• Title/Summary/Keyword: mass transfer model

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Finite element analysis for prediction of weld bead shape of Nd:YAG pulse laser welding for AISI 304 stainless steel plate (AISI 304 스테인리스 강판의 Nd:YAG 펄스 레이저 용접비드 형상예측을 위한 유한요소해석)

  • Cho Haeyong;Kim Kwanwoo;Hong Jinuk;Lee Jaehoon;Suh Jeong
    • Laser Solutions
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    • v.8 no.1
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    • pp.19-25
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    • 2005
  • Pulse laser welding of AISI 304 stainless steel plate was simulated to optimize welding conditions by using commercial finite element code MARC. Due to geometric symmetry, a half model of AISI 304 stainless steel plate was considered. for the heat transfer analysis, user subroutines were applied to boundary condition. The material properties such as conductivity, specific heat, and mass density were given as a function of temperature and the latent heat associated with a given temperature range was considered. A moving heat source was designed on the basis of experimental data. As a result, Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

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Sustained Nuclear Star Formation and the Growth of a Nuclear Bulge

  • Kim, Sung-Soo S.
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.142.2-142.2
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    • 2011
  • Hydrodynamic simulations of gas clouds in the central hundred parsecs region of the Milky Way that is modeled with a three-dimensional bar potential are presented. Our simulations consider realistic gas cooling and heating, star formation, and supernova feedback. A ring of dense gas clouds forms as a result of $X_1-X_2$ orbit transfer, and our potential model results in a ring radius of ~200 pc, which coincides with the extraordinary reservoir of dense molecular clouds in the inner bulge, the Central Molecular Zone (CMZ). The gas clouds accumulated in the CMZ can reach high enough densities to form stars, and with an appropriate choice of simulation parameters, we successfully reproduce the observed gas mass and the star formation rate (SFR) in the CMZ, ${\sim}2{\times}10^7\;M_{\odot}$ and ${\sim}0.1\;M_{\odot}/yr$. Star formation in our simulations takes place mostly in the outermost $X_2$ orbits, and the SFR per unit surface area outside the CMZ is much lower. These facts suggest that the inner Galactic bulge may harbor a mild version of the nuclear star-forming rings seen in some external disk galaxies. We also find that the stellar population resulting from sustained star formation in the CMZ would be enlogated perpendicularly to the main bar, and this "inner bar" can migrate the gas in the CMZ further down to the central parsecs region.

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Characteristic Analysis of Cyclic Voltammetry on a Self-Assembled Mono-layer Electrode (자가조립 단층 전극에 대한 순환전위법의 특성해석)

  • Cho, Hana;Yoon, Do-Young
    • Journal of the Korean Electrochemical Society
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    • v.16 no.4
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    • pp.217-224
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    • 2013
  • In this paper, we have investigated the characteristics of cyclic voltammetry of a self-assembled mono-layer(SAM) electrode which was modified by 3-Mercaptopropionic acid (3-MPA) on gold nanoparticle(AuNP)-deposited electrode. Also, the transport phenomena of electrons and ions around the electrode have been analyzed. The governing equation and its boundary conditions by adopting the semi-infinite diffusion model were formulated for the mass-transfer dominant system. In order to obtain the numerical solutions of cyclic voltammetry(CV) on SAM electrodes, MATLAB program was implemented by applying the explicit finite difference method. Resulting CV program for the SAM-modified electrode was verified in good agreements with the experimental CV results for the 3-MPA on AuNP electrode.

Numerical Analysis of Thermal and Flow Characteristics for an Optimum Design of Automotive Catalytic Converter (자동차용 촉매변환기의 최적설계를 위한 열 및 유동특성에 대한 수치적 연구)

  • Jeong, Soo-Jin;Kim, Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.7
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    • pp.841-855
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    • 1999
  • In the present work, the effect of a flow maldistribution on the thermal and conversion response of 8 monolith catalytic converter is Investigated. To achieve this goal, a combined chemical reaction and multi-dimensional fluid dynamic mathematical model has been developed. The present results show that flow uniformity within the monolith brick has 8 great impact on light-off performance of the catalytic converter. In the case of lower flow uniformity, large portions of the monolith remain cold due to locally concentrated high velocities and CO, HC are unconverted during warm-up period, which loads to retardation of light-off. It has been also found that the heat-up pattern of the monolith ill similar to the flow distribution profile, In the early stage of the reaction. It may be concluded that flow maldistribution can cause a significant retardation of the light-off and hence can eventually worsen tho conversion efficiency of automotive catalytic converter.

Low-frequency Vibration Suppression Control in a Two-mass System by Using a Torque Feed-forward and Disturbance Torque Observer

  • Li, Qiong;Xu, Qiang;Wu, Ren
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.249-258
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    • 2016
  • Given that elastic connection is often used between motor drives and load devices in industrial applications, vibration often occurs at the load side. Vibration suppression is a crucial problem that needs to be addressed to achieve a high-performance servo-control system. Scholars have presented many strategies to suppress vibration. In this study, we propose a method to diminish vibration by using a torque feed-forward and disturbance torque observer. We analyze the system performance and explain the principle of the proposed vibration suppression method based on the transfer functions of the system. The design of controller parameters is another important issue in practical applications. We accordingly provide a succinct outline of the design specifications based on the coefficient diagram method. Furthermore, we build a model under the Simulink environment and conduct experiments to validate the proposed method. Results show that speed and position vibrations are successfully suppressed by the proposed method.

Theory of Nanoparticles Mechanosynthesis

  • Urakaev, Farit Kh.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.405-406
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    • 2005
  • A theoretical investigation of the solid-phase mechanochemical synthesis of nano-sized target product on the basis of dilution of the initial powdered reagent mixture by another product of an exchange reaction is presented. On the basis of the proposed 3-mode particle size distribution in mechanically activated mixture, optimal molar ratios of the components in mixture are calculated, providing the occurrence of impact-friction contacts of reagent particles and excluding aggregation of the nanosized particles of the target reaction product. Derivation of kinetic equations for mechanochemical synthesis of nanoscale particles by the final product dilution method in the systems of exchange reactions is submitted. On the basis of obtained equations the necessary times of mechanical activation for complete course of mechanochemical reactions are designed. Kinetics of solid phase mechanosynthesis of nano-TlCl by dilution of initial (2NaCl + $Tl_2SO_4$) mixture with the exchange reaction product (diluent, $zNa_2SO_4$, $z=z^*=11.25$) was studied experimentally. Some peculiar features of the reaction mechanism were found. Parameters of the kinetic curve of nano-TlCl obtained experimentally were compared with those for the model reaction KBr + TlCl + zKCl = (z + 1) KCl + TlBr ($z=z_l^*=13.5$), and for the first time the value of mass transfer coefficient in a mechanochemical reactor with mobile milling balls was evaluated. Dynamics of the size change was followed for nanoparticle reaction product as a function of mechanical activation time.

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Characteristic Study on Effect of the Vent Mixer to Supersonic Fuel-Air Mixing with Stereoscopic-PIV Method (3차원 PIV 기법을 사용한 벤트혼합기가 초음속 연료-공기 혼합에 미치는 특성 연구)

  • Kim, Chae-Hyoung;Jeung, In-Seuck;Choi, Byung-Il;Kouchi, Toshinori;Masuya, Goro
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2012.05a
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    • pp.378-385
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    • 2012
  • Vent mixer can provide main flow directly into a recirculation region downstream of the mixer to enhance fuel-air mixing efficiency. Based on experimental results of three-dimensional velocity, vorticity and turbulent kinetic energy obtained by a stereoscopic PIV method, the performance of the vent mixer was compared with that of the step mixer which was used as a basic model. Thick shear layers of the vent mixer induced the increase of the penetration height. The turbulent kinetic energy mainly distributed along a boundary layer between the main flow and the jet plume. This turbulent field activates mass transfer in a mixing region, leading to the mixing enhancement.

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The impact of ram pressure on the multi-phase ism probed by the TIGRESS simulation

  • Choi, Woorak;Kim, Chang-Goo;Chung, Aeree
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.2
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    • pp.33.1-33.1
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    • 2018
  • Ram pressure stripping by intracluster medium (ICM) can play a crucial role in galaxy evolution in the high-density environment as seen by many examples of cluster galaxies. Although much progress has been made by direct numerical simulations of galaxies (or a galaxy) as a whole in a cluster environment, the interstellar medium (ISM) in galactic disks is not well resolved to understand responses of the ISM in details. In order to overcome this, we utilize the TIGRESS simulation suite that focuses on a local region of galactic disks and resolves key physical processes in the ISM with uniformly high resolution. In this talk, we present the results from the solar neighborhood TIGRESS model facing the ICM winds with a range of ram pressures. When ram pressure is weaker than and comparable to the ISM weight, the ICM winds simply reshape the ISM to the one-sided disk, but star formation rates remain unchanged. Although there exist low-density channels in the multiphase ISM that allow the ICM winds to penetrate through, the ISM turbulence quickly closes the channels and prevents efficient stripping. When ram pressure is stronger than the ISM weight, a significant amount of the ISM can be stripped away rapidly, and star formation is quickly quenched. While the low-density gas is stripped rapidly, star formation still occurs in the extraplanar dense ISM (1-2kpc away from the stellar disk). Finally, we quantify the momentum transfer from the ICM to the ISM using the mass-and momentum-weighted velocity distribution functions of each gas phase.

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Analysis of the flow distribution and mixing characteristics in the reactor pressure vessel

  • Tong, L.L.;Hou, L.Q.;Cao, X.W.
    • Nuclear Engineering and Technology
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    • v.53 no.1
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    • pp.93-102
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    • 2021
  • The analysis of the fluid flow characteristics in reactor pressure vessel is an important part of the hydraulic design of nuclear power plant, which is related to the structure design of reactor internals, the flow distribution at core inlet and the safety of nuclear power plant. The flow distribution and mixing characteristics in the pressurized reactor vessel for the 1000MWe advanced pressurized water reactor is analyzed by using Computational Fluid Dynamics (CFD) method in this study. The geometry model of the full-scaled reactor vessel is built, which includes the cold and hot legs, downcomer, lower plenum, core, upper plenum, top plenum, and is verified with some parameters in DCD. Under normal condition, it is found that the flow skirt, core plate holes and outlet pipe cause pressure loss. The maximum and minimum flow coefficient is 1.028 and 0.961 respectively, and the standard deviation is 0.019. Compared with other reactor type, it shows relatively uniform of the flow distribution at the core inlet. The coolant mixing coefficient is investigated with adding additional variables, showing that mass transfer of coolant occurs near the interface. The coolant mainly distributes in the 90° area of the corresponding core inlet, and mixes at the interface with the coolant from the adjacent cold leg. 0.1% of corresponding coolant is still distributed at the inlet of the outer-ring components, indicating wide range of mixing coefficient distribution.

Discovery of Raman-scattered He II Features at 6545 Å in Planetary Nebulae NGC 6886 & NGC 6881 from BOES Spectroscopy

  • Choi, Bo-Eun;Lee, Hee-Won
    • The Bulletin of The Korean Astronomical Society
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    • v.45 no.1
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    • pp.50.4-51
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    • 2020
  • We report our discovery of Raman-scattered He II λ6545 feature in young planetary nebulae NGC 6886 and NGC 6881 which indicates the existence of atomic hydrogen components. Considering sharply increasing cross-section of hydrogen atom near the resonance, Raman-scattered He II features are a useful diagnostic tool to investigate the distribution and kinematics of H I region in planetary nebulae. The high-resolution spectroscopic observation was carried out using BOES installed on the 1.8 m telescope of BOAO. We estimate the column density of H I region and its expansion velocity using our grid-based Monte-Carlo radiative transfer code. We assume that the H I region is uniformly distributed in spherical shell geometry with an opening angle and expands with constant speed. Our best-fit model is shown with the column density NHI = 3 × 1020 cm-2 and expansion speed vexp = 25 km s-1 with the opening angle ~ 25° for NGC 6886, and NHI = 4 × 1020 cm-2 and vexp = 30 km s-1 with the opening angle ~ 35° for NGC 6881. We present brief discussions on the late-stage of evolution of stars with mass > 3 M⊙.

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