Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session L35: Atomization and Sprays I |
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Chair: Kee Onn Fong, University of Washington; Dorrin Jarrahbashi, Texas A&M University Room: 243 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L35.00001: Influence of swirl on gas-liquid coaxial atomization in high-pressure environments Kee Onn Fong, Xinzhi Xue, Rodrigo Osuna-Orozco, Alberto Aliseda We present recent experimental results on the dynamics of atomization of a liquid column by a coaxial turbulent gas jet, under varying gas angular momentum (swirl) conditions and densities. We compare between atomization under atmospheric conditions and in a 5 bar environment. For both pressure conditions, the parameter space includes a gas-to-liquid momentum ratio in the range of M = 25–56 and swirl ratios of SR = 0-1. High-speed shadowgraphy images are used to quantify the liquid-gas interface in the spray near-field. In the mid-field, Phase Doppler Particle Analyzer (PDPA) measurements quantify the droplet sizes, velocity distributions, and their radial variations across the spray. At high pressures and increasing M, we observe a decrease in spray angles at SR = 0, but an increase in spray angles when SR > 0.5. We reconcile these observations with the crown de-wetting mechanism. First observed in X-ray shadowgraphs of the spray, crown de-wetting is found to depend on the gas inertia relative to the liquid (gas density increases linearly with atomization environment pressure), potentially switching behavior. This leads to the altered spray angle trends observed, and modified droplet radial distributions in the mid-field, which are characterized via the PDPA measurements. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L35.00002: Scaling Relationships Volumetric Size Distributions in Flat Fan Sprays of Agricultural Tank Mixes Steven A Fredericks, Long Nguyen, Ian A Marabella, Elizabeth R Alonzi, Christopher J Hogan Jr. In the application of pesticides via sprays, the volumetric droplet size distribution (VDSD) influences the efficacy of the application as well as the risk of off-target spray deposition. However, VDSD prediction is complicated in agrochemical sprays because the nozzles employed have unique, complex geometries, and because of the influence that active herbicides and adjuvants have on the properties of the spray. We have utilized conservation of energy arguments to develop a scaling relationship to predict VDSDs from flat fan sprays of agricultural tank mixes, and experimentally tested this relationship using laser diffraction interferometry for agriculturally relevant tank mixtures, including active pesticides and both emulsion-forming and rheology-modifying drift control adjuvants, sprayed with complex geometry, flat fan nozzles typical of field application. Specifically, for 9 nozzle-tank mix combinations and across multiple nozzle sizes, we show that VDSDs can be normalized by the Sauter mean diameter (), and normalized distributions collapse for given nozzle type-spray tank mix combination. We also show that the Sauter mean diameter normalized by the nozzle hydraulic diameter () scales with the ratio of product of tank mix surface tension and hydraulic diameter divided by the nozzle pressure drop, with a scaling exponent of 1/3. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L35.00003: Near-Field Spray Characterization in a Pressurized Environment using High-Speed X-ray Imaging Timothy C Dahlstrom, Timothy B Morgan, Alan L Kastengren, Theodore J Heindel Sprays are commonly found in many industrial applications, from chemical applications for agricultural use to fuel injection in gas turbine engines to powder formation for 3D printing. Many of the processes like fuel injection occur in a pressurized ambient environment. Experimental visualization of the spray near-field region under these conditions is extremely challenging. To study high-pressure atomization, a Chamber for Assorted Pressurized Spray sUrveiLlancE, or CAPSULE, has been installed at the Advanced Photon Source (APS) at Argonne National Laboratory to perform high-speed X-ray flow visualization of the spray near-field. An airblast coaxial two-fluid atomizer was used in this study and white beam X-ray imaging focused on the nozzle exit. High-speed X-ray imaging revealed different atomization conditions as the swirl ratio, momentum flux ratio, and ambient pressure were increased. The variations were quantified through image analysis, which is only possible in the spray near-field with X-ray imaging. |
Monday, November 21, 2022 8:39AM - 8:52AM |
L35.00004: Prediction of the droplet size distribution from twin-fluid sprays Isaac M Jackiw, Nasser Ashgriz The present work studies low viscosity twin-fluid atomization experimentally and analytically to characterize and predict the droplet size distribution of the spray. The study is based on experiments conducted using commercially available twin-fluid nozzles with water as the liquid. Shadowgraph images were used to visualize the near-nozzle flow while the droplet size distribution was measured in the far-field using a Malvern Spraytec. To analytically model the atomization of the spray, the authors' recent works on aerodynamic droplet breakup, which describe the formation and breakup of ligament and bag structures by multiple mechanisms, are implemented to provide an analytical prediction of the droplet size distribution of the spray that is validated against the present experiments. The present model is developed to be a good physical representation of the spray behaviour at practical operating conditions. A Python implementation of the present model is made openly available. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L35.00005: Mechanisms of droplet generation following mechanical impact on liquid-filled container Sungkyu Kim, Benoit Lebon, Chelsea Preble, Simo A Makiharju Aerosol generation from laboratory accidents has been a subject of periodic interest for decades. While it is known based mostly on deposition-dependent cell culture data that vast numbers of droplets can be generated, these can exhibit notable variability due to the complex dynamics of fluid-structure interaction caused by impact and resultant free surface response. Our experimental study focuses on micro-scale droplets generated from liquid-filled laboratory ware impacting a rigid surface. We developed a Repeatable Accident INitiator (RAIN), a drop tower setup that ensures highly repeatable impact velocities and angles, placed inside a vertical flow chamber with filtered air. Inline holography, high-speed imaging, and optical particle counter are used to examine the droplets' quantity, paths, and forming mechanisms. Preliminary data suggests either vibration-induced Faraday instability or subsequent impulse concentration on the already corrugated free surface to be of significance. We also consider what facilitates the formation of a liquid ligament that eventually undergoes capillary force-triggered instability to create multiple small droplets, rather than a single droplet pinch-off which tends to result in a larger droplet. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L35.00006: On Hydrodynamics of Dry Slag Granulation of LD/BOF Slag: Developments for New Liquid D S Kushan, Goutam Chakraborty, Biswajit Maiti, Sukanta K Dash, Arun K Samantaray, Sanat K Singha Experimental trials of dry granulation process have been widely performed to granulate the blast furnace (BF) slag, in addition to, heat recovery from the molten material. In this study, a development of technology for dry granulation of LD slag under research has been discussed, using experimental methodology. The first two stages of experimental setup, with water as the working fluid, have been discussed in brief and their limitations have been noted. Then, the modifications that were performed in the third stage experimental setup, have been discussed in detail. The working liquid, which was water for the first two stages of experimental study, has also been changed to a more viscous liquid, so as to mimic the properties of slag as close as possible. Further, the possibility of using air blast has also been tested to assist in atomization, and hence, granulation, and was observed to be effective. However, due to some design flaws, that have been discussed in detail, a novel design for air blast method has been achieved and a successful trial has been performed. The photographs of the trial have been shown. This paper is compiled to state the updates in the development of technology of LD slag granulation and to show the trial as a proof of the direction of work being right. |
Monday, November 21, 2022 9:18AM - 9:31AM |
L35.00007: A Revised Model for Impinging Sheet based on the Velocity Measurement Weixiao Shang, Jun Chen As two liquid jets impinge on each other, a liquid sheet surrounded by a rim is formed around the impinging point. In the existing sheet models, the velocity of the sheet is assumed to be a constant along the radial direction centered to the impinging point. With this assumption, the sheet thickness and rim diameter are estimated by evaluating the conservations of mass, momentum, and energy. To verify such an assumption, in the present work, the velocity of an impinging sheet formed by two ethanol jets is measured via particle tracking velocimetry (PTV) by adding tracer particles into the fluid. With the aid of an imaging acquiring system and the post-processing algorithm, the locations of those particles in different frames are identified and the fluid velocity is measured. When PTV images are recorded, the shadow of the particles is enlarged by the liquid wrapped around them. This lens effect enables a magnified measurement of much smaller particles. The experimental results show a velocity distribution that changes both along the angular and radial directions on the impinging sheet. To explain the observed velocity change, the air friction must be taken into consideration and the theoretical analysis is given. The air boundary layer over the sheet is solved by introducing the stream function and similarity approach. Additionally, with the air velocity distribution attached to the sheet, a revised sheet model is developed to describe the impinging sheet. The model coefficients are determined using the experimental data. The comparisons between the model prediction and the experimental results of the sheet velocity show a relative error lower than five percent. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L35.00008: Self-pulsation characteristics of gas-liquid swirl coaxial atomizer with serrated gas jet nozzle Santanu K Sahoo, Hrishikesh Gadgil The self-pulsation phenomenon, commonly observed in gas-liquid coaxial injectors under certain flow conditions, is a result of the shear layer instability between the two fluids. The self-pulsating spray possesses a global mode with intrinsic frequency, which is undesirable in the context of thermoacoustic stability of the combustors. The dynamics of the central gas jet possibly governs the self-pulsation phenomenon and hence the present experiments focus on the effect of serrated gas jet exit (like chevron nozzles) on the pulsation characteristics of the gas-centered swirl coaxial injector. Time-resolved shadowgraphy images of the spray are captured near the injector with different recess values. The POD analysis of the spray images highlights a distortion of the pulsating mode to an azimuthal mode with the serrated gas jet exit when the recess is relatively high. The sharp frequency peak of the spectrum from the temporal coefficients gets suppressed and changed into a broadband mode indicating the breakdown of the periodically self-oscillating flow. The loss of coherence in the gas jet may be the possible cause of suppression of self-pulsation. However, at a low recess, the pulsating modes are still prevalent indicating the strong influence of the recess. |
Monday, November 21, 2022 9:44AM - 9:57AM |
L35.00009: Heterogeneous liquid sheets: from emulsions to suspensions Sara Gonzalez, Emilie Dressaire Multiphase fluids such as emulsions and suspensions are involved in industrial spraying and atomization processes, including pesticide application and spray painting. The dispersed phase is known to alter the effective viscosity of the liquid in the continuum approximation. Yet atomization processes confine the multiphase fluids between interfaces, over length scales comparable to the drop or particle size. To determine the limitations of the effective viscosity approach to describe atomization processes, we conduct drop impact experiments on a small target. Upon impact, a transient liquid sheet of pure fluid, emulsion, or suspension expands radially before breaking into secondary droplets. We use high-speed imaging to record and compare the expansion and retraction of the self-suspended sheets. Our study finds that the effective viscosity fails to capture the complex dynamics of multiphase liquid sheet. The interactions between the dispersed phase and the air/liquid interfaces contribute to the dynamics of the liquid sheet and depend on whether the dispersed phase is a solid or a liquid. |
Monday, November 21, 2022 9:57AM - 10:10AM |
L35.00010: Influence of nanobubbles on the surface tension and atomization characteristics of water VIVEK K, Kalyani Agarwal, Neelkanth Nirmalkar, Lipika Kabiraj Atomization of bulk fluid and its characterization is of importance in various applications like combustion of liquid fuels, crop sprays, and manufacturing. Influencing the physical properties of the fluid by different means is a way to achieve desired atomization quality. It has been recently reported that stable suspensions of nano-meter-sized bubbles in liquids can be obtained for a large number of liquid-gas combinations. The possibility of having a high concentration of such nanobubbles and the long-term stability of nanobubble suspensions can be seen as an opportunity to manipulate the physical properties of base liquid. The present study involves the introduction of oxygen nanobubbles in pure water, and characterization of the resulting nanobubble suspension, including the measurement of surface tension and its atomization by impinging jets. Our investigations reveal a surface tension drop of the order of 5 % to 12% of water on the introduction of nanobubbles. Correspondingly, better liquid atomization behavior in terms of drop in liquid sheet breakup length of the order 15% compared to pure water is also observed and reported in terms of the liquid sheet dimensions. |
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