High-speed Video Image Analysis Research Articles

HIGH-SPEED VIDEO IMAGE ANALYSIS OF LIQUID METAL ATOMIZATION PROCESS

Gas-assisted atomization is used to produce metal powders for additive manufacturing. In these systems the primary atomization governs the powder size distribution, but it is experimentally challenging to investigate. In this study, the primary atomization of a molten metal spray was monitored with a calibrated high-speed camera and digital image processing. The technique enabled the generation of spatio-temporal maps at different distances from the nozzle. Among the characteristics of the spray, mean values and standard deviation of the spray width along the spraying direction, and the frequency of the oscillation of the spray boundaries are presented. Statistically relevant spray asymmetries were identified, which can be caused by faulty spray operation in form of a localized metal solidification at the pouring nozzle. By systematically varying the gas temperature and the gas atomization pressure, it is shown that heating of the gas up to 573 K stabilizes the spraying process and enhances the liquid dispersion in the recirculation zone.

Front side metallization of silicon solar cells – A high-speed video imaging analysis of the screen printing process

Aiming at higher cell efficiency and lower Ag consumption, research focuses on achieving smaller finger lines for silicon solar cell front side metallization. In-depth understanding of the printing process is mandatory to achieve uniform, defect free lines with high aspect ratio. An innovative high-speed video imaging setup allows for tracking of the mechanisms happening within ≈10–50 ms during the screen printing process. Two pastes differing significantly with respect to their rheological as well as wetting properties are used in this study. A paste spreading mechanism consisting of different consecutive process steps determines the final line shape. During nip contact the paste is squeezed between screen emulsion and substrate. Paste spreading further proceeds as long as the screen clings to the substrate, it occurs in a regular pattern and is most pronounced in the regions were mesh wires approach the emulsion surface. Then sudden retraction takes place during snap-off and the final line width is essentially fixed. Spreading is more pronounced for the paste exhibiting low viscosity at high shear rates and strong wetting of screen emulsion and substrate. The overall paste transfer is promoted by poor screen wetting and strong paste cohesion. These insights will stimulate further improvement of Ag paste formulation for solar cell metallization.

Effect of nozzle size scaling in co-flow water cavitation jet peening

Water Cavitation Peening (WCP) employs cavitation to introduce compressive residual stresses in metals while limiting the surface roughening typical of similar surface enhancement processes such as shot peening and laser shock peening. As shown by a number of authors, cavitation intensity is greatly affected by the jet velocity as well as by the nozzle dimensions and shape. This paper reports on an investigation how nozzle dimensions affect cavitation intensity and peening performance in co-flow WCP of Al 7075-T651. Scalability of the process is investigated by comparing co-flow nozzles of increasing size but the same diameter ratios. The results show a substantial increase in cavitation intensity with nozzle size and a considerable decrease in the processing time required for saturation of the strip curvature and residual stress. The observed trends are explained by means of high-speed video imaging analysis and pitting tests, which show that the increase in cavitation intensity is due to an increase in the amount of cavitation when nozzle dimensions increase, while the pit depths and pit shape factor, which are measures of the strength of the cavitation events occurring at the workpiece surface, are largely unaffected. The process yields compressive residual stresses as high as 400MPa and as deep as 350μm below the surface, which are both a significant improvement upon previous results reported for shot peening.

Ignition and Combustion of Single Particles of Coal and Biomass under O2/CO2 Atmospheres

Biomass energy with carbon dioxide capture and storage (CCS) technologies like oxy-fuel is the only way to achieve net removal of CO2 from the atmosphere in power generation. A single particle apparatus has been developed for rapid heating and combustion of individual fuel particles in air or O2/CO2 atmospheres. This wire mesh apparatus was used as a heating element to heat the particle by radiation while optical access allowed particle combustion characterization by high speed camera recording. Four different biomass and a bituminous coal were used in air and 21, 30 and 40% O2 atmospheres with balance of CO2. High speed video image analysis showed differences in ignition and devolatilization behaviour. The influence of particle size and mass on burnout times was higher in the coal, while biomass particle size can have a greater range of sizes for the same burnout times. The 30%O2 atmosphere was enough to have less burnout time than in air atmosphere for all the samples. During biomass particle combustion, the results showed that the surface tension on the biomass char particle plays a significant role due to partial melting of the char particle. This effect modifies the char particle shape during its combustion, with particles becoming more spherical particle even for those that initially had a fibrous shape.

Ignition and combustion of single particles of coal and biomass

Co-firing technology at large power plants can contribute to reducing emissions and maintaining stable and secure electricity supplies. Due to the higher reactivity of biomass, a larger particle size range is generally used for biomass fuels compared with pulverized coal. A single particle apparatus has been developed for rapid heating and combustion of individual fuel particles. This wire mesh apparatus is used as a heating element to heat the particle by radiation while optical access allows particle combustion characterization by high speed camera recording. A woody biomass and a bituminous coal were used in this study. Both fuels showed a sequential combustion of volatile matter followed by char combustion. High speed video image analysis showed differences in ignition and devolatilization behaviour. The biomass volatile flame was smooth along the overall particle, while coal volatile matter release was delivered by jets. Times for the volatile matter combustion were much shorter for the coal while pyrolysis seemed to be the dominant step for around half of total combustion time. During devolatilization, the bituminous coal showed a significant swelling that was not seen in the biomass. As particle mass increased the overall times required for drying, devolatilization and burnout increased for both samples, and this was the dominant parameter to predict burnout time. Impact of particle size and mass was much higher in coal, with a dramatic increase in burnout times for particles above 300µm, while biomass particle size can have a greater range of sizes for the same burnout times. During biomass particle combustion, the results showed that the surface tension on the biomass char particle plays a significant role due to partial melting of the char particle. This effect modifies the char particle shape during its combustion, with particles becoming more spherical even for the initial fibrous shape of the woody biomass particles.

High-speed video image analysis of ski jumping flight posture

Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers.

Flame structure in aluminized wide-distribution AP composite propellants

Flame structure in wide-distribution ammonium-perchlorate (AP), hydroxyl-terminated-polybutadiene (HTPB) binder, aluminum (Al) composite propellants is studied using 2-D laminates with oxygenated binder. Very fine (2-μm) AP (FAP) is used to produce fuel-rich, matrix propellant (oxygenated binder) with a FAP/binder ratio of 75/25. Coarse AP (CAP) is simulated by pressed AP lamina. A flame-structure regime map for the CAP/oxy-fuel matrix interaction flame is generated as a function of oxy-fuel matrix thickness and pressure using high-speed video imaging analysis. The flame structure is found to be similar to that previously described using UV and IR imaging for non-aluminized laminates with split (diffusion) flame structure at high pressures ( P) and low fuel thicknesses ( L) and merged (partially premixed) flame structure for low P and L. The CAP/matrix flame regime boundary is shown to be correlated by Peclet number, indicating the relevance of conserved-scalar (Shvab–Zeldovich) theory with simple, global AP/hydrocarbon chemistry to describe the CAP/matrix diffusion-flame stoichiometry. Other findings include a slight stabilizing effect of Al on the 1-D premixed combustion of the marginally stable fuel-rich matrix. Also, when burning in 2-D laminates assisted slightly by the CAP/matrix interaction flame, the 75/25 matrix is found to burn flat (perpendicular to regression direction) even in the split-flame regime, in contrast to lower FAP/binder ratio matrices, which protrude into the gas-phase. Findings such as these are essential for developing a fundamental understanding of and truly predictive simulation capability for combustion of wide-distribution AP propellants, including plateau, mesa and bi-plateau propellants.

B-31 高速度ビデオカメラの画像解析によるスキージャンプの飛型と飛距離の相関(ウィンタースポーツ)

B-31 高速度ビデオカメラの画像解析によるスキージャンプの飛型と飛距離の相関(ウィンタースポーツ)

High-speed imaging and CFD simulations of a deforming liquid metal droplet in an electromagnetic levitation experiment

Electromagnetic levitation of a liquid metal droplet is of great interest to study gas–liquid metal reactions. An important prerequisite for the evaluation of the overall mass transfer between the gas and metal is to characterize the geometry of the deforming molten droplet, which determines the interfacial reaction area. In this article, the free surface shape and dynamics of a molten 80%Ni–20%Cr droplet is investigated both experimentally and numerically. The frequencies associated to the oscillatory translational motions of the drop and to the vibrations of its free surface are measured using high-speed video image analysis. A 2D transient model is then presented, in which three interacting phenomena are considered: electromagnetic phenomena, the turbulent flow of liquid metal in the drop and the change in the drop shape. The numerical results presented demonstrate the capabilities of the model.

An overview of the various techniques used in routine cleaning and maintenance of clay, concrete and plastic drains

The application of experimental techniques to analyse the physical behaviour of a cavitating water jet at pressures up to 10 000 psi (69.0 MPa) and flow rates up to 6.56 gallons (UK)/min (4.97 × 10 −4 m 3 s −1) is described. In British civil engineering practice, this range of pressures and flow rates covers that used in the routine cleaning and maintenance of drains and sewers. The techniques used were: high-speed video image analysis at 20 000 frames/s, thermal image analysis of the nozzle, vena contracta and divergent jet, and laser scattering analysis for spray droplet or bubble sizing in the jet. The jet was illuminated by coherent pulsed laser: the subsequent Mie scattering of the light was related to the size of bubbles, spray droplets, and the cavitation nuclei forming in the jet. Having outlined this physical characterisation of the jet, its capacity to damage a range of typical drain and sewer materials was measured.

Influence of Particles and Electrolyte on Gas Hold-Up and Mass Transfer in a Slurry Bubble Column

In this paper, the influence of carbon and silica particle slurry concentration up to 20 g/l (4 vol%) on regime transition, gas hold-up, and volumetric mass transfer coefficient is studied in a 2-dimensional slurry bubble column. From high speed video image analysis, the average large bubble diameter, the frequency of occurrence of large bubbles, the gas-liquid interfacial area, and the large bubble hold-up are obtained. The liquid side mass transfer coefficient is calculated from the volumetric mass transfer coefficient and the gas-liquid interfacial area. The lyophilic silica particles are rendered lyophobic by a methylation process to study the influence of particle wettability. The influence of organic electrolyte (sodium gluconate) and the combination of electrolyte and particles is also studied. It is found that lyophilic silica, lyophobic silica, and lyophobic carbon particles at concentrations larger than 2 g/l (0.4 vol%) decrease the gas hold-up and shift the regime transition point (where the first large bubbles appear) to a lower gas velocity. The volumetric mass transfer coefficient increases with gas velocity, increases with electrolyte concentration, decreases with slurry concentration, and is higher for lyophobic particles. The liquid side mass transfer coefficient increases with gas velocity, bubble diameter, and is higher for lyophobic particles. A correlation for the mass transfer coefficient based on dimensionless numbers is proposed for the heterogeneous regime.

溶滴形成・移行過程における銅めっきの挙動に関する考察―ソリッドワイヤの溶滴表面張力に関して―

High speed video image analysis, optical measurement, and sound pressure analysis were conducted to reveal the difference between Cu-coated solid wire's and non-Cu-coated solid wire's molten droplet formation and transfer. It was obvious that the molten droplet size of non-Cu-coated solid wire was smaller than that of Cu-coated solid wire in any welding conditions except for very slow droplet formation. As Cu coating diffusion time was similar to molten droplet formation and transfer time, Cu coating on solid wire surface influenced the formation and the transfer of molten droplet. Cu coating prevented oxidization on solid state wire surface, and reduced the amount of oxygen on the molten droplet surface. Non-Cu-coated solid wire was the ideal material for the formation of small molten droplets of the short-circuit and the spray transfer.

High speed video image analysis of flow of fine particles in fluidized bed jets

The hydrodynamics of gas/solids mixtures, e.g. in fluidization and pneumatic conveying, has a distinct effect on the breakage and degradation of powders. Visualization by means of high speed video imaging of these processes enables a better understanding of the mechanics of these processes and verification of the models developed for describing the process. In this paper, the development and use of high speed photography and video imaging and image processing and analysis for the measurement of particle velocities and concentrations, and divergent angles of gas jets in fluidized beds are described. The implications of the observations and measurements on design and control of these processes are indicated.

Automatic Measurement of Lymphocyte Velocity by High-Speed Video Image Analysis

Automatic Measurement of Lymphocyte Velocity by High-Speed Video Image Analysis