Dynamics of Elastic Capsules in Cross-Junction and T-Junction Microfluidic Channels
Dynamics of Elastic Capsules in Cross-Junction and T-Junction Microfluidic Channels
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Date
2017
Authors
Mputu udipabu, Pompon
Advisor
Dimitrakopoulos, Panagiotis
Citation
DRUM DOI
Abstract
In this dissertation, we investigate via numerical computations the dynamicsof elastic capsules (made from a thin strain-hardening elastic membrane) in two
microfluidic channels of cross-junction and T-junction geometries. For the cross-junction
microfluidic channel, we consider an initially spherical capsule with a size
smaller than the cross-section of the square channels comprising the cross-junction,
and investigate the effects of the capsule size, flow rate, and lateral flow rates on the
transient dynamics and deformation of low-viscosity and equiviscous capsules. In
addition, we also study the effects of viscosity ratio on the transient capsule dynamics
and deformation. Our investigation shows that the intersecting lateral flows at
the cross-junction act like a constriction. Larger capsules, higher flow rates and
higher intersecting lateral flows result in stronger hydrodynamic forces that cause a
significant capsule deformation, i.e., the capsule’s length increases while its height
decreases significantly. The capsule obtains different dynamic shape transitions due
to the asymmetric shape of the cross-junction. Larger capsules take more time to
pass through the cross-junction owning to the higher flow blocking. As the viscosity
ratio decreases, the capsule’s transient deformation increases and tail formation
develops transiently, especially for low-viscosity capsules owing to the normal-stress
effects of the surrounding fluid on the capsule’s interface. However, the viscosity
ratio does not affect much the capsule velocity due to a weak inner circulation.
Our findings suggest that the tail formation of low-viscosity capsule may promote membrane breaking and thus drug release of pharmaceutical capsules in the microcirculation.
Furthermore, we investigate via numerical computations the motion of an elastic
capsule (made from an elastic membrane obeying the strain-hardening Skalak
law) flowing inside a microfluidic T-junction device. In particular, we consider the
effects of the capsule size, flow rate, lateral flow rate, and fluid viscosity ratio on
the motion of the capsule in the T-junction micro-channel. As the capsule’s initial
lateral position increases, the capsule moves faster and reaches different final lateral
positions. As the capsule size increases, the gap between the capsule’s surface and
the channel wall decreases. This results in the development of stronger hydrodynamic
forces and a decrease in the capsule velocity due to flow blocking. As the
capsule size increases, there is a small lateral migration towards the micro-channel
centerline, which is the low-shear region of the T-junction micro-channel. This migration
is in agreement with experimental and numerical studies on non-inertial
lateral migration of vesicles in bounded Poiseuille flow by Coupier et al. [13] who
showed that the combined effects of the walls and of the curvature of the velocity
profile induce a lateral migration toward the centerline of the channel. As the capillary
number Ca increases, the stronger hydrodynamic forces cause the capsule to
extend along the flow direction (i.e., the capsule’s length Lx increases as the capsule
enters the T-junctions and decreases as the capsule exits the T-junction). There is
a small lateral migration away from the micro-channel centerline as the flow rate Ca
increases. The capsule lateral position zc, main-flow velocity Ux and migration velocity
Uz are practically not affected by the fluids viscosity ratio λ. As the channel’s
lateral flow rate increases, the capsule migrates downwards towards the bottom of
the device. Our findings on the lateral migration in the T-junction micro-channel
suggest that there is a great potential for designing a T-junction microfluidic device
that can be used to manipulate artificial and biological capsules.