• 대한기계학회논문집B
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• 제24권7호
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• pp.1020-1027
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• 2000

A simple model for describing the non-spherical particle growth phenomena has been developed. In this model, we solve simultaneously particle volume and surface area conservation sectional equations that consider particles' non-sphericity. From the correlation between two conserved properties of sections, we can predict the evolution of the aggregates' morphology. This model was compared with a simple monodisperse-assumed model and more rigorous two-dimensional sectional model. For comparison, formation and growth of silica particles have been simulated in a constant temperature reactor environment. This new model showed good agreement with the detailed two-dimensional sectional model in total number concentration and primary particle size. The present model successfully predicted particle size distribution and morphology without costing very heavy computation load and memory needed for the analysis of two dimensional aerosol dynamics.

• 전기화학회지
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• 제16권4호
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• pp.191-197
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• 2013

리튬2차전지용 양극소재인 $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$를 공침법을 이용해 $Ni_{0.5}Co_{0.2}Mn_{0.3}(OH)_2$ 전구체로부터 합성하였고, 공침조건을 조절하여 전구체의 1차 입자 형상을 Flake형상과 Needle형상으로 제어하였다. 동일한 공정으로 리튬과 혼합하고 열처리하여, 입도, 탭밀도, 화학적 성분 등이 동일한 분체물성의 양극 소재를 합성하였다. 전구체의 1차입자 형상에 따른 $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$의 전기화학적 특성을 평가하고, 이 특성의 변화를 SEM, XRD, EELS로 이용하여 분석하여 연관성을 고찰하였다. Needle형상 전구체로 합성한 $Li(Ni_{0.5}Co_{0.2}Mn_{0.3})O_2$ 양극의 1차입자는 Flake형상 전구체로 합성한 경우보다 작고, EELS결과로는 입자표면의 Li농도가 내부보다 상대적으로 높았다. 전기화학적인 수명과 출력특성에서 Needle형상 전구체로 합성한 양극이 Flake형상 전구체의 경우보다 우수한 특성을 보였는데, 임피던스 측정으로부터 낮은 전하이동저항에 연관되어 있을 것으로 생각된다.

• Structural Engineering and Mechanics
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• 제55권2호
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• pp.315-334
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• 2015

This study's primary aim is to check the existence of a representative volume element for granular materials and determine the link between the properties (responses) of macro structures and the size of the discrete particle assembly used to represent a constitutive relation in a two-scale model. In our two-scale method the boundary value problem on the macro level was solved using finite element method, based on the Cosserat continuum; the macro stresses and modulus were obtained using a solution of discrete particle assemblies at certain element integration points. Meanwhile, discrete particle assemblies were solved using discrete element method under boundary conditions provided by the macro deformation. Our investigations focused largely on the size effects of the discrete particle assembly and the radius of the particle on macro properties, such as deformation stiffness, bearing capacity and the residual strength of the granular structure. According to the numerical results, we suggest fitting formulas linking the values of different macro properties (responses) and size of discrete particle assemblies. In addition, this study also concerns the configuration and displacement fluctuation of discrete particle assemblies on the micro level, accompanied with the evolution of bearing capacity and deformation on the macro level.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.637-643
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• 2001

Two-phase flow in a combustion chamber is experimentally analyzed according to the five different conditions in the Reynolds numbers of $1.02{\times}10^4$. As the height difference between the primary and secondary jets increases, the secondary has a little less effect on the primary one in the case on the same height difference, the primary jet is affects as the velocity of th secondary on increase. The primary-jet flow field cause the particle concentration since is controlled by the velocity of secondary jet, the height difference, and the angle of primary jet in the test section.

• 열처리공학회지
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• 제18권3호
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• pp.157-163
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• 2005

Effects of refinement of primary Si and residual stress on the mechanical properties of Aluminum B.390 alloy have been examined. Calcium was found to have an effect on the size of primary silicon particles. Primary silicon particle was refined as Ca content decreased. Refinement of primary Si particles led to an improvement in mechanical properties of the alloy; increase of elongation was prominent, above all. By the increase of compressive residual stress in the matrix alloy, tensile strength increased but elongation decreased.

• 한국주조공학회지
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• 제14권6호
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• pp.530-540
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• 1994

Aluminium-silicon alloy(JIS AC8A) matrix composites reinforced with SiC particles were fabricated by spray-cast forming process, and the microstructure of powders and preforms produced were studied by using an optical and scanning electron microscopy. SiC particles were co-sprayed by mixed phase injection method during the spray casting process. Most of the composite powders formed by this mixed phase injection method exhibit morphology of particle-embedded type, and some exhibits the morphology of particle attached type due to additional attachment of the SiC particles on the surface of the powders in flight. The preforms deposited were resulted in dispersed type microstructure. The pre-solidified droplets and the deposited preform of SiC-reinforced aluminium alloy exhibit finer equiaxed grain size than that of unreinforced aluminium alloy. Eutectic silicons of granular type are crystallized at the corner of the aluminum grains in the preforms deposited, and some SiC particles seem to act as nucleation sites for primary/eutectic silicon during solidification. Such primary/eutectic silicons seem to retard grain growth during the continued spray casting process. It is envisaged from the microstructural observations for the deposited preform that the resultant distribution of SiC injected particles in the Al-Si microsturcture is affected by the amount of liquid phase in the top part of the preform and by the solidification rate of the preform deposited.

• 한국기계가공학회지
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• 제19권8호
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• pp.88-93
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• 2020

The goal of this study is to determine the influence of major factors on the spiral surface microparticle injection machining of cylindrical specimens by the statistical method ANOVA. Before the experiment, rod-shaped test specimens and jigs for helical surface spraying were prepared, and the surface roughness was measured with a surface roughness meter. The injection particle, nozzle diameter, and injection pressure were the primary parameters of the experiment. Other factors that were considered were injection height, injection time, revolutions, and feed distance. The surface roughness after machining was measured, and the effects of the surface roughness data on the primary factors were determined with ANOVA.

• 대한기계학회논문집B
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• 제29권12호
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• pp.1335-1343
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• 2005

The calibration technique of Time Resolved Laser Induced Incandescence was investigated both experimentally and numerically by using standard-sized carbon black particles for the instantaneous soot measurement at exhaust tail pipe in engine. The carbon black particles (19nm, 25nm, 45nm and 58nm) used in this study are similar, though not identical, to soot particle generated from flame not only in morphology but also in micro-structure. The amount of soot loading in flow was controled by a diluted gas (nitrogen) and was measured by the gravimetric method at exhaust pipe in calibrator. The successful calibrations of primary particle size and soot mass fraction were carried out at the range from 19nm to 58nm and from $0.25mg/m^3$ to $37mg/m^3$ respectively. And based on these results the numerical simulation of LII signal was tuned and the effect of an exhaust temperature variation on the decay rate of LII signal was corrected.

• 한국염색가공학회지
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• 제27권4호
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• pp.245-260
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• 2015

The effect of salt milling process on the crystal size, morphology, and color characteristics of C.I. Pigment Red 57:1 was studied. The primitive morphology and color properties of the pigment after synthesis were studied in the former series work. The size and morphology of primary particles and the second aggregation features should be considered because they are very important to determine pigment quality. We compared the primary morphology of pigment particles before drying with the secondary aggregated morphology of pigment particles after drying and salt milling process. Morphological properties were investigated by particle size analysis, X-ray diffraction, and scanning electron microscopy and color measurement was carried out. Significant reduction in particle size as well as enhanced crystallite size after salt milling process was observed. This result might give a difference in color of the pigment, turning into brighter and more blue-toned red color. It was revealed that synthesis condition affect the morphology and color of the pigment even after milling. Increase in HCl concentration in the synthesis process enhanced crystal size and quality forming bluer-red pigments but an increase in $CaCl_2$ concentration resulted in more amorphous crystals forming darker-red pigments after salt milling.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.827-838
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• 2023

Centrifugal pump is a key part of nuclear power plant systems, and its health status is critical to the safety and reliability of nuclear power plants. Therefore, fault diagnosis is required for centrifugal pump. Traditional fault diagnosis methods have difficulty extracting fault features from nonlinear and non-stationary signals, resulting in low diagnostic accuracy. In this paper, a new fault diagnosis method is proposed based on the improved particle swarm optimization (IPSO) algorithm-based variational modal decomposition (VMD) and relevance vector machine (RVM). Firstly, a simulation test bench for rotor faults is built, in which vibration displacement signals of the rotor are also collected by eddy current sensors. Then, the improved particle swarm algorithm is used to optimize the VMD to achieve adaptive decomposition of vibration displacement signals. Meanwhile, a screening criterion based on the minimum Kullback-Leibler (K-L) divergence value is established to extract the primary intrinsic modal function (IMF) component. Eventually, the factors are obtained from the primary IMF component to form a fault feature vector, and fault patterns are recognized using the RVM model. The results show that the extraction of the fault information and fault diagnosis classification have been improved, and the average accuracy could reach 97.87%.