Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X21: Multiphase Flow General |
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Chair: Rozie Zangeneh, Stanford University Room: 250 E |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X21.00001: Effect of polymers on the suppression of satellite droplets during the jet breakup in inkjet printing Mandeep Saini, Youssef Saade, Detlef Lohse In inkjet printing, high speed liquid jets break up into droplets due to a capillary instability. This instability often leads to the formation of secondary satellite droplets that deteriorate the quality of a print. In this work, we study the jet formation and the breakup process using Direct Numerical Simulations (DNS). In particular, we investigate the effect of polymer additives in suppressing the formation of satellite drops. Our results show that the addition of small concentrations of polymers can lead to the suppression of satellite droplets. However, if the polymer concentration increases beyond a certain limit, the jet breakup is impeded altogether. Similar phenomenology was observed in the experimental study of Sen et al. [1]. We further analyze the flow inside the jet during breakup and examine the relative contribution of the polymeric stresses, the viscous stresses and the surface-tension force, to the jet formation and breakup processes. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X21.00002: An Experimental Framework to Study Controlled Unsteady Particle Mobilization Vaishak Thiruvenkitam, Robert H Bryan, Zheng Zhang, Ebenezer P Gnanamanickam This work describes an experimental framework to characterize the unsteady mobilization of solid particles from a particle bed. The measurements were carried out in an incoming zero-pressure gradient turbulent boundary layer that proceeded to develop over a particle bed. The bed contained spherical soda lime particles with diameters ranging from 450-600 microns, positioned 3 m from the sandpaper trip. It was determined that at friction Reynolds numbers less than 1600, the naturally occurring large-scale structures mobilized a negligible number of particles. The base flow was then set at a friction Reynolds number of 1600. Large-scale structures were then introduced onto this base flow using a NACA-0010 oscillating airfoil, creating a controllable free-stream disturbance and large-scale shear stress at the particle bed leading to initiation of particle mobilization. This introduced scale's frequency and amplitude could be controlled, and intermittent bursts of large scales could be added. High-speed imagery was utilized to capture the mobilization of the particles under the influence of these large-scale structures. These measurements demonstrated the ability of this framework to initiate particle mobilization through the introduced large-scale structures. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X21.00003: Dynamics of disc impact onto a boiling liquid: effect of phase change Yee Li (Ellis) Fan, Bernardo Palacios Muniz, Nayoung Kim, Devaraj R.M. Van Der Meer The dynamics of disc impact onto a boiling liquid, i.e., a liquid that is in thermodynamic equilibrium with its vapour phase, differs from that on water at ambient air conditions. The key distinction lies in that the entrapped gas pocket beneath the disc contains a condensable vapour which can undergo a phase change due to energy exchange with the surrounding liquid during impact. In this study, we demonstrate that at high impact velocity and low ambient temperature, the entrapped vapour pocket under a circular flat disc collapses rapidly upon impact, resulting in exceptionally high impact pressure at the disc centre. We rationalise this effect as a result of the condensation of the vapour pocket due to compression upon impact. We show that the impact velocity and the vapour density, which changes with the ambient temperature, determine the condensation rate and the subsequent contraction of the vapour pocket. Additionally, by increasing the temperature of the impacting disc, we attempt to frustrate condensation during boiling liquid impact. We will discuss the effectiveness of counteracting the vapour condensation by heating in reducing the impact pressure on the disc. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X21.00004: Investigation of liquid film evolution on a rotating wafer through optical calibration Heeyun Choi, Hyunji Lee, Hyungmin Park Many industries including semiconductor processing and rotating disk reactors use a process that involves dispensing various chemical solutions onto a rotating plate. During this process, a thin liquid film forms on the surface and spreads radially driven by the disk rotation (inertia) and surface tension, creating distinct and complex wave patterns. Analyzing the shape, thickness, and wavelength of these wave patterns is critical to understanding the characteristics of the liquid film. In this study, we present a high-speed photography technique combined with an optical thickness correction method that allows us to accurately measure the film thickness distribution in a relatively larger area. With this approach, detailed wave information can be obtained by placing only a single camera above the disk. We have validated that this correction method is accurate to within 10%. By systematically varying the disk rotation speed from 200 to 500 rpm and the flow rate from 0.5 to 2.0 LPM, we characterized the wave patterns of the liquid film. Depending on the conditions, the wave patterns were analyzed as concentric or spiral, and the thickness of the waves was measured. The results of this research are expected to significantly improve the efficiency and quality of both semiconductor and reactor processes. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X21.00005: Abstract Withdrawn
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Tuesday, November 26, 2024 9:05AM - 9:18AM |
X21.00006: On ideal and real two-fluid mixtures of dispersed type: bubbly and droplet flow. Azeddine ZAIDNI, Philip J Morrison, Saad Benjelloun Starting from Hamilton's principle, we derive an ideal two-phase fluid model in Lagrangian form. With this description, insight toward understanding the ill-posedness of such two-phase flow models is obtained. Issues related to non-hyperbolicity, stability, and existence of strong solutions are also revisited. Adding the effect of viscosity to each fluid, we study the behavior of (linear) sound waves in this type of media (real multi-fluid). This classical physics question is a continuation of the wave studies of Kirchhoff (1868) and Stokes (1845) in a (mono)fluid. We give attenuation and dispersion formulae due to viscous effect in real two-fluid mixtures of dispersed type. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X21.00007: Computational studies of gas-liquid-solid flows in froth flotation Lei Zeng, jiacai Lu, Gretar Tryggvason Froth flotation, where air bubbles are used to separate hydrophobic and hydrophilic particles in a slurry, is examined using fully resolved simulation. As bubbles rise through the suspension, hydrophobic particles are captured and brought to the top while the hydrophilic ones remain in the water. The Navier-Stokes equations are solved using a structured staggered grid and a finite volume method. The bubbles are followed using a front-tracking method and solid particles are treated as rigid immersed objects of different densities with zero deformation gradient. The Generalized Navier Boundary Condition (GNBC) models the contact line where particles stick to bubbles. We show results for a single bubble and several bubbles moving through fluid containing solid particles and examine the effects of various governing parameters, such as bubble deformability and the volume fraction of solids particles on the capture rate of hydrophobic particles by bubbles. Preliminary results for the formation of particle-laden foam at the free surface are also shown. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X21.00008: Kinetic theory closures for electrostatic charge separation and transport accounting for finite contact time Saykat Poddar, Manjil Ray, Alberto Passalacqua Closure models based on the kinetic theory of granular flows (KTGF) have been recently developed to describe charge separation and transport in granular flows induced by binary collisions between particles, or a particle and a metallic wall. However, the KTGF relies on the assumption of instantaneous collisions, while charge separation models use the Hertzian theory to determine the contact area, assuming deformation and finite contact time. The latter implies lower collision frequency and, consequently, a lower rate of collisional charge transfer. We derive a set of kinetic theory closures for charge separation and transport accounting for finite contact time and show the impact on the prediction of the amount of charge transferred in the case of particle-particle and particle-wall collisions. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X21.00009: Numerical Investigations of Thermal Performance of Cooling Pipes for an Ionic Liquid-Piston Compressor VAN TINH HUYNH, DONG KIM Inside a cylindrical chamber, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate compressed hydrogen gas from 220 bar to 752.3 bar, raising its temperature from 298.15 K to 394.2 K within approximately 6 seconds. A three-dimensional liquid-piston compressor model was developed and validated with experimental data. Two-phase flow simulations were performed using the finite volume method and volume of fluid model in ANSYS Fluent software. Various cooling scenarios were investigated to improve compression and thermal performance, focusing on parameters such as the number of pipes, their cross-sectional shape, diameter, and temperature. To achieve the desired pressure ratio, employing four cooling circular pipes reduced the hydrogen temperature from 394.2 K to 355 K, resulting in a significant 40.8% improvement in thermal efficiency. Furthermore, compression performance reached 95.8% with a power density of 3221.4 kW·m-3, compared to 90.9% and 4550.6 kW·m-3 without cooling. This work is crucial as it expands the repertoire of cooling methods for gas in liquid-piston compressors. The findings provide deeper insights into flow dynamics and heat transfer mechanisms within the chamber, while also demonstrating heat transfer enhancement and compression efficiency using cooling tubes. Moreover, these results could potentially promote the development of fuel cell electric vehicles, particularly benefiting the automotive sector overall. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X21.00010: Predicting aerosol dispersal in indoor spaces and the associated uncertainties due to turbulence Krishnaprasad K A, Rupal Patel, Kailash Choudhary, Nadim Zgheib, Jorge Salinas, Man Yeong Ha, S Balachandar Turbulent dispersal of aerosol pollutants in a ventilated indoor space is often characterized by the mean concentration using theoretical frameworks such as the well-mixed, near-field/far-field, and eddy diffusivity models. Although their accuracy and efficiency in predicting this mean behavior have been well-established in the literature, this problem demands a deeper analysis, involving the uncertainties associated with the fluid mechanics of the problem. Quantifying these uncertainties requires a rigorous statistical description of the inherent stochastic turbulent dispersal process and the inhomogeneous nature of the indoor flow. This work addresses the importance of going beyond accurate prediction of the mean ensemble-averaged exposure, by evaluating the expected level of variability in individual realizations. We leverage large datasets from turbulence-resolving Euler-Lagrange simulations of aerosol dispersal in varying indoor geometries. The statistical information is used to develop a data-driven, stochastic model that can accurately predict the mean behavior as well as the variances as a function of the separation distance between the pollutant source and the receiver. The validity of the model's predictions is further demonstrated with comparisons to experiments and existing theoretical models. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X21.00011: CNN-Based Ultrasonic Measurements in Vertical Gas-Liquid Two-Phase Flows Issei Watanabe, Yu Watanabe, Sadanori Matsubara, Tomoaki Watamura, Shu Takagi This study presents a method that integrates ultrasonic sensing and convolutional neural networks (CNN). The target flows are mainly vertical gas-liquid two-phase flows. This method can be applied to measure various pipe flow systems, such as those used in subsea resource extraction and other industrial applications. The aim of this study is to distinguish different flow patterns and obtain superficial velocities accurately by using pulsed ultrasound. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X21.00012: Data-driven Modelling of EHD-Assisted Melting Sankaranarayanan Vengadesan, Hanok Endigeri Solid-liquid phase change materials have poor thermal conductivities that affects the performance of latent heat thermal energy storage systems. One solution is heat transfer enhancement by the induction of electrohydrodynamic (EHD) flow. In this work, we present a data-driven approach to EHD-assisted melting. The geometry is a heated square cavity with a circular electrode at the centre for charge injection. The electric Rayleigh number (T), Rayleigh number (Ra) and Stefan number (St) are fed as inputs to the data-driven setup to analyse the role played by electroconvection, buoyancy-driven convection and pure conduction. A ANN is trained using data from simulations. This ANN captures the relationship between nondimensional numbers and the growth of total liquid fraction. This network is then used to generate a large number of samples for a sensitivity analysis to understand the influence of nondimensional numbers. It is observed that the sensitivity of the melting rates to T and Ra become non-trivial only when the liquid fraction (LF) exceeds 0.2. Further, this threshold LF below which electroconvection does not assist the melting rate remains independent of the buoyancy force strength. Second-order sensitivity indices are significant only for the T and Ra, implying interactions between buoyancy-driven convection and electroconvection |
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