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Yixiang Gan - One of the best experts on this subject based on the ideXlab platform.
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rupture of Liquid Bridges on porous tips competing mechanisms of spontaneous imbibition and stretching
Langmuir, 2020Co-Authors: Si Suo, Yixiang GanAbstract:Liquid Bridges are commonly encountered in nature and the Liquid transfer induced by their rupture is widely used in various industrial applications. In this work, with the focus on the porous tip,...
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Dynamic contact angle hysteresis in Liquid Bridges
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018Co-Authors: Zhang Shi, Yi Zhang, Mingchao Liu, Dorian A. H. Hanaor, Yixiang GanAbstract:Abstract This work presents an experimental study of dynamic contact angle hysteresis using Liquid Bridges under cyclic compression and stretching between two identical plates. Under various loading rates, contact angle hystereses for three different Liquids were measured by examination of advancing and receding Liquid Bridges, and the capillary forces were recorded. It is found that for a given Liquid, the hysteretic behaviour of the contact angle is more pronounced at higher loading rates. By unifying the behaviour of the three Liquids, power-law correlations were proposed to describe the relationship between the dynamic contact angle and the capillary number for advancing and receding cases. It is found that the exponents of obtained power-law correlations differ from those derived through earlier methods (e.g., capillary rise), due to the different kinematics of the contact line. The various hysteretic loops of capillary force in Liquid Bridges under varied cyclic loading rates were also observed, which can be captured quantitatively by the prediction of our developed model incorporating the dynamic contact angle hysteresis. These results illustrate the importance of varying contact line geometries during dynamic wetting and dewetting processes, and warrant an improved modelling approach for higher level phenomena involving these processes, e.g., multiphase flow in porous media and Liquid transfer between surfaces with moving contact lines.
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Dynamic contact angle hysteresis in Liquid Bridges
arXiv: Soft Condensed Matter, 2017Co-Authors: Zhang Shi, Yi Zhang, Mingchao Liu, Dorian A. H. Hanaor, Yixiang GanAbstract:This work presents a combined experimental and theoretical study of dynamic contact angle hysteresis using Liquid Bridges under cyclic compression and stretching between two identical plates. Under various loading rates, contact angle hysteresis for three different Liquids was measured by examination of advancing and receding angles in Liquid Bridges, and the capillary forces were recorded. It is found that, for a given Liquid, the hysteretic phenomenon of the contact angle is more pronounced at higher loading rates. By unifying the behaviour of the three Liquids, power-law correlations were proposed to describe the relationship between the dynamic contact angle and the capillary number for advancing and receding cases. It is found that the exponents of obtained power-law correlations differ from those derived through earlier methods (e.g., capillary rise), due to the different kinematics of the triple-line. The various hysteretic loops of capillary force in Liquid Bridges under varied cyclic loading rates were also observed, which can be captured quantitatively by the prediction of our developed model incorporating the dynamic contact angle hysteresis. These results illustrate the importance of varying triple-line geometries during dynamic wetting and dewetting processes, and warrant an improved modelling approach for higher level phenomena involving these processes, e.g., multiphase flow in porous media and Liquid transfer between surfaces with moving contact lines.
Hendrik C Kuhlmann - One of the best experts on this subject based on the ideXlab platform.
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structure and dynamics of particle accumulation in thermocapillary Liquid Bridges
Fluid Dynamics Research, 2014Co-Authors: Hendrik C Kuhlmann, Roman Mukin, Tomoaki Sano, Ichiro UenoAbstract:The accumulation of small mono-disperse heavy particles in thermocapillary Liquid Bridges is investigated experimentally and numerically. We consider particle accumulation near the center of the toroidal vortex, the so-called toroidal core of particles (COP), and the particle-depletion zone near the axis of the Liquid bridge. Based on the acceleration and deceleration of the tangential flow along the thermocapillary free surface it is argued that the interaction of the particles with the free surface is of key importance for the fast particle accumulation within a few characteristic momentum diffusion times. The experimentally determined particle-accumulation times are compared with time-scale estimates for accumulation due to either particle free-surface interaction or due to inertia of particles which are heavier than the Liquid. We show that the experimental accumulation times are compatible with the accumulation times predicted by the particle–free-surface interaction (PSI) while the time-scale estimates based on the inertia of the particles are too large to explain the fast de-mixing observed in experiments. The shape of the COP resembles certain KAM tori of the incompressible flow of a hydrothermal wave. Two scenarios are proposed to explain the structure and the dynamics of the COP depending on the existence or non-existence of suitable KAM structures. The shape of the experimental particle-depletion zone agrees well with the release surface which is defined by the particle–free-surface interaction process. The favorable comparison of the dynamics and structure of experimental and numerical accumulation patterns provides strong evidence for the existence and relevance of the PSI as the most rapid physical accumulation mechanism.
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the jeremi project on thermocapillary convection in Liquid Bridges part b overview on impact of co axial gas flow
FDMP: Fluid Dynamics & Materials Processing, 2014Co-Authors: Valentina Shevtsova, Marcello Lappa, A. Mialdun, Koichi Nishino, Satoshi Matsumoto, J M Montanero, Hendrik C Kuhlmann, Yuri Gaponenko, M Lukasser, Ichiro UenoAbstract:Pure surface-tension-driven flow is a unique type of flow that can be controlled through external manipulation of thermal and/or mechanical boundary conditions at the free Liquid surface where the entire driving force for the convection is generated. This unique feature has been exploited in recent studies for the active control of the flow instability. The use of forced coaxial gas streams has been proposed as a way to stabilize the Marangoni convection in Liquid Bridges in the planned space experiment JEREMI (Japanese and European Research Experiment on Marangoni Instabilities). It is aimed at understanding the mechanism of the instability and the role of the surface heat transfer and surface shear stresses. This overview presents corresponding preparatory experimental and numerical studies.
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dynamic free surface deformations in thermocapillary Liquid Bridges
Fluid Dynamics Research, 2002Co-Authors: Hendrik C Kuhlmann, Ch NienhuserAbstract:Flow-induced dynamic free-surface deformations in thermocapillary Liquid Bridges are investigated in the limit of small capillary number. The asymptotic solution in lowest order is calculated numerically. Dynamic deformations caused by steady axisymmetric flows and by time-dependent three-dimensional critical modes are considered for representative Prandtl numbers (Pr=0.02 and 4.38). The magnitude and phase of the dynamic surface-deformation wave relative to the magnitude of the temperature field of a hydrothermal wave are predicted and discussed. It is shown that the total dynamic deformation can be decomposed to elucidate the relative importance of the hydrodynamic pressure, the viscous stress, the change of the volume due to thermal expansion, the temperature-dependence of the surface tension, and the temperature-dependence of the hydrostatic pressure. Since the dynamic deformations are caused by flow fields which arise at lower orders of the capillary number, the leading-order dynamic deformations do not feed back to the leading-order thermocapillary flow. This conclusion holds for steady axisymmetric flows as well as for non-axisymmetric three-dimensional flows close to the critical onset of hydrothermal waves.
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stability of thermocapillary flows in non cylindrical Liquid Bridges
Journal of Fluid Mechanics, 2002Co-Authors: Ch Nienhuser, Hendrik C KuhlmannAbstract:The thermocapillary flow in Liquid Bridges is investigated numerically. In the limit of large mean surface tension the free-surface shape is independent of the flow and temperature fields and depends only on the volume of Liquid and the hydrostatic pressure difference. When gravity acts parallel to the axis of the Liquid bridge the shape is axisymmetric. A differential heating of the bounding circular disks then causes a steady two-dimensional thermocapillary flow which is calculated by a finite-difference method on body-fitted coordinates. The linear-stability problem for the basic flow is solved using azimuthal normal modes computed with the same discretization method. The dependence of the critical Reynolds number on the volume fraction, gravity level, Prandtl number, and aspect ratio is explained by analysing the energy budgets of the neutral modes. For small Prandtl numbers (Pr = 0.02) the critical Reynolds number exhibits a smooth minimum near volume fractions which approximately correspond to the volume of a cylindrical bridge. When the Prandtl number is large (Pr = 4) the intersection of two neutral curves results in a sharp peak of the critical Reynolds number. Since the instabilities for low and high Prandtl numbers are markedly different, the influence of gravity leads to a distinctly different behaviour. While the hydrostatic shape of the bridge is the most important effect of gravity on the critical point for low-Prandtl-number flows, buoyancy is the dominating factor for the stability of the flow in a gravity field when the Prandtl number is high.
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three dimensional numerical simulation of thermocapillary flows in cylindrical Liquid Bridges
Journal of Fluid Mechanics, 2000Co-Authors: J Leypoldt, Hendrik C Kuhlmann, H J RathAbstract:The dynamics of thermocapillary flows in differentially heated cylindrical Liquid Bridges is investigated numerically using a mixed finite volume/pseudo-spectral method to solve the Navier–Stokes equations in the Boussinesq approximation. For large Prandtl numbers (Pr = 4 and 7) and sufficiently high Reynolds numbers, the axisymmetric basic flow is unstable to three-dimensional hydrothermal waves. Finite-amplitude azimuthally standing waves are found to decay to travelling waves. Close to the critical Reynolds number, the former may persist for long times. Representative results are explained by computing the coefficients in the Ginzburg–Landau equations for the nonlinear evolution of these waves for a specific set of parameters. We investigate the nonlinear phenomena characteristic of standing and pure travelling waves, including azimuthal mean flow and time-dependent convective heat transport. For Pr [Lt ] 1 the first transition from the two-dimensional basic flow to the three-dimensional stationary flow is inertial in nature. Particular attention is paid to the secondary transition leading to oscillatory three-dimensional flow, and this mechanism is likewise independent of Pr. The spatial and temporal structure of the perturbation flow is analysed in detail and an instability mechanism is proposed based on energy balance calculations and the vorticity distribution.
S Yoda - One of the best experts on this subject based on the ideXlab platform.
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effect of heating orientation on oscillatory thermocapillary flow in Liquid Bridges
International Communications in Heat and Mass Transfer, 2008Co-Authors: L Wang, Y Kamotani, S YodaAbstract:Oscillatory thermocapillary flow in Liquid Bridges of high Prandtl number fluids is investigated experimentally as well as numerically. Heat loss from the free surface is shown to have significant influence on the onset of oscillations. In the present work the surrounding air flow pattern is changed by heating the Liquid bridge from the top or from the bottom. The results show that the local free surface heat transfer rate, especially near the hot wall, has strong effects on the oscillations.
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oscillatory thermocapillary flow in Liquid Bridges of high prandtl number fluid with free surface heat gain
International Journal of Heat and Mass Transfer, 2007Co-Authors: Aihua Wang, Yasuhiro Kamotani, S YodaAbstract:Abstract Oscillatory thermocapillary flow in Liquid Bridges of high Prandtl number fluid is studied. The effect of free surface heat transfer, especially heat gain, on the oscillation phenomenon is investigated experimentally and numerically. It is shown that the critical temperature difference (ΔTcr) changes substantially when the free surface heat transfer changes from loss to gain in the case of nearly straight Liquid Bridges. In contrast, ΔTcr is not affected by the free surface heat transfer with concave Liquid Bridges. The free surface heat transfer rate is computed numerically by simulating the interaction of the Liquid and the surrounding air. The oscillatory flow is also investigated numerically by analyzing the Liquid flow in three-dimensions for straight Bridges. The computed results agree well with the experimental data. The simulation shows that the free surface heat gain enhances the surface flow and that the oscillatory flow is a result of interactions between the convection effect and buoyancy. The flow does not become oscillatory if there is no net heat gain at the free surface in the range of Marangoni number of the present work (⩽1.8 × 104), so the present cause of oscillations is different from that in the free surface heat loss case we investigated in the past.
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onset of oscillatory thermocapillary convection in acetone Liquid Bridges the effect of evaporation
International Journal of Heat and Mass Transfer, 2006Co-Authors: S Simicstefani, M Kawaji, S YodaAbstract:Experiments have been carried out for half-zones of acetone (Pr = 4.3) to investigate the effects of evaporative cooling on the flow structures and temperature fields during transition from steady to oscillatory convection. The unstable flow phenomena have been measured using a variety of diagnostic techniques to determine the effects of evaporative cooling on Marangoni convection in Liquid Bridges of intermediate Prandtl number. The results show that Marangoni convection in acetone Liquid Bridges with and without strong evaporation becomes unstable due to the same mechanism but the evaporation has a strong stabilizing effect on the onset of oscillatory Marangoni convection.
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free surface heat loss effect on oscillatory thermocapillary flow in Liquid Bridges of high prandtl number fluids
International Journal of Heat and Mass Transfer, 2003Co-Authors: Yasuhiro Kamotani, L Wang, Aihua Wang, S Hatta, S YodaAbstract:Abstract The effect of free surface heat loss on oscillatory thermocapillary flow is investigated in Liquid Bridges of high Prandtl number fluids. It is shown experimentally that the critical temperature difference changes by a factor of two to three by changing the air temperature relative to the cold wall temperature. In order to understand the nature and extent of the interaction between the Liquid flow and the surrounding air, the heat transfer from the Liquid free surface is investigated numerically for the conditions of the present experimental work. The airflow analysis shows that even when the heat loss is relatively weak (the Biot number is unity or smaller), the critical temperature difference is affected appreciably. It is shown that the heat loss effect is significant in widely conducted tests near room temperature and that the critical temperature difference is much larger than the room temperature value when the heat loss is minimized. The analysis suggests that an interaction between the surface heat loss and dynamic free surface deformation near the hot wall is responsible for the observed heat loss effect.
Yasuhiro Kamotani - One of the best experts on this subject based on the ideXlab platform.
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Report on Microgravity Experiments of Dynamic Surface Deformation Effects on Marangoni Instability in High-Prandtl-Number Liquid Bridges
Microgravity Science and Technology, 2018Co-Authors: Taishi Yano, Koichi Nishino, Satoshi Matsumoto, Ichiro Ueno, Atsuki Komiya, Yasuhiro Kamotani, Nobuyuki ImaishiAbstract:This paper reports an overview and some important results of microgravity experiments called Dynamic Surf , which have been conducted on board the International Space Station from 2013 to 2016. The present project mainly focuses on the relations between the Marangoni instability in a high-Prandtl-number ( Pr = 67 and 112) Liquid bridge and the dynamic free surface deformation (DSD) as well as the interfacial heat transfer. The dynamic free surface deformations of large-scale Liquid Bridges (say, for diameters greater than 10 mm) are measured with good accuracy by an optical imaging technique. It is found that there are two causes of the dynamic free surface deformation in the present study: the first is the time-dependent flow behavior inside the Liquid bridge due to the Marangoni instability, and the second is the external disturbance due to the residual acceleration of gravity, i.e., g-jitter. The axial distributions of DSD along the free surface are measured for several conditions. The critical parameters for the onset of oscillatory Marangoni convection are also measured for various aspect ratios (i.e., relative height to the diameter) of the Liquid bridge and various thermal boundary conditions. The characteristics of DSD and the onset conditions of instability are discussed in this paper.
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sensitivity of hydrothermal wave instability of marangoni convection to the interfacial heat transfer in long Liquid Bridges of high prandtl number fluids
Physics of Fluids, 2017Co-Authors: Taishi Yano, Koichi Nishino, Satoshi Matsumoto, Ichiro Ueno, Yasuhiro KamotaniAbstract:This paper reports the sensitivity of hydrothermal wave (HTW) instability of Marangoni convection to the interfacial heat transfer in Liquid Bridges (LBs) of high Prandtl number fluids (Pr = 67, 112, and 207) formed under the microgravity environment on the International Space Station. The data for instability are collected for a wide range of AR and for TC = 15 and 20 °C, where AR is the aspect ratio (=height/diameter) of the LB and TC is the cooled disk temperature. A significant decrease in critical oscillation frequency as well as an appreciable decrease in the critical Marangoni number is observed for AR > 1.25. This drastic change of instability mechanisms is associated with the reversal of axial traveling direction of HTWs and roll-structures as reported previously. It is found that this reversal is closely related to the interfacial heat transfer, which is evaluated numerically through accounting for both convective and radiative components. A heat transfer ratio, QI/QH, is introduced as a dimensi...
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oscillatory thermocapillary flow in Liquid Bridges of high prandtl number fluid with free surface heat gain
International Journal of Heat and Mass Transfer, 2007Co-Authors: Aihua Wang, Yasuhiro Kamotani, S YodaAbstract:Abstract Oscillatory thermocapillary flow in Liquid Bridges of high Prandtl number fluid is studied. The effect of free surface heat transfer, especially heat gain, on the oscillation phenomenon is investigated experimentally and numerically. It is shown that the critical temperature difference (ΔTcr) changes substantially when the free surface heat transfer changes from loss to gain in the case of nearly straight Liquid Bridges. In contrast, ΔTcr is not affected by the free surface heat transfer with concave Liquid Bridges. The free surface heat transfer rate is computed numerically by simulating the interaction of the Liquid and the surrounding air. The oscillatory flow is also investigated numerically by analyzing the Liquid flow in three-dimensions for straight Bridges. The computed results agree well with the experimental data. The simulation shows that the free surface heat gain enhances the surface flow and that the oscillatory flow is a result of interactions between the convection effect and buoyancy. The flow does not become oscillatory if there is no net heat gain at the free surface in the range of Marangoni number of the present work (⩽1.8 × 104), so the present cause of oscillations is different from that in the free surface heat loss case we investigated in the past.
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free surface heat loss effect on oscillatory thermocapillary flow in Liquid Bridges of high prandtl number fluids
International Journal of Heat and Mass Transfer, 2003Co-Authors: Yasuhiro Kamotani, L Wang, Aihua Wang, S Hatta, S YodaAbstract:Abstract The effect of free surface heat loss on oscillatory thermocapillary flow is investigated in Liquid Bridges of high Prandtl number fluids. It is shown experimentally that the critical temperature difference changes by a factor of two to three by changing the air temperature relative to the cold wall temperature. In order to understand the nature and extent of the interaction between the Liquid flow and the surrounding air, the heat transfer from the Liquid free surface is investigated numerically for the conditions of the present experimental work. The airflow analysis shows that even when the heat loss is relatively weak (the Biot number is unity or smaller), the critical temperature difference is affected appreciably. It is shown that the heat loss effect is significant in widely conducted tests near room temperature and that the critical temperature difference is much larger than the room temperature value when the heat loss is minimized. The analysis suggests that an interaction between the surface heat loss and dynamic free surface deformation near the hot wall is responsible for the observed heat loss effect.
Satish Kumar - One of the best experts on this subject based on the ideXlab platform.
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the dynamics of three dimensional Liquid Bridges with pinned and moving contact lines
Journal of Fluid Mechanics, 2012Co-Authors: Shawn Dodds, Marcio S Carvalho, Satish KumarAbstract:Liquid Bridges with moving contact lines are relevant in a variety of natural and industrial settings, ranging from printing processes to the feeding of birds. While it is often assumed that the Liquid bridge is two-dimensional in nature, there are many applications where either the stretching motion or the presence of a feature on a bounding surface lead to three-dimensional effects. To investigate this we solve Stokes equations using the finite-element method for the stretching of a three-dimensional Liquid bridge between two flat surfaces, one stationary and one moving. We first consider an initially cylindrical Liquid bridge that is stretched using either a combination of extension and shear or extension and rotation, while keeping the contact lines pinned in place. We find that whereas a shearing motion does not alter the distribution of Liquid between the two plates, rotation leads to an increase in the amount of Liquid resting on the stationary plate as breakup is approached. This suggests that a relative rotation of one surface can be used to improve Liquid transfer to the other surface. We then consider the extension of non-cylindrical Bridges with moving contact lines. We find that dynamic wetting, characterized through a contact line friction parameter, plays a key role in preventing the contact line from deviating significantly from its original shape as breakup is approached. By adjusting the friction on both plates it is possible to drastically improve the amount of Liquid transferred to one surface while maintaining the fidelity of the Liquid pattern.
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stretching Liquid Bridges with moving contact lines the role of inertia
Physics of Fluids, 2011Co-Authors: Shawn Dodds, Marcio S Carvalho, Satish KumarAbstract:Liquid Bridges with moving contact lines are found in a variety of settings such as capillary feeders and high-speed printing. Although it is often assumed that the length scale for these flows is small enough that inertial effects can be neglected, this is not the case in certain applications. To address this issue, we solve the Navier-Stokes equations with the finite element method for the stretching of a Liquid drop between two surfaces for non-zero Reynolds numbers. We consider an axisymmetric Liquid bridge between a moving flat plate and either a stationary flat plate or a cavity. The contact lines are allowed to slip, and we evaluate the effect of the Reynolds number and contact angles on the transfer of Liquid to the moving plate. In the case of two flat plates, we find that inertia forces the interface to map onto a similarity solution in a manner that shifts the breakup point toward the more wettable surface. Inertia and wettability are thus competing effects, with inertia driving fluid toward th...
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stretching Liquid Bridges with bubbles the effect of air bubbles on Liquid transfer
Langmuir, 2011Co-Authors: Shawn Dodds, Marcio S Carvalho, Satish KumarAbstract:Liquid Bridges containing bubbles are relevant to industrial printing and are also a topic of fundamental scientific interest. We use flow visualization to study the stretching of Liquid Bridges, both with and without bubbles, at low capillary numbers. We find that whereas the breakup of wetting fluids between two identical surfaces is symmetric about the bridge midpoint, contact line pinning breaks this symmetry at slow stretching speeds for nonwetting fluids. We exploit this observation to force air bubbles selectively toward the least hydrophilic plate confining the Liquid bridge.
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stretching and slipping of Liquid Bridges near plates and cavities
Physics of Fluids, 2009Co-Authors: Shawn Dodds, Marcio S Carvalho, Satish KumarAbstract:The dynamics of Liquid Bridges are relevant to a wide variety of applications including high-speed printing, extensional rheometry, and floating-zone crystallization. Although many studies assume that the contact lines of a bridge are pinned, this is not the case for printing processes such as gravure, lithography, and microcontacting. To address this issue, we use the Galerkin/finite element method to study the stretching of a finite volume of Newtonian Liquid confined between two flat plates, one of which is stationary and the other moving. The steady Stokes equations are solved, with time dependence entering the problem through the kinematic boundary condition. The contact lines are allowed to slip, and we evaluate the effect of the capillary number and contact angle on the amount of Liquid transferred to the moving plate. At fixed capillary number, Liquid transfer to the moving plate is found to increase as the contact angle on the stationary plate increases relative to that on the moving plate. When the contact angle is fixed and the capillary number is increased, the Liquid transfer improves if the stationary plate is wetting, but worsens if it is nonwetting. The presence of a cavity on the stationary plate significantly affects the contact line motion, often causing pinning along the cavity wall. In these cases, Liquid transfer is controlled primarily by the cavity shape, suggesting that the effects of surface topography dominate over those of surface wettability. At low capillary numbers, bridge breakup can be understood in terms of the Rayleigh–Plateau stability limit, regardless of the combination of contact angles or the plate geometry. At higher capillary numbers, the bridge is able to stretch beyond this limit although the deviation from this limit appears to depend on contact line pinning, and not directly on the combination of contact angles or the plate geometry.
