High-speed Camera Research Articles

Vibration monitoring of rotating shafts using DIC and compressed sensing

Monitoring vibrations in rotating shafts is essential for diagnosing and detecting mechanical faults. Digital image correlation (DIC), an optical full-field measurement technique, is increasingly employed in experimental mechanics. This study introduces a novel measurement approach that combines DIC with compressed sensing to monitor high-speed rotating shafts accurately. Traditionally, analyzing rotating shafts requires high-speed sampling devices, which increases experimental costs and reduces spatial resolution. To overcome these limitations, a random exposure sampling method was developed to capture speckle images on the shaft surface with a low frame-rate camera. By leveraging compressed sensing and DIC, the method reconstructs high-speed vibration signals from captured images. Step motion experiments demonstrated that the DIC system achieves a measurement accuracy of 10 µm. Experimental validation was conducted using various setups, including low-speed motors, high-speed rotating shafts, and milling machines, demonstrating the effectiveness of the approach. The measurement results of rotating shafts at 1200 rpm and 6000 rpm, compared with those obtained from laser Doppler vibrometry, demonstrated the effectiveness of the method in vibration measurement. Additionally, experiments on a milling machine showed that vibrations reconstructed using compressed sensing closely matched those measured with a high-speed camera. This measurement system shows significant potential for accurately assessing vibrations in high-speed rotating shafts, offering valuable insights for machinery monitoring and fault diagnosis.

High spatiotemporal resolution measurement of water flow boiling heat transfer in a horizontal square minichannel using infrared thermography

In this study, the heat transfer fluctuations of water flow boiling in a horizontal square minichannel with a side length of 2 mm was investigated using infrared thermography with a high spatiotemporal resolution (4000 fps, 0.025 mm/pixel). Simultaneously, two high-speed cameras were used to visualize the behavior of the gas-liquid interface. The mass flux was 100 or 200 kg/(m2·s), and the vapor quality ranged from slug to annular flow. The wall heat flux was varied in the range of 10–220 kW/m2, focusing on the case of 220 kW/m2, where fast and complex fluctuations in the flow-boiling heat transfer were clearly visualized. In addition, image analysis was performed to partition the instantaneous heat transfer coefficient distribution into the fundamental processes of flow boiling (liquid convection, microlayer evaporation, dryout, three-phase contact line, and rewetting), and the contribution of each process to the heat transfer was investigated. The results showed that liquid convection was dominant under the present experimental conditions, accounting for approximately 85–95 % of the total heat transfer. Here, liquid convection includes the effects of turbulence in the liquid phase caused by boiling nucleation and acceleration associated with the two-phase gas-liquid flow. The contribution of microlayer evaporation due to boiling nucleation was approximately 5–8 % of the total heat transfer when the heat flux was 220 kW/m2, which decreased significantly as the heat flux decreased. It was also found that dryout occurred even under low vapor quality, and that when the dryout was partial, the decrease in heat transfer was limited by the contribution of the three-phase contact line formed at the outer edge of the dryout.

Tuning the performances of smoke-light signaling agents by Zn-Mg alloys

In this study, the thermal behavior, combustion behavior, and smoke/light signal effects of smoke-light signaling agents were regulated using Zn-Mg alloys with different Mg contents (10 wt%, 20 wt%, 30 wt%, 50 wt%, 70 wt%) and particle sizes (100–200 mesh, 200–325 mesh, >325 mesh) under an oxygen balance of −20. The Zn-Mg alloy’s morphology and phase composition were characterized using SEM/EDS and XRD. The thermal performance was analyzed with TG/DSC, while the combustion process was recorded using high-speed camera and infrared thermal imaging. The visible light spectrophotometer and smoke chamber experiment tested the smoke and light effects. The results showed that increasing Mg content raised the combustion temperature to over 1400 °C, enhanced luminous intensity to over 5000 cd, reduced solid residue to under 6 %, and shortened combustion time from 7.9 s to 2.24 s. Smaller particle sizes also improved these effects. Alloys with higher Zn content produced denser smoke but had higher solid residue. This study demonstrates the potential for precise control over combustion and smoke-light effects by adjusting alloy composition and particle size, making Zn-Mg alloys promising candidates for future pyrotechnic formulations.

An experimental study on the erosion of solid propellant by cavitation water jet in submerged environment

The submerged cavitation water jet (SCWJ) is a promising technology for removing solid propellant from old solid rocket engines and recycling them. In this study, the feasibility of using SCWJ to break solid propellant is investigated. The structure of the cavitation cloud was captured by a high-speed camera and then analyzed using the Proper Orthogonal Decomposition (POD) and Frame Difference Method (FDM) method for exploring the unsteady characteristic of SCWJ, the HTPB propellant erosion experiments were performed, and the relationship of the SCWJ unsteady characteristic and the erosion results on HTPB propellant was analyzed. The results show that the SCWJ develops in the flow field including inception, development, shedding, and collapse stages, the maximum density of cavitation cloud changes exponentially, and the cavitation cloud length grows as the cavitation numbers increase. Lower cavitation number is always beneficial to high penetration rate and low energy consumption when erosion on the HTPB propellant. When the erosion time of 120 s, in high cavitation number under the least amount of energy consumed, the unit energy consumption minimum. The mass loss curve is double peak, the first peak is caused by water jet effect, standoff distance is located on the stage of development, the formation of erosion pit diameter is small, the depth is larger, the second peak is caused by cavitation effect, and its standoff distance is located on the shedding phase, forming the erosion pit diameter is bigger, the depth is shallow. The optimum standoff distance for the cavitation effect for the cavitation numbers 0.0135, 0.0081, 0.0058 and 0.0045 is 35 mm, 50 mm, 60 mm and 70 mm in order, and the mass loss rate of HTPB propellant is 90 mg s−1, 200 mg s−1, 277 mg s−1 and 521 mg s−1, respectively. At best cavitation effect standoff distance, cavitation number by 2 times, mass loss rate can increase 3 times. The matrix brittle fractures occur when the SCWJ strikes the HTPB propellant at a high strain rate. Besides, the erosion mechanism of HTPB propellant is discussed.

Characterizing Turbulence and Wave Dynamics Under Rotation: Enhancing Semiconductor Processes through CFD Analysis and High-Speed Imaging

IntroductionIn semiconductor manufacturing, precision in wafer processing is crucial for advancing device technology. The spinning system, essential for wafer cleaning and etching, significantly impacts device quality by facilitating dynamic air-liquid interactions, affecting surface chemistry. This study utilizes Computational Fluid Dynamics (CFD) and high-speed camera analysis to explore turbulence and wave dynamics, confronting Fast Fourier Transform (FFT) analysis against the Kolmogorov cascade to improve manufacturing outcomes by understanding these dynamics more thoroughly.Experimental SetupOur approach integrates high-speed imaging with advanced CFD simulations to capture and analyze the wave phenomena in spinning liquid films. High-speed cameras are strategically positioned to provide comprehensive side and top views, enabling detailed observation of wave formation and interaction with the air. Concurrently, CFD simulations offer a granular view of the fluid dynamics, focusing on the generation and propagation of turbulence within the liquid film. The application of FFT analysis to CFD data allows us to delve into the turbulent wave dynamics, specifically investigating the energy cascade, per the Kolmogorov theory [1]. This methodology not only deepens our understanding of wave behavior but also highlight its potential impacts on key factors defining the exchange kinetics of the liquid-air interface.DiscussionFor a single wafer, a gas molecule, characterized by a diffusion coefficient D, will diffuse through the liquid film of thickness h to reach the wafer surface in a time approximated by t ~ h²/D. Specifically for oxygen, (D~2×10⁻⁹ m²/s) and 100µm thin film, the process takes about 5 seconds, while the coverage of the liquid takes less than 0.5s so an order of magnitude lower [2]. The Peclet number (Pe), defined by Pe=Uh/D, represents the advection to diffusion ratio. Here, Pe~10-4 >> 1 indicating advection dominance. This suggests wave and hydrodynamics (laminar vs. turbulence) primarily transport air into the liquid. Near the wafer edge, where the flow speeds up and the liquid film thins out, gas molecules reach the wafer faster than at its center.Advection rates are higher on wavy surfaces due to complex streamlines shaped by the undulating contours of the interface. This will enhance mixing transport, while the increased surface area boosts heat and mass exchange. Depending on wave celerity, recirculation atop the waves further boost local mixing [3,4].In Figure 1, the FFT analysis indicates that turbulent dynamics align with the Kolmogorov cascade, highlighting a spectrum of energy dissipation that could significantly impact oxygen diffusion and heat transfer. These findings suggest that the wave-induced turbulence could be leveraged to optimize the distribution of reactive species and thermal management during the spinning process. It highlights that the energy is injected by the swirling and concentric waves near the center of the wafer.In Figure 2, the Iribaren number, a dimensionless metric for classifying wave breaking patterns [5], is extracted from the liquid thickness distribution on wafer. It compares the slope steepness to the wave steepness, predicting whether waves will spill, plunge, or surge. Spilling waves, associated with low Iribarren numbers below 0.5 as found in our study, gently dissipate energy over wide areas. These spilling waves dissipate energy over long distances, breaking into smaller wavelets and introducing turbulence showing complex interactions between wave dynamics and the wafer.Figure 3 shows the dynamics of spilling waves with concentric waves collapsing towards the edge using a high-speed camera. This phenomenon is observed in a side view of a centrally dispensed fluid on a rotating wafer. The captured speed range is notably high, exceeding 50 km/h. The size and number of waves are affected by the rotation speed. A wave will collapse faster at high rpm because of a thinner film and higher centrifugal forces.ConclusionThis research reveals the relationship between wave dynamics in spinning liquid films and their potential impact on semiconductor manufacturing efficiency. The synergy of high-speed imaging, CFD analysis, and FFT insights not only enhances our understanding of fluid dynamics but also paves the way for optimizing wafer cleaning and etching techniques. This study lays the groundwork for future technological advancements, promising to elevate the precision, efficiency, and quality of semiconductor production.

Bubble Management through Electrolyte Engineering to Reduce Bubble Induced Resistance in Zero-Gap Water Electrolyzers

Hydrogen production through water electrolysis will play a central role to obtain a sustainable energy carrier. Although the community targets to operate at high current density (>1 A cm− 2) to reduce the production cost, the intense operation forms massive gas bubbles leading to detrimental effects on the resultant cell voltage. Gas bubbles may reduce the electrochemical active surface area leading to an increase in kinetic overpotential. The voids in the electrolyte inhibit the ion conduction and the mass transfer. Surface modifications and structuring are often performed on electrodes to control the wettability.[1] In this study, we demonstrate bubble management through electrolyte engineering. Bubble detachment diameters measured in various electrolytes were analyzed through an analytical equation and multiphase fluid dynamics simulations to clarify the major contributions from the electrolytes.[2] The knowledge was further implemented in a homemade zero-gap water electrolyzer to reduce bubble induced ohmic losses.Ni plate was employed as a model electrode to produce oxygen gas bubbles at 50 mA cm− 2. Electrolyte solutions were various concentrations of alkaline KOH and potassium-based buffer solutions (phosphate, borate, and carbonate) at non-extreme pH levels and room temperature. Bubble detachment diameters measured by a high-speed camera were found to continuously decrease in these electrolyte solutions by increasing the molality. After quantifying the electrolyte properties (density, surface tension and viscosity), the measured bubble diameters were compared with an analytical equation, which considers the force balance between the buoyancy force and the surface tension force on a textured surface,[3] to clarify the contributions from the electrolytes and the electrode surface to determine the diameters. The density of buffer solutions significantly increases in the concentrated solutions, which helps to reduce the diameter due to the buoyancy force. The deconvoluted surface contribution was also found to help reducing the diameter in the dense solutions. The electrode surface may be reconstructed during the oxygen evolution in the concentrated conditions, which was also inferred from contact angle measurements after the reactions. The analytical bubble detachment diameter is just derived from the force balance on a bubble at static condition. To cover the viscous force, which appears during the deformation of fluids, numerical simulations using volume of fluid method were performed. In viscous solutions and at high gas inlet assuming high current density, the diameters were found to increase indicating that the viscous force is working on the bubbles towards the electrode surface.Having clarified the major roles from electrolytes in the bubble detachment diameter, ohmic resistance in a homemade zero-gap water electrolyzer was investigated (schematics in Figure 1). NiMoOx on Ni felt (0.2 mm thick), NiFeOx on Ni felt and hydrophilic polyethersulfone (PES, 0.14 mm thick, porosity of 80%) were used as a cathode, an anode, and a porous separator, respectively, in various molality of potassium carbonate solutions at pH 10.5 and 80 °C. Uncompensated resistances were obtained from high-frequency intersects in Nyquist plots obtained from electrochemical impedance spectroscopies at an open circuit voltage (OCV) and a potential at 800 mA cm− 2. A volcano trend of the resistance at OCV (blue bars in Figure 1) reflects the bulk electrolyte conductivity.[4] Notably, additional resistance (red bars in Figure 1) was observed at 800 mA cm− 2 indicating the inhibition of ion conduction due to the presence of massive gas bubbles in the stacked structure. The increment of resistance at 800 mA cm− 2 also exhibited a volcano trend. The ratio of resistances between OCV and 800 mA cm− 2 reflects how the effective ion conduction path was inhibited by the void fraction due to the gas bubbles.[5] The estimated void fractions also demonstrated the volcano trend as a function of the solute molality. Its decreasing trend agreed with the detachment diameters from the Ni plate model electrode discussed above indicating that the quantitative understanding of the bubble dynamics is also effective to reduce the ohmic losses.[2] Accumulation of gas bubbles were indeed observed by the high-speed camera using a transparent dialyzer separator which was closely stacked with NiMoOx/Ni cathode. Overall, our study demonstrates the significance of the electrolyte engineering to control the gas bubbles and the resultant losses.Reference[1] R. Iwata, et al., Joule, 2021, 5, 887.[2] H. Qiu, et al., Langmuir, 2023, 39, 4993.[3] J. Li, et al., Langmuir, 2022, 38, 3180.[4] T. Nishimoto, et al., ACS Catal., 2023, 13, 14725.[5] D. A. G. Bruggeman, Ann. Phys. 1935, 39, 4993. Figure 1

Non-Uniform Activity at High Current Density through Stacked Mesh Substrates Due to Gas Bubbles and Ohmic Losses

Water electrolysis driven by renewable energy is a promising method to produce green hydrogen that can work as a clean energy carrier for a sustainable energy society. Various water electrolysis systems have been developed and commercialized, however, operations at high current density produce large quantity of bubbles leading to additional overpotentials. Engineering on electrodes, such as surface modifications and 3D-printed structure, is one of the strategies to minimize the bubble influence. Previous studies revealed hydrophilic and periodic structure is preferred for fast bubble departure to reduce overpotential.[1,2] Substrates with three-dimensional structures, including foams and felts, are often employed to deposit sufficient amount of electrocatalysts to minimize overpotentials at a given geometric current density. However, requirements for the substrate thickness have not yet been thoroughly discussed. In this study, we used Ni mesh substrate as a simple model structure and stacked them to vary the thickness to minimize the overpotential during oxygen evolution reaction (OER). Optimization strategy is discussed based on bubble observations, kinetics of electrocatalysts, and electrolyte conductivity.The steady state chronopotentiometries at various current densities were conducted in 1 mol kg−1 KOH at 353 K using pristine and NiFeOx coated Ni mesh (NiFeOx/NM) with various stacking number of meshes. NiFeOx was selected as a model OER electrocatalyst because of its high activity in alkaline media.[3] Tafel slope values were nearly identical among various stacking numbers in the low current density region (<100 mA cm− 2 geo) on both pristine and NiFeOx/NM. However, the value became larger in the high current density region (>500 mA cm− 2 geo) using highly stacked mesh electrodes. The measured potentials at 10 and 800 mA cm− 2 geo as a function of the stacking number were summarized in Figure 1. A monotonic decay of potential was observed at 10 mA cm− 2 geo. Tafel equation predicts surface area enlargement leads to a logarithm potential decay following their Tafel slope values (shown as dashed lines in Figure 1). Their agreements suggest the electrode surface is used uniformly through the thickness direction at 10 mA cm− 2 geo. However, volcano trends were observed at 800 mA cm− 2 geo suggesting the additional overpotential at high current density using thick electrodes. In addition, the optimum stacking number changes by the presence of the catalyst and the aperture of meshes. NiFeOx/NM showed a smaller thickness as an optimum compared to the pristine (Figure 1). The optimum thickness of the stacked electrode with 200 mesh (aperture width of 77 mm) was smaller than that using 20 mesh (aperture width of 1020 mm), which may be due to the bubble accumulation within the stacked meshes.The bubble observation using a high-speed camera was conducted to compare 20 and 200 mesh with various stacking number at 800 mA cm− 2 geo in 1 mol kg−1 KOH at 298 K. Although the average bubble size from 200 mesh was smaller than that from 20 mesh, the size was comparable to the aperture width of 200 mesh. The bubbles filled in the aperture of 200 mesh may reduce the available active sites and the ion conduction path, which can be the reason for the smaller optimum thickness using the dense mesh.To clarify the contribution from the electrocatalysts, particularly Tafel slope values, 1D numerical simulation at 800 mA cm− 2 geo without bubbles was conducted through the stacked direction assuming a porous electrode. The electrode potential no longer decreases above the thickness of 0.5 mm with Tafel slope values of 40 mV dec−1 while continuous decay is predicted with the value of 120 mV dec−1. At 800 mA cm− 2 geo, the electrolyte ohmic voltage loss builds up to 10 – 100 mV within the porous electrode, which results in the loss of local overpotential. The electrode with lower Tafel slope value easily suffers from the additional ohmic voltage loss, which localizes the active region to the near-surface and limits the benefit from the enlarged surface area through the stacking.This study highlights the necessity of substrate structure optimization based on the nature of the deposited electrocatalyst, the electrolyte conductivity, and the dynamics of the bubbles.Reference[1] T. Kou et al., Adv. Energy Mater. 2020, 10, 2002955.[2] J. Das et al, Adv. Funct. Mater. 2024, 34, 2311648.[3] C. C. L. McCrory et al., J. Am. Chem. Soc. 2015, 137, 4347–4357. Figure 1

Effect of Cathode PTL Wettability on Gas-Water-Oil Transport in a Direct Toluene Electro-Hydrogenation Electrolyzer

To achieve carbon neutrality, it is envisioned that electricity generated from renewable energy sources will be converted to hydrogen for use. There are several methods for storing and transporting hydrogen, but one of the most promising is the toluene-MCH organic hydride process. These organic compounds are liquid at room temperature and pressure and can utilize petroleum infrastructure. Direct toluene electro-hydrogenation electrolyzer is an attractive method that can simultaneously perform water electrolysis and toluene hydrogenation in a single system. This alternative is gaining attention because of its simple system, low energy loss, and low cost. However, one problem with this method is the presence of water droplets and hydrogen bubbles in the cathode PTL. The water dragged by electro-osmosis from the anode side blocks the toluene supply to the cathode reaction site. As a result, protons unable to react with toluene then convert into hydrogen bubbles on the cathode side. These bubbles also block the supply of toluene, resulting in significant decrease in toluene-MCH conversion efficiency.A simulation approach is essential for the practical implementation of the system. We have conducted numerical analyses using single-cell scale models, but the parameters for modeling and verification were insufficient. Thus, experimental methods such as visualization of inside the PTL using an X-ray CT have been conducted [1]. In addition to this, a high-speed camera was used in this study to visualize dragged water, which is a difficult task to do with CT alone.Figure A, shows an overview of the electrolyzer and visualization method employed. The electrolyzer with a sapphire glass window allowed visualization of the surface of the cathode PTL during its operation. Pure water was pumped to the anode side and toluene to the cathode side. Constant-current electrolysis at 100 mA/cm² was operated with a reaction area of 1 cm². Hydrophilic, hydrophobic, and lipophilic coatings were applied to the PTL and compared to the non-coated PTL, in order to investigate the effect of PTL wettability of toluene, hydrogen bubbles, and dragged water transport. Figure B is the non-coated and lipophilic PTL at 30 minutes after beginning electrolysis, with hydrogen bubbles shown in red and dragged water in blue. Under both conditions, hydrogen bubbles were quickly discharged, while the dragged water remained on the PTL surface and channel wall. Comparing the figures, the amount of water observed on the surface of the lipophilic PTL increased while the diameter of the hydrogen bubbles tended to be larger in the non-coated PTL. Calculated Faraday efficiencies for toluene-MCH were 60.7% for the non-coated PTL and 84.4% for the lipophilic PTL, indicating that lipophilicity improved the performance of the electrolyzer. Considering these results, lipophilic coating likely promoted the discharge of dragged water from inside the PTL to outside and enhanced toluene supply to the cathode reaction site.Overall, the utilization of the high-speed camera enabled the visualization of the three phases of gas-water-oil, suggesting that the PTL wettability influences the transport behavior of these phases. These findings provide valuable insights for developing models to simulate the three-phase transport within the PTL.

Suppression of the Leidenfrost Effect By Controlling the Nanostructure of Aluminum Surfaces

The Leidenfrost effect is a phenomenon in which a liquid droplet forms a thin film of its vapor on a substrate hotter than the boiling point, causing the droplet to float above the hot substrate. The vapor film inhibits heat transfer between the droplet and the substrate, which reduces the cooling efficiency when the droplet cools the high-temperature substrate. It has been known that the Leidenfrost effect can be suppressed by forming nano- and micro-scale pillars and spikes on the substrate surface [1, 2]; however, conventional methods of constructing nano- and micro-structures require expensive equipment and the process is complicated. Anodic porous alumina films with self-ordered cylindrical nanopore channels can be fabricated on aluminum substrate simply by anodizing in appropriate aqueous electrolyte solutions. The structure parameters of porous alumina, such as pore size, interpore distance, and pore length, can be easily controlled by anodizing voltage and time. This study demonstrates that the anodic porous alumina films can be applied to control the Leidenfrost effect.Ultrasonically cleaned and electropolished Al plates (99.999%, 1.0-mm thick) were used as specimens. The specimens were immersed in 0.3 M sodium tetraborate solution (343 K) and anodized at 10-200 V for 60 min. The nanostructure of the anodic porous alumina was observed by SEM. The static contact angle of the specimen was measured with a contact angle meter. The behavior of water droplets on the specimen at 473 K was captured by a high-speed camera. The temperature of the specimen was measured using a thermal imaging camera.Constant voltage anodizing of Al resulted in the formation of porous alumina films with numerous pores. As the anodizing voltage was increased, the pore size increased, with an average pore size of 294 nm at 200 V (Fig. 1a). The static contact angle of the anodized surface became smaller as the pore size increased.Fig. 1b shows snapshots of the behavior of a water droplet (6 μL) on a smooth aluminum surface at 473 K. The water droplet bounced after dropping and took a long time to evaporate due to the Leidenfrost effect. On the other hand, when the same experiment was performed on the surface of an anodized specimen, the water droplets wetted and spread immediately after contact with the substrate and evaporated in about 50 ms while splitting into fine droplets (Fig. 1c). The surface temperature after dropping the water droplet (12 μL) decreased significantly on the porous alumina with large pores. Therefore, the formation of anodic porous alumina film on the substrate surface effectively suppresses the Leidenfrost effect, suggesting that increasing the pore size can improve the substrate cooling efficiency.[1] H. Kim, B. Truong, J. Buongiorno, L. W. Hu, Applied Physics Letters, 98, 083121 (2011).[2] C. Kruse, T. Anderson, C. Wilson, C. Zuhlke, D. Alexander, G. Gogos, S. Ndao, Langmuir, 29, 9798-9806 (2013). Figure 1

Composition of Quantum Dot Color Conversion Layer with ZnS Nanoparticle for Facile Ink Formulation and Uniform Inkjet Printing

Quantum dot (QD) is excellent material for next-generation displays because of their superior optical properties, such as high quantum efficiency, narrow full width at half maximum, high color purity, and photoluminescence quantum yield. QD demonstrated efficient absorption of blue light, coupled with high color-conversion efficiency, fabricated them suitable for use as color-conversion layers (CCLs). However, robustness in pixel patterning uniformity and a printing resolution should be further studied. Light emission via conversion through QD films or converter pixels still need to be improved because the blue light can directly transmit the QD layers, sometimes leading to insufficient energy to excite the QDs. Thus, many studies on QD CCLs have focused on improving the absorption and emission properties of QDs, formulating CCL resins with enhanced color conversion efficiency. Scattering can alter the optical path and incident angle of the emitted light to increase internal reflection so that light emission of the optical film can be enhanced for excitation of photons. Thus, light scattering particles, such as titanium dioxide (TiO2), silicon dioxide (SiO2), zinc oxide (ZnO), and zirconium oxide (ZrO2) were carefully tuned to achieve outstanding properties as QD CCLs, increasing color conversion efficiency.In this work, zinc sulfide (ZnS) light diffusers with hydrophobic properties and various size distribution were synthesized. ZnS and QD were mixed in acrylic resin, isobornyl acrylate, with proper composition of initiator and photocrosslinker. The recipe of mixing was considered for a fabrication of QD CCL ink with optimum viscosity, dispersion stability and uniformity, and printability. For the QD-CCL ink with relatively high viscosity, evaluation of jetting profile and pixel-patterning was conducted with commercial ink cartridge, Sapphire QE-256/30AAA (Fujifilm), combined with the custom-built inkjet printer and high-speed camera. With the scale up to 200ppi QD-CCL pattern, the color spectrum, printability, dispersion, optical properties (evaluation of color-emitting image), and surface uniformity were evaluated. Overall, this work will demonstrates the enhanced light converion behavior of QD-CCL layer fabricated by inkjet-printing process and provide a novel evaluation prorocol of uniformity for QD-CCL layer and color conversion device using blue micro-LED.

Development of a novel method to characterize shock waves interaction with solid objects

Nuclear explosion in a densely populated area is the worst that can happen to any country in the world due to enormous loss of life, property and severe economic damage. Nuclear explosions immediately cause radiological damage and destruction of infrastructure. This hydro-magnetic shock propagation due to blast gives rise to simultaneous signals around the world. The effect of shockwave from nuclear explosion is an area that can be used to handle post and pre-disaster from nuclear explosion. This study focuses on the effects of shockwave on solid objects oriented in different formation. Experiments conducted in a horizontally placed shock tube and a solid object holder on the floor of the test section. These solid objects placed inside the test section of a shock tube collided with a planner shock wave which was generated by rupturing a diaphragm of different thickness. Four high speed pressure transducers strategically placed at different locations of this shock tube were used to characterize the blasts as well as interaction with the samples. A high-speed Kronos and Phantom camera were used to record the exact moment of interaction to characterize the solid objects under the impact of different shock waves. Representative results of these experiments are reported here along with review of previous work done in this area.

Kinematic and Aerodynamic Analysis of a Coccinella septempunctata Performing Banked Turns in Climbing Flight.

Many Coccinella septempunctata flights, with their precise positioning capabilities, have provided rich inspiration for designing insect-styled micro air vehicles. However, researchers have not widely studied their flight ability. In particular, research on the maneuverability of Coccinella septempunctata using integrated kinematics and aerodynamics is scarce. Using three orthogonally positioned high-speed cameras, we captured the Coccinella septempunctata's banking turns in the climbing flight in the laboratory. We used the measured wing kinematics in a Navier-Stokes solver to compute the aerodynamic forces acting on the insects in five cycles. Coccinella septempunctata can rapidly climb and turn during phototaxis or avoidance of predators. During banked turning in climbing flight, the translational part of the body, and the distance flown forward and upward, is much greater than the distance flown to the right. The rotational part of the body, through banking and manipulating the amplitude of the insect flapping angle, the stroke deviation angle, and the rotation angle, actively creates the asymmetrical lift and drag coefficients of the left and right wings to generate right turns. By implementing banked turns during the climbing flight, the insect can adjust its flight path more flexibly to both change direction and maintain or increase altitude, enabling it to effectively avoid obstacles or track moving targets, thereby saving energy to a certain extent. This strategy is highly beneficial for insects flying freely in complex environments.

Directional DIC method with automatic feature selection

Using displacement identification via high-speed cameras is a non-contact, full-field technique for characterizing the dynamic properties of engineered structures. Achieving reliable measurements of structural deformation through conventional Digital Image Correlation (DIC) requires a well-defined spatial gradient in two orthogonal directions within an image subset of pixels. However, DIC is susceptible to the aperture problem, which leads to an ill-conditioned optimization problem. An example of such a case is cable systems on which no speckle patterns can be applied. This study proposes Directional DIC (D-DIC) as an alternative technique to overcome the limitations posed by the aperture problem in conventional DIC methods. Directional DIC assumes the local direction of motion, which is often a valid assumption in structural vibration tests, as individual vibration shapes are often unidirectional at localized parts of the structure. This alleviates some restrictions on trackable image subsets, enabling more trackable locations. A parameter for quantifying expected tracking performance for D-DIC is introduced. The parameter enables automatic feature selection for D-DIC, making optical methods more accessible for displacement identification on structures where no speckle patterns can be applied. Experimental modal tests are conducted using a flexible spider web-like structure to validate the D-DIC method and compare it to conventional DIC. The experimental findings show that the Directional DIC method allows for measuring displacements at significantly more locations than conventional DIC. Additionally, D-DIC provided less noisy frequency response functions, more retrieved stable poles, and more fitted vibrational modes. Lastly, the findings show that D-DIC is especially superior to DIC when using small subsets since D-DIC is less inhibited by the aperture problem.

Splashing effects and mechanism in water jet-guided laser processing of Cf/SiC composites

Water jet-guided laser (WJGL) processing of ceramic matrix composites offers smooth cutting surfaces and minimizes defects such as delamination, burrs, and recast layers. However, the processing ability of WJGL is limited by the stability of the water jet. Splashing is a critical factor that affects water jet stability. This study investigates the splashing morphology and its impact mechanism during WJGL processing of continuous carbon fiber reinforced silicon carbide (Cf/SiC) composites. High-speed cameras were used to capture splashing morphologies and laser transmission states during drilling and grooving. The results indicate that the splashing morphology was significantly affected by the water jet speed and the micro-hole/groove depth, resulting in behaviors such as water accumulation, droplets falling, rebound droplets, splash impact, water film, and mist, which distorted or even broke the water jet. The laser escaped in the distorted water jet, leading to a reduction in material removal rate. The splashing at the water jet speed of 160 m/s resulted in a 61.1 % reduction in material removal rate during drilling compared to 40 m/s. In addition, a method of placing a porous water-absorbing material on the workpiece surface was proposed, which effectively improved the material removal rate. This paper presents a theoretical basis for comprehending and addressing splashing in WJGL processing.

Experimental study on flow boiling of fluorocarbon fluid in the pin-ribbed micro-channel with rigid tails

In this work, a novel type of pin-ribbed micro-channel with rigid tails is designed based on the conventional pin-ribbed micro-channel. A comparative experimental study is carried out using fluorocarbon fluid Novec649. The flow boiling heat transfer and pressure drop characteristics are investigated under horizontal/vertical placement at inlet subcooling temperature of 25 °C. The ranges of inlet mass flux and heat flux are 519–1818 kg·m−2·s−1 and 50–500 kW·m−2, respectively. The results show that at a given mass flux, and heat flux of 300–500 kW·m−2, the vertical pin-ribbed micro-channel with rigid tails has the lowest average wall temperature, the largest average heat transfer coefficient, and the smallest total pressure drop, therefore it has the largest j-factor, more than 60% higher than that of the horizontal/vertical channel without rigid-tails. With the aid of a high-speed camera, the localized bubble movement phenomena in horizontal/vertical micro-channel with rigid tails was photographed at a mass flux of 519 kg·m−2·s−1 and a heat flux of 100 kW·m−2. Three types of bubble detachment modes in the wake region at the boiling stable state are observed: natural shedding, one-sided shear and two-sided shear. The bubble detachment diameter under the one-sided shear is more than 23% smaller than that of two-sided shear, and that of the horizontal channel is more than 44% higher than that in the vertical channel, whereas its bubble detachment frequency is only 50% of that in the vertical channel. Therefore, the vertical placement is more helpful for the rigid tails playing a role in the breakup and detachment of bubbles. The experimental results confirm the advantages of adding rigid tails behind the square-rib to enhance the comprehensive heat transfer performance of flow boiling, which can provide a guidance for the structural design of two-phase miniature heat sinks.

Damage characteristics and failure mechanism analysis of NEPE propellant at high strain rates

The study of mechanical properties and failure mechanism of propellants under impact loads is crucial for analyzing structural integrity of propellant charges. An experimental investigation was conducted on NEPE propellant using a separated Hopkinson pressure bar to conduct high strain rate uniaxial impact tests. Deformation and failure processes of the propellant under impact conditions were recorded with a high-speed camera. The microscopic failure forms of the propellants were observed using a scanning electron microscope and an optical microscope. Stress-strain curves and high-speed images revealed that the damage behavior and failure mechanism of NEPE propellants are significantly influenced by strain rate. As the strain rate increases, there is a notable increase in the deformation degree of the propellant specimens, with a more pronounced shear effect. This leads to an earlier occurrence of failure and a more severe degree of failure. The predominant failure forms observed in NEPE propellants include transgranular failure, matrix tearing, and cavity merging. A nonlinear visco-hyperelastic constitutive model with damage at high strain rates was established to provide a precise account of the mechanical response of NEPE propellant under high strain rates.

Experimental study of twin-fluid flow differences and Sauter mean diameter prediction according to Y-jet nozzle mixing-tube design

In this study, we experimentally investigate the effect of internal flow variation on the design characteristics of a Y-jet twin-fluid nozzle and its utilization for spray droplet size prediction. For this study, a laboratory-scale twin-fluid nozzle spray test system was constructed. Sauter mean diameter (SMD) measurements were made by a droplet measurement system using the laser diffraction principle, and spray images were obtained using a high-speed camera. The mass flow rate of the twin fluids under different spray conditions was expressed in terms of the gas-to-liquid mass flow rate ratio (GLR) and turn-down ratio. The GLR tended to decrease when the nozzle orifice diameter increased because the pressure of the supplied twin-fluid was the same. By contrast, increasing the nozzle mixing-tube length resulted in a negligible increase in GLR. This is because the nozzle design characteristics affect the internal pressure of the nozzle, which changes its spray characteristics. In general, the spray characteristics of Y-jet nozzles are most affected by GLR. However, in this study, a generalised GLR was devised to consider not only GLR but also the difference in the flow rate of the twin-fluid due to nozzle design factors. The generalised GLR has the advantage that it is constant under changes in twin-fluid pressure, unlike the GLR expressed by considering only the mass flow rate of the twin-fluid. Therefore, to estimate the SMD more accurately under different spray pressures for a constant GLR, we investigated the SMD estimation using the internal pressure ratio and generalised GLR.

Reduction of aerosol and droplet dispersions using intraoral and extraoral vacuums for dental treatments with face-up, diagonal and upright positions

PurposeThe COVID-19 pandemic has affected lives and dental treatment. Aerosols and droplets generated during dental treatment present a risk of infection for dental care workers. However, detailed elucidation of the conditions under which those are generated has yet to be presented, and no clear countermeasures for protection have been established. The present study aimed to clarify the process of generation of aerosol and droplets in dental treatment, as well as their dynamics for establishment of effective countermeasures and protection strategies.MethodsImages were obtained using a high-speed camera of aerosol and droplets generated during dental treatments performed on a mannequin. The effects of intraoral vacuum and extraoral vacuum to reduce those, as well as splash range with different body position were examined. Quantitative evaluations of aerosol and droplets were also performed using water-sensitive paper.ResultsAerosol and droplets quantities were significantly reduced by use of both intraoral and extraoral vacuums as compared to no vacuum in both image analysis and findings obtained with water-sensitive paper (p < 0.05). Additionally, the intensity of aerosol and droplets when using the intraoral and extraoral vacuum devices with a body position of 45 degrees was a significantly less as compared to the other settings (p < 0.001).ConclusionsThe present study demonstrated the effectiveness of visualization of the aerosol and droplets generated by dental tools using a high-speed camera. Use of an extraoral vacuum resulted in a reduction of those generated during simulated dental treatment, and also contributed to diffusion prevention to protect the operator and assistant. Nevertheless, it is necessary to be careful because the use of extraoral vacuums may reverse the spread of aerosol and droplets depending on the position of patient.

Investigation of the impact load characteristics of micro-jet induced by cavitation collapse on rigid wall surface

This study examines the micro-jet generated by cavitation collapse, a phenomenon prevalent in chemical processes, with a focus on the impact load characteristics of the micro-jet on rigid wall surfaces. The expansion and collapse of cavitation bubbles generated by electric spark near the wall were recorded using a high-speed camera. Coupled with numerical simulations, a parameter λ, representing the ratio of bubble size to the distance from the wall, was introduced to comprehensively analyze the micro-jet morphology, velocity, impact force, and the resulting impact intensity on the wall surface. It was observed that the impact effect of the micro-jet on the wall surface is most pronounced when λ ≈ 1. The rapidly varying impact force of the micro-jet on the wall can be approximated as the impulse due to the average force acting on the wall over an extremely short time interval Δt. Under the condition where λ ≈ 1, both the velocity and impact force of the micro-jet, as well as the resulting impact intensity on the wall surface, increase with the bubble size. Through impact experiments on aluminum foil, it was determined that the cross-sectional shape of the micro-jet head is circular. Identified the three-dimensional shape of the micro-jet as a conical structure with a circular base. A size relationship coefficient was introduced to define the geometric model of the micro-jet. This model was based on the size relationship between the upper and lower cross-sections of the conical jet, as determined from experimental results. Key parameters affecting the impact intensity of the micro-jet were identified. The intensity values for micro-jets of different bubble sizes under the condition of λ≈1 were calculated.

Design, manufacturing, and multi-modal imaging of stereolithography 3D printed flexible intracranial aneurysm phantoms.

Physical vascular phantoms are instrumental in studying intracranial aneurysms and testing relevant imaging tools and training systems to provide improved clinical care. Current vascular phantom production methods have major limitations in capturing the biophysical and morphological characteristics of intracranial aneurysms with good fidelity and multi-modal imaging capacity. With stereolithography (SLA) 3D printing technology becoming more accessible, newer flexible and transparent printing materials with higher precision controls open the door for improving the efficiency and quality of producing anthropomorphic vascular phantoms but have rarely been explored for the application. This technical note intends to report the feasibility of using SLA 3D printing technology to manufacture flexible intracranial aneurysm phantoms with similar scales to the real anatomy, as well as their capacity for multi-modal flow imaging and analysis, including ultrasound flow imaging, high-speed filming, and particle image velocimetry analysis. We designed and 3D-printed two intracranial aneurysm phantoms with an SLA 3D printer using Formlabs Elastic 50A resin. By using a micropump to introduce cyclical flows in the phantoms, we first employed conventional Doppler and vector flow ultrasonography to observe and measure different fluidic properties. Then, a high-speed camera was used to record particles flowing within the phantom, and we further conducted a particle image velocimetry analysis, including the distribution of mean 2D velocity vectors, average velocity magnitudes, and the mean vorticity fields in the phantom for the high-speed imaging data. We successfully 3D-printed flexible intracranial aneurysm phantoms with similar dimensions to the real anatomy. Additionally, we validated the phantoms' ability to allow visualization, measurement, and analysis of flow dynamics based on both real-time ultrasound and optical imaging. Our proof-of-concept study illustrates that SLA 3D printing using commercial elastic resins can significantly contribute towards facilitating the fabrication of flexible intracranial aneurysms phantoms for training, research, and preoperative planning.