Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E31: Focus Session: Interfacial Engineering in Thermal-Fluids II |
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Chair: Kripa Varanasi, Massachusetts Institute of Technology Room: 33B |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E31.00001: Condensation enhancement using Liquid Impregnated Surfaces Sushant Anand, Adam Paxson, Rajeev Dhiman, J. David Smith, Kripa Varanasi Controlling the surface morphology of a low surface energy solid surface by imparting nano/micro-textures leads to water droplets existing in a Cassie-Baxter state characterized by minimal pinning of droplets, resulting in extremely low adhesion and low roll-off angles. These benefits are diminished during condensation as droplets form in the Wenzel state, causing high adhesion and extremely low shedding rates. Here we show that condensing on a hybrid surface comprised of a rough solid surface and an encapsulating liquid immiscible to water results in shedding of droplets much smaller than capillary length of water. It is shown that such hybrid surfaces have high nucleation capability usually associated with hydrophilic surfaces. The spreading coefficient of encapsulating liquid on water plays a crucial role during the condensation process. The surface morphology of the solid fraction of the hybrid surface needs to be adapted to stabilize encapsulating liquid on its surface and reduce contact between the solid surface and condensing droplets. This can be achieved by imparting nano/micro-textures on the surface. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E31.00002: Novel microfluidic diodes: one-way wicking in open micro-channels controlled by channel topography Jiansheng Feng, Jonathan Rothstein A series of open microfluidic channels with specially designed asymmetric internal structures were fabricated using standard photo-lithography and soft molding techniques. These micro-channels were shown to produce an asymmetric wicking behavior for a series of IPA-water mixtures. In some cases, the test liquids were found to completely wick in one direction while not wicking at all in the opposite direction. The wicking speed and degree of asymmetry was affected by the contact angle of the wicking fluid and the specific geometry of the angled fin-like structures added to the sides of the micro-channels. Surface-tension effects induced by the presence of the channels' internal structures were found to be the dominating physical mechanism responsible for the observed wicking behavior. Numerical simulations were performed to investigate the interface profile developed by the liquid front as it wicked through the channels. These simulations showed that three-dimensional effects were important in determining the extent and speed of wicking in these micro-channels. The findings of this study are expected to provide a better understanding of how fluids interact with micro-scaled structures and to offer a new way of manipulating fluids at the micron and nanometer scale. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E31.00003: Leidenfrost Vapor Layer Stabilization on Superhydrophobic Surfaces Ivan Vakarelski, Neelesh Patankar, Jeremy Marston, Derek Chan, Sigurdur Thoroddsen We have performed experiments to investigate the influence of the wettability of a superheated metallic sphere on the stability of a thin vapor layer during the cooling of a sphere immersed in water. For high enough sphere temperatures, a continuous vapor layer (Leidenfrost regime) is observed on the surface of non-superhydrophobic spheres, but below a critical sphere temperature the layer becomes unstable and explosively switches to nuclear boiling regime. In contrast, when the sphere surface is textured and superhydrophobic, the vapor layer is stable and gradually relaxes to the sphere surface until the complete cooling of the sphere, thus avoiding the nuclear boiling transition altogether. This finding could help in the development of heat exchange devices and of vapor layer based drag reducing technologies. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E31.00004: Viscoelasticity measurement of gel formed at the liquid-liquid reactive interfaces Tomohiro Ujiie, Yutaka Tada, Shuichi Iwata, Yoshihito Kato, Yuichiro Nagatsu We have experimentally studied a reacting liquid flow with gel formation by using viscous fingering (VF) as a flow field. Here, two systems were employed. In one system, sodium polyacrylate (SPA) solution and ferric ion solution were used as the more and less viscous liquids, respectively. In another system, xthantan gum (XG) solution and the ferric ion solution were used as the more and less viscous liquids, respectively. We showed that influence of gel formation on VF were qualitatively different in these two systems. We consider that the difference in the two systems will be caused by the difference in the properties of the gels. Therefore, we have measured the rheological properties of the gels by means of a rheometer. In the present study, viscoelasticity measurement was performed by two methods. One is the method which uses Double Wall Ring sensor (TA instrument) and another is the method using parallel plate. In both viscoelasticity measurements, the behavior of the formed gel was qualitatively consistent. We have found that the gel in the SPA system shows viscoelastic fluid like behavior. Moreover, we have found that the gel in the XG system shows solid like behavior. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E31.00005: Seeing Below the Drop: Direct Nano-to-microscale Imaging of Complex Interfaces involving Solid, Liquid, and Gas Phases Konrad Rykaczewski, Trevan Landin, Marlon L. Walker, John Henry J. Scott, Kripa K. Varanasi Nanostructured surfaces with special wetting properties have the potential to transform number of industries, including power generation, water desalination, gas and oil production, and microelectronics thermal management. Predicting the wetting properties of these surfaces requires detailed knowledge of the geometry and the composition of the contact volume linking the droplet to the underlying substrate. Surprisingly, a general nano-to-microscale method for direct imaging of such interfaces has previously not been developed. Here we introduce a three dimensional imaging method which resolves this one-hundred-year-old metrology gap in wetting research. Specifically, we demonstrate direct nano-to-microscale imaging of complex fluidic interfaces using cryofixation in combination with cryo-FIB/SEM. We show that application of this method yields previously unattainable quantitative information about the interfacial geometry of water condensed on silicon nanowire forests with hydrophilic and hydrophobic surface termination in the presence or absence of an intermediate water repelling oil. We also discuss imaging artifacts and the advantages of secondary and backscatter electron imaging, Energy Dispersive Spectrometry (EDS), and three dimensional FIB/SEM tomography. [Preview Abstract] |
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