1,398 research outputs found
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Finding the optimal design of a passive microfluidic mixer.
The ability to thoroughly mix two fluids is a fundamental need in microfluidics. While a variety of different microfluidic mixers have been designed by researchers, it remains unknown which (if any) of these mixers are optimal (that is, which designs provide the most thorough mixing with the smallest possible fluidic resistance across the mixer). In this work, we automatically designed and rationally optimized a microfluidic mixer. We accomplished this by first generating a library of thousands of different randomly designed mixers, then using the non-dominated sorting genetic algorithm II (NSGA-II) to optimize the random chips in order to achieve Pareto efficiency. Pareto efficiency is a state of allocation of resources (e.g. driving force) from which it is impossible to reallocate so as to make any one individual criterion better off (e.g. pressure drop) without making at least one individual criterion (e.g. mixing performance) worse off. After 200 generations of evolution, Pareto efficiency was achieved and the Pareto-optimal front was found. We examined designs at the Pareto-optimal front and found several design criteria that enhance the mixing performance of a mixer while minimizing its fluidic resistance; these observations provide new criteria on how to design optimal microfluidic mixers. Additionally, we compared the designs from NSGA-II with some popular microfluidic mixer designs from the literature and found that designs from NSGA-II have lower fluidic resistance with similar mixing performance. As a proof of concept, we fabricated three mixer designs from 200 generations of evolution and one conventional popular mixer design and tested the performance of these four mixers. Using this approach, an optimal design of a passive microfluidic mixer is found and the criteria of designing a passive microfluidic mixer are established
Concentration-adjustable micromixer using droplet injection into a microchannel
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
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A Passive Micromixer for Bioanalytical Applications
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Three passive micromixers with different geometries, i.e. zigzag, spiral, and split and merge (SaM) with labyrinthine channels, are compared with respect to their mixing efficiency by means of a computational study. The specifications are imposed from flexible printed circuit (FPC) technology which is used for their fabrication and from the applications to be implemented, i.e. the mixing of biochemical reagents. The computations include the numerical solution of continuity, Navier-Stokes, and mass conservation equations in 3d by ANSYS Fluent. The highest mixing efficiency is calculated for the SaM micromixer with the labyrinthine channel. Compared to a linear micromixer, the spiral micromixer improves the mixing efficiency by 8%, the zigzag by 11%, and the SaM by 92%; the diffusion coefficient of the biomolecule is 10-10 m2/s, the Reynolds number is 0.5, and the volume of each micromixer is 2.54 μl. The best of the three designs is realized by FPC technology and is experimentally evaluated by fluorescence microscopy
Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents
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
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Computational and experimental investigation of mixing in microchannels
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Mixing is a key process for the successful of all chemical or biochemical reactions, so effective micromixers represent essential components for micro total analysis systems (μTAS) or lab-on-a-chip. In the present study a combined computational and experimental approach was adopted to evaluate how the efficiency of a Y-mixer can be enhanced by modifying its downstream geometry. Three different geometries were studied and compared: Y-straight channel, Y-sine channel and Y-wrinkled wall channel. For each of them the influence of perfusing flow rates and channel cross section aspect ratio was investigated. Physical prototypes were built using a simple technique based on a xerographic process, and their mixing
performance was experimentally evaluated. Computational models of the designed micromixers were generated: the Navier-Stokes equations for an incompressible Newtonian fluid and the advection-diffusion
equation were solved with an uncoupled approach by means of the finite volume method. The computational and experimental results were critically compared, revealing Y-wrinkled wall mixer as the best performer
among those considered and suggesting criteria of possible improvements and optimization
Modeling of Electrothermal Flow Mixing in Lab on Chip Microfluidic Devices
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
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Numerical optimization of passive chaotic micromixers
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Due to the lack of turbulence in micromixers diffusion is the main process contributing to microfluidic mixing. Especially mixing of
uids with low diffusivity is a difficult task. The recently discovered mechanism of "chaotic-advection" enhances the diffusion process by stretching and folding the fluid interfaces in order to provide a larger interface. Certain passive micromixers like the staggered herringbone mixer (SHM) apply this concept and succeed in enhancing the mixing process considerably. The optimization of such micromixers is a time consuming and often expensive process. We demonstrate that the application of the lattice Boltzmann (LB) method to study advection and diffusion processes can be an efficient tool to optimize micromixers. By combining finite time Lyapunov exponents to study chaotic advection and Danckwert's intensity of segregation to study the diffusion, we demonstrate how optimal geometrical parameters for the SHM can be found and
how diffusion is improved by the complex
ow pattern inside the mixer. The current article provides a review of our results published in [1] together with additional studies on modelling diffusive mixing
with the LB method.This work was financed within the DFG priority program "nano- and microfluidics", the DFG collaborative research center 716, and by the NWO/STW VIDI grant of J. Harting
Effect of Patterned Slip on Micro and Nanofluidic Flows
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
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
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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