  
Santosh Kumar Gugulothu
Keyword(s):  
Transport Model ◽  
Weight Ratio ◽  
Combustion Efficiency ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Injection Technique ◽  
Mixing Rate ◽  
Navier Stokes Equation ◽  
Ansys Fluent ◽  
Scramjet Combustor

Abstract A detailed numerical analysis on a scramjet combustor is carried out by introducing an innovative shaped strut in place of the conventional strut. The design of newly added strut aids in generating intense vorticity which helps in efficient mixing of fuel and oxidizer. The air from the isolator enters the combustor at Mach 2.0, whereas fuel enters from the trailing edge of the strut sonically. In this study the flow dynamics with finite volume approach on commercial software Ansys-Fluent 20.0 to solve the two-dimensional Reynolds average Navier Stokes equation (RANS) with compressible fluid flow by considering the density-based solver with SST k-ε turbulent model. The species transport model with volumetric reaction and finite rate/eddy dissipation turbulence chemistry interaction is adopted to study the combustion phenomena and validated with the experimental results, and it is found that the interaction of the shear shock layer enhances the mixing rate by intensifying turbulence. The modified strut injector’s mixing efficiency is compared to the base strut and observed that with a 40% reduction in length, the modified strut injection technique exhibited a mixing efficiency of >95%. The combustion efficiency is then estimated streamwise, and the plot follows the same pattern as the mixing efficiency with fuel burns down completely when x = 150 mm for the modified strut whereas x = 200 mm for the base strut. This can compact the combustion chamber and increases the thrust-to-weight ratio. So, the innovative strut adopted can improvise the combustion efficiency.

scholarly journals Evaluation of Mixing and Mixing Rate in a Multiple Spouted Bed by Image Processing Technique

2017 ◽  
Vol 15 (1) ◽  
Author(s):  
Yong Zhang ◽  
Wenqi Zhong ◽  
Xiao Rui ◽  
Baosheng Jin ◽  
Hao Liu
Keyword(s):  
Image Processing ◽  
Scale Up ◽  
Processing Technique ◽  
Visual Observation ◽  
Image Processing Technique ◽  
Mixing Efficiency ◽  
Bubble Motion ◽  
Spouted Bed ◽  
Mixing Rate ◽  
Particle Mixing

Abstract Mixing efficiency is one of the most significant factors, affecting both performance and scale-up of a gas-solid reactor system. This paper presents an experimental investigation on the particle mixing in a multiple spouted bed. Image processing technique was used to extract the real-time information concerning the distribution of particle components (bed materials and tracer particles). A more accurate definition of the tracer concentration was developed to calculate the mixing index. According to the visual observation and image analysis, the mixing mechanism was revealed and the mixing rate was evaluated. Based on these results, the effects of operation parameters on the mixing rate were discussed in terms of the flow patterns. It is found that the detection of the pixel distribution of each component in RGB images is not affected by the interference of air void, thus maintaining good measurement accuracy. Convective transportation controls the particle mixing in the internal jet and spout, while shear dominants the particle mixing in the dense moving region. Global mixing takes place only when the path from one spout cell to the other is open. This path can be formed either by the bubbles or particle circulation flows. The mixing rate is linked to the bubble motion and particle circulation. Provided that there are interactions between the spout cells, any parameters promoting the bubble motion and circulation can increase the mixing rate. Finally, a mixing pattern diagram was constructed to establish the connection between the flow structure and mixing intensity.

scholarly journals Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids

Micromachines ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 731 ◽  
Author(s):  
Eriola-Sophia Shanko ◽  
Yoeri van de Burgt ◽  
Patrick D. Anderson ◽  
Jaap M. J. den Toonder
Keyword(s):  
Magnetic Beads ◽  
External Source ◽  
Magnetic Bead ◽  
Mixing Efficiency ◽  
Microfluidic Mixing ◽  
Low Reynolds Number Flows ◽  
Passive Mixing ◽  
Magnetic Mixing ◽  
Low Reynolds ◽  
Active Mixing

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as “passive” mixing. In addition, when rapid and global mixing is essential, “active” mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids.

Flow Measurements in a Model Burner—Part 1

1991 ◽  
Vol 113 (4) ◽  
pp. 668-674 ◽  
Author(s):  
D. F. G. Dura˜o ◽  
M. V. Heitor ◽  
A. L. N. Moreira
Keyword(s):  
Velocity Ratio ◽  
Laser Doppler ◽  
Jet Flows ◽  
Mixing Efficiency ◽  
Mixing Rate ◽  
Flow Measurements ◽  
Seed Particles ◽  
Circular Jets ◽  
Unequal Number ◽  
Air Streams

Laser-Doppler measurements of mean and turbulent velocity characteristics are reported in the developing region of the isothermal flow of a model of an industrial oxy-fuel burner. The burner consists of a central axisymmetric jet surrounded by sixteen circular jets, simulating the injection of oxygen in pratical burners. Errors incurred in the laser-Doppler measurements are estimated and bias effects due to unequal number density of seed particles in the various jet flows are investigated. The experiments have been carried out to investigate the mixing efficiency of the burner assembly without swirl motion and to assess the accuracy of calculation procedures in industrial burners. The results show that the present flow develops faster than related coaxial free jets with the same velocity ratio between central and peripheral air streams due to the comparatively high mixing rate peculiar to the present configuration. The existence of zones characterized by large turbulence anisotropy indicates the need to take account of the normal stresses in any proposed mathematical model to simulate the present flow field.

DC-Biased AC Electrokinetics Effect on V-Shaped Electrode Patterns for Microfluidics Applications

2019 ◽  
Author(s):  
Mohammad Salman Parvez ◽  
Mohammad Fazlay Rubby ◽  
Samir Iqbal ◽  
Nazmul Islam
Keyword(s):  
Research Work ◽  
Hydrophobic Surface ◽  
Surface Characteristics ◽  
The Other ◽  
Uniform Electric Field ◽  
Heat Sources ◽  
Ac Electroosmosis ◽  
Ac Electrokinetics ◽  
Mechanical Parts ◽  
Spatially Varying

Abstract AC electrokinetics is one of the widely used methods as an actuating mechanism in the lab-on-a-chip devices because of the absence of moving mechanical parts. In this paper, an analysis is done by using two perpendicular electrodes which are placed in V-shape to each other while maintaining an angle of 45 degrees with the third horizontal electrode. A semiconductive fluid was used to observe the microfluidic behavior and characteristics under the application of a DC biased AC signal. Applying the AC signal produced two different mechanisms of electrokinetics such as DC-biased AC electrothermal (ACET) and DC-biased AC electroosmosis (ACEO). In the ACEO process, a time-varying voltage was applied to the electrodes to create the double layer capacitance and zeta potential. This ACEO mechanism required lower voltage. On the other hand, the AC Electrothermal (ACET) flow produced a non-uniform electric field that generated spatially varying heat sources which in turn created a non-uniform temperature distribution. Two surface characteristics were also analyzed experimentally; one of these was by using the hydrophobic surface and the other used glass-surface only. At the microscale, mechanical microdevice encounter very high flow resistance and put stringent requirements on the strength of fluid channels, chambers and the interconnects. While many types of microfluidic manipulations can be effectively done by AC electrokinetics techniques, current research work focused on the observation of varying frequencies and voltages and their effects on microfluidic manipulations.

A Numerical Study on the Flow Characteristics of Opposed Impinging Jets

2012 ◽  
Vol 516-517 ◽  
pp. 854-857
Author(s):  
Shu Xia Qiu ◽  
Ning Pang
Keyword(s):  
Unsteady Flow ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Impinging Jets ◽  
Mixing Efficiency ◽  
Fluid Temperature ◽  
Mixing Rate ◽  
Numerical Work ◽  
Mixing Performance ◽  
Flow Pulsations

Inspired by the increasing interests on mixing effectiveness of opposed impinging jets, a numerical work is carried out to study the flow characteristics. The fluid temperature is used as a passive tracer to evaluate the mixing rate in the current mathematical models. The effect of Reynolds number on the mixing performance is discussed. Furthermore, in order to enhance the mixing efficiency and reduce the energy cost, unsteady flow pulsations are induced at the jet inlets. The numerical results indicate that the mixing efficiency can be improved by the unsteady flow pulsations via adjusting the hydrodynamics characteristics in the opposed jets.

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