1,398 research outputs found

    Concentration-adjustable micromixer using droplet injection into a microchannel

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    A novel micromixing technique that exploit a thrust of droplets into the mixing interface is developed. The technique enhances the mixing by injecting immiscible droplets in a mixing channel and the methodology enables a control of the mixing level simply by changing the droplet injection frequency. We experimentally characterize the mixing performance with various droplet injection frequencies, channel geometries, and diffusion coefficients. Consequently, it is revealed that the mixing level increases with the injection frequency, the droplet-diameter-to-channel-width ratio, and the diffusion coefficient. Moreover, the mixing level is found to be a linear function of the droplet volume fraction in the mixing section. The results suggest that the developed technique can produce a large amount of sample solution whose concentration is arbitrary and precisely controllable with a simple and stable operation.Comment: 12 + 3 pages, 6 + 4 figure

    Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents

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    Chaotic micromixers such as the staggered herringbone mixer developed by Stroock et al. allow efficient mixing of fluids even at low Reynolds number by repeated stretching and folding of the fluid interfaces. The ability of the fluid to mix well depends on the rate at which "chaotic advection" occurs in the mixer. An optimization of mixer geometries is a non trivial task which is often performed by time consuming and expensive trial and error experiments. In this paper an algorithm is presented that applies the concept of finite-time Lyapunov exponents to obtain a quantitative measure of the chaotic advection of the flow and hence the performance of micromixers. By performing lattice Boltzmann simulations of the flow inside a mixer geometry, introducing massless and non-interacting tracer particles and following their trajectories the finite time Lyapunov exponents can be calculated. The applicability of the method is demonstrated by a comparison of the improved geometrical structure of the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure

    Modeling of Electrothermal Flow Mixing in Lab on Chip Microfluidic Devices

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    Electrokinetics involves the study of liquid or particle motion under the action of an electric field; it includes electroosmosis, electrophoresis, dielectrophoresis, and electrowetting, etc. AC Electrokinetics (ACEK) has attracted much research interest for microfluidic manipulation for the last few years. It shows great potential for functions such as micropumping, mixing and concentrating particles. Based upon the actuation pattern microfluidic - based mixing devices can be categorized in two types. They are passive mixing microfluidic device and active mixing microfluidic device. Passive mixers typically utilize geometrical advantages to enhance mixing and they do not require external forces but a long mixing path was required. Active mixers are generally more effective than passive mixers. They utilize external driving forces like acoustics vibrations, electric and magnetic instability, temperature gradient due to joule heating etc. Like AC electroosmosis (AC EO) phenomena, AC electrothermal (ACET) effect is a hydrodynamic phenomena and acts on a suspended particle only through fluid drag because of Joule Heating. The challenges with ETE devices are the deciding threshold voltage, used for clinical diagnostic t o protect the cell from damage, choosing conductivity of the fluid, Electrode patterning and the switching of the electrode

    Effect of Patterned Slip on Micro and Nanofluidic Flows

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    We consider the flow of a Newtonian fluid in a nano or microchannel with walls that have patterned variations in slip length. We formulate a set of equations to describe the effects on an incompressible Newtonian flow of small variations in slip, and solve these equations for slow flows. We test these equations using molecular dynamics simulations of flow between two walls which have patterned variations in wettability. Good qualitative agreement and a reasonable degree of quantitative agreement is found between the theory and the molecular dynamics simulations. The results of both analyses show that patterned wettability can be used to induce complex variations in flow. Finally we discuss the implications of our results for the design of microfluidic mixers using slip.Comment: 13 pages, 12 figures, final version for publicatio

    Design and Simulation of Microfluidic Passive Mixer With Geometric Variation

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    Microfluidic designs are advantageous and are extensively used in number of fields related to biomed ical and biochemical engineeri ng. The objective of this paper is to perform numerical simulations to optimize the design of microfluidic mixers in order to achieve optimum mixing. In the present study, fluid mixing in different type of micro channels has b een investigated. Numeric al si mulations are performed in order to understand the effect of channel geometry parameters on mixing p erformance. A two dimensional “ T shaped ” passive microfluidic mixer is restructured by employing the rectangular shaped obstacles in the chan nel to improve the mixing performance. The impact of proper placement of obstacles in the channel is demonstrated b y applying the leakage concept. It has been observed that, the channel design with non - leaky obstacles (i.e. without leaky barriers) has presented better mi xing performance in contrast to channel design with leaky obstacles (i.e. leaky barriers) and channe l design without obstacles. The mixing occurs by virtue of secondary flow and generation of vortices due to curling o f fluids in the channel o n account of t he presence of obstacles. This passive mixer has achieved complete mixing of fluids in few seconds o r some milliseconds , which is certainly acceptable to utilize in biological applications such as cell dynamics, drug scre ening , toxicological screening and others

    Three-dimensional flows in slowly-varying planar geometries

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    We consider laminar flow in channels constrained geometrically to remain between two parallel planes; this geometry is typical of microchannels obtained with a single step by current microfabrication techniques. For pressure-driven Stokes flow in this geometry and assuming that the channel dimensions change slowly in the streamwise direction, we show that the velocity component perpendicular to the constraint plane cannot be zero unless the channel has both constant curvature and constant cross-sectional width. This result implies that it is, in principle, possible to design "planar mixers", i.e. passive mixers for channels that are constrained to lie in a flat layer using only streamwise variations of their in-plane dimensions. Numerical results are presented for the case of a channel with sinusoidally varying width
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