Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E12: Multiphase Flows: Mixing |
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Chair: Cheng Li, Johns Hopkins University Room: C123 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E12.00001: Subsurface Droplet Size Distribution generated as breaking waves entrain an oil slick Cheng Li, Jesse Miller, Joseph Katz Breaking waves are a primary mechanism for entraining and dispersing oil spills. Knowledge of the resulting droplet size distribution is crucial for predicting the transport and fate of this oil. In this on-going experimental study, a controlled oil slick of varying viscosity ($\mu_{d})$, density ($\rho_{d})_{,\thinspace }$interfacial tension ($\sigma )$, and thickness $\delta =$0.5mm are entrained by waves of varying energy ($E_{w})$. The changes to droplet size over time, from seconds to hours, are measured at several locations using multi-resolution holography, which covers sizes ranging from $\mu $m to mm. Using dispersants to reduce $\sigma $, the Webber number, \textit{We}$=E_{w}\delta /\sigma $, and Ohnesorge number, \textit{Oh}$= \mu_{d} /(\rho_{d}\delta \sigma )^{0.5}$, are varied from 6 to 813 and from 0.09 to 0.95, respectively. Droplets smaller than the turbulence scale (2-30 $\mu $m -- diameter), are generated by ``micro-threading''. Their size distribution becomes steeper and their total number increase substantially with decreasing interfacial tension. For slopes smaller than -3, measured for $\sigma $ around 10$^{\mathrm{-1\thinspace }}$mN/m, the volumetric size distribution decreases with diameter, i.e. most of the oil breaks into micron-scale droplets. For high interfacial tension oil, the concentration of small droplets increases with wave energy, but this effect diminishes as $\sigma $ decreases. Droplets larger than 100 $\mu $m are generated by turbulent shear. Hence, their number is impacted by $\mu_{d}$ and $E_{w}$. Increasing \textit{We} from 6 to 15 (\textit{Oh} from 0.09 to 2.95) increases the initial number of droplets by up to 5 times, but the distribution slopes remain largely similar. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E12.00002: Laser imaging in liquid-liquid flows M.I.I. Zainal Abidin, Kyeong H. Park, Victor Voulgaropoulos, Maxime Chinaud, Panagiota Angeli In this work, the flow patterns formed during the horizontal flow of two immiscible liquids are studied. The pipe is made from acrylic, has an ID of 26 mm and a length of 4 m. A silicone oil (5cSt) and a water/glycerol mixture are used as test fluids. This set of liquids is chosen to match the refractive indices of the phases and enable laser based flow pattern identification. A double pulsed Nd:Yag laser was employed (532mm) with the appropriate optics to generate a laser sheet at the middle of the pipe. The aqueous phase was dyed with Rhodamine 6G, to distinguish between the two phases. Experiments were carried out for mixture velocities ranging from 0.15 to 2 m/s. Different inlet designs were used to actuate flow patterns in a controlled way and observe their development downstream the test section. A static mixer produced dispersed flow at the inlet which separated downstream due to enhanced coalescence. On the other hand, the use of a cylindrical bluff body at the inlet created non-linear interfacial waves in initially stratified flows from which drops detached leading to the transition to dispersed patterns. From the detailed images important flow parameters were measured such as wave characteristics and drop size. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E12.00003: Flow separation characteristics of unstable dispersions Victor Voulgaropoulos, Lusheng Zhai, Panagiota Angeli Drops of a low viscosity oil are introduced through a multi-capillary inlet during the flow of water in a horizontal pipe. The flow rates of the continuous water phase are kept in the turbulent region while the droplets are injected at similar flow rates (with oil fractions ranging from 0.15 to 0.60). The acrylic pipe (ID of 37mm) is approximately 7m long. Measurements are conducted at three different axial locations to illustrate how the flow structures are formed and develop along the pipe. Initial observations are made on the flow patterns through high-speed imaging. Stratification is observed for the flow rates studied, indicating that the turbulent dispersive forces are lower than the gravity ones. These results are complemented with a tomography system acquiring measurements at the same locations and giving the cross-sectional hold-up. The coalescence dynamics are strong in the dense-packed drop layer and thus measurements with a dual-conductance probe are conducted to capture any drop size changes. It is found that the drop size variations depend on the spatial configuration of the drops, the initial drop size along with the continuous and dispersed phase velocities. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E12.00004: Jet-mixing of initially-stratified liquid-liquid pipe flows: experiments and numerical simulations Stuart Wright, Roberto Ibarra-Hernandes, Zhihua Xie, Christos Markides, Omar Matar Low pipeline velocities lead to stratification and so-called ‘phase slip’ in horizontal liquid-liquid flows due to differences in liquid densities and viscosities. Stratified flows have no suitable single point for sampling, from which average phase properties (e.g. fractions) can be established. Inline mixing, achieved by static mixers or jets in cross-flow (JICF), is often used to overcome liquid-liquid stratification by establishing unstable two-phase dispersions for sampling. Achieving dispersions in liquid-liquid pipeline flows using JICF is the subject of this experimental and modelling work. The experimental facility involves a matched refractive index liquid-liquid-solid system, featuring an ETFE test section, and experimental liquids which are silicone oil and a 51-wt\% glycerol solution. The matching then allows the dispersed fluid phase fractions and velocity fields to be established through advanced optical techniques, namely PLIF (for phase) and PTV or PIV (for velocity fields). CFD codes using the volume of a fluid (VOF) method are then used to demonstrate JICF breakup and dispersion in stratified pipeline flows. A number of simple jet configurations are described and their dispersion effectiveness is compared with the experimental results. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E12.00005: Experiments and simulations of oil-water flows in horizontal pipes Roberto Ibarra-Hernandes, Stuart Wright, Zhihua Xie, Christos Markides, Omar Matar The extraction of detailed information (e.g. velocity and turbulent data) in the flow of two immiscible liquid phases in horizontal pipes is of great importance for the fundamental understanding of the in situ hydrodynamics (and transport properties) of these flows, and the validation and improvement of advanced multiphase flow models. This detailed flow information can be obtained by the application of advanced laser-based diagnostic techniques, such as Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), however, the difference in the refractive index between the most relevant test fluids (oil, water) prevents the extraction of accurate information simultaneously in both phases, especially when the phases begin to develop interfacial instabilities, droplets and dispersions. In this work, a simultaneous, combined two-line technique is employed to obtain spatiotemporally resolved information in a 32 mm ID quartz pipe in terms of liquid phase distributions, velocity profiles and turbulence measurements. The experimental results are compared with numerical simulations carried out using the Fluidity code based on control-volume, finite-elements, and adaptive, unstructured meshing. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E12.00006: Proper Orthogonal Decomposition on Experimental Multi-phase Flow in a Pipe Bianca Viggiano, Murat Tutkun, Raúl Bayoán Cal Multi-phase flow in a 10 $cm$ diameter pipe is analyzed using proper orthogonal decomposition. The data were obtained using X-ray computed tomography in the Well Flow Loop at the Institute for Energy Technology in Kjeller, Norway. The system consists of two sources and two detectors; one camera records the vertical beams and one camera records the horizontal beams. The X-ray system allows measurement of phase holdup, cross-sectional phase distributions and gas-liquid interface characteristics within the pipe. The mathematical framework in the context of multi-phase flows is developed. Phase fractions of a two-phase (gas-liquid) flow are analyzed and a reduced order description of the flow is generated. Experimental data deepens the complexity of the analysis with limited known quantities for reconstruction. Comparison between the reconstructed fields and the full data set allows observation of the important features. The mathematical description obtained from the decomposition will deepen the understanding of multi-phase flow characteristics and is applicable to fluidized beds, hydroelectric power and nuclear processes to name a few. [Preview Abstract] |
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