An Electrokinetic Micro Mixer for Lab-on-Chip Applications: Modeling, Validation, and Optimization

2011 ◽  
Author(s):  
Hendryk Bockelmann ◽  
Vincent Heuveline ◽  
Peter Ehrhard ◽  
Dominik P. J. Barz
Keyword(s):  
Electrical Potential ◽  
Reynolds Numbers ◽  
Base Flow ◽  
Secondary Flows ◽  
Electrical Field ◽  
Lab On Chip ◽  
Low Reynolds Numbers ◽  
Micro Particle Image Velocimetry ◽  
Low Reynolds ◽  
Micro Mixer

Mixing of liquids in micro mixers at low Reynolds numbers is a challenging task since the flow regime is laminar and it is difficult to engage instabilities of the flow. In many microfluidic systems, mixing can be improved by means of electrokinetic effects. A favorable micro mixer design consists of a Y-junction, where the different liquid streams merge, and a subsequent meandering microchannel. A pressure gradient pumps the liquids to be mixed through the microchannel. An oscillating electrical field is superimposed onto the pressure-driven base flow which generates an additional electrokinetic (electro osmotic) flow. These oscillating secondary flows in conjunction with the meandering geometry are responsible for stretching and folding of the contact area of the liquids to be mixed which enhances the mass transfer rates considerably. In this contribution, we present a mathematical model which allows for the numerical simulation of flow, electrical potential, and species concentration. The model is validated by experiments relying on Micro Particle Image Velocimetry (μPIV). Consequently, this model can be used to numerically optimize the electrical field in order to achieve fast and high mixing even at low Reynolds numbers.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

Novel Low Reynolds Number Mixers for Microfluidic Applications

2003 ◽  
Author(s):  
S. P. Vanka ◽  
C. M. Winkler ◽  
J. Coffman ◽  
E. Linderman ◽  
S. Mahjub ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Rhodamine 6G ◽  
Rectangular Cross Section ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Sucrose Solutions ◽  
Low Reynolds ◽  
Rhodamine 6G Dye ◽  
Microfabrication Techniques

We present two new designs of compact mixers that can provide good mixing at low Reynolds numbers encountered in many microfluidic devices. The new designs benefit from curvature induced cross-stream vortices to enhance mixing of two co-flowing streams of fluids arranged side by side. One of the designs is a spiral of rectangular cross-section, while the other is a series of concentric circular channels arranged as a labyrinth. Both utilize the formation of sustained secondary flows to enhance mixing between two streams. Currently, the devices are fabricated in aluminum using standard machining techniques. However, they can be reduced further in size using standard microfabrication techniques. Mixing experiments were conducted in these channels at a Reynolds number of 6.8 using two sucrose solutions, one of which was laced with Rhodamine 6G dye. Compared to a experiment in an equivalent straight channel, a significant enhancement in the mixing of the two streams, as indicated by the intensity of the second fluid’s color, was observed. The present designs provide a compact and easy-to-fabricate alternative to various other concepts proposed in literature.

Global Linear Instability of Flow Through a Converging–Diverging Channel

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Mamta R. Jotkar ◽  
Gayathri Swaminathan ◽  
Kirti Chandra Sahu ◽  
Rama Govindarajan
Keyword(s):  
Reynolds Numbers ◽  
Linear Instability ◽  
Stability Study ◽  
Base Flow ◽  
Low Reynolds Numbers ◽  
Critical Reynolds Numbers ◽  
Diverging Channel ◽  
Order Of Magnitude ◽  
Flow Through ◽  
Low Reynolds

The global linear stability, where we assume no homogeneity in either of the spatial directions, of a two-dimensional laminar base flow through a spatially periodic converging–diverging channel is studied at low Reynolds numbers. A large wall-waviness amplitude is used to achieve instability at critical Reynolds numbers below ten. This is in contrast to earlier studies, which were at lower wall-waviness amplitude and had critical Reynolds numbers an order of magnitude higher. Moreover, our leading mode is a symmetry-breaking standing mode, unlike the traveling modes which are standard at higher Reynolds numbers. Eigenvalues in the spectrum lie on distinct branches, showing varied structure spanning the geometry. Our global stability study suggests that such modes can be tailored to give enhanced mixing in microchannels at low Reynolds numbers.

scholarly journals Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tianlong Zhang ◽  
Misuzu Namoto ◽  
Kazunori Okano ◽  
Eri Akita ◽  
Norihiro Teranishi ◽  
...  
Keyword(s):  
Flow Rate ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Flow ◽  
Live Cells ◽  
Low Reynolds Numbers ◽  
Particle Focusing ◽  
Human T Cell ◽  
Fs Laser ◽  
Low Reynolds

AbstractMicrofluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

scholarly journals Characteristics of an Annular Turbine Cascade at Low Reynolds Numbers

1998 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Hiroyuki Abe ◽  
Yasukata Tsutsui ◽  
Koji Murata
Keyword(s):  
Reynolds Number ◽  
Gas Turbines ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Secondary Flows ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Reynolds

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure gradient of the accelerating flow. But within the low Reynolds number region of approximately 6×104 where the 300kW ceramic gas turbines which are being developed under the New Sunshine Project of Japan operate, the characteristics such as boundary layer separation, reattachment and secondary flow which lead to prominent power losses can not be easily predicted. In this research, experiments have been conducted to evaluate the performance of an annular turbine stator cascade. Wakes of the cascade were measured using a single hot wire and five hole pressure tube, for a range of blade chord Reynolds numbers based on the inlet condition from 2×104 to 12×104. Flow visualizations on the suction surface of the blade were carried out using oil film method. At low Reynolds numbers, the flow structure in the annular cascade was quite complex and three-dimensional. The separation line on the suction surface moved upstream due to the decrease of Reynolds number. In addition, the growth of secondary flows, i.e., passage vortices and leakage vortex, was extremely under the influence of Reynolds number.

Drag of a heated sphere at low Reynolds numbers in the absence of buoyancy

2019 ◽  
Vol 869 ◽  
pp. 264-291 ◽  
Author(s):  
Swetava Ganguli ◽  
Sanjiva K. Lele
Keyword(s):  
Reynolds Numbers ◽  
Boussinesq Approximation ◽  
Base Flow ◽  
Subsequent Paper ◽  
Heating Regime ◽  
Low Reynolds Numbers ◽  
Low Mach Number ◽  
Low Reynolds ◽  
Drag Law ◽  
O 10

Fully resolved simulations are used to quantify the effects of heat transfer in the absence of buoyancy on the drag of a spatially fixed heated spherical particle at low Reynolds numbers ($Re$) in the range $10^{-3}\leqslant Re\leqslant 10$ in a variable-property fluid. The case where buoyancy is present is analysed in a subsequent paper. This analysis is carried out without making any assumptions on the amount of heat addition from the sphere and thus encompasses both the heating regime where the Boussinesq approximation holds and the regime where it breaks down. The particle is assumed to have a low Biot number, which means that the particle is uniformly at the same temperature and has no internal temperature gradients. Large deviations in the value of the drag coefficient as the temperature of the sphere increases are observed. When $Re<O(10^{-2})$, these deviations are explained using a low-Mach-number perturbation analysis as irrotational corrections to a Stokes–Oseen base flow. Correlations for the drag and Nusselt number of a heated sphere are proposed for the range of Reynolds numbers $10^{-3}\leqslant Re\leqslant 10$ which fit the computationally obtained values with less than 1 % and 3 % errors, respectively. These correlations can be used in simulations of gas–solid flows where the accuracy of the drag law affects the prediction of the overall flow behaviour. Finally, an analogy to incompressible flow over a modified sphere is demonstrated.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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