Journal: International Journal of Multiphase Flow

Abbreviation

Int. j. multiph. flow

Publisher

Elsevier

Journal Volumes

ISSN

0301-9322
1879-3533

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Publications 1 - 10 of 65
  • Stability of a Liquid Jet into Incompressible Gases and Liquids: Part 2. Effects of the irrotational viscous pressure
    Item type: Journal Article
    Funada, Toshio; Saitoh, M.; Wang, Jing; et al. (2005)
    International Journal of Multiphase Flow
  • Synchrotron X-ray phase-contrast imaging of ultrasonic drop atomization
    Item type: Journal Article
    Prasanna, Anunay; Biasiori-Poulanges, Luc; Yu, Ya-Chi; et al. (2024)
    International Journal of Multiphase Flow
    Ultrasonic atomization is employed to generate size-controllable droplets for a variety of applications. Here, we minimize the number of parameters dictating the process by studying the atomization of a single drop pending from an ultrasonic horn. Spatiotemporally resolved X-ray phase-contrast imaging measurements show that the number-median sizes of the ejected droplets can be predicted by the linear Navier–Stokes equations, signifying that the size distribution is controlled by the fluid properties and the driving frequency. Experiments with larger pendant water drops indicate that the fluid–structure interaction plays a pivotal role in determining the ejection onset of the pendant drop. The atomization of viscoelastic drops is dictated by extended ligament formation, entrainment of air, and ejection of drop-encapsulated bubbles. Existing scaling laws are used to explain the required higher input amplitudes for the complete atomization of viscoelastic drops as compared to inviscid drops. Finally, we elucidate the differences between capillary wave-based and cavitation-based atomization and show that inducing cavitation and strong bubble oscillations quickens the onset of daughter drop ejection but impedes their size control.
  • Machine learning based flow regime recognition in helically coiled tubes using X-ray radiography
    Item type: Journal Article
    Breitenmoser, David; Prasser, Horst-Michael; Manera, Annalisa; et al. (2023)
    International Journal of Multiphase Flow
    The understanding of flow regimes in helical coils is essential in the design and operation of modern heat exchangers and has been studied therefore intensively over the past decades. However, due to the subjective nature in defining these flow regimes, previous studies showed conflicting results. The scope of the present study is to perform automatic flow regime recognition for helical two-phase flows by a novel two-step machine learning approach without any prior knowledge. The machine learning algorithms are trained on X-ray radiography based high-resolution high-speed void fraction measurements at adiabatic conditions. The trained machine learning models successfully predict the number of flow regimes as well as the flow regimes themselves. The classifier models show excellent classification accuracy >98%. Comparison of the experimental results with available flow regime models revealed significant discrepancies >2 orders of magnitude in the superficial liquid velocity. The novel machine learning based flow regime recognition methodology presented herein shows not only a significant improvement in the classification accuracy compared to previous studies but offers also a novel data-driven way to define and investigate the very nature of the flow regimes themselves in a more consistent and objective way.
  • Intrusive effects of dual-tip conductivity probes on bubble measurements in a wide velocity range
    Item type: Journal Article
    Pagliara, Simone; Felder, Stefan; Boes, Robert Michael; et al. (2024)
    International Journal of Multiphase Flow
    High-velocity air-water flows in hydraulic structures, such as spillways and low-level outlets, are characterised by high turbulence levels and strong self-aeration. In air-water flows, the void fraction varies from values close to zero at the invert up to near unity in the upper spray region. Because of the strong aeration, non-intrusive optical measurement techniques can only be applied to a limited extent, and intrusive phase-detection probes are widely used to estimate air-water flow properties, including void fraction, interfacial velocity, and chord sizes. However, these probes are often used without independent validation. Herein, this study systematically investigated the uncertainties of phase-detection probe measurements of individual bubbles traveling at a wide range of velocities (up to 7.5 m/s) in a vertically upward bubbly pipe flow. Velocities and chord times of air bubbles were simultaneously measured with an intrusive dual-tip conductivity probe and stereo-view high-speed videos, and a comparative analysis identified various effects of bubble-probe interactions on the measurement accuracy of the bubble velocities. The bubble deceleration due to these bubble-probe interactions were quantified. For standard interactions (i.e., bubbles undergoing no significant deformation and slowing down), the velocity estimates compared well with a theoretical model (errors less than 2 %), while larger errors were found for non-standard interactions such as those characterised by crawling, drifting, and waking mechanisms. In addition, a novel correction scheme for chord times was proposed, improving the accuracy of chord length, bubble size and void fraction estimations in air-water flows.
  • Modeling of bubble flows in vertical pipes with the N-phase compressible algebraic slip model
    Item type: Journal Article
    Agarwal, B.; Narayanan, C. (2018)
    International Journal of Multiphase Flow
  • CMFD and the critical-heat-flux grand challenge in nuclear thermal–hydraulics – A letter to the Editor of this special issue
    Item type: Journal Article
    Yadigaroglu, George (2014)
    International Journal of Multiphase Flow
  • Bubbles in turbulent flows: Data-driven, kinematic models with history terms
    Item type: Journal Article
    Wan, Zhong Y.; Karnakov, Petr; Koumoutsakos, Petros; et al. (2020)
    International Journal of Multiphase Flow
  • Two phase liquid–liquid flows in pipes of small diameters
    Item type: Journal Article
    Wegmann, Adrian; Rudolf von Rohr, Philipp (2006)
    International Journal of Multiphase Flow
  • Best practices for velocity estimations in highly aerated flows with dual-tip phase-detection probes
    Item type: Journal Article
    Kramer, Matthias; Hohermuth, Benjamin; Valero, Daniel; et al. (2020)
    International Journal of Multiphase Flow
  • Interfacial structure of upward gas–liquid annular flow in inclined pipes
    Item type: Journal Article
    Fershtman, Adam; Robers, Lukas; Prasser, Horst-Michael; et al. (2020)
    International Journal of Multiphase Flow
    Temporal and spatial-resolved data on the interfacial structure in upward vertical and inclined two-phase annular flows were accumulated using a novel non-intrusive multilayer conductance sensor. The sensor provides simultaneous measurement of the film thickness across the entire pipe circumference, enabling a three dimensional reconstruction of the wavy interface. Measurements were performed for two liquid (water) flow rates and a single high gas (air) flow rate. Three types of interfacial waves were identified, including ripples, disturbance and rogue waves. Rogue waves can be described as an infrequent solitary disturbance wave propagating over a ripple-dominant interface. Detailed statistical properties of the interfacial shape, such as the mean film thickness, wave height distribution, wave frequency spectra, wave propagation velocities and more, were obtained as a function the pipe inclination and azimuthal angle. The statistical analysis of the wavy interface presented in this study sheds light on a complex flow pattern of annular flow in inclined pipes, which has remained relatively unstudied experimentally. For inclined pipes, gravity imposes an asymmetric film distribution resulting in the thickest film at the bottom of the pipe. At this location, waves attain larger amplitudes while maintaining slower propagation velocities as compared to smaller amplitude waves at the top of the pipe. Generally, the wave frequency throughout the pipe circumference increases with inclination angle. For a larger liquid flow rate, the interface was found to be primarily dominant by disturbance waves. For a lower liquid velocity, the interfacial structure was found to be highly dependent on both the azimuthal and the inclination angles. An interface wave type map is presented as a function of those angles. © 2020 Elsevier Ltd
Publications 1 - 10 of 65