Comparison of X-ray and optical measurements in the near-field of an optically dense coaxial air-assisted atomizer

Bothell, Julie; Machicoane, Nathanaël; Li, Danyu; Morgan, Timothy B.; Aliseda, Alberto; Kastengren, Alan L.; Heindel, Theodore J.

doi:10.1016/j.ijmultiphaseflow.2020.103219

Cited by 22 publications

(18 citation statements)

References 20 publications

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“…The development of the third-generation synchrotron radiation sources promotes the application of X-ray phasecontrast imaging, which enables clear visualization of boundaries between phases with different refractive index (Kastengren & Powell 2014). The short high-flux X-ray pulses emitted from synchrotron sources allow for the capture of fast dynamic events and minimize motion blur (Bothell et al 2020). Aside from detailed illustration of two-phase morphology (Karathanassis et al 2018), X-ray phase-contrast images can also be used to perform velocimetry by tracking either seeded particles or phase interfaces inside the opaque regions.…”

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confidence: 99%

Experimental investigation of internal two-phase flow structures and dynamics of quasi-stable sheet cavitation by fast synchrotron x-ray imaging

et al. 2020

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The quasi-stable sheet cavitation produced in a small Venturi channel is investigated using a fast synchrotron X-ray imaging technique aided with conventional high speed photography. The use of X-rays instead of visible light solves cavitation opacity related issues, and X-ray phase contrast-based edge enhancement enables high-definition visualization of the internal two-phase morphology. The simultaneous acquisition of time-resolved velocity and void fraction fields through post-processing the recorded X-ray images reveals, for the first time, the complex diphasic flow structures inside the sheet cavity, which is essentially divided into 6 characteristic parts. Distinct from the current mainstream view, the globallysteady sheet cavitation is found to be characterized by a weak but constantly-existing re-entrant flow that can penetrate the entire cavity. The turbulent velocity fluctuations inside the sheet cavity are also investigated. The turbulence level in the reverse flow region is observed to be as low as in the outer main flow demonstrating the relatively steady status of the reentrant flow. Unlike the streamwise and cross-stream fluctuations, the shear stress appears to be weakly correlated with the velocity gradient. The collapse of vapor phase and the vaporization at the upstream cavity interface are found to be the primary causes of shear stress intensification.Partial cavitation has two main forms of appearance: sheet and cloud cavitation (Pelz et al. 2017). The former generally appears as a quasi-stable sheet cavity with only small vapor shedding at its closure region, i.e. with an open closure. While in the latter case, the cavity is highly unstable as a consequence of periodic shedding of large vapor structures.The transition from sheet to cloud cavitation is, in a classic view, related to the motion of a re-entrant jet that breaks off the sheet cavity from the leading edge and consequently causes a large cavitation cloud to shed (Knapp, 1955). The existence of the re-entrant jet in periodic cloud cavitation was confirmed through the method of dye injection (Le et al. 1993). Kawanami et al. (1997) placed a small obstacle on the suction side of a hydrofoil to prevent the re-entrant jet from moving upstream, and the large cloud shedding disappeared, demonstrating the dominant role of the re-entrant jet. The conditions necessary for the development of the re-entrant jet has been explored by Callenaere et al. (2001). They showed the critical role of adverse pressure gradient at the cavity closure in the onset of the re-entrant jet instability.Regarding the relatively stable sheet cavitation, Gopalan & Katz (2000), Callenaere et al. (2001) and Laberteaux & Ceccio (2001) described that no clear re-entrant jet was observed or only the weak reverse flow existed at the trailing edge

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Section: Please Cite This Articlementioning

confidence: 99%

Experimental investigation of internal two-phase flow structures and dynamics of quasi-stable sheet cavitation by fast synchrotron x-ray imaging

et al. 2020

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“…Thus, the CAPSULE was constructed for a 1 MPa maximum operating pressure, with the initial operation and flow loop rating set at 0.5 MPa. Data collected with the CAPSULE will be compared to recent data collected under atmospheric conditions using the same canonical airblast atomizer design [8,9]. Under atmospheric conditions, the highest gas flow rate was 1270 SLPM.…”

Section: Methodsmentioning

confidence: 99%

A Pressurized Tank for High Flow Rate Atomization Studies

Burtnett

Morgan

Dahlstrom

et al. 2021

ICLASS

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Atomization is useful in many applications including combustion, spray painting, and fire suppression. To form a more complete understanding of the atomization process, it is necessary to study the near-, mid-, and far-field regions of a spray. Previous studies from this group, as well as from collaborators, have explored the near-and mid-field regions of a canonical airblast atomizer under atmospheric conditions. To provide a more complete atomization assessment, experimental spray measurements in pressurized environments are necessary. The Chamber for Assorted Pressurized Spray sUrveiLlancE, or CAPSULE, has been designed and constructed to operate the canonical airblast atomizer at pressures up to 1 MPa and volumetric gas flow rates of nearly 4000 SLPM. The CAPSULE is a 190 L (50 gallon), 316L stainless steel pressure vessel equipped with six sight glasses to collect atomization data using multiple experimental techniques, including backlit imaging, Phase Doppler Particle Analysis (PDPA), and high-intensity X-ray radiography. The CAPSULE is fed by compressed air lines for both co-axial and swirl flow conditions. This paper provides an overview of the CAPSULE design, the major components in the flow loop, and the canonical airblast atomizer. Preliminary backlit imaging results are presented for ambient pressures in the range 0.1-0.5 MPa.

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“…In the former, high spatial and temporal resolution back-lit imaging is considered, yielding almost binary images indicating liquid presence, where simple thresholding can be used to identify the liquid interface's time evolution [5]. In the latter, EPL is measured using a focused monochromatic X-ray beam [4].…”

Section: Experimental Methodsmentioning

confidence: 99%

“…These experimental measurements have resulted in useful engineering tools such as regime maps of swirl number and momentum flux ratio [1], liquid entrainment models that well predict liquid ligament shedding frequency [2], and correlations for liquid longitudinal wavelength and transverse corrugation sizes [3]. Most recently, X-ray imaging utilizing specialized facilities at Argonne National Lab's Advanced Photon Source has been used successfully to visualize 3D structures in the flow, enabling the study of physics like bubble entrainment and contact line dynamics [4,5]. The wide range of length scales in air-blast atomization, starting from the large combustion chamber and nozzle scales, down to the small interfacial and turbulence scales, have made simulations challenging.…”

Section: Introductionmentioning

confidence: 99%

Detailed Validation of Numerical Simulations of Air-blast Spray Atomization against Experimental Shadowgraphs and Radiographs

Machicoane

et al. 2021

ICLASS

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Sprays appear in a variety of industrial applications ranging from powder production used in additive manufacturing to fuel nozzles. Air-blast atomization is a specific injection strategy whereby a high-speed gas shears and destabilizes a low-speed liquid which causes a cascade of instabilities leading to the creation of a spray. The flow physics around the nozzle are challenging to quantify and complex. Inside the nozzle, traditional PIV and hot-wire methods cannot be used to measure turbulence and boundary layer growth and at the nozzle exit, radiographs and back-lit images show complex time-varying wetting and contact line dynamics. In this study, we explore different computational strategies to model these flow physics and validate them against equivalent path length data (EPL), a measure of the liquid depth along a line-of-sight. Further downstream, thin liquid structures that fall below the mesh size are prone to numerical break-up and as a consequence, we employ a thin-film model to improve agreement. We make use of a multi-block simulation strategy to address the multi-scale nature of atomization. Finally, using these models, we make direct comparisons of quantities such as the liquid intact length.

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Comparison of X-ray and optical measurements in the near-field of an optically dense coaxial air-assisted atomizer

Cited by 22 publications

References 20 publications

Experimental investigation of internal two-phase flow structures and dynamics of quasi-stable sheet cavitation by fast synchrotron x-ray imaging

Experimental investigation of internal two-phase flow structures and dynamics of quasi-stable sheet cavitation by fast synchrotron x-ray imaging

A Pressurized Tank for High Flow Rate Atomization Studies

Detailed Validation of Numerical Simulations of Air-blast Spray Atomization against Experimental Shadowgraphs and Radiographs

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