High-speed Video Technology Research Articles

Reduction of Oxide Inclusions in Aluminum Cylinder Heads Through Autonomous Designs of Experiments

Oxide inclusions, which are created during the pouring process of aluminum alloys, are the main cause of leaks in castings. This contribution shows how the integration of autonomous design of experiments (DOEs) into the casting process simulation tool MAGMASOFT® provides the basis for the evaluation and subsequent optimization of process parameters in the melt transport and pouring process, which are responsible for the creation and distribution of oxide inclusions. At the same time, quality criteria describing the creation of oxides during the casting process of cylinder heads were evaluated quantitatively. The utilization of autonomous DOEs creates variations of the gating system and process parameters autonomously. It will be shown that autonomous DOEs are leading to optimized gating designs and process parameters resulting in a significant reduction of oxides in castings. The experiments supported by simulation were accompanied and validated by high-speed video technology and the PREFIL-measurement technology.

Contribution of Specimen Surface Friction to Size Effect and Rupture Behavior of Concrete

Four common specimen types were tested in uniaxial compression under the influence of two distinct loading surfaces to analyze concrete’s shape effect, strength performance, and crack propagation. Inferential data analysis using analysis of variance (ANOVA) was applied, proving a main effect for specimen shape. Pairwise comparison revealed a geometric effect between all but two sample types. Decreased surface friction showed a significant strength reduction, ranging between 9.5 and 31.5%. The influence of surface friction, combined with geometric properties, was assessed, with one shape to be mutually different from all other shapes. The development of rupture was captured by high-speed video technology with 2000 frames per second. Clear differences in crack initiation and propagation were observed for different surface treatments, regardless of specimen type. While cracks under conventional confinement formed inclined failure facets (45 to 60 degrees), cracks were free to develop vertically under reduced friction, forming slender concrete shards that failed in buckling.

Simulation of drop formation in a single hole in solvent extraction using the volume-of-fluid method

Computational fluid dynamics (CFD) simulations were performed to investigate drop formation in single holes in solvent extraction. The effects of various operating and design parameters were investigated in order to optimize the drop formation. The obtained results show that CFD simulations can give useful information about drop formation in sieve plates. The numerical results indicated different drop formation periods. These periods were different for the straight and conical holes. Furthermore, it was shown that the shape of the hole has considerable effect on the size of the drops formed. The simulation results were verified by comparison with experimental observations obtained using high-speed video technology. The numerical results for the drop sizes, shapes and formation times were found to be consistent with images of experimental drops across a wide range of solvent volumetric flow rates.

Numerical calculation of shapes and detachment times of bubbles generated from a sieve plate

A mathematical model describing the formation, breakage and rising of a gas bubble generated in a submerged orifice is proposed. The model considers an axisymmetric bubble based on a finite-difference formulation. The model can predict detachment of the bubble from the plate as a result of the predictive equations. Bubble shapes and detachment times obtained theoretically are compared with images of experimental bubbles obtained using high-speed video technology, finding good agreement between both. A theoretical description of the different stages of bubble formation and rising supported on the basic equations of fluid mechanics is the first step in the development of an accurate mass transfer correlation for devices where bubbles are generated in sieve plates.

The Effect of Nanopowder Attributes on Reaction Mechanism and Ignition Sensitivity of Nanothermites

AbstractNanothermite composites have several properties that are not typical of conventional thermites. The nanoscale size of individual reactants is responsible for the significant differences in these properties, especially the rate of energy release and mechanism of combustion front propagation. Several thermite mixtures were investigated, including Al-Fe2O3, Al-CuO, Al-MoO3, and Al-Bi2O3. Previous studies have reported on the behavior of these mixtures during unconfined burning and on the characterization of particle attributes such as particle size, surface area, and reactive metal content. This study was focused on several other attributes, including mixing of nanoreactants in water and measurements of reaction kinetics and combustion front propagation characteristics under confined conditions. The nanoscale nature of the thermite components also has an effect on the kinetics of the reaction. Differential scanning calorimetry was used to determine activation energy of these reacting systems. Several experimental setups were used to monitor the nanothermite mixtures during combustion. The mixtures were monitored during combustion in small diameter tubes using high speed video technology and a pressure sensor system. These tests were used to characterize combustion propagation under confined conditions and to determine the effect of pressure and mixture density on propagation rate. Experiments were also performed using both a closed volume pressure cell and recoil force cell to measure the reactive energy of the mixtures.

Microscopic visualization of insect cell-bubble interactions. I: Rising bubbles, air-medium interface, and the foam layer.

Through the use of microscopic, high-speed video technology, the interactions of two suspended insect cell lines, Trichoplusia ni (TN-368) and Spodoptera frugiperda (SF-9), with air and oxygen bubbles were studied. Events such as cell-bubble attachment, cell-bubble collision, cell transport into the foam layer, and trapping of cells in the foam layer are presented and discussed. Based on these observations and those in a companion paper (Chalmers, J. J.; Bavarian, F. Biotechnol. Prog. 1991, following paper in this issue) and the experimental and theoretical work of other researchers, several mechanisms of cell damage as a result of sparging are presented.