Theodore Heindel
Iowa State University, Mechanical Engineering, Faculty Member
- Bergles Professor of Thermal Scienceedit
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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... more
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 strategies to model the inflow and compare them against equivalent path length data (EPL), a measure of the liquid depth along a line-of-sight. In particular, we discuss the impact of different contact line models and the importance of modeling the flow inside the nozzle. ∗Corresponding Author: lxv2@cornell.edu
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Numerical and experimental studies, with and without surface augmentation, were performed for a 3 x 3 array of discrete heat sources. This geometry was addressed to quantify heat transfer edge effects in multi-chip electronic packages.... more
Numerical and experimental studies, with and without surface augmentation, were performed for a 3 x 3 array of discrete heat sources. This geometry was addressed to quantify heat transfer edge effects in multi-chip electronic packages. Numerical models were developed to simulate two- and three-dimensional nonconjugate and conjugate laminar natural convection. Experimental facilities were designed and constructed to perform heat transfer measurements and flow visualization of natural convection from flush-mounted and finned discrete heat sources in a cavity. The three-dimensional numerical model captured edge effects which could not be predicted by the two-dimensional model and should be employed for accurate heat transfer predictions when $\rm A\sb{htr}\sbsp{\sim}{\u3c}3.0.$ Experimental data, corrected for conjugate heat losses, were in excellent agreement with three-dimensional predictions. The data were also well correlated for each heater row. Two-dimensional conjugate heat transfer models can be used to predict general heat transfer trends from discrete heat sources as well as from the substrate in which they are mounted. If the substrate/fluid thermal conductivity ratio is relatively high ($\rm R\sb{s}\sbsp{\sim}{\u3e}4.7),$ three-dimensional conjugate calculations should be utilized to obtain accurate thermal spreading predictions. Overall, thermal resistances were recorded between $\rm40\ cm\sp{2\circ}C/W\ and\ 110\ cm\sp{2\circ}C/W$ for a 3 x 3 array of flush-mounted heat sources immersed in FC-77. Modeling dense parallel plate fin arrays as a porous medium was shown to be a good first-order approximation, with numerical predictions being in fair agreement with experimental data. Discrete heat sources with attached parallel plate fin arrays increased heat transfer over flush-mounted heat sources by as much as 24 and 15 times when the cavity was oriented vertically and horizontally, respectively. Furthermore, orienting the cavity horizontally produced uniform heat transfer from the discrete heat source array. Thermal resistances on the order of $\rm2\ cm\sp{2\circ}C/W$ can be expected with the dense parallel plate fin arrays used in this study, while using FC-77 as the coolant and maintaining the maximum temperature difference below $70\sp\circ$C
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Plunging liquid jets are a multiphase flow studied to understand how gas is entrained in a liquid and the resulting mixing capabilities. From existing literature, it has been hypothesized that rising bubbles play a noticeable role in the... more
Plunging liquid jets are a multiphase flow studied to understand how gas is entrained in a liquid and the resulting mixing capabilities. From existing literature, it has been hypothesized that rising bubbles play a noticeable role in the multiphase hydrodynamics of the plunging liquid jet bubble plume, and that separating the rising bubbles from the incoming liquid jet can result in a significant increase in the depth of the bubble plume. This study explores the effects of separating the incoming liquid jet from the rising bubble plume through floor interactions and compression effects due to a finite tank depth. This configuration is found in many natural and industrial systems, but not within published literature. Using existing theoretical models of infinite depth plunging liquid jet systems, which align reasonably well with captured baseline data, two models are developed for when floor interactions are present, one theoretical and one empirical. The models show a correlation be...
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Optimization of jet engine sprays has the potential to improve efficiency and reduce environmental impact. Sprays can be continually optimized in multivariate scenarios using real-time feedback control, but a method of controlling the... more
Optimization of jet engine sprays has the potential to improve efficiency and reduce environmental impact. Sprays can be continually optimized in multivariate scenarios using real-time feedback control, but a method of controlling the sprays based on physical properties must first be established. In this study, a spray controller was developed to optimize the spray angle obtained from shadowgraphs, with the assumption that the largest angle is desired. The spray angle was used as an example, as it is a physically important parameter which is easily found through shadowgraph imaging. Varying ratios of swirled air to straight air, determined by the image-based feedback controller were introduced into the air portion of a coaxial airblast nozzle while keeping the total air flow rate constant. A golden section search converged on the swirled air ratio that provided the largest angle and was validated from the distribution of spray angle versus swirled air ratio. The ratio that produced a spray with the greatest angle of 25.8 ± 2 deg was found at a swirled air ratio of 0.66 ± 0.03 for a spray with a momentum ratio of 6. The successful design and implementation of this image-based feedback controller is intended to provide a foundation for developing real-time active feedback controllers for sprays.
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Abstract Hydrate plug formation remains a common issue in off-shore oil extraction. These plugs usually form within low temperature, high pressure environments over a short timeframe. It is desirable to visualize and quantify hydrate... more
Abstract Hydrate plug formation remains a common issue in off-shore oil extraction. These plugs usually form within low temperature, high pressure environments over a short timeframe. It is desirable to visualize and quantify hydrate formation, where the results can later be used to validate formation models. This study presents preliminary findings from the use of X-ray imaging to capture temporal images of the hydrate formation process using cyclopentane, which forms a structure II hydrate, similar to that formed in oil extraction. A hydrate region was formed within a mixing chamber, and the formation process was captured using both X-ray radiography and X-ray computed tomography (CT). Image processing procedures were developed to extract qualitative and quantitative measures of hydrate formation. Formation trends correlated to the recorded time-temperature histories within the mixing tank. Additionally, formation growth patterns were qualitatively consistent across multiple trials. Quantitative analysis, however, remained difficult due to slight variations in X-ray intensity and temperature histories that resulted in significant differences in the measured hydrate region.
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Natural gas hydrates form under high pressure and low-temperature environments common in deepwater off-shore petroleum production operations. Once hydrates form, they can agglomerate and deposit resulting in solid plugs within the piping... more
Natural gas hydrates form under high pressure and low-temperature environments common in deepwater off-shore petroleum production operations. Once hydrates form, they can agglomerate and deposit resulting in solid plugs within the piping system, which could require extensive downtime for remediation and recommission of the systems. Hydrate plug formation is difficult to characterize because of the challenging environments in which they form, the lack of instrumentation for such environments, and the fast reaction time compared to other blocking mechanisms. This study explores the use of X-ray flow visualization, including X-ray radiography and X-ray computed tomography, to help characterize hydrate formation in a laboratory setting. A structure II hydrate was formed in a concentric cylinder mixing tank where a mixture of distilled water and cyclopentane was stirred in the inner tank while the outer tank was cooled. As the tank cooled, the distilled water-cyclopentane mixture convert...
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Plunging jets have been extensively studied for their relatively simple set-up but complex multiphase interactions. This phenomenon includes gas carry-under and mixing, which occurs when shear effects between the plunging liquid jet and... more
Plunging jets have been extensively studied for their relatively simple set-up but complex multiphase interactions. This phenomenon includes gas carry-under and mixing, which occurs when shear effects between the plunging liquid jet and surrounding gas are sufficient to entrain gas at the impact site. Previous investigations typically assume the floor has an infinite depth and neglect compressive effects caused by the jet interacting with the catch tank floor. While this assumption is ideal for breaking waves in the middle of the ocean, many other applications have to contend with floor effects. These include waterfalls, wastewater treatment, dams, fish farms, mineral separation, and molten metal pouring. It is hypothesized that floor interactions will significantly affect the multiphase flow hydrodynamics, especially in places where the uninhibited jet would approach or pass the floor region. Using a large catch tank with an adjustable floor region designed to hold a constant water...
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Research Interests: Materials Science, Flotation, Liquids, Bleaching, Fibers, and 4 moreSystems, Deinking, Dispersions, and Gas
In the present work, gas-liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian-Eulerian ensemble-averaging method in a two dimensional Cartesian system. The time-averaged gas holdup simulations are compared... more
In the present work, gas-liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian-Eulerian ensemble-averaging method in a two dimensional Cartesian system. The time-averaged gas holdup simulations are compared to experimental measurements of a cylindrical bubble column performed by Rampure et al. [1]. Numerical predictions are presented for the time-averaged gas holdup at various axial heights as a function of radial position. The effects of grid resolution, bubble pressure model, and drag coefficient models on the numerical predictions are examined. The bubble pressure model is reported to account for bubble stability, thus providing physical solutions. The objectives are to obtain grid-independent numerical solutions to resolve unphysical results observed in FLUENT with increasing grid resolutions [2], and to validate computational fluid dynamics simulations with experimental data to demonstrate the use of numerical simulations as a viable design tool fo...
Flotation deinking is a complete process. A better understanding of its fundamentals would help in developing models that can predict whether a given process change would help flotation performance before attempting an expensive mill... more
Flotation deinking is a complete process. A better understanding of its fundamentals would help in developing models that can predict whether a given process change would help flotation performance before attempting an expensive mill trial. Knowledge of flotation fundamentals can also be used to improve equipment design and performance. This paper reviews the fundamentals of flotation separation. Because the use of flotation in paper recycling was adapted from the mineral processing industry, the discussion begins with a comparison of the similarities and differences between flotation deinking and mineral flotation. The flotation macroprocess is presented as a function of four sequential microprocesses : particle capture (or interception), attachment by sliding, three-phase contact, and stability. These microprocesses are reviewed in detail, followed by a discussion of selected flotation deinking models. Application : better knowledge of flotation fundamentals can enhance deinking performance and improve the design of future flotation cells.
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Mixing and segregation in particulate systems have been studied extensively over the past two decades because multi-component granular systems are important to many industrial processes such as fluidized bed gasification, food processing,... more
Mixing and segregation in particulate systems have been studied extensively over the past two decades because multi-component granular systems are important to many industrial processes such as fluidized bed gasification, food processing, and pharmaceutical production. Product quality is often identified by the homogeneity (or lack thereof) of the mixture. Several methods have been developed to assess the mixing or segregation quality in granular systems and various segregation measures have been proposed. This paper presents a method to quantify mixing/segregation in collapsed fluidized beds by using 3D X-ray computed tomography. Additionally, a new characterization measure, the particle segregation number (PSN), is introduced. The PSN expresses the level of "mixedness" in a collapsed fluidized bed (or any granular system) with a single number, thus providing a single measure to quantify mixing or segregation in 3D granular systems.
Liquid jets are found in many applications, from printing to manufacturing to entertainment. This study uses three different noninvasive imaging modalities to compare resulting images of a liquid jet operating at three Reynolds numbers... more
Liquid jets are found in many applications, from printing to manufacturing to entertainment. This study uses three different noninvasive imaging modalities to compare resulting images of a liquid jet operating at three Reynolds numbers that cover laminar, transitional, and turbulent flow. Selected measurement quantities from each image type are also compared. High-speed backlit (BL) imaging is a simple imaging technique found in many laboratories, and this is compared to two high-speed X-ray imaging techniques, white beam (WB) imaging and focused beam (FB) radiography. BL imaging can provide a wide field of view and is easy to implement, but it only shows the presence or absence of liquid. WB imaging can show detailed contours on the surface of the liquid jet, but the imaging region is much smaller. FB radiography produces a point-source measurement and can provide the quantitative, instantaneous local liquid path length, termed the equivalent path length (EPL). All three techniques...
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Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the... more
Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the hydrodynamics of a fluidized bed. Experimental studies on the effects of bed height on the minimum fluidization velocity and gas holdup were carried out using a 10.2 cm diameter cylindrical fluidized bed filled with 500–600 μm glass beads. In this study, four different bed height-to-diameter ratios were used: H/D = 0.5, 1, 1.5, and 2. Minimum fluidization velocity was determined for each H/D ratio using pressure drop measurements. Local time-average gas holdup was determined using non-invasive X-ray computed tomography imaging. Results show that minimum fluidization velocity is not affected by the change in bed height, while local gas holdup does appear to be affected by the change in bed height.© 2010 ASME
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Introduction Understanding the jetting phenomena near the gas distributor plate in a fluidized bed is important to gassolids mixing, heat and mass transfer, and erosion on any bed internals, which can all affect the performance of the... more
Introduction Understanding the jetting phenomena near the gas distributor plate in a fluidized bed is important to gassolids mixing, heat and mass transfer, and erosion on any bed internals, which can all affect the performance of the bed. Moreover, acoustic vibration in a fluidized bed can be used to enhance the fluidization quality of particulate matter. Visualizing the jetting structure using X-ray computed tomography in a 3D fluidized bed, with and without acoustic intervention, is completed in this study. A 10.2 cm ID fluidized bed filled with glass beads, with material density of 2500 kg/m 3 and particles sizes ranging between 212-600 μm, is used in these experiments. X-ray computed tomography (CT) imaging is used to determine local time-average gas holdup. From this information, qualitative characteristics of the hydrodynamic structure of the multiphase flow system are visualized. Jetting has been studied extensively in the gas-solid fluidized bed literature [1-3]. However, m...
ABSTRACT Granular flows are commonly encountered in many industrial processes, but are difficult to characterize due to the opaque nature of the flow. For instance, screw pyrolyzers are being developed for the thermochemical conversion of... more
ABSTRACT Granular flows are commonly encountered in many industrial processes, but are difficult to characterize due to the opaque nature of the flow. For instance, screw pyrolyzers are being developed for the thermochemical conversion of biomass into bio-oil, but the granular flow and mixing process inside the reactor lacks fundamental understanding. In this study, X-ray particle tracking velocimetry (XPTV) is used to qualitatively and quantitatively characterize the three-dimensional (3D) granular flow structures in a double screw mixer, which geometrically replicates double screw pyrolyzers, by visualizing the position and speed profiles and quantifying the dimensionless pathlength and dimensionless residence time of individual tracer particles. The influence of screw rotation speed, dimensionless screw pitch, screw rotation orientation, and material injection configuration are investigated. Certain operating conditions are shown to significantly influence the granular flow structures and, in some instances, cause the double screw mixer to behave similar to two single screw conveyors. Comparisons with previous granular mixing studies are made to provide a link between granular flow behavior and mixing effectiveness.
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ABSTRACT Granular flows are commonly encountered in many industrial processes, but are difficult to characterize due to the opaque nature of the flow. For instance, screw pyrolyzers are being developed for the thermochemical conversion of... more
ABSTRACT Granular flows are commonly encountered in many industrial processes, but are difficult to characterize due to the opaque nature of the flow. For instance, screw pyrolyzers are being developed for the thermochemical conversion of biomass into bio-oil, but the granular flow and mixing process inside the reactor lacks fundamental understanding. In this study, X-ray particle tracking velocimetry (XPTV) is used to qualitatively and quantitatively characterize the three-dimensional (3D) granular flow structures in a double screw mixer, which geometrically replicates double screw pyrolyzers, by visualizing the position and speed profiles and quantifying the dimensionless pathlength and dimensionless residence time of individual tracer particles. The influence of screw rotation speed, dimensionless screw pitch, screw rotation orientation, and material injection configuration are investigated. Certain operating conditions are shown to significantly influence the granular flow structures and, in some instances, cause the double screw mixer to behave similar to two single screw conveyors. Comparisons with previous granular mixing studies are made to provide a link between granular flow behavior and mixing effectiveness.
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Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work will focus on computational simulations of a fluidized bed gasifier with a... more
Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work will focus on computational simulations of a fluidized bed gasifier with a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. The simulations described in this paper will model cold-flow fluidized bed experiments, and consider factors such as particle sphericity, coefficient of restitution, and drag coefficient calibration. Hydrodynamic results from the simulations will be qualitatively compared with X-ray flow visualization studies of a similar bed.Copyright © 2007 by ASME
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Plunging jets occur when a liquid stream enters a slower moving or stationary liquid body after first passing through a gaseous region. The most commonly studied plunging jet structure is that of water entering water. Plunging jets have... more
Plunging jets occur when a liquid stream enters a slower moving or stationary liquid body after first passing through a gaseous region. The most commonly studied plunging jet structure is that of water entering water. Plunging jets have been studied in order to understand and model mixing and transport from the atmosphere into the liquid. Shear forces at the edge of the jet cause air entrainment both in the free jet and at the impact point on the pool surface. Plunging jet applications range from large scale environments, such as ocean waves, waterfalls, wastewater treatment, and dams, to small scale environments, such as liquid-gas fuel mixing, mineral separation, and molten metal pouring. The majority of the literature today involve facilities designed to approximate an infinite liquid pool; few of these studies take into account the compression effects prevalent in several of the real systems. Therefore, a tank has been developed for the visualization of plunging jet flows with varying pool depth. This study involved the creation of a 32 cm by 32 cm, 91.4 cm deep rectangular acrylic tank with an interior adjustable acrylic bottom for the visualization of plunging jet flows with bottom compression effects. The pool height was held constant using a secondary tank with an overflow weir. In this study high-speed backlit images were taken of the plunging jet region. Preliminary results indicate that there is a significant change in both the shape and estimated entrained air volume when the plunging jet is subjected to compression effects. This is attributed to the plate spreading the bubble plume and allowing for easier bubble rise.
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Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the... more
Characterizing the hydrodynamics of a fluidized bed is of vital importance to understand the behavior of these multiphase flow systems. Minimum fluidization velocity and gas holdup are two important factors used to understand the hydrodynamics of a fluidized bed. Experimental studies on the effects of bed height on the minimum fluidization velocity and gas holdup were carried out using a 10.2 cm diameter cylindrical fluidized bed filled with 500–600 μm glass beads. In this study, four different bed height-to-diameter ratios were used: H/D = 0.5, 1, 1.5, and 2. Minimum fluidization velocity was determined for each H/D ratio using pressure drop measurements. Local time-average gas holdup was determined using non-invasive X-ray computed tomography imaging. Results show that minimum fluidization velocity is not affected by the change in bed height, while local gas holdup does appear to be affected by the change in bed height.© 2010 ASME
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The near-field region of a spray has a significant impact on the downstream dynamics. However, the nearfield region remains one of the most difficult areas to characterize due to its optical density to visible light. One of the methods... more
The near-field region of a spray has a significant impact on the downstream dynamics. However, the nearfield region remains one of the most difficult areas to characterize due to its optical density to visible light. One of the methods used to probe the near-field region is high-speed white beam (broad-spectrum) X-ray radiography, which generates path integrated, time sequenced images of the spray. While white beam imaging is effective at probing the near-field region, high intensity synchrotron sources are required to acquire high-speed time-resolved image sequences. The drawback to a synchrotron source is it emits a significant portion of its X-ray spectrum at energies that are minimally attenuated by most sprays. This paper will examine the various parameters that can be tuned to improve the characterization of sprays with white beam X-rays, and will assess their effects on the X-ray image quality. A representative spray conditions will be shown using a canonical coaxial gas-liqu...
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The ability to control spray formation and dispersion is extremely important to many spray applications such as combustion systems, coating and painting methods, 3D printing processes, and fire suppression designs. The ultimate outcome of... more
The ability to control spray formation and dispersion is extremely important to many spray applications such as combustion systems, coating and painting methods, 3D printing processes, and fire suppression designs. The ultimate outcome of our ONR Multidisciplinary University Research Initiative (MURI) project is to demonstrate multiphysics control of liquid sprays issuing from airblast atomizers through the novel integration of advanced diagnostics and the application of dataand simulation-driven model reduction in easy-to-implement control algorithms. Some of the advanced diagnostics used in this project to better understand spray formation include: (1) 2D X-ray radiography and 3D X-ray computed tomography obtained from common tube X-ray sources, and (2) high-speed 2D radiographic movies and detailed 2D density projections from high intensity white beam and focused beam radiography from a synchrotron X-ray source. All of these techniques will focus on imaging the near-field region ...
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Shadowgraphs, tube-source X-ray radiographs, and synchrotron X-ray radiographs from a coaxial two-fluid spray are analyzed to measure the liquid core length of the spray. Two flow conditions: Rel = 1,100, Reg = 21,300, We = 40, and Rel =... more
Shadowgraphs, tube-source X-ray radiographs, and synchrotron X-ray radiographs from a coaxial two-fluid spray are analyzed to measure the liquid core length of the spray. Two flow conditions: Rel = 1,100, Reg = 21,300, We = 40, and Rel = 1,100, Reg = 46,700, We = 196 are investigated. The standard deviation of the fluctuating intensity values are calculated and analyzed to estimate the liquid core length. Additionally, the largest connected domain is used to find an instantaneous breakup position of the spray. The results show that the high standard deviation region is related to the ligament development region, and the instantaneous position identifies ligament formation in the spray. Disciplines Mechanical Engineering Comments This proceeding is published as Li, D., Bothell, J.K., Morgan, T.B., Heindel, T.J., Machicoane, N., Aliseda, A., and Kastengren, A.L., "Measurement of Liquid Core Length of a Coaxial Two-Fluid Spray," ILASS-30th Annual Conference on Liquid Atomizat...
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The use of X-ray flow visualization has brought a powerful new tool to the study of multiphase flows. Penetrating radiation can probe the spatial concentration of the different phases without the refraction, diffraction, or multiple... more
The use of X-ray flow visualization has brought a powerful new tool to the study of multiphase flows. Penetrating radiation can probe the spatial concentration of the different phases without the refraction, diffraction, or multiple scattering that usually produce image artifacts or reduce the signal-to-noise ratio below reliable values in optical visualization of multiphase flows; hence, X-ray visualization enables research into the three-dimensional (3D) structure of multiphase flows characterized by complex interfaces. With the commoditization of X-ray laboratory sources and wider access to synchrotron beam time for fluid mechanics, this novel imaging technique has shed light onto many multiphase flows of industrial and environmental interest under realistic 3D configurations and at realistic operating conditions (high Reynolds numbers and high volume fractions) that had defied study for decades. We present a broad survey of the most commonly studied multiphase flows (e.g., spray...