Numerical modeling of centrifugal microfluidic flow in rectangular ... · Element Method (FEM)...
Transcript of Numerical modeling of centrifugal microfluidic flow in rectangular ... · Element Method (FEM)...
Numerical modeling of centrifugal microfluidic flow in rectangular channels for Lab-on-a-CD platform applications
Viorel IONESCUa
aDepartment of Physics and Electronics, Ovidius University, Constanta, Romania
1. Abstract A rectangular radial microchannel model having the same geometric
dimensions as one type of microchannel placed on a PC-controlled
centrifugal Disk: length l = 2.1 cm, height h = 65 µm and width Δy =
320 µm (AR = 4.9) was considered here from an experimental work
reported in the literature. Fluid flow transport through this
standard channel was numerically developed with the Finite
Element Method (FEM) based Comsol Multiphysics software,
simulation performed at rotating speeds ω between 25 and 300 rad/s.
Other three rotating microchannel models with different aspect
ratios AR have been simulated after by increasing the channel height
from 65 µm to 160 µm, 200 µm and 240 µm and by maintaining the
same width of 320 µm. From the simulations of rotating channel
with AR = 4.9 resulted that even at 300 rad/s, transverse Coriolis
force was only close to half of centrifugal force (β = 0.44), no
secondary flow being induced in this case and a diffusion-based
mixing is developed for this particular channel geometry.
4. Conclusions
Simulation study regarding the effect of AR reduction on the fluid flow transport showed that
when the channel height h increased from 65 µm to 160 µm for the same channel width Δy = 320
µm, a secondary flow start to arise under the Coriolis force based mixing regime (1 < β < 2).
A further increase of h at 240 µm generated a concave shape of velocity distribution near the
channel right wall (at outlet) for the channel model with the lowest hydraulic resistance R and the
highest average wall shear stress .
Simulations performed at ω = 300 rad/s for the microchannels with different AR values showed
that Coriolis force is manifesting with higher intensity along with an increasing channel distance
(starting from inlet) when AR decreased from 2 to 1.3 and Dh increased from 213.3 to 273.3 µm,
with a distortion of the convex pressure profile in the channel inlet direction.
2. Introduction. Model set-up In recent years, the areas of chemical analysis and biomedical
diagnostics have been boosted by the centrifugally operated
microfluidic devices [1,2]. These devices are based on an array of
microchannels placed on a circular substrate under rotation at a
specific frequency, an arrangement known as a lab-on-a-CD
platform (LabCD) [3]. When the rotation speed of a LabCD
platform is low, centrifugal force fω will dominate the flow in
microchannels. At higher rotation frequency, the dominant force will
be Coriolis force fc and a secondary flow will be developed,
perpendicular to the primary flow velocity. So, the enhanced fluid
mixing at such small scales appears by generating this secondary
flow caused by inertial forces [4].
One of the main advantages offered by the centrifugal techniques
is the simple motor actuation mechanism witch reduce the necessity
of an external pumping system, so this type of mixing system can be
ideal for low-cost applications.
A better understanding on the mixing effect produced by the
Coriolis force inside the channels of a CD-based platform after the
initiation of secondary flow can lead to an improved design
efficiency of the rotating microchannels through a proper selection
of their cross-section dimensions.
Fig. 3. Velocity field distribution pattern at different downstream positions close
to channel inlet for the first channel model with AR = 4.9 at ω = 300 rad/s
Fig. 4. Normalized axial velocity profiles along y-axis at Z-mid-plane at the channel outlet
with AR = 4.9 and (b) pressure drop along the radial direction for different rotational speeds
Fig. 5. Contour velocity profiles at the outlet of the rotating
microchannel models having: a) AR = 4.9, b) AR = 2, c) AR
= 1.6 and d) AR = 1.3, simulated at ω = 300 rad/s.
3. Results
References [1] Shamloo, A., Selahi, A. A., and Madadelahi, M., J. Micromech. Microeng. 26, 035017-035026 (2016). [2] Kong, L. X., Perebikovsky, A., Moebius, J., Kulinsky, L. and Madou, M., Journal of Laboratory Automation 21(3), 323–355 (2016). [3] Silva, G., Semiao, V., and Reis, N., “Flow Measurement and Instrumentation 67, 153–165 (2019). [4] Sengupta, S., Ghosh, S., Saha, S., Chakraborty, D., Physics of Fluids 31, 054101 (2019). [5] S. Haeberle, T. Brenner, H.-P. Schlosser, R. Zengerle, L. Ducree, Centrifugal Micromixer, Chem. Eng. Technol. 2005, 28(5), 613 – 617.
Fig.1. Geometry and forces for a mixing microchannel placed
on a microfluidic disk [5]
Fig. 2. Closer view of mesh discretization network (extra fine mesh) for
microchannel model under validation (l = 10 mm, Δy = h = 200 μm),
along with complete mesh statistics
2
0
D
yt
DMixing time: , y0 – diffusion distance
Average residence time of water molecules in the channel tres = ratio between
the channel volume (m3) and volumetric flow rate (m3/s)
tres ≥ tD at the end of the channel => complete diffusion of the fluids.
Fig. 6. (a) Pressure drop profile and
b) transversal velocity profile along the
channels center direction formed by
the intersection of Y and Z mid-planes
a = 22/7 and b = 65/3.