Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HK: Multiphase Flows IV |
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Chair: Joe Oefelein, Sandia National Laboratories Room: 101J |
Monday, November 23, 2009 10:30AM - 10:43AM |
HK.00001: ABSTRACT WITHDRAWN |
Monday, November 23, 2009 10:43AM - 10:56AM |
HK.00002: Molecular Gas Dynamics on Evaporation and Condensation Induced by Nonlinear Gas Oscillation Masashi Inaba, Takeru Yano, Masao Watanabe, Shigeo Fujikawa The resonant gas oscillation excited in a finite one-dimensional space between an oscillating plate (sound source) and a vapor-liquid interface is studied. In particular, we focus on the case where the vapor is a polyatomic gas, e.g. water vapor, the liquid is its own condensed phase and no other species of molecules are existent in the space. The behavior of the gas accompanied with the evaporation and condensation at the interface is analyzed by applying the asymptotic theory for Kn $\ll $ M $\ll $ 1 to the polyatomic version of Gaussian-BGK Boltzmann equation, where Kn is the Knudsen number defined by the ratio of the mean free path of gas molecules and M is the Mach number defined by the ratio of the maximum speed of oscillating plate to the sound speed. The result shows that the gas region consists of the three regions of that governed by wave equation, the thermal boundary layer and the Knudsen layer. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HK.00003: One-Dimensional Steady Solutions and Correlations of Internal Condensing Flows in Channels/Tubes and their Comparisons with Experiments Soumya Mitra, Amitabh Narain, Shantanu Kulkarni Quasi-1 D steady simulation for internal condensing flows that employs solutions of singular non-linear ordinary differential equations is presented along with the governing equations and computational approach. The computational simulation results presented are for internal condensing flows in channel and tube geometry. The quasi-1 D steady simulation results are compared to the experimental results as well as full 2-dimensional CFD based results. These results are shown to be self-consistent and in agreement with one another. The paper further reports some reliable and useful correlations for internal condensing flows (covering most refrigerants of common interest) for the gravity driven case. The quasi-1 D steady simulation results are available from micrometer to larger scale condensers and in various gravity environments. For the micro-meter scale condensers, a critical diameter condition is identified, below which the flows are insensitive to the orientation of the gravity vector as the condensate is always shear driven. The paper discusses transition from gravity dominated flow to shear dominated flows. Paper outlines the difference between transverse gravity and zero gravity flow in a channel. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HK.00004: An Introduction to mm Scale Low Kinematic Viscosity Horizontal Channel Flow Morphology in Condensation and Pool Condensation in the Presence of Vapor Flow Michael Kivisalu, Amitabh Narain, Jorge Kurita Preliminary experimental flow regime types have been observed for partial and full condensation in a horizontal channel of millimeter scale. Effects of hydrostatic pooling, wall vibrations, vapor flow pulsations, and solid-liquid-vapor contact on the top surface of the condenser are observed. Wave phenomena such as wave reflection, standing waves, and waves on the interface of vapor bubbles are presented in 2 and 3 dimensions. Due to the high density and low kinematic viscosity of the liquid phase of the fluid (perfluorohexane), the effects observed are primarily inertial. It is found that in these flows pressure pulsation and surface tension effects very strongly influence the morphology of the interface where it contacts the top wall. Wall vibrations contribute to standing waves on the interface. This investigation outlines some of the types of flow one might expect to encounter in a millimeter scale horizontal condenser with wall vibration and pressure pulsation where inertial effects dominate the liquid flow. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HK.00005: Experimental study on condensation heat transfer inside a single vertical tube Jorge Kurita, Amitabh Narain, Michael Kivisalu In this paper, results from a new computational model for condensation inside vertical cylindrical tubes have been compared to test data for FC-72 obtained in an actively controlled flow loop. This correlation was developed taking in account thermo physical properties of the 9 most common refrigerants. The present paper reports heat transfer coefficient, length of full condensation, vapor quality and direct measurement of the saturation and wall temperatures during condensation within a single cylindrical tube of 6.6 mm diameter and 700 mm length. The new model has been tested over the following range of experimental conditions: mass flux from 2.9 to 87.7 kg/(m2s), vapor qualities from 0.33 to 0.64 and full condensation. The saturation minus wall temperature difference was varied from 5 to 45 C. This model predicts heat transfer coefficients to within 15 percent accuracy over 70 percent of data points and predicts within 30 percent accuracy over 87 percent of data points in full and partial condensation cases respectively. [Preview Abstract] |
Monday, November 23, 2009 11:35AM - 11:48AM |
HK.00006: Condensing Flows in High Aspect Ratio Channel Geometries Catherine Koveal, Matthew McCarthy, Evelyn N. Wang We investigate condensing flow regimes in high aspect ratio rectangular geometries, where the width to height ratio ranges from 20-to-1 to 65-to-1. These geometries are designed for condenser layers of a novel capillary-pumped loop heat pipe design in a high performance heat sink. In this work, we study the effect of geometry, vapor mass flow rate, and surface design on condensing flow regimes and heat removal capability. We fabricated an experimental test rig which allows for optical access from the top, temperature measurements on the condensing surface, and controlled cooling from the bottom. In addition, the rig was placed on a tilt stage to examine the effect of a gravitational head on condensation. The experimental results show that the flow regimes are largely dictated by the dominant force, i.e., gravity, surface tension, or inertia. In addition, as the backside cooling temperature increased, the condensing length increased. Current work is focused on incorporating surface features to enhance heat transfer coefficients and to eliminate unstable condensation regimes. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HK.00007: Collisions in a liquid fluidized bed Alicia Aguilar-Corona, Roberto Zenit, Olivier Masbernat Collisional phenomena in a liquid fluidized bed were studied in terms of two parameters: the collision frequency and the coefficient of restitution. Experimental measurements of these parameters were conducted by particle tracking in an index-matched array. Collision detection was based on the use of a peak acceleration threshold of the instantaneous speed of dark tracers. The measurements of collision frequency were compared with the theoretical expression derived from the kinetic theory for granular flow (KTGF). The normal and tangential restitution coefficients were measured from the trajectories before and after contact for both particle-particle and particle-wall collisions. A comparison with previous theoretical and experimental works is presented and discussed. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HK.00008: Multi-dimensional Shock Fluidization of Particle Assemblies Svetlana Sushchikh, Vladimir Mitkin, Chih-Hao Chang, Theo Theofanous We present new kinds of experiments that resolve the transient dynamics of shock-fluidized particle (glass, lead) assemblies in 1D and 2D geometries, covering both subsonic and supersonic after-shock flows (shock Mach numbers 1.5 to 2.5). From high speed video records time-wise evolutions of particle number densities could be recovered, as on this basis complete clouds (with spatially-distributed particle number densities) could be reconstructed at various positions along the flow channel, up to 1.3 m away from the point of initial interaction. We also discuss numerical simulations, based on a two-fluid model made consistently hyperbolic over the complete range of Mach numbers, thus allowing the grid-refinements needed to capture sharp density gradients at such intense flow conditions. These simulations are a priory in that the only constitutive law is for the drag coefficient; it is obtained from single- particle tests and direct numerical simulations, augmented with standard approaches to account for particle proximity effects. These simulations are in excellent agreement with the experiments, and so are shown to be sample, initial results of overall cloud dynamics in explosive dissemination of bulk liquids (10's of kilogram quantities, km/s speeds). [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HK.00009: Crack propagation speed in quasi two-dimensional dry foam Shehla Arif, Sascha Hilgenfeldt Quasi two-dimensional dry foam in a Hele-Shaw cell is used as a model system to study crack propagation, with the mm-sized bubbles playing the role of discrete atoms or molecules in a lattice. Pressurized air induces finger-like ductile failure (at low rate of applied stress) or brittle cleavage with breakage of successive films (at high rate of applied stress). We find that the upper limit speed of ductile cracks is lower than the lower limit speed of brittle failure (a velocity gap exists). To understand both processes requires balancing viscous and surface tension forces in the Plateau borders of the foam bubbles. Time scales can then be derived for the lateral gliding of bubbles past each other (necessary for ductile failure) and the stretching and rupture of films (necessary for brittle failure). We compare the derived brittle-crack speeds with the experimentally observed values of several m/s, resolved by high-speed photography. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HK.00010: Direct Current Electrorheological Stability Determination of Water-in-Crude Oil Emulsions Vladimir Alvarado, Xiuyu Wang Emulsion stability is a fundamental determination for separation technologies. We use the critical electric field (CEF) and viscosity changes in DC eletrorheological (ER) experiments in dynamic mode to determine the stability of water-in-crude oil emulsions, previously studied through bottle tests. The CEF value corresponds to the value of electric field at which the current reaches 95{\%} or larger of the plateau value. The results show that CEF can be consistently obtained through current measurements, resulting from emulsion structure breakdown. Viscosity changes are not good proxies of stability unless a robust emulsion structure is found. Emulsion structure breakdown is explored through rheological characterization before and after voltage sweeps have been performed. When the electric field applied is below the CEF value, the storage and loss moduli responses as well as viscosity as functions of frequency are recovered. However, when the electric field is greater than the CEF value, the emulsion structure breaks down irreversibly. [Preview Abstract] |
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