Papers by Keyword: Particle

Abstract: A simple numerical model has been generated for developing a code of Smoothed Particle Hydrodynamics (SPH) method. Those will be modified and used for future research. In this computational research domain is a square that consists of a real particle and virtual particle as the boundary treatment. In the initial condition, particle occupies a certain position. Circular flow has been generated by a rotating vertical cylinder to produce shear velocity to the real particle. The particles movement has been observed during time integration. A physical model has been constructed to compare the numerical model. The movement of real particles on the numerical model agrees with the movement of water particles on the physical model.

Abstract: The structure of the thin liquid films determines the stability of foams and emulsions. In this work the bubbles stretched length with different hollow SiO₂ particles concentration is measured when the foam has been stilled for different time. The results show that the bubbles stretched length is longer than that of bubbles when the foam is free of hollow SiO₂ particles even when the foam has been stilled for 500mins. The bubbles stretched length increases with increasing the concentration of hollow SiO₂ particles. A strong hydration effect leaves a large volume of hydration layers on the solid particles surfaces in aqueous solutions. The water in hydration layers can help the film keep a certain thickness. The existence of hydration forces leads that two particles cannot be too close each other. The high concentration surfactant limited in the fixed area helps the film keep good elasticity. Therefore the film has a long life time with compatible thickness and elasticity and the three-phrase foam is upper stable.

Abstract: Due to the restriction of passive layers containing Cr⁶⁺ [1], which were characterized by excellent corrosion protection due to their self-healing effect for scratches on metal surfaces, current corrosion protection systems consist of chromium (III) -containing thick layer passivation. Due to their lower hardness, current corrosion protection systems are susceptible to mechanical stress. This is particularly critical at barrel plating of screws, rivets etc. where the manufacturing process leads to damages of the corrosion protection layer and consequently to reduced corrosion resistance.To counter this problem, we point out one approach to install hard particles into the passivation layer. The entrapment of the hard particles into the passivation is detected by Glow Discharge Optical Emission Spectrometry. Comparative investigations in the corrosion chamber prove the improvement of the corrosion protection of steel parts with passivation layers containing hard particles.

Abstract: We are developing plasma nanofabrication, namely, nanoand micro scale guided assembly using plasmas. We manipulate nanoand micro objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of a fine particle (= each object) in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. In the first experiment, we grabbed a fine particle in plasma using an optical tweezers. The fine particle moves in a potential well made by the optical tweezers. This is a kind of Brownian motion and the position fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one. In the second experiment, we deduced interaction potential between two fine particles during their Coulomb collision. We found that there exist repulsive and attractive forces between them. The repulsive force is a screened Coulomb one, whereas the attractive force is likely a force due to a shadow effect, a non-collective attractive force. Moreover, we noted that there is a fluctuation of the potential, probably due to fluctuation of electrostatic force. These position and potential energy fluctuations may limit the accuracy of guided assembly using plasmas.

Abstract: Retaining structure of homogeneous fluid and granular stream is one of the main criteria for technological process assuring the high quality outcome in many industries, including mechanical engineering and oil & gas industry. For example, in oil and gas industry during the pipeline transportation of oils there is a strong trend for cluster aggregation, and particle coarsening and entanglement. Dehomogenization of particle stream results in reverse dynamics of the stream. The importance of prevention and minimization of small particles coalescence by separating the oil stream leads to the need of improving the properties of the dispersers to boost their efficiency. Our paper investigates the operating principle of the disperser for separating particles (separator), which is designed by the authors. We have considered a particle stream of dispersed structure. We have obtained the conformity with the stability of the disperser operation. To yield the results we use the extremum problems for differential equations. This approach provides strong evidence that there are optimum parameters of the dispersers, which result in better stability of the particle stream.

Abstract: Supercritical CO₂ is commonly used in the processing of natural products due to several advantageous factors such as inexpensiveness, moderate operating parameters and simple purification step. In the processing of phyto-pharmaceuticals, CO₂ has been used mostly for extraction, purification and particle formation. This article is a review of supercritical particle formation processes applied to phenolic compounds, specifically curcumin. In summary, supercritical technologies constitute a process platform for the modification of curcumin physicochemical properties. The use of supercritical CO₂ as a solute, solvent or anti-solvent in curcumin processing enabled the production of material with particle size as small as 15 nm and improved antioxidant activity.

Abstract: This article summarizes the main topics related to the issue of particle size analysis. It provides a discussion of the term ’particle’ and briefly describes the advantages and disadvantages of the most important particle size analysis methods.

Abstract: This work aims to obtain the well-implemented laser cleaning to remove polypropylene (PP) contamination of sizes ragne 10-60 µm on magnetic head slider by excimer laser at 248 nm. The finite element: FEM [1] simulations shows non-destructive cleaning at laser fluence of 100mJ/cm². The experiment shows that laser fluence is non-destructive at 70mJ/cm² and can remove 15-40% of polypropylene (PP) contamination.

Abstract: Nowadays, hard disk drives (HDD) technology are being developed continuously in order to increase the capacity, and reduce the size of HDD to meet user requirements. To increase the capacity which is equivalent to increasing read/write ability, the flying clearance must be reduced. Current new HDD models show that the fly height is lower than 0.3 μm. If the height of a particle or contamination is higher than 0.3 μm, the magnetic head will scratch the magnetic disk surface. However the process of cleaning in the HDD industry cannot remove particles with size smaller than 0.3 μm [1]. Therefore laser cleaning is selected first because this method can remove small particles [2]. and it does not damage the magnetic head. This research compares the range of temperature needed for cleaning the magnetic head between two types of heat source’s profile. The technique used is the heat transfer by finite element: FEM[3]. This technique provides an important factor of the laser cleaning method that increases the efficiency of particle removal. It is also a non-destructive method for cleaning the surface of the magnetic head slider.

Abstract: During the experimental study we examined the ignition of the litter of hardwood species by the particle heated up to high temperatures. Our study involved conducting tests, using a carbonic particle and samples of typical forest fuels, formed of birch leaves. We determined a mechanism for litter ignition by a local heating source, and obtained the dependence of ignition delay of birch leaves on the particle's initial temperature.