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 E3: Multiphase Flows: Boiling |
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Chair: Peter Taborek, University of California Irvine Room: 23B |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E3.00001: Lattice Boltzmann Simulation of Thermal Multiphase Flows with Dynamic Wall Interactions Michael Ikeda, Laura Schaefer As energy densities in electronic devices rapidly increase, improved two-phase microchannel heat exchanger designs are of great interest. However, a better understanding of flow boiling in these regimes is required. The lattice Boltzmann method (LBM) has shown great promise in the simulation of multiphase flows due to its ability to easily capture interfacial dynamics. Although there have been many recent developments to the standard thermal, multiphase LBM, wall interactions are typically oversimplified. These simplifications lead to interactions which are only appropriate for isothermal, static simulations. In this work, we extend wall interactions based on the pseudopotential multiphase approach to include the variable wetting behavior that occurs with changing temperatures. This will enable the future modeling of the flow boiling process with temperature-dependent wetting characteristics. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E3.00002: Computations of Nucleate Boiling Gretar Tryggvason, Jiacai Lu Simulations of boiling flows have progressed significantly in the last decade and it is now possible to accurately compute the film boiling of fluids under a wide range of conditions, for example. Although some progress has been made in simulating nucleate boiling, considerable challenges remain, particularly for water under atmospheric pressure. The challenges include the resolution of thin film between a growing vapor bubble and the hot wall, steep thermal gradient at the phase boundary, and the determination of the distribution and activation of nucleation sites. We report on recent progress using a front tracking method to follow the phase boundary, coupled with a multiscale strategy to capture the microlayer and resolve steep thermal gradients. The results including comparison with experimental results and simulations of bubbles released from multiple nucleation sites for both pool and flow boiling. Preliminary results indicate that for moderate nucleation site density the bubbles are formed relatively independently of each other. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E3.00003: Transient two-phase flow in microfluidics and nanofluidics Angel Velasco, Andrew Song, Serah Friedman, Matthew Pevarnik, Zuzanna Siwy, Peter Taborek We have studied the flow of a high pressure liquid (nitrogen and water) into vacuum through large aspect ratio pipes with diameters ranging from 25 microns to 50 nanometers. The decreasing pressure in the pipe induces boiling when the saturated vapor pressure is reached, creating a two-phase liquid/vapor flow. A novel method of measuring extremely small flow rates based on mass spectrometry will be presented. The validity of the method was verified using measurements of the flow of helium and argon through standard micron scale capillary tubes; subsequent measurements used single ion track pores which were 12 microns long with diameters in the range of 800-50 nm. A systematic study with nitrogen at 77 K was done with inlet pressures above and below the saturated vapor pressure. When the applied pressure is below the saturated vapor pressure the single phase flow was observed to obey the compressible Navier-Stokes equation. At pressures greater than the saturated vapor pressure, a stable flow was observed in pipes with diameters greater than 5 microns. For diameters below 2 microns significant fluctuations in the flow rate are observed at applied pressures up to 35 Atm, suggesting the onset of two-phase flow. [Preview Abstract] |
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