Curved microchannels

Chaotic advection can be induced with a 2D alternatively curved microchannel (2D serpentine) [112, 113] or zigzag channel shape [111]. In the first case, the chaotic advection is induced in the curved microchannel by consecutive generation of Dean vortices (Fig. 11a). Typically such type of micromixer can provide an effective mixing only for high Re in the range of few hundreds. These micromixers are generally described using another dimensionless number, the Dean number De) ... 

Fig. 2 Comparison of experimental and computational diffusion results in a curved microchannel using an osmotic pump (a) experimental data and (b) computational simulation [27]...

This approach involves the measurement of the distribution of swimming distances made by the spermatozoa in various chambers, such as curved microchannels in microchips [87] or cervical mucus-fiUed capillaries [3, 82, 106]. The swimming distances are a measure of the progressive velocity and the percent motile cells in the sperm population. 

Frame, M. D., Chapman, G B., Makino, Y., and Sarelius, I. H., Shear stress gradient over endothelial cells in a curved microchannel system. Biorheology, 35, 245,1998. 

Jiang, F., Drese, K. S Hardt, S., Kiipper, M-, Schonfeld, F. Helical flows and chaotic mixing in curved microchannels, AIChE J. 50, (2004), 2297-2305. 

The dependence of this ratio on particle size (d), charge ( p), and conductivity (CTp) indicates the particle specific deflection in curving microchannels. Moreover, the deflection is a function of the applied DC and AC fields and the spanning angle of the curve. 

Zhu J, Xiian X (2009) Particle electrophoresis and dielectrophoresis in curved microchannels. J Colloid Interface Sci 340 285—290... 

It is often necessary to drive fluids from one part of a microfluidic device to another, to control the fluid motion, to enhance mixing, or to separate fluids. The fluids are transported through channels with characteristic cross-sectional dimensions in the micrometer range. A channel of this size is called microchannel. If the channels are not in a straight line, then they are called a curved microchannel. 

The channel geometry of a microfluidic device is commonly characterized by a rectangular curved microchannel. The flow field conditions within such a microchannel have a significant influence upon the performance of the device when... 

They reported that the interface configuration of the two hquids was affected by the secondary flows induced by inertial forces acting at the corners of the microchannel. The results showed that the interface ccaifiguration was also dependent on the velocity, the density, and the viscosity of the fluid, as well as on the curvature radius and aspect ratio of the cross-sectional plane of the channel. Ookawara et al. [6] proposed a novel application for curved microchannels in which the curved channels were used to classify contained particles. The feasibflity of the proposed micro-separator/ classifier was verified both numerically and experimentally. Ueda et al. [7] investigated the curvature effect on the dynamics of long DNA in microfluidic devices. It was shown that under weak hydrodynamic flow, long DNA exhibited a curvature entropy trapping effect. However, this effect disappeared as the hydrodynamic flow was increased. 

This section focuses on the electmkinetically driven flow in a rectangular curved microchanneL It is assumed that the fluid in the microchannel is filled with an incompressible Newtoiian... 

Curved MicroChannel Flow, Fig. 1 Geometry and related coordinate system of curved microchannel. Note that u, V, and w denote the velocities in the X-, Y-, and Z-directions, respectively... 

Eor fully developed flow field in the curved microchannel, the Eqs. 1, 7, and 8 transformed the toroidal coordinate system (R, Y, 6) to the related coordinate system (X, Y, Z) and can be expressed as... 

Curved MicroChannel Flow, Fig. 2 Axial velocity distribution along Y-direction. (The microchannel has a curvature ratio of C/A = 50.) The applied DC electric field has an intensity of450 V/cm... 

Curved MicroChannel Flow, Fig. 3 Velocity distributions along X-direction in microchannels with different curvature ratios (the DC electric field intensity is 450 V/cm)... 

Curved MicroChannel Flow, Fig. 5 Transient velocity response in center of microchannel with Wo = 0.5, 1.0, and 1.5... 

Curved MicroChannel Flow, Fig. 6 Streamline contours in transverse section of curved microchannel over half-period fiom t = 2.20 to 2.70 for driving frequency of 1.0 kHz (Wo = 0.50)... 

Microfiuidic devices require a mixing operation for complex chemical synthesis and analysis. However, diffusive mixing tends to be slow and hence requires a relatively long mixing channel. A curved microchannel can be fabricated to save chip material. The formation of the vortices in the curved microchannel can be crated by the... 

Yamaguchi Y, Takagi F, Wataii T, Yamashita K, Nakamura H, Shimizu H, Maeda H (2004) Interface configuration of the two layered laminar flow in a curved microchannel. Chem Eng J 101 367... 

Chen JK, Luo WJ, Yang RJ (2006) Electroosmotic flow driven by DC and AC electric fields in curved microchannels. Jpn J Appl Phys 45(10A) 7983... 

The larger inertia of denser CTCs has also been used to isolate them on the microscale. MicroChannel structures such as herringbones can be used to induce secondary vortex flows which can promote movement of cells so that wall adhesion is promoted. Similarly, curved microchannels can induce Dean flows, which will laterally displace cells based upon their inertia. 

Cell sorting in curved microchannels is attributed to the combination of inertial forces and Dean... 

F. Jiang, K.S. Drese, S. Hardt, M. Kupper, F. Schonefeld, Helical flow and chaotic mixing in curved microchannels, AIChE., 2004, 50, 2297-2305. 

L. Wang, F. Liu, Forced convection in slightly curved microchannels, Int.J. Heat Mass Transfer, 2007, 50, 881-896. 

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