High-speed Digital Video Camera Research Articles

Liquid film characterization in horizontal, annular, two-phase, gas–liquid flow using time-resolved laser-induced fluorescence

A non-intrusive optical technique was developed to provide time-resolved longitudinal and cross-sectional images of the liquid film in horizontal annular pipe flow of air and water, revealing the interfacial wave behavior. Quantitative information on the liquid film dynamics was extracted from the time-resolved images. The planar laser-induced fluorescence technique was utilized to allow for optical separation of the light emitted by the film from that scattered by the air–water interface. The visualization test section was fabricated from a tube presenting nearly the same refractive index as water, which allowed the visualization of the liquid film at regions very close to the pipe wall. Longitudinal images of the liquid film were captured using a high-frame-rate digital video camera synchronized with a high-repetition-rate laser. An image processing algorithm was developed to automatically detect the position of the air–water interface in each image frame. The thickness of the liquid film was measured at two axial stations in each processed image frame, providing time history records of the film thickness at two different positions. Wave frequency information was obtained by analyzing the time-dependent signals of film thickness for each of the two axial positions recorded. Wave velocities were measured by cross-correlating the amplitude signals from the two axial positions. For the film cross-section observations, two high-speed digital video cameras were used in a stereoscopic arrangement. Comparisons with results from different techniques available in literature indicate that the technique developed presents equivalent accuracy in measuring the liquid film properties. Time-resolved images of longitudinal and cross-section views of the film were recorded, which constitute valuable information provided by the technique implemented.

Vacuum Arc Characteristics of CuW70 Alloy

Abstract The fine-grained and coarse-grained CuW70 alloys were prepared by sintering and infiltrating. The motion of cathode spots was observed by a digital high speed video camera and a scanning electron microscope (SEM). The results show that the fine-grained CuW70 alloy has larger breakdown strength, longer average arc life and lower chopping current. For coarse-grained CuW70 alloy, the cathode spots ignite and extinguish alternately beneath the anode, the breakdown is mainly located on copper phase, and the erosion pits are much deeper. However, the cathode spots of fine-grained CuW70 alloys have the characteristics of division and deviation, with the uniform distribution of the erosion pits on the entire cathode surface.

Effect of Mo addition on microstructure and vacuum arc characteristics of CuCr50 alloy

The work functions of Cu, Cr, Mo and CrMo were calculated utilizing the first principle. The effect of Mo addition on the microstructure of CuCr50 alloy was characterized by a scanning electron microscope, and the arc motion characteristic was recorded and investigated by a digital high-speed video camera. The calculated results show that the selectivity of breakdown is closely related to the work function of close-packed plane. The experimental results show that Mo addition can strengthen Cr phase, the first breakdown transfers from Cr phase to Cu phase, and the cathode spots present the characteristics of division and deviation, thus avoiding concentrated erosion. In addition, the chopping current is reduced and the breakdown strength is enhanced as well.

Study on In-Flow Oscillation of Couples of Cylinders by Cross-Flow

The importance of the in-flow oscillation of a single cylinder in cross-flow has been in the spotlight since an accident in a FBR-type reactor. However, in-flow oscillations can also be observed in heat exchanger tube arrays. Previous reports show some interesting phenomena on the oscillation of cylinder arrays. In this paper, detailed observation on the effect of the pitch ratio for pairs of cylinders, in parallel and in tandem, is highlighted in the range of low flow velocities, where each cylinder can move only in a given direction. The motion of the cylinders is measured by attached strain gages and by a high-speed digital video camera. As a result, it is found that the response of cylinders is greatly affected by their pitch ratio due to the separated vortex, and that the symmetric vortex is restricted when the motion of cylinder is restricted.

Bubble Lift-off Diameter and Nucleation Frequency in Vertical Subcooled Boiling Flow

A series of experiments were carried out to investigate phenomena from bubble nucleation to lift-off for a subcooled boiling flow in a vertical annulus channel. A high-speed digital video camera was used to capture the bubble dynamics. The bubble lift-off diameter and bubble nucleation frequency were evaluated in terms of heat flux, mass flux, and degree of subcooling. The fundamental features of the lift-off diameter and nucleation frequency (i.e., the variations across nucleation sites and the dependence on the flow and heat flux conditions) were addressed based on the present observation. A database for the bubble lift-off diameter was built by gathering and summarizing the data of Prodanovic et al., Situ et al., and the present experiments. We evaluated the predictive capabilities of Unal's model, Situ et al.'s model, and Prodanovic et al.'s correlation against the database. We obtained the best prediction results by modifying the wall superheat correlation in Unal's model. In addition, we suggested a new correlation for a combined parameter of the bubble nucleation frequency and bubble lift-off diameter.

OS1901 超弾性固体材料における超音速破壊現象の実験的研究(OS19-1 ゴム材料とゴム製品の力学解析/強度評価1,OS-19 ゴム材料とゴム製品の力学解析/強度評価)

Rupture speeds (Mach numbers) obtained by ordinary laboratory fracture experiments using monolithic brittle linear elastic materials are by far lower than those predicted by classical theories of mechanics and inferred from seismic inversions. Some seismological recordings even imply the existence of supersonic (supershear) rupture speeds. Here, in order to possibly explain these discrepancies, dynamic mode-I fracture in hyperelastic materials is experimentally investigated. Utilizing a high-speed digital video camera system, rupture (crack) initiation and propagation process is recorded. The preliminary results clearly show that if the magnitude of static crack-parallel stress is relatively large and comparable to that of remote mode-I loading stress, the crack propagates surprisingly straight and, even without the existence of material heterogeneities, the crack front accelerates from sub-Rayleigh to a constant supershear speed to capture the shear wave front generated upon rupture initiation.

Effect of Fe on microstructures and vacuum arc characteristics of CuCr alloys

In order to clarify the effect of Fe addition on vacuum arc characteristics of CuCr alloys, the CuCr50, CuCr45Fe5 and CuCr40Fe10 alloys were prepared by vacuum sintering and infiltrating, and the simulated electrical breakdown experiment was undertaken in a vacuum interrupter. The characteristics of the motion of vacuum arcs were analyzed by a digital high-speed video camera and the erosion morphology was characterized by a scanning electron microscope (SEM). The results show that Fe additions can strengthen the Cr phase, promote the first breakdown phase to transfer from Cr to Cu and increase the strength of the alloy breakdown voltage by 80%. Meanwhile, Fe additions can still retain the arc stability of CuCr50 alloys during the generation and extinguishing process, decrease the chopping current, and prolong the arc life. Furthermore, the characteristics of the split and motion of cathode spots on the surface of the CuCr40Fe10 alloy were improved, which prohibits the concentrated arc erosion.

Empirical study on drainage stack terminal water velocity

A building drainage network is an essential provision of each developed city all over the world. The terminal velocity at discharging drainage stack is a crucial issue as it provides the permitted flow rate of a building drainage system. The National Plumbing Code (NPC) of the US has specified the permitted flow rate for drainage systems. Mathematical expressions for terminal velocity were reported in research studies since the 1920s but discrepancies among calculations remained. This study proposes an empirical approach in determining the terminal velocity in a drainage stack using the air pressure distribution mechanism. New experimental observations of the stack terminal velocity using a digital high-speed video camera were presented as a validation database. The proposed model was validated in terms of the measured terminal velocities and the locations of the maximum air pressure in a discharging stack at a steady water flow rate (1.0, 2.0, 3.0 and 4.0 L/s). This article offers an empirical approach and validation for terminal velocity instead of using the existing deductive approach. Practical applications: This article proposes an empirical approach with experimental validation for terminal velocity at a drainage stack. New evidence presented would lead to a review of the terminal velocity in drainage stacks in future drainage network designs. Due to the importance of terminal velocity, it is anticipated that this result would be used to lead the new technical development of building drainage system.

Open Areas of Vibrating Lips in Trombone Playing

In brass instruments the player's lips are used as a control valve that allows an oscillating flow of air into the instrument. The behaviour of this valve, the lip-reed, is determined by both the pressure difference across the lips and the open area between the lips. Computer simulations of brass instrument playing frequently represent the lips as an oscillating system with one degree of freedom, representing the height of the lip opening. This study aims to provide experimental evidence to determine values of an exponential coefficient q defining the area-height function for the lips of trombone players. A high speed digital video camera and transparent mouthpiece have been used to produce detailed images of the motion of the vibrating lips of a range of musicians and an artificial mouth over a large set of playing frequencies and sound levels. These images are analysed to investigate how the open area varies as a function of the height between the lips.

The Motion Analysis Of Side-Step Cutting In Football Players

High agility performance is important for football players and the acquirement of this skill has been discussed recently. The purpose of this study was to analyze the agility test and the motion of side-step cutting by biomechanical method. Twenty college-football players (mean ± SD age = 20.6 ± 1.4yrs; height = 174.0 ± 4.2cm; weight = 78.4 ± 12.0kg) were participated in this study. Subjects performed 40 yard straight dash and pro-agility test and assigned to three groups: group A; QB, WR, DB, group B; LB, RB, group C; OL, DL. For the biomechanical analysis of side-step cutting, three subjects with different levels of agility performed 5 yard dash in a straight line and change of direction. The angle of change of direction was 90 degree and 135 degree to the right. The motion of side-step cutting was monitored by two high speed digital video cameras and analyzed by a 3-D analysis system (DKH system, Japan). The total time, the contact time of left sole and the angle of left lower leg to the ground during the change of direction were analyzed. Correlation analysis showed relatively high validity between 40 yard straight dash and pro-agility tests (r = 0.715). The values of 40 yard straight dash and pro-agility test in groups A and B were significantly higher than in group C (p < 0.05). From the biomechanical analysis, the players with high scored pro-agility test showed the contact time was short and the angle of lower leg was small in both 90 degree and 135 degree. By player position, high agility performance was observed in QB, WR, DB. The players with high agility can perform side-step cutting with small angle of lower leg to the ground within a short span of time. From this result, minimizing the angle of ankle joint may produce larger horizontal power for change of direction. This study suggested the angle of lower leg to the ground is important for side-step cutting. The above is valuable information for coaches and athletes involved in improving the skill of agility.

G0300-6-4 鉄道車両構造の強度解析に関する研究([G0300-6]材料力学部門一般講演(6):強度解析)

The railway car body is required to carry passengers safely and comfortably. Due to train accident, it is necessary to improve impact resistance and prevent the deformation of the railway car body. So, increasing adoption of double skin construction which is produced by a hollow extruded aluminum railway car body. This study analyzed the amount of displacement of the load plus the double-skin structure used in railway vehicles. The specimen is made using an epoxy resin. Analysis, using a three-point bending test, the amount of displacement is calculated by digital image correlation method and high-speed video camera, a comparative study.

The Typical Flight Performance of Blowflies: Measuring the Normal Performance Envelope of Calliphora vicina Using a Novel Corner-Cube Arena

Despite a wealth of evidence demonstrating extraordinary maximal performance, little is known about the routine flight performance of insects. We present a set of techniques for benchmarking performance characteristics of insects in free flight, demonstrated using a model species, and comment on the significance of the performance observed. Free-flying blowflies (Calliphora vicina) were filmed inside a novel mirrored arena comprising a large (1.6 m1.6 m1.6 m) corner-cube reflector using a single high-speed digital video camera (250 or 500 fps). This arrangement permitted accurate reconstruction of the flies' 3-dimensional trajectories without the need for synchronisation hardware, by virtue of the multiple reflections of a subject within the arena. Image sequences were analysed using custom-written automated tracking software, and processed using a self-calibrating bundle adjustment procedure to determine the subject's instantaneous 3-dimensional position. We illustrate our method by using these trajectory data to benchmark the routine flight performance envelope of our flies. Flight speeds were most commonly observed between 1.2 ms−1 and 2.3 ms−1, with a maximum of 2.5 ms−1. Our flies tended to dive faster than they climbed, with a maximum descent rate (−2.4 ms−1) almost double the maximum climb rate (1.2 ms−1). Modal turn rate was around 240°s−1, with maximal rates in excess of 1700°s−1. We used the maximal flight performance we observed during normal flight to construct notional physical limits on the blowfly flight envelope, and used the distribution of observations within that notional envelope to postulate behavioural preferences or physiological and anatomical constraints. The flight trajectories we recorded were never steady: rather they were constantly accelerating or decelerating, with maximum tangential accelerations and maximum centripetal accelerations on the order of 3 g.

Experimental study of underwater rock drilling using a pulsed Ho:YAG laser-induced jets

This paper is primarily an assessment of laser-induced water jets for boring rock surfaces. It also reports the result of preliminary experiments of pulsed Ho:YAG laser-induced jets applied to drill a submerged rock specimen. The irradiation of pulsed Ho:YAG laser beams at 3 Hz inside a thin metal tube produces intermittent water vapor bubbles which result in liquid jet discharge from the exit of the metal tube. The laser-induced water jets are visualized by shadowgraphs and images are recorded by a high-speed digital video camera. High stagnation pressures were eventually generated by the jet impingements. Simultaneously shock waves of about 22.7 MPa were generated at bubble collapse, which effectively cracked the surface of the rock specimens. Repeated exposures of these laser-induced jets against submerged rock specimens have a potential to practically bore holes on rock surfaces.

Effect of the injection angle on liquid spray development in a high-speed direct-injection optical diesel engine

In this paper, the spray development and its interaction with the piston geometry were investigated in a small-bore high-speed direct-injection optical diesel engine. The effects of injection angle, injection timing, injection pressure, and injection fuel quantity were studied. The entire liquid spray cycle was visualized by a background-corrected Mie-scattering technique using a high-speed digital video camera synchronized with a high-repetition-rate copper vapour laser. For some conditions, the initial injection velocity was estimated quantitatively. The results show that the injection angle and injection timing predominantly control the spray interaction with the piston geometry and the resulting air—fuel mixing mode. Narrow-angle injection leads to a significantly different air—fuel mixing process from the traditional wide-angle injector. If properly controlled, the narrow-angle direct-injection technique offers more flexibility on injection timing control with the fuel confined in the central bowl region without wetting the cylinder liner.

The critical role of channel cross-sectional area in microchannel flow boiling heat transfer

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to identify the critical geometric parameters that affect flow boiling heat transfer and flow patterns in microchannels. In recent work by the authors (Harirchian and Garimella, 2009), seven different silicon test pieces containing parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm were tested and it was shown that for a fixed channel depth, the heat transfer coefficient was independent of channel width for microchannels of widths 400 μm and larger, with the flow regimes in these microchannels being similar; nucleate boiling was also found to be dominant over a wide range of heat fluxes. In the present study, experiments are performed with five additional microchannel test pieces with channel depths of 100 and 250 μm and widths ranging from 100 to 1000 μm. Flow visualizations are performed using a high-speed digital video camera to determine the flow regimes, with simultaneous local measurements of the heat transfer coefficient and pressure drop. The aim of the present study is to investigate as independent parameters the channel width and depth as well as the aspect ratio and cross-sectional area on boiling heat transfer in microchannels, based on an expanded database of experimental results. The flow visualizations and heat transfer results show that the channel cross-sectional area is the important governing parameter determining boiling mechanisms and heat transfer in microchannels. For channels with cross-sectional area exceeding a specific value, nucleate boiling is the dominant mechanism and the boiling heat transfer coefficient is independent of channel dimensions; below this threshold value of cross-sectional area, vapor confinement is observed in all channels at all heat fluxes, and the heat transfer rate increases as the microchannel cross-sectional area decreases before premature dryout occurs due to channel confinement.

Deformable wing kinematics in free-flying hoverflies.

Here, we present a detailed analysis of the deforming wing kinematics of free-flying hoverflies (Eristalis tenax, Linnaeus) during hovering flight. We used four high-speed digital video cameras to reconstruct the motion of approximately 22 points on each wing using photogrammetric techniques. While the root-flapping motion of the wing is similar in both the downstroke and upstroke, and is well modelled as a simple harmonic motion, other wing kinematic parameters show substantial variation between the downstroke and upstroke. Whereas the magnitude of the angle of incidence varies considerably within and between different hoverflies, the twist distribution along the wing is highly stereotyped. The angle of incidence and camber both show a recoil effect as they change abruptly at stroke reversal. Pronation occurs consistently after stroke reversal, which is perhaps surprising, because this has been found to reduce lift production in modelling studies. We find that the alula, a hinged flap near the base of the wing, operates in two discrete states: either in plane with the wing, or flipped approximately normal to it. We hypothesize that the alula may be acting as a flow-control device.

Dynamic behavior of splitting flames in a heated channel

Flame-propagation dynamics with dual peaks in a heated microchannel is predicted by employing a thermal-diffusive model taking into account two reactants. After auto-ignition, the flame immediately splits into two reaction fronts with different luminosities. One front propagates upstream, whereas the other moves downstream, and finally they both extinguish. After some delay, the process is repeated, and reignition of the fuel-air mixture is induced by hot walls. It is also shown that the commonly used infinitely thin reaction zone model, which has no reactant concentration dependence, is not capable of capturing this phenomenon. The splitting flame dynamics with dual fronts is confirmed by photographs taken with a high-speed digital video camera in experimental investigations with a propane-air mixture. The experiments reveal interesting details, namely, coexistence of triple reaction peaks during the process of propagation of splitting flames is observed, and the flame splitting phenomenon occurs twice in one extinction-ignition period.

Near-field instability of variable property jet in normal gravity and microgravity fields

The near-field instability of variable property jets of air, CO2, and He, issued into the ambient air, has been investigated experimentally within normal gravity and microgravity fields. The density ratio to the ambient air is unity for air jets, more than unity (1.53) for CO2 jets, and less than unity (0.14) for He jets, respectively. The ratio of kinematic viscosity to the ambient air is unity for air jets, less than unity for CO2 jets (0.53), and more than unity for He jets (7.75), respectively. The jet velocity is varied from 0.4 to 1.8 m/s and then the jet Reynolds number varies from 60 for Helium jet to 2,000 for CO2 jet, while the Richardson number varies from negative to positive values. The motion of the jet is visualized using a laser tomographic method and recorded by a high-speed digital video camera with 250 frames/s. The result shows that the instability of the jet is intensified when Re > 800 while it is weakened at Re < 800 at the microgravity field, indicating that the viscosity plays an important role in weakening the instability. Under a normal gravity field, the buoyancy also becomes important. In order to quantify the instability criteria, the quantity of the instability is introduced, which consists of the Kelvin–Helmholtz instability, buoyancy effect and viscous effect. When the ratio of the sum of Kelvin–Helmholtz and buoyancy forces to viscous force exceeds a certain value, around 12 in the present study, the jet becomes unstable even when Re < 800. These results reveal that the instability of variable property jets is influenced by the Kelvin–Helmholtz instability, the viscous effect and the buoyancy effect.

Study on flow regimes of high-pressure and dense-phase pneumatic conveying

High-pressure and dense-phase pneumatic conveying of pulverized coal is a key technology in the field of large-scale entrained bed coal gasification. Flow regime plays an important role in two-phase flow because it affects not only flow behavior and safety operation, but also the reliability of practical processes. Few references and experiences in high-pressure and dense-phase conveying are available, especially for the flow regimes. And because of the high stickiness and electrostatic attraction of pulverized coal to the pipe wall, it is very difficult to make out the flow regimes in the conveying pipe by visualization method. Thus quartz powder was chosen as the conveyed material to study the flow regime. High-speed digital video camera was employed to photograph the flow patterns. Experiments were conducted on a pilot scale experimental setup at the pressure up to 3.6MPa. With the decrease in superficial gas velocity, three distinguishable flow regimes were observed: stratified flow, dune flow and plug flow. The characteristics of pressure traces acquired by high frequency response pressure transmitter and their EMD (Empirical Mode Decomposition) characteristics were correlated strongly with the flow regimes. Combining high-speed photography and pressure signal analysis together can make the recognition of flow patterns in the high-pressure and dense-phase pneumatic conveying system more accurate. The present work will lead to better understanding of the flow regime transition under high-pressure.

Effects of channel dimension, heat flux, and mass flux on flow boiling regimes in microchannels

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to investigate the effects of channel size and mass flux (225–1420 kg/m 2s) on microchannel flow boiling regimes by means of high-speed photography. Seven different silicon test pieces with parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm, are considered. Flow visualizations are performed with a high-speed digital video camera while local measurements of the heat transfer coefficient are simultaneously obtained. The visualizations and the heat transfer data show that flow regimes in the microchannels of width 400 μm and larger are similar, with nucleate boiling being dominant in these channels over a wide range of heat flux. In contrast, flow regimes in the smaller microchannels are different and bubble nucleation at the walls is suppressed at a relatively low heat flux for these sizes. Two types of flow regime maps are developed and the effects of channel width on the flow regime transitions are discussed.