Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H8: Microscale Flows: Flow in Microchannels |
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Chair: Panagiota Angeli, University College London Room: 108 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H8.00001: Experimental investigation of liquid-liquid plug formation in a T-junction microchannel Panagiota Angeli, Maxime Chinaud, Eynagelia-Panagiota Roumpea, Weheliye Weheliye Plug formation mechanism of two immiscible liquids was studied experimentally in a 200 $\mu $m microchannel using two innovative micro Particle Image Velocimetry ($\mu$ PIV) techniques i.e. two-colour $\mu$ PIV and high speed bright field $\mu$ PIV. The aqueous phase was a water/glycerol solution whereas the organic phase was silicon oil with a range of viscosities from 5 to 155 cSt. Experiments were conducted for different fluid flow rate combinations in the T-junction inlet and it was observed that velocity profiles within the forming plugs depend on the flow rate ratios. The velocity field studies provided insight into the plug mechanism revealing that the interface curvature at the rear of the forming plug changes sign at the later stages of plug formation and accelerates the thinning of the meniscus leading to plug breakage. Results from the two-colour PIV show that the continuous phase resists the flow of the dispersed phase into the main channel at the rear of the plug meniscus and causes the change in the interface curvature. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H8.00002: Experimental and numerical investigations of ionic liquid-aqueous flow in microchannel Qi Li, Dimitrios Tsaoulidis, Panagiota Angeli The hydrodynamic characteristics of plug flow of an ionic liquid-aqueous two-phase system in a microchannel were studied experimentally and numerically. A mixture of 0.2M N-octyl(plenyl)-N,N-diisobutylcarbamoylmethyphosphine oxide (CMOP)- 1.2 M Tri-n-butylphosphate (TBP) in room temperature ionic liquid 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide ([C$_{4}$min][NTf$_{2}$]), and a nitric acid solution of 1M were chosen. These fluids are relevant Eu(III) separation by extraction from nitric acid solutions. The two liquid phases were introduced into microchannels of 0.2 and 0.5mm internal diameter through a T-junction inlet. The flow pattern was visualized during plug formation at the inlet section and further downstream by means by bright field planar micro-Particle Image Velocimetry. Key features of plug flow, such as plug velocity, film thickness, plug length and recirculation intensity were measured under various experimental conditions. To gain further understanding of the 3-D flow field, Computation Fluid Dynamics (CFD) simulations approach were also conducted. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H8.00003: Interaction of Particles with Recirculating Flow Regions inside Cavities of Inertial Microchannels Hamed Haddadi, Dino Di Carlo Confined inertial flow over cavities of a microfluidic device leads to formation of recirculating flow regions, i.e flow cells, inside cavities which can entrap particles from the free stream. Besides its significance as a fundamental problem in fluid mechanics of mixtures, understanding particle interaction with recirculating flow regions inside cavities is important in biomedical applications, such as Circulating Tumor Cell (CTC) separation and platelet deposition in arterial stenosis. In the present work, a lattice-Boltzmann model with resolved particle-corner interaction combined with microfluidic experiments enabled improved understanding of the particle exchange within flow cells in confined inertial flow. Formation of a limit cycle trajectory, observed in experiments and numerical simulations, is a key feature in particle accumulation. By varying the dimensions of the cavity and channel Reynolds number, The length and location of the limit cycle trajectory also varies, altering of the rate of particle exchange and level of accumulation with recirculating zones inside cavities. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H8.00004: Experiment and computational simulations of liquid-liquid flow displacement in microchannels Yu Lu, Mark Simmons Microfluidics has great potential for tight process control in the generation of high value-added products and there is a requirement to understand how one fluid displaces another for either cleaning or control of the interfacial phenomena. Micro-Particle Image Velocimetry ($\mu$-PIV) and shadowgraphy have been used to examine the injection of a fluid into a circular or semi-circular microchannel (with diameters of 200 $\mu$m and 205 $\mu$m respectively) which is pre-filled with another fluid. Both immiscible and miscible Newtonian fluid pairs with varying viscosity ratio have been used. Flow instabilities and regimes have been observed which can be characterised using dimensionless flow maps. Displacement efficiency, residual liquid film thickness on the wall, velocity fields and the effect of wall conditions such as wall wettability are also studied. The flow phenomena observed have been modelled using the finite volume ANSYS Fluent CFD package and compared with the experiments. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H8.00005: Numerical simulation of liquid-liquid plug formation in a T-shaped cylindrical micro-channel Maxime Chinaud, Evangelia Roumpea, Panagiota Angeli, Jalel Chergui, Damir Juric, Seungwon Shin, Lyes Kahouadji, Omar Matar We present experimental studies and three-dimensional simulations using the code BLUE for different fluid flow rate combinations in a tubular T-junction. All branches have internal diameters equal to 200 $\mu$m. The dispersed phase consists of a water/glycerol solution injected from the side branch of the junction, while the continuous phase is silicon oil injected along the main channel axis. BLUE is a new massively parallel Navier-Stokes solver for multiphase flows. Communication across process threads is handled by MPI message passing procedures. The method for the treatment of the fluid phase interfaces and, in particular, capillary forces uses a hybrid Front Tracking/Level Set technique which defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. This structure allows the interface to undergo large deformations including rupture or coalescence of fluid interfaces. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H8.00006: Numerical study of mixing viscous fluids in T-shaped micro-channels with compressibility effects Junfeng Yang, Omar Matar, Christopher Harrison, Matthew Sullivan We study numerically the mixing processes of two miscible fluids in T-shaped micro-channels in the presence of compressibility effects. Three mixing modes are considered: ‘passive’ mixing, which relies on the molecular diffusion and chaotic advection; ‘active’ mixing relies on external disturbances, e.g. due to periodic compression; and a combination of these modes. In all cases considered, one of the fluids, fluid ‘A’, is initially present in the dead-end region of the micro-channel. In the `passive’ mixing case, the other fluid, fluid ‘B’, flows through the open part of the channel at a constant flow rate. In the ‘active’ case, this fluid is initially at rest but is then set in motion through pressure cycling. The combined case, involves the flow of fluid ‘B’ in the presence of compression-decompression cycles. Numerical simulations are carried out for three different fluids, accounting for their compressibility, and their pressure-dependent e.g. density, viscosity, and diffusivity; a simple mixing rule is used to model the properties of the mixed fluids. Our results indicate that the vortices in the dead-end zone, engendered by the relative motion of the fluids leads to their mixing; the combination of mixing modes is shown to promote mixing efficiency significantly. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H8.00007: Physical mechanisms of flow resistance in textured microchannels Simon Game, Demetrios Papageorgiou, Eric Keaveny, Marc Hodes Transport in microchannels can be enhanced by replacing flat, no-slip boundaries with boundaries etched with longitudinal grooves containing an inert gas, resulting in an effective slip flow. Various physical considerations which are often omitted from mathematical models play a significant role in the behaviour of this flow. Such considerations include: gas viscosity, meniscus curvature, finite channel cross-sections, molecular slip on the gas/liquid or gas/solid interfaces. Using a computationally efficient, multi-element, Chebyshev collocation method, we are able to quantify and combine each of these physical effects. We have shown that for physically realistic parameter values, including each of these effects significantly alters the volumetric flow rate, and hence these effects should not be ignored. Using this framework, we hope to manipulate these effects in order to minimise the flow resistance of the channel. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H8.00008: Fluid flow and heat transfer in polygonal micro heat pipes Sai Rao, Harris Wong Micro heat pipes have been used to cool microelectronic devices, but their heat transfer coefficients are low compared with those of conventional heat pipes. We model heat and mass transfer in triangular, square, hexagonal, and rectangular micro heat pipes under small imposed temperature differences. A micro heat pipe is a closed microchannel filled with a wetting liquid and a long vapor bubble. When a temperature difference is applied across a micro heat pipe, the equilibrium vapor pressure at the hot end is higher than that at the cold end, and the difference drives a vapor flow. As the vapor moves, the vapor pressure at the hot end drops below the saturation pressure. This pressure drop induces continuous evaporation from the interface. Two dimensionless numbers emerge from the momentum and energy equations: the heat-pipe number H, and the evaporation exponent S. When H $\gg$ 1 and S $\gg$ 1, vapor-flow heat transfer dominates and a thermal boundary layer appears at the hot end, the thickness of which scales as L/S, where L is the half-length of the pipe. A similar boundary layer exists at the cold end. Outside the boundary layers, the temperature is uniform. We also find a dimensionless optimal pipe length Sm$=$Sm(H) for maximum evaporative heat transfer. Thus, our model suggests that micro heat pipes should be designed with H $\gg$ 1 and S$=$Sm. We calculate H and S for four published micro-heat-pipe experiments, and find encouraging support for our design criterion. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H8.00009: Conjugate thermal creep flow with hydrodynamics and thermal slip conditions in a slit microchannel Ian Monsivais, Jos\'e Lizardi, Federico M\'endez In this work, we study the conjugate heat transfer between a gas flow and the walls of the microchannel, when the laminar motion of the fluid is caused uniquely by the thermal creep effect on the lower wall. Taking into account that this can represent a microchip or a similar device over which occurs a well defined heat dissipation rate; in our case, we have assumed that the bottom face of this lower wall with finite thermal conductivity, is exposed to a uniform heat flux. On the other hand, the upper wall of the microchannel is subject to a well-known prescribed thermal boundary condition. The heat conduction equation for the lower wall and the mass, momentum and energy equations for the phase gas together with the corresponding boundary conditions are written in dimensionless form, assuming that the Reynolds number associated with the characteristic velocity of the thermal creep and the aspect ratio of the microchannel are both very small. The velocity and temperature fields for the gas phase and the temperature profiles for the lower solid wall are predicted as functions of the involved dimensionless parameters and the main results confirm that the phenomenon of conjugate thermal creep exists whenever the temperature of the lower wall varies linearly or nonlinearly. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H8.00010: Rarefaction effects in microchannel gas flow driven by rhythmic wall contractions Krishnashis Chatterjee, Anne Staples Current state of the art microfluidic devices employ precise and timely operation of a complex arrangement of micropumps and valves for fluid transport. A much more novel flow transport mechanism is found in entomological respiratory systems, which involve rhythmic wall contractions for driving the fluid flow. The practical viability of using this technique in future microfluidic devices has been studied earlier. The present study investigates the incorporation of rarefaction effects in the above model of microscale gas flow by including slip boundary conditions. The Navier Stokes equations for gas flow in rectangular microchannel are solved analytically with microscale and lubrication theory assumptions. First order slip boundary conditions are incorporated to account for the rarefaction effects. The dependence of fluid velocities and pressure gradient on the slip boundary conditions is studied. Time averaged unidirectional fluid flow rates are plotted for different phase lags between the contractions, with and without slip in order to obtain an optimum range under different conditions. [Preview Abstract] |
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