Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session D6: Microfluids: Flow in Microchannels |
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Chair: Soojung Claire Hur, Harvard University Room: 328 |
Sunday, November 24, 2013 2:15PM - 2:28PM |
D6.00001: ABSTRACT WITHDRAWN |
Sunday, November 24, 2013 2:28PM - 2:41PM |
D6.00002: Measuring the thermal diffusion coefficients of artificial and biological particles in a microfluidic chip Chao Zhao, Alparslan Oztekin, Xuanhong Cheng Particle thermophoresis refers to the migration of colloids under a temperature gradient. The thermophoretic velocity is proportional to the particle thermal diffusion coefficient and temperature gradient. However, in the literature, there are discrepancies about the mechanism for thermal diffusion and the reported values of the thermal diffusion coefficients are inconsistent for comparable systems. Furthermore, the thermal diffusion behavior of biological vesicles is underinvestigated. Here an optical method based on capillary is presented to measure the thermal diffusion coefficients of artificial and biological particles. By applying a temperature gradient along the width of the capillary, net velocity of microparticles and fluorescent intensity redistribution of nanoparticles are quantified to derive the thermal diffusion coefficients. The thermal diffusion coefficients of polystyrene beads as well as pseudoviral particles in physiological solutions are obtained in our work, and the values are compared with those from the literature. The differences are discussed in terms of interfacial interactions. This study provides insight into the transport of biological particles in a thermal gradient and will aid the design of separation devices. [Preview Abstract] |
Sunday, November 24, 2013 2:41PM - 2:54PM |
D6.00003: The clogging cascade of an array of microchannels Erin Barney, Emilie Dressaire, Howard Stone The manipulation and filtration of dilute suspensions of microparticles are important processes for both natural and engineered systems. Relying on the comparable lengthscales of the microchannels and microparticles, these systems are particularly susceptible to blockage. Studies at the single-pore level have established that the clogging of a microchannel is controlled by colloidal and hydrodynamic interactions. However, clogging is a multiscale process; the formation of single-pore level clogs often results in the blockage of a macroscopic system. The dynamics of this series of clogging events or clogging cascade are studied here. We investigate the blockage of an array of parallel microchannels and show in particular, that the rate of clog formation decreases during the clogging cascade. Through experimental measurements and theoretical analysis, we demonstrate the roles of colloidal and hydrodynamic effects in the dynamics of the clogging cascade. [Preview Abstract] |
Sunday, November 24, 2013 2:54PM - 3:07PM |
D6.00004: Dissipative particle dynamics modeling of blood flow in arterial bifurcations Xuejin Li, Kirill Lykov, Igor V. Pivkin, George Em Karniadakis The motion of a suspension of red blood cells (RBCs) flowing in bifurcations is investigated using both low-dimensional RBC (LD-RBC) and multiscale RBC (MS-RBC) models based on dissipative particle dynamics (DPD). The blood flow is first simulated in a symmetric geometry between the diverging and converging channels to satisfy the periodic flow assumption along the flow direction. The results show that the flowrate ratio of the daughter channels and the feed hematocrit level has considerable influence on blood-plasma separation. We also propose a new method to model the inflow and outflow boundaries for the blood flow simulations: the inflow at the inlet is duplicated from a fully developed flow generated by DPD fluid with periodic boundary conditions; the outflow in two adjacent regions near the outlet is controlled by adaptive forces to keep the flowrate and velocity gradient equal, while the particles leaving the microfluidic channel at the outlet at each time step are removed from the system. The simulation results of the developing flow match analytical solutions from continuum theory. Plasma skimming and the \textit{all-or-nothing }phenomenon of RBCs in bifurcation have been investigated in the simulations. The simulation results are consistent with previous experimental results and theoretical predictions. [Preview Abstract] |
Sunday, November 24, 2013 3:07PM - 3:20PM |
D6.00005: Identification of viscous droplets' physical properties that determine droplet behaviors in inertial microfluidics Soojung Claire Hur Inertial effects in microfluidic systems have recently recognized as a robust and passive way of focusing and ordering microscale particles and cells continuously. Moreover, theoretical analysis has shown that there exists a force away from channel walls in Poiseuille flow that locates deformable particles closer to the channel center than rigid counterparts. Then, the particle deformability can be extrapolated from the positions of particles with known sizes in the channel. Here, behaviors of various viscous droplets in inertial flow were investigated to identify critical properties determining their dynamic lateral position. Fluorinated oil solutions ($\mu =$1.7mPas and 5mPas) containing droplets (1mPas\textless $\mu $\textless 1.3Pas) were injected into a microfluidic channel with a syringe pump (8\textless $R_{c}$\textless 50). Interfacial tension between aqueous and oil phases were varied by adding controlled amount of a surfactant. The diameter, $a$, deformability, \textit{Def}, and dynamic lateral position, $X_{eq}$, were determined using high-speed microscopy. $X_{eq}$, was found to correlate with the particle Capillary Number, \textit{Ca}$_{P}$, regardless of droplet viscosities when \textit{Ca}$_{P}$ \textless 0.02 or \textit{Ca}$_{P}$ \textgreater 0.2, suggesting that the viscous drag from the continuous phase and the interfacial tension were competing factors determining $X_{eq}$. Experimental results suggested that (i) interplay among droplet's viscosity, interfacial tension and inertia of carrier fluid determines dynamic lateral position of droplets and (ii) the dominant property varies at a different regime. [Preview Abstract] |
Sunday, November 24, 2013 3:20PM - 3:33PM |
D6.00006: Forces on near-wall dielectric microparticles in combined electroosmotic and Poiseuille flow through microchannels Minami Yoda, Necmettin Cevheri Recent studies of electroosmotic (EO) flows have shown that neutrally buoyant radii $a \quad = \quad O$(0.1-1 $\mu $m) particles experience a ``dielectrophoretic-like'' repulsive force whose magnitude scales as $a^{\mathrm{2}}$ [\textit{Phys. Fluids} \textbf{18}:031702; \textit{Langmuir} \textbf{27}:11481]. Tracers with different sizes could then have different velocities in the same nonuniform flow. Evanescent-wave particle velocimetry was therefore used to study $a \quad =$ 125 nm and 245 nm fluorescent polystyrene (PS) tracers in combined EO and Poiseuille flow, which is effectively the superposition of simple shear and uniform flows within 1 $\mu $m of the wall. For ``coflow,'' where the EO and Poiseuille flows are in the same direction, the larger particles are strongly repelled from the wall; surprisingly, estimates of the magnitude of the repulsive force exceed the sum of the dielectrophoretic-like force and the shear induced electrokinetic lift force [\textit{J Colloid Interf Sci} \textbf{175}:411]. For ``counterflow,'' where the EO and Poiseuille flows are in opposite directions, these particles are instead \textit{attracted} to the wall. These unexpected results suggest that the nonlinear interaction between the electric field and shear could be used to manipulate near-wall microparticles. [Preview Abstract] |
Sunday, November 24, 2013 3:33PM - 3:46PM |
D6.00007: Measurement and characterization of lift forces on drops and bubbles in microchannels Claudiu Stan, Laura Guglielmini, Audrey Ellerbee, Daniel Caviezel, George Whitesides, Howard Stone The transverse motion of drops and bubbles within liquids flowing in pipes and channels is determined by the combination of several types of hydrodynamic lift forces with external forces. In microfluidic channels, lift forces have been used to position and sort particles with high efficiency and high accuracy. We measured lift forces on drops and bubbles and discriminated between different lift mechanisms under conditions characterized by low particle capillary numbers (0.0003 \textless\ Ca$_{P}$ \textless\ 0.3) and low particle Reynolds numbers (0.0001 \textless\ Re$_{P}$ \textless\ 0.1). The measured lift forces were often much larger (up to a factor of 1000) than the predictions of analytical models of inertial and deformation-induced lift, indicating that another lift mechanism was the largest contributor to the total lift force. The systems we investigated exhibited either (i) a deformation-induced lift force enhanced by confinement effects, or (ii) a lift force for which to our best knowledge is based on physicochemical effects at the interfaces of drops and bubbles. We will present new experimental data that supports a dynamic interfacial mechanism for the second type of lift force, and discuss possible avenues for creating an analytical model for it. [Preview Abstract] |
Sunday, November 24, 2013 3:46PM - 3:59PM |
D6.00008: ABSTRACT WITHDRAWN |
Sunday, November 24, 2013 3:59PM - 4:12PM |
D6.00009: Viscoelasticity of dilute capsule suspension under Stokes flows Daiki Matsunaga, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa A capsule is a liquid drop enclosed by a deformable membrane. Though the capsule deformation and suspension rheology in a simple shear flow is well understood, study of those in oscillating shear flow has been limited to small deformation theory. We investigated the viscoelasticity of dilute capsule suspension by applying an oscillating shear flow. We a used numerical method developed by Walter et al., in which the boundary element method for fluid mechanics is coupled with the finite element method for membrane mechanics. Simulations were performed by changing three parameters: capillary number, viscosity ratio and non-dimensional frequency of the applied shear. We found that the maximum deformation keeps a constant value in the low frequency range, while it is inversely proportional to the frequency in the high frequency range. The result of viscoelasticity suggests that both the capillary number and viscosity ratio are important parameters in the low frequency range, while only the viscosity ratio affects the viscoelasticity in the high frequency range. [Preview Abstract] |
Sunday, November 24, 2013 4:12PM - 4:25PM |
D6.00010: Harnessing Passive Cilia for Surface Cleaning of Microfluidic Devices Anurag Tripathi, Henry Shum, Anna Balazs Many biological organisms, such as mollusks and corals, utilize active cilia to prevent settlement of various fouling agents and debris on their surfaces. Inspired by these examples, we investigate if passive, non-actuated cilia can be harnessed for surface cleaning applications by utilizing oscillations in the ambient flow. By mimicking the oscillating shear flow near a ciliated wall in a channel, we show, by means of computational modeling, that the waving motion of cilia due to the oscillations in the flow can repel sticky, adhesive particles away from the surface. The results can be understood by means of a theoretical model by considering the motion of a particle penetrating an oscillating elastic layer and accounting for elastic, adhesive and hydrodynamic forces on the particle. The findings suggest a novel surface cleaning and fouling prevention mechanism for microfluidic devices dealing with transport and processing of microparticles. [Preview Abstract] |
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