Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L15: Microchannels: Dynamic and StaticMicro

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Chair: Ivan Christov, Purdue Room: 601 
Monday, November 20, 2017 4:05PM  4:18PM 
L15.00001: Static response of deformable microchannels Ivan C. Christov, Tanmay C. Sidhore Microfluidic channels manufactured from PDMS are a key component of labonachip devices. Experimentally, rectangular microchannels are found to deform into a nonrectangular crosssection due to fluidstructure interactions. Deformation affects the flow profile, which results in a nonlinear relationship between the volumetric flow rate and the pressure drop. We develop a framework, within the lubrication approximation ($\ell\gg w\gg h$), to selfconsistently derive flow ratepressure drop relations. Emphasis is placed on handling different types of elastic response: from pure platebending, to halfspace deformation, to membrane stretching. The ``simplest'' model (Stokes flow in a 3D rectangular channel capped with a linearly elastic KirchhoffLove plate) agrees well with recent experiments. We also simulate the static response of such microfluidic channels under laminar flow conditions using ANSYS$\copyright$ Workbench. Simulations are calibrated using experimental flow ratepressure drop data from the literature. The simulations provide highly resolved deformation profiles, which are difficult to measure experimentally. By comparing simulations, experiments and our theoretical models, we show good agreement in many flow/deformation regimes, without any fitting parameters. [Preview Abstract] 
Monday, November 20, 2017 4:18PM  4:31PM 
L15.00002: Electrified Flow in Slender VGroove Microchannels: Generalized Stability of Steady State Configurations Vilda Markeviciute, Nicholas White, Sandra Troian Although spontaneous capillary flow can be an especially rapid process in slender open microchannels resembling Vgrooves, enhanced flow control is possible through implementation of electric field distributions which generate opposing electrohydrodynamic pressures along the air/liquid interface to modulate the capillary pressures. Important fundamental work by Romero and Yost (1996) and Weislogel(1996) has elucidated the behavior of Newtonian films in slender Vgrooves driven to flow solely by the streamwise change in capillary pressure due to the change in radius of curvature of the circular arc describing the interface of wetting or nonwetting fluids. Here we augment the Romero and Yost model with inclusion of Maxwell stresses for perfectly conducting wetting films and examine which electric field distributions allow formation of steady state film shapes for various inlet and outlet boundary conditions. We investigate the stability of these steady solutions to small perturbations in film thickness using a generalized stability analysis. These results reveal how the ratio of Maxwell to capillary stresses influences the degree of linearized transient growth or decay for thin films confined to flow within an open Vgroove. [Preview Abstract] 
Monday, November 20, 2017 4:31PM  4:44PM 
L15.00003: Longitudinal Heat Conduction Effects on a Conjugate Thermal Creep Flow in a Microchannel Ian Monsivais, Jos\'e J. Lizardi, Federico M\'endez In this work, we use asymptotic and numerical techniques to analyze the conjugate heat transfer between a rarified gas flow and the lower wall of a thin horizontal microchannel exposed to a uniform heat flux, when the laminar motion of the gas is only caused by the thermal creep or transpiration effect on the lower wall of the microchannel. Usually, it is enough to impose a linear temperature profile as a boundary condition to produce the thermal creep effect. However, we prefer to avoid this arbitrary simplification taking into account that for real cases, the temperature profile at the lower wall can be unknown. We can assume then that the lower face of this heat sink with finite thermal conductivity and thickness is exposed to a uniform heat flux, while the upper wall of the microchannel is subject to a wellknown prescribed thermal boundary condition. The resulting governing equations 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. Thermal creep effect depends strongly on a dimensionless conjugate parameter that represents the competition between the heat driven by the gas and the heat that longitudinally conducts the lower wall. [Preview Abstract] 
Monday, November 20, 2017 4:44PM  4:57PM 
L15.00004: Conjugate heat transfer analysis of multiharmonic microwavy channels Justin Moon, Arturo PachecoVega, J. Rafael Pacheco In this study, numerical simulations are performed to investigate the conjugate heat transfer in threedimensional multiharmonic microscale wavy channels. The focus here is on the analysis of the channel surfacetopography, modeled as a sinusoidal wave of square crosssectional area, through which cold water flows within the laminar regime, and its influence on the enhancing mechanisms. A device of length of 20 mm, 16 mm of which are of sinusoidal shape, with 2 mm straight sections at the channel inlet and outlet, is used as baseline for comparison purposes. The channel is enclosed by a solid rectangular prism block, on which heat flux of 47 W/cm$^2$ acts at the bottom surface within the sinusoidal region. Using the performance factor ($PF$); i.e., the ratio of the Nusselt number to the pressure drop, as objective function, a parametric analysis is carried out for a set of inlet velocities ($Re$=50, 100 and 150), the investigate whether (and how) the addition of harmonicwaves for the channel geometry enhances the value of the PF when compared to a singlewave device. [Preview Abstract] 
Monday, November 20, 2017 4:57PM  5:10PM 
L15.00005: Viscous wave breaking in microchannels Xiaoyi Hu, Thomas Cubaud Destabilization processes of viscousstratified flows are experimentally investigated for twolayer configurations with both miscible and immiscible fluid pairs using straight square microchannels. We systematically characterize the appearance and dynamics of waves propagating at the interface of highly viscous fluid layers and delineate flow regimes based on flow parameters and fluid properties. We examine in particular the mechanism of wave breaking, which is characterized with the development of viscous filamentous structures entrained from wave crests, in the presence and absence of interfacial tension between fluids. The wave breaking phenomenon offers new means for mixing miscible fluids or emulsifying immiscible fluids having large viscosity contrasts in confined microsystems. [Preview Abstract] 
Monday, November 20, 2017 5:10PM  5:23PM 
L15.00006: Entropy and Multifractal Dimensions of Complex Structures in Microchannel Mixing Miron Kaufman, Petru S. Fodor, Robert White Since the fluid flow is microchannels is laminar, mixing of advected particles is achieved by using patterns on the walls. We solve numerically the NavierStokes equations describing flows in patterned microchannel: the staggered herring bone which consists of periodic groves and ridges distributed along the channel length and a fractal microchannel where by employing a Weierstrass function we generate a nonperiodic pattern of ridges on the channel bottom. We analyze the advection of light particles carried by a creeping flow in those channels. The quality of the mixing between two types of tracers is determined by using ShannonRenyi entropic measures and fractal dimensions of Poincare plots along the channels. We find that the various geometric measures of mixing do not depend strongly on the different type of image file. [Preview Abstract] 
Monday, November 20, 2017 5:23PM  5:36PM 
L15.00007: Microchannel slip flow structure near superhydrophobic surface Yoshiyasu Ichikawa, Ken Yamamoto, Masahiro Motosuke Superhydrophobic surface (SHS) is well known to generate slip flow by forming liquidgas (LG) interface which contributes the drag reduction effect. However, the flow structure itself including the deformation of the LG interface and slip length at the surface is still in discussion. Therefore, it is considered that the acquisition of the deformation and velocity profile nearSHS flow is essential to evaluate the shear stress on the interface which is closely correlated to flow resistance. In this study, we measured the flow velocity nearSHS which has microgrooves and microribs located parallel to the water flow direction to reveal nearSHS flow structures by astigmatism particle tracking velocimetry (APTV) technique which can obtain threedimensional and threecomponent velocity. This technique enables us to determine threedimensional particle locations and their velocities simultaneously. From the measured velocity profile, both the deformed shape of LG interface and the local slip length distribution around the interface was obtained. It was also found that the local slip length distribution becomes smaller than theoretical values. Moreover, we evaluated shear stress distribution on the SHS as well as the drag reduction effect of the SHS. [Preview Abstract] 
Monday, November 20, 2017 5:36PM  5:49PM 
L15.00008: Influence of Dissipative Particle Dynamics parameters and wall models on planar microchannel flows Yuyi Wang, Jiangwei She, ZheWei Zhou Dissipative Particle Dynamics (DPD) is a very effective approach in simulating mesoscale hydrodynamics. The influence of solid boundaries and DPD parameters are typically very strong in DPD simulations. The present work studies a microchannel Poisseuille flow. Taking the neutron scattering experiment and molecular dynamics simulation result as bench mark, the DPD results of density distribution and velocity profile are systematically studied. The influence of different levels of coarsegraining, the number densities of wall and fluid, conservative force coefficients, random and dissipative force coefficients, different wall model and reflective boundary conditions are discussed. Some mechanisms behind such influences are discussed and the artifacts in the simulation are identified with the bench mark. [Preview Abstract] 
Monday, November 20, 2017 5:49PM  6:02PM 
L15.00009: Density Distribution of Liquid Argon in Nanochannel Poiseuille Flows Jiangwei She, Yuyi Wang, ZheWei Zhou The density layering parallel to the boundaries of liquid has been measured in many experiments and also observed in molecular dynamics (MD) simulations. In this study, a detail and systematic investigation of density distribution in nanoscale Poiseuille flows is carried out. Through analyzing the difference of density distribution curves obtained under different conditions, the influence of interaction parameters, configuration form of solid wall and temperature on the layering are investigated. The internal mechanism is also explored in this paper. The detail description of the density distribution results and simulation algorithm is given. [Preview Abstract] 
Monday, November 20, 2017 6:02PM  6:15PM 
L15.00010: Generalized Stability Analysis of Capillary Flow in Slender VGrooves Nicholas White, Sandra Troian Spontaneous capillary flow, an especially rapid process in slender open microchannels resembling Vgrooves, is of significant importance to many applications requiring passive robust flow control. Many types of biomedical devices for pointofcare use in developing countries are being designed around this principle. Important fundamental work by Romero and Yost (1996) and Weislogel(1996) elucidated the behavior of Newtonian films in slender Vgrooves driven to flow by the streamwise change in capillary pressure due to the change in radius of curvature of the circular arc describing the interface of wetting or nonwetting fluids. Selfsimilar solutions describing Washburn type dynamics were found but other solutions are possible. Here we extend the Romero and Yost model to include a variety of inlet and outlet boundary conditions and examine the transient growth and generalized stability of perturbations to steady state and selfsimilar flows. Although most cases examined for wetting fluids exhibit robust stability against small perturbations, some exceptions reveal unstable flow. In total, these results support decades of experimental work which has found this method of flow control to be especially reliable, robust and selfhealing. [Preview Abstract] 
Monday, November 20, 2017 6:15PM  6:28PM 
L15.00011: Asymptotic solutions for flow in microchannels with ridged walls and arbitrary meniscus protrusion Toby Kirk Flow over structured surfaces exhibiting apparent slip, such as parallel ridges, have received much attention experimentally and numerically, but analytical and asymptotic solutions that account for the microstructure have so far been limited to unbounded geometries such as sheardriven flows. Analysis for channel flows has been limited to (close to) flat interfaces spanning the grooves between ridges, but in applications the interfaces (menisci) can highly protrude and have a significant impact on the apparent slip. In this presentation, we consider pressuredriven flow through a microchannel with longitudinal ridges patterning one or both walls. With no restriction on the meniscus protrusion, we develop explicit formulae for the slip length using a formal matched asymptotic expansion. Assuming the ratio of channel height to ridge period is large, the periodicity is confined to an inner layer close to the ridges, and the expansion is found to all algebraic orders. As a result, the error is exponentially small and, under a further "diluteness" assumption, the explicit formulae are compared to finite element solutions. They are found to have a very wide range of validity in channel height (even when the menisci can touch the opposing wall) and so are useful for practitioners. [Preview Abstract] 
(Author Not Attending)

L15.00012: Numerical Modeling of Surface and Volumetric Cooling using Optimal T and Yshaped Flow Channels Srinivas Kosaraju The layout of T and Vshaped flow channel networks on a surface can be optimized for minimum pressure drop and pumping power. The results of the optimization are in the form of geometric parameters such as length and diameter ratios of the stem and branch sections. While these flow channels are optimized for minimum pressure drop, they can also be used for surface and volumetric cooling applications such as heat exchangers, air conditioning and electronics cooling. In this paper, an effort has been made to study the heat transfer characteristics of multiple T and Yshaped flow channel configurations using numerical simulations. All configurations are subjected to same input parameters and heat generation constraints. Comparisons are made with similar results published in literature. [Preview Abstract] 
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