High-speed Camera Images Research Articles

Optical emission spectroscopy diagnostics of DBD plasma with particles in a two-dimensional spouted bed

To gain an insight into the effect of fluidization behavior of particles on the characteristic of plasma in a plasma-enhanced spouted bed, we investigated the changes of plasma optical emission spectroscopy (OES) with fluidized particles in this paper. Fluidization experiments under the irradiation of a dielectric barrier discharge (DBD) plasma generator were performed in a two-dimensional spouted bed. Essential operation parameters, such as particle type, applied voltage, gas velocity, and particle number were changed. The pressure drop of particles, emission intensity (EI) of plasma, and high-speed camera images of plasma pattern were measured. As the results, the fluidization behavior of particles had been changed by the plasma irradiation, especially for polypropylene (PP) particles. The emission spectra of argon (Ar) plasma had been changed significantly with particles. The emission intensities of the Ar I transition lines were increased, and Ar II lines were decreased with PP particles compared to the case of no particle. The emission intensity of Ar I lines was enhanced with the applied voltage regardless of the addition of particles. The emission intensity changed with a gas velocity versus particle numbers was identified with the fluidization behavior, that emission intensity was increased at first and then decreased. The gas velocities corresponded to the highest value of emission intensity with various particle number were similar to the trend of the changes of minimum spouted velocity. The electrical conductivity and color of particles may affect the difference of pressure drop and detected emission intensity for two kinds of particles. Our research extends the knowledge of the relationship between fluidization behavior and plasma optical characteristic.

Rotating spoke instabilities in a wall-less Hall thruster: experiments

Properties of rotating spokes have been investigated in the plasma discharge of the 200 W-class permanent magnet ISCT200 Hall thruster (HT) in wall-less (WL) configuration under various operating conditions. For comparison purposes, the HT was also operated in the standard configuration. High-speed camera imaging combined with sophisticated image processing allowed the observation of the plasma inhomogeneity dynamics and the determination of characteristics such as mode number, sizes, rotation frequency and propagation velocity. The time varying Xe+ ion azimuthal velocity distribution function has been measured in front of the anode of the WL thruster by means of laser-induced fluorescence spectroscopy in photon-counting regime. Experiments show ions move at the thermal speed on average, yet some ions have a negative velocity, i.e. they rotate in the direction opposite to the E × B drift, in agreement with numerical simulations performed with a 3D-3V PIC code.

Ultrasonic Bonding of Multi-Layered Foil Using a Cylindrical Surface Tool

A cylindrical tool was applied for ultrasonic bonding of multi-layered copper foil and a copper sheet to prevent damage to the foil during bonding. The strength of the joints bonded with the cylindrical tool was comparable to that of the joints bonded with a conventional knurled tool. The effect of the cylindrical surface tool on bondability was investigated thorough relative motion behaviors between the tool surface and the bonding materials, as well as on bond microstructure evolution. The relative motion was visualized with in-situ observation using a high-speed camera and digital image correlation. At shorter bonding times, relative motions occurred at the bonding interfaces of the foil and the copper sheet. Thereafter, the relative motion between the tool and the bonding material became predominant owing to bond formation at the bonding interface, resulting in a macroscopic plastic flow in the bonded region. This relative motion damaged the foil in knurled tool bonding, and the cylindrical tool achieved bonding without any damage.

Thermal hydraulic characteristics of unstable bubbling of direct contact condensation of steam in subcooled water

The study of direct contact condensation (DCC) of steam is important owing to the diverse range of DCC applications, including uses in power plants, heat exchangers, and steam ejectors. In this study, an experimental investigation was performed to study the thermal hydraulic characteristics of the DCC of steam in an unstable condensation regime. Deionized water was used as the working fluid obtained with the use of a reverse osmosis method. The experiments were performed with pool temperatures in the range of 70 to 92 °C ± 2 °C, with different steam mixture mass fluxes in the range of 5 and 64 kg/m2 s, and with a gas injection nozzle with an inner diameter of 9.525 mm. The pool temperature was measured using thermocouples, and the surface area of the bubble and the volume flow rate were evaluated with high-speed camera image acquisitions. Subsequently, image processing was used to obtain the heat-transfer coefficient and other thermal hydraulic characteristics, such as the bubble condensing frequency and the bubble centroid velocity. The calculated condensation heat-transfer coefficients were found to be 24.57–179.78 kW/m2⋅K. According to the experimental results at various boundary conditions, a unified correlation of the heat-transfer coefficient was identified at the bubbling frequency in the unstable condensation regime, regardless of the pool subcooling temperature and steam mass flux. It was also found that the characteristic frequency of the steam bubble can be determined based on the boundary conditions to allow the determination of the heat-transfer coefficient with the given boundary conditions.

3D experimental visualization of water flooding in proton exchange membrane fuel cells

In Proton Exchange Membrane Fuel Cell (PEMFC) heat and water are generated as a side production. The accumulated water leads to a decrease in PEMFCs' efficiency. Hence, water has to be removed in order to prevent flooding inside the cell. In this study, by using experimental transparent Gas Diffusion Layer (GDL) water transport in PEMFC is visualized, and the capillary fingering mechanisms are studied. The effect of adding Micro Porous Layer (MPL) on water flooding inside the GDL is also examined. The images of high-speed camera confirmed the characteristics of capillary fingering in the GDL. It is observed that lateral flow on the surface of Catalyst Layer (CL) leads to an increase in water flooding in GDL while PEMFC efficiency is decreased. By using the MPL and increasing its thickness, the amount of lateral flow on the CL is decreased, and the generated fingers are entered into the GDL at specific discrete locations on the surface of the MPL. In this condition, the fingers choose straight paths to reach the gas channel (GC). Adding the MPL, with a maximum thickness of 2 cm, leads to a 51.5% reduction in the expansion length of the penetrating fluid inside the GDL in comparison with the GDL without MPL. Also, at the end of the test, the residual volume of the non-wetting fluid inside the GDL and MPL layers is measured. By employing the MPL and increasing its thickness, the volume of the non-wetting fluid inside the cell is reduced down to 38% which causes a decrease in saturation level of water in the GDL, and the cell performance is also improved.

Analysis of voice quality parameters in patients with vestibular voice.

Vestibular voice includes participation of larynx structures which are absent in physiological process. Vestibular phonation may be desired when vocal folds are damaged as in paralytic dysphonia, or undesired in marginal hyperfunction. Vestibular voice may result from psychogenic dysphonia - phononeurosis. The aim of the study is perceptive evaluation of vestibular voice, objective larynx visualization, acoustic and aerodynamic examination. The study included 40 patients: 20 with vestibular voice, 20 with euphonic voice. Voice quality has been evaluated using perceptual GRBAS scale. Endoscopic and stroboscopic larynx examination used Endo-STROB-EL-Xion GmbH with visual tract. High-Speed Digital Imaging (HSDI) and High Speed (HS) camera registered true vocal folds vibrations. Acoustic evaluation of voice with DiagnoScope Specjalista, DiagNova Technologies included analysis of F0, Jitter, Shimmer, NHR, nonharmonic components. MPT has been analyzed. In examined group, hoarseness (95%), roughness (75%) and voice strain (55%) have been recorded. Endoscopy revealed edema of vestibular folds with dilation of vessels covering glottis. Stroboscopy and HSDI confirmed coexistence of hyperfunctional (95%) or paralytic (5%) dysphonia. Acoustic assessment revealed increase in Jitter, Shimmer, NHR and decrease in F0 and MPT. The vestibular voice is observed most frequently in women with hyperfunctional dysphonia (phononeuroses) or in paralytic dysphonia. Visualization techniques confirm the coexistence of vestibular folds hypertrophy and edema with vibration disorders. In the perceptual assessment, vestibular voice was hoarse, rough and strained. Acoustic examination showed increase of Jitter, Shimmer, NHR, presence of nonharmonic components and decrease of F0 and MPT.

A new method for the study of parabolic impact of foam-core sandwich panels

Lightweight sandwich panels with composite facesheets and foam core have high impact energy absorption capability and are widely employed in multifunctional applications such as aircraft and marine structures. The dynamic behaviour of sandwich panels is typically studied for impact loading at normal angle of incidence but the structures are more frequently loaded at some oblique angle or with a complex tri-dimensional trajectory in real engineering situations. The damage area and damage modes for these trajectories are significantly different and it is not sufficient to study only normal impacts. There are well established experimental protocols for normal or oblique impact tests using devices like the drop tower, but impacts with complex trajectory are difficult to characterise experimentally. In this paper, a Gough-Stewart platform with six degrees of freedom has been modified to develop an original tri-dimensional impact device called Hexapod. The trajectory is defined to an impactor attached to the seventh jack of the Hexapod to study the response of sandwich plates to impact loading with complex trajectories. The applicability of the newly developed device is demonstrated by studying parabolic impact with different trajectories on sandwich plates with Kevlar facesheets and Rohacell foam core. The time history of vertical and horizontal components of force is measured using tri-axial load cell and strain history is obtained from Digital Image Correlation of a high speed camera images. The results of the parabolic impact show the importance of shear behaviour of the foam in the progression of damage in the sandwich panels. Additionally, the response of the sandwich panels to parabolic impact was simulated numerically using explicit finite element code LS-DYNA. The results of the FE model are compared with experimental data in terms of the force history and strain contours.

Studying the rate of velar elevation across different vowel contexts in normal speech using high speed nasopharyngoscopy

Velum has a range of positions across different speech segments, with the lowest velum position for nasal consonants, a high (closed) position for obstruent consonants, and a range of positions in the middle for sonorant consonants and vowels varying according to constriction degree. Vowel environment has a considerable influence on the rate of velum closure. Changes in the rates of velar positioning during production of vowels in non-nasal speech (H-words) was studied in seven typically speaking adults with general American dialect and normal oral-nasal resonance. The participants were scoped using a Phantom Miro 310 high-speed video camera (Image acquisition rate of 5000 fps) connected to a flexible scope. Measurements were taken simultaneously with capturing acoustic data. The data suggested that velum tends to have a higher elevation point for vowels with higher degree of constriction in the oral cavity like /i/. Further results will be discussed.

Fluidization in small-scale gas-solid 3D-printed fluidized beds

Additive manufacturing could be used to facilitate the rapid fabrication and testing of small-scale fluidized beds for use in screening applications, such as adsorbent screening for carbon capture. In this work, experiments were performed in order to map the different flow regimes produced in small-scale (Dh = 3–15 mm) gas-solid fluidized beds that were fabricated using additive manufacturing using the stereolithography approach. Here, the effects of bed hydraulic diameter (Dh), static particle height (Hs), and particle type/size (Dp and ρp) were considered. Pressure drop data and high speed camera images were used to develop simple flow regime maps for these printed beds showing the operating windows for packed bed, bubbling, slugging and turbulence applicable to a wide range of bed size to particle diameter ratios (Dh/Dp = 20–200) and gas velocities (Ug = 1–400 mm/s) in both ‘2D’ and ‘3D’ bed aspect ratios. Fast Fourier transforms of the pressure drop signals were also used to study the evolution of bubbling/slugging behaviour as the gas velocity was increased by creating 2D colour maps of the frequency spectra. These allowed a new quantitative method to be proposed for the identification of slugging – the point where the dominant frequency in the power spectrum becomes constant as the gas velocity increases. It is concluded in this study that the rougher surfaces generated by additive manufacturing do not influence the fluidization characteristics nor modify the wall effects of small-scale beds. Macro-scale fluidization could also be achieved at smaller Dh/Dp ratios in these 3D printed beds compared to more conventional Plexiglas beds (Dh/Dp = 75 compared to Dh/Dp = 300).

Structural Low-Level Dynamic Response Analysis Using Deviations of Idealized Edge Profiles and Video Acceleration Magnification

The development of high-speed camera systems and image processing techniques has promoted the use of vision-based methods as a practical alternative for the analysis of non-contact structural dynamic responses. In this study, a deviation extraction method is introduced to obtain deviation signals from structural idealized edge profiles. Given that the deviation temporal variations can reflect the structural vibration characteristics, a method based on singular-value decomposition (SVD) is proposed to extract valuable vibration signals from the matrix composed of deviations from all video frames. However, this method exhibits limitations when handling low-level motions that reflect high-frequency vibration components. Hence, a video acceleration magnification algorithm is employed to enhance low-level deviation variations before the extraction. The enhancement of low-level deviation variations is validated by a light-weight cantilever beam experiment and a noise barrier field test. From the extracted waveforms and their spectrums from the original and magnified videos, subtle deviations of the selected straight-line edge profiles are magnified in the reconstructed videos, and low-level high-frequency vibration signals are successfully enhanced in the final extraction results. Vibration characteristics of the test beam and the noise barrier are then analyzed using signals obtained by the proposed method.

Control of Coherent Structures via External Drive of the Breathing Mode

The Hall thruster exhibits two types of large-scale coherent structures: axially propagating breathing mode (m = 0) and azimuthal, with low m, typically m = 1, spoke mode. In our previous work, it was demonstrated that axial breathing mode can be controlled via the external modulations of the anode potential. Two regimes of the thruster response, linear and nonlinear, have been revealed depending on the modulation amplitude. In this work, using the high-speed camera images and developed image-processing technique, we have investigated the response of the azimuthal mode to the external modulations. We have found that, in linear regime, at low modulation voltages, axial and azimuthal structures coexist. At larger amplitudes, in the nonlinear regime, the azimuthal mode is suppressed, and only axial driven mode remains.

High-Speed Camera Imaging of the Ignition Process in a Heaterless Hollow Cathode

The plasma discharge inside a heaterless hollow cathode (HHC) is studied during its ignition process. A partly transparent HHC device is developed for this purpose. The temporal evolution images of the plasma in the cathode are obtained by a high-speed camera imaging method. It is observed that the ignition process is started with a gas breakdown that originates between the cathode plate and the keeper plate. After that the plasma discharge spreads out of the keeper through the orifice on the keeper plate. Then, the discharge moves back into the emitter region through the orifice on the cathode plate. It is seen that an arc discharge is formed as the plasma propagates from the downstream end of the emitter to its upstream region. Because of this process, part of the emitter (that next to the cathode plate) is heated gradually to the steady-state operating temperature. The HHC achieves thermal electron emission after the ignition process.

Conditions and Characteristics in Ignition of Composite Fuels Based on Coal with the Addition of Wood

In this paper, we experimentally determined the conditions and characteristics of the ignition of the fuel mixture samples of various composition of crushed coal and wood in stationary air heated to high temperatures (from 600 to 1000°C). The heating of fuel mixtures under study that are promising for heat power engineering and their subsequent ignition and combustion were registered by using a high-speed video camera (image size is 1024 × 1024 pixels, frame rate is up to 105 frame/s), which ensures high reliability of the obtained results. The ignition delay times of all the studied mixtures based on lean and long-flame coals were established to decrease with an increase in the wood fraction. The limits of the stable (with small deviations of the delay time from the average values) ignition of weights of the studied mixtures are selected. At an increase in the wood waste fraction up to 50%, the decrease in the ignition delay time of mixed fuel based on grade T coal was found to be 11.2% at 600°C and 55.3% at 1000°C. For fuel mixtures based on grade D coal and wood, similar indicators are 17.6 and 64.3%. At temperatures typical for the furnace environment (approximately 1000°C), the ignition delay time for such fuels was determined to be less than 1 s, which is significantly less than the similar ignition characteristics of long-flame and lean-coal dust. The ash content of the fuel mixture is established to be a nonadditive characteristic relative to the ash content of the corresponding coal and wood. The increase in the wood fraction to 50% leads to a decrease in ash content to 10.44% for grade D coal and to 11.08% for grade T coal.

Single-Station-Based Lightning Mapping System With Electromagnetic and Thunder Signals

A single-station-based lighting mapping system comprising a microphone array, which detects electromagnetic (EM) and thunder signals, has recently been developed and deployed for lightning observations. Using one microphone array consisting of 19 electret microphones installed on a 3-D steel frame, this system receives and processes the EM and thunder signals to determine the location of lightning thunder sources. We implement a new broadband direction-of-arrival estimation technique, namely, the maximum power beamforming algorithm and derive the 3-D location results based on the time difference between the acoustic signal and the EM signal. In this paper, four cloud-to-ground flashes with different branch channels recorded by the system are analyzed and presented in which the located thunder sources of two lightning flashes are compared with the photograph of the high-speed camera. The details of the system implementation along with the successful reconstruction of the lightning channel in 2-D and 3-D space are discussed. The results indicate that the location system could effectively map the lightning thunder sources, and the result is highly consistent with the high-speed video camera images. Moreover, the acoustic mapping system is capable of locating the main channel produced by the return stroke process; it also depicts the branching channels. It is shown that the system is capable of distinguish different branches of the same lightning; it also obtains different lightning channels occurring almost simultaneously.

Dynamic Force Spectroscopy Analysis on the Redox States of Protein Disulphide Bonds.

An emerging concept in chemical biology is that protein function that can be regulated by the redox state of disulphide bonds. This chapter describes the dynamic force spectroscopy method for analyzing redox regulation of receptor-ligand interactions at the surface of living cells. The main method described in this chapter is the biomembrane force probe (BFP), in which an ultrasoft human red blood cell is used as an ultrasensitive mechanical force probe. The BFP uses a high-speed camera and real-time imaging tracking techniques to characterize a single molecular bond with ~1 pN (10-12N), ~3nm (10-9 m), and ~0.5ms (10-3s) in force, spatial, and temporal resolution. As a test bed model, we use the BFP to examine the autoregulation of von Willebrand factor function by a disulphide bond switch in its A2 domain. With the survival frequency analysis on measured bond lifetimes, we can identify distinct states of VWF binding kinetics and correlate with redox states of its A2 disulphide bond validated by mass spectrometry. The methodologies and analytical frameworks can be used to study other membrane receptor-ligand interactions under redox regulation.

Gas-liquid flow regimes in horizontal annulus

Gas-liquid flows in annulus channels are frequently encountered in the underbalanced drilling operation when the gasified drilling fluid is used. Accurate characterization of two-phase flow regimes in such conduits is critically important in order to gain a better understanding of the flow behaviours in the channels, thus to ensure a successful drilling operation achieved. In this paper experimental studies regarding gas-liquid flows in a concentric and fully eccentric horizontal annulus were reported. The test section setups of the flow loop have a length of 10.8 m, with outer and inner pipe diameters of 0.0768 m and 0.060 m respectively. Air and water at atmospheric pressure constituted the gas and liquid phases and the range of gas and liquid superficial velocities investigated during this study was 0.14–24 m/s and 0.15–2.78 m/s respectively. Flow regimes observed in both annulus setups by high speed camera imaging were dispersed bubble, elongated bubble, slug, wavy slug, churn, wavy annular and annular. A detailed description of the flow regimes with different features are presented together with high quality images. The local liquid holdup time series together with its probability density function (PDF) are used to gain more insights about the characteristics of the observed flow regimes. Effects of the annulus eccentricity on the observed flow regimes are also investigated. It is found that the annulus eccentricity affects the shape and structure of the elongated bubble, wavy annular and annular flow regimes. It is also observed that the annulus eccentricity causes the transition from elongated bubble to dispersed bubble to take place at higher liquid superficial velocities. It is also found that in the fully eccentric annulus causes transitions between different flow regimes to occur at higher liquid and lower gas superficial velocities when compared with that of concentric ones. An improved flow regime map is proposed based on gas and liquid Froude numbers by integrating the test results from this study with over 1000 data points found in literature.

High strain rate tensile behavior of a quenching and partitioning (Q&P) Fe-0.25C-1.5Si-3.0Mn steel

The mechanical behavior and microstructural evolution of a quenching and partitioning (Q&P) Fe-0.25C-1.5Si-3.0Mn (wt%) steel were investigated in a wide range of strain rates (10−4–103 s−1). The static tensile tests (10−4 and 10−2 s−1) were conducted using a universal testing machine, while high strain rate tests (500–1000 s−1) were carried out on a split Hopkinson tensile bar system. High speed camera imaging combined with the digital image correlation (DIC) technique were employed to study homogeneity of plastic deformation. Electron backscatter diffraction (EBSD) and scanning electron microscopy were used to characterize the microstructure evolution in the deformed zone and the fracture surface, respectively. The results indicate that the yield strength of the Q&P steel in dynamic tests (500–1000 s−1) is by 200 MPa higher compared to static tests (10−4 and 10−2 s−1), while the ultimate tensile strength tends to increase linearly with strain rate. The results of DIC analysis demonstrate that the homogeneity of plastic deformation is similar in static and dynamic test conditions. EBSD characterization shows that the retained austenite (RA) fraction decreases exponentially with the increase of plastic strain during both static and dynamic tensile testing. Additionally, examination of the fracture surfaces reveals the largest dimples in the statically tested specimens.

On bubble dynamics in subcooled nucleate boiling on a platinum wire

While much attention has been given to the phenomenon of boiling, the underlying physics and mechanisms are still not fully understood due to its complicated and illusive nature. In this study, an experimental investigation of subcooled pool boiling of de-ionized (DI) water, at a bulk temperature of 30 °C and atmospheric pressure, was performed on a platinum wire with a diameter of 250 μm, starting from the onset of nucleate boiling (ONB) point and rising to higher heat fluxes. A high speed camera system was utilized for visualization. Images of bubbles growth, migration, coalescence, leaping and detachment were recorded. Each of these events was investigated separately, and a comprehensive discussion undertaken. High speed camera images were analyzed by taking the most important parameters, such as surface tension, bubble-bubble interactions, nucleation site-bubble interactions, Marangoni convection and accumulation of non-condensable gases inside the bubbles. Lower applied heat fluxes led to bubble nucleation from the nucleation sites and slow growth of bubbles to a certain diameter, which were ready to migrate along the wire. Increasing the heat flux made the bubbles grow faster and favored coalescence, leaping and detaching that be observed one after another due to an increase in the temperature gradient and perturbation of the temperature field near the nucleation sites. Another important mechanism considered was the momentum of the non-condensable gases inside the bubbles, especially while the bubble tail disappeared and the bubble shrank whilst stopping near an immobile bubble or near the nucleation sites.

Experimental study of sloshing noise in a partially filled rectangular tank under periodic excitation

Liquid sloshing is becoming a major source of noise in hybrid and high-end luxury cars, especially during acceleration/deceleration driving conditions. This is due to the reduction in noise from other sources, namely, engine, transmission system, road–tyre interaction and so on. Sloshing noise is highly dependent on fluid motion in the containers. Based on the fluid motion in the containers, sloshing is classified into different regimes. The present experimental study discusses the noise generation mechanisms for various sloshing regimes. It is done by emulating different sloshing regimes in a partially filled rectangular tank by imposing longitudinal periodic excitation. The effect of fill level on noise generation phenomenon in each regime is analysed, individually, using dynamic response parameters and high-speed camera images. In this study, the measured dynamic response parameters are pressure, force, acceleration and sound pressure levels as a function of time. The fundamental reasons for the cause of sloshing noise in partially filled rectangular tanks are identified in terms of fluid motion and its interaction with the surrounding objects. The excitations upto the sloshing resonance condition cause hydraulic jumps along the tank walls leading to hit noise. Excitations beyond the sloshing natural frequency cause the predominant interaction of surface waves with surrounding fluid leading to splash noise.

Crack tip opening angle during unstable ductile crack propagation of a high-pressure gas pipeline

A full gas burst test was conducted to clarify the CTOA history during ductile crack propagation in a high-pressure pipeline. The measurement results obtained by high-speed camera observation and image processing showed that the CTOA value remains constant during crack propagation despite the large changes in the crack velocity. The numerical results of a series of finite element analyses supported the intrinsic implications of the experimental results. Consequently, the validity of the constant CTOA criterion, which has the potential to improve the accuracy and efficiency of numerical simulations of unstable ductile crack propagation in a high-pressure pipeline, was verified.