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 M25: Multiphase and Electrokinetic FlowsElectro Multiphase
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Chair: Guodong Jin, LNM, Institute of Mechanics, Chinese Academy of Sciences Room: 705 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M25.00001: The Self-Similarity of the Near-Field Liquid Region from an Airblast Atomizer Julie Bothell, Danyu Li, Timothy Morgan, Alberto Aliseda, Nathanael Machicoane, Alan Kastengren, Theodore Heindel The atomization process in liquid gas coaxial injectors has been the subject of intense investigation that has identified multiple break-up regimes for the liquid jet and the dominant instabilities that determine the final liquid droplet size distribution. There are, however, many unknowns in the basic physics and practical applications of this atomizer configuration including the liquid gas interface dynamics in the presence of swirl as well as injection rate fluctuations. This study uses advanced X-ray imaging to characterize the complex, two-phase system in the near-field region of a canonical coaxial airblast atomizer. The Advanced Photon Source at Argonne National Laboratory was used to collect time resolved measurements of the liquid volume fraction in the flow. The resulting data, containing quantitative information about the interface dynamics and phenomena controlling droplet break-up, was analyzed to improve the understanding of the natural mechanisms that drive the atomization process. In the analysis, self-similarity models are used to relate the upstream liquid flow structures to the downstream atomization at various flow conditions. These self-similarity models show great potential in characterizing complex liquid flow in the near-field region of the atomizer. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M25.00002: Broadband X-ray Imaging in the Near-Field Region of an Airblast Atomizer Danyu Li, Julie Bothell, Timothy Morgan, Theodore Heindel The atomization process has a close connection to the efficiency of many spray applications. Examples include improved fuel atomization increasing the combustion efficiency of aircraft engines, or controlled droplet size and spray angle enhancing the quality and speed of the painting process. Therefore, it is vital to understand the physics of the atomization process, but the near-field region is typically optically dense and difficult to probe with laser-based or intrusive measurement techniques. In this project, broadband X-ray radiography and X-ray computed tomography (CT) imaging were performed in the near-field region of a canonical coaxial airblast atomizer. The X-ray absorption rate was enhanced by adding 20\% by weight of Potassium Iodide to the liquid phase to increase image contrast. The radiographs provided an estimate of the liquid effective mean path length and spray angle at the nozzle exit for different flow conditions. The reconstructed CT images provided a 3D map of the time-average liquid spray distribution. X-ray imaging was used to quantify the changes in the near-field spray characteristics for various coaxial airblast atomizer flow conditions. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M25.00003: Instantaneous Optical Wall-Temperature of Vertical Two-Phase Annular Flow Brian Fehring, Simon Livingston-Jha, Roman Morse, Jason Chan, James Doherty, Colby Brueggeman, Gregory Nellis, Kristofer Dressler, Arganthaƫl Berson We present a non-invasive optical technique for measuring the instantaneous temperature at the inner wall of a flow duct. The technique is used to characterize a fully-developed vertical annular flow of R245fa refrigerant. The test section includes transparent heating windows made of glass coated with fluorine-doped tin-oxide. A 15 mW helium-neon laser is directed through a prism mounted on one of the glass windows and reflected off of the interface between the 150-micron-thick liquid film and the inside wall of the testing section window. The intensity of the laser light reflected at the liquid film-window interface depends on the index of refraction of liquid R245fa, which itself depends on the temperature of the fluid. The intensity of the reflected light is measured using a photodiode and calibrated to a light reflectance model based on the Fresnel equations and Snell's law. Instantaneous temperature data is combined with optical liquid film thickness measurements to calculate the local instantaneous heat transfer coefficient at the wall. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M25.00004: Experimental Determination of Heat Transfer Coefficient in Two-phase Annular Flow Kristofer Dressler, Brian Fehring, Roman Morse, Simon Livingston-Jha, James Doherty, Jason Chan, Colby Brueggeman, Arganthael Berson The goal of the presented work is to validate published mechanistic heat transfer models in two-phase annular flow under transient conditions. Annular flow occurs in many steam generation and refrigeration systems. Knowledge of the heat transfer coefficient (HTC) between the wall and the thin liquid film is critical to the design and safe operation of these systems. In heat exchangers with multiple parallel channels, thermal hydraulic instabilities often lead to unsteady flow conditions. The current study is performed in a facility capable of producing pulsed two-phase, single-species annular flow in a heated test section while simultaneously measuring local film thickness and wall temperature using non-intrusive optical techniques. Available correlations between the HTC and wall shear at steady state are compared to our measurements. The HTC can be derived from the known heating power and measured wall temperature, while wall shear is deduced from film thickness measurements. The validity of steady-state correlations under oscillating flow conditions is assessed by performing tests at a variety of pulse frequencies and amplitudes. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M25.00005: Oil-Water Flow Investigations using Planar-Laser Induced Fluorescence and Particle Velocimetry Roberto Ibarra, Omar K. Matar, Christos N. Markides The study of the complex behaviour of immiscible liquid-liquid flow in pipes requires the implementation of advanced measurement techniques in order to extract detailed in situ information. Laser-based diagnostic techniques allow the extraction of high-resolution space- and time resolve phase and velocity information, which aims to improve the fundamental understanding of these flows and to validate closure relations for advanced multiphase flow models. This work shows a novel simultaneous planar-laser induced fluorescence and particle velocimetry in stratified oil-water flows using two laser light sheets at two different wavelengths for fluids with different refractive indices at horizontal and upward pipe inclinations (\textless 5$^{\circ}$) in stratified flow conditions (i.e. separated layers). Complex flow structures are extracted from 2-D instantaneous velocity fields, which are strongly dependent on the pipe inclination at low velocities. The analysis of mean wall-normal velocity profiles and velocity fluctuations suggests the presence of single- and counter-rotating vortices in the azimuthal direction, especially in the oil layer, which can be attributed to the influence of the interfacial waves. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M25.00006: Considerations and Optimization of Time-Resolved PIV Measurements near Complex Wind-Generated Air-Water Wave Interface Matthew Stegmeir, Corey Markfort Time Resolved PIV measurements are applied on both sides of air-water interface in order to study the coupling between air and fluid motion. The multi-scale and 3-dimensional nature of the wave structure poses several unique considerations to generate optimal-quality data very near the fluid interface. High resolution and dynamic range in space and time are required to resolve relevant flow scales along a complex and ever-changing interface. Characterizing the two-way coupling across the air-water interface provide unique challenges for optical measurement techniques. Approaches to obtain near-boundary measurement on both sides of interface are discussed, including optimal flow seeding procedures, illumination, data analysis, and interface tracking. Techniques are applied to the IIHR Boundary-Layer Wind-Wave Tunnel and example results presented for both sides of the interface. The facility combines a 30m long recirculating water channel with an open-return boundary layer wind tunnel, allowing for the study of boundary layer turbulence interacting with a wind-driven wave field. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M25.00007: Phase Detection aided Thermometry for Two-Phase Flow Mao Takeyama, Tomoaki Kunugi, Zensaku Kawara, Takehiko Yokomine Since temperature and void fraction (or phase fraction) are important parameters to characterize and grasp multiphase flow behaviors, various methods have been developed and applied to. However, these multi-phase flow parameters cannot be measured at the same time and position because they need the individual sensor. A new thermometry to detect the phase for two-phase flow and simultaneously measure the liquid/gas temperature with a miniature thermocouple with high temporal-spatial resolutions is developed; this method was named as a phase detection aided thermometry (PDaT). The principle of PDaT is that a miniature ($\varphi $25$\mu $m) thermocouple with 10 kHz of the sampling rate is used not only as a thermometer with the high temporal-spatial resolution, but also as an electrical conductance probe as a phase detector. The results of the proof of principle experiments will be presented. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M25.00008: Study of oscillating electroosmotic flows with high temporal and spatial resolution Guiren Wang, Xin Liu, Fang Yang, Kaige Wang, Jintao Bai, Rui Qiao, Wei Zhao In AC electrokinetic (EK) flow where solid-fluid interface exists, oscillating electroosmotic flow (OEOF) is an inevitable flow phenomenon. However, few experimental investigations have been reported on instantaneous velocity of OEOF driven by AC electric field. Here, we studied the near-wall velocity of OEOF by Laser-induced Fluorescence Photobleaching Anemometer (LIFPA). For the first time, an up to 3 kHz velocity response of OEOF had been successfully measured experimentally, even though the oscillating velocity was as low as 600 nm/s. It was found that the oscillating velocity decays with forcing frequency $f_{f}$, as $f_{f}^{-0.66}$. This had never been predicted by any known theoretical investigations. In the investigated range of electric field intensity ($E_{A})$, when $f_{f}$ is below 1 kHz, the linear relation between oscillating velocity and $E_{A}$ was observed. Besides, we also found the bulk flow velocity can significantly affect the oscillating velocity of OEOF. This was also newly observed and implied the bulk flow can affect the formation process of electric double layer. This investigation could be crucial for understanding all OEOF-related phenomena and designing OEOF-based micro/nanofluidics systems. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M25.00009: Cascade of kinetic energy and scalar variance in DC electrokinetic turbulence Wei Zhao, Guiren Wang Turbulent flow can be generated by DC electrokinetic (EK) force based on the electric conductivity and permittivity variations in fluids, as have been demonstrated by Varshney et al (2016), where a -1.4 slope of velocity power spectrum is observed. Here, we theoretically found the scaling exponents of velocity and scalar structures in the electric-body-force (EBF) dominant subregion of DC EK turbulence were 2/5 (equivalent to the -7/5 slope of velocity power spectrum) and 4/5 respectively. The theory perfectly explains the experimental results of Varshney et al. (2016). Based on K\'{a}rm\'{a}n-Howarth equation with forcing terms, the energy cascade process of DC EK turbulence was also investigated. Depending on the electric Rayleigh number (Ra$_{\mathrm{e}})$, two different energy cascade processes may happen. When Ra$_{\mathrm{e}}$ is small, the kinetic energy cascades along inertial subregion and EBF dominant subregion in sequence, before it is dissipated by fluid viscosity. When Ra$_{\mathrm{e}}$ is sufficiently large, the inertial subregion may be absent with EBF dominant subregion left. This investigation is very important on understand EK turbulence, which could be widely existed in nature and applied in engineerings. [Preview Abstract] |
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