Jo Mar 26, 2024
Induction channel furnace (ICF) is widely used for melting, holding and casting metals and alloys in many processing industries because it has high overall efficiency, low electric power consumption and operation costs, better degassing and homogenization of melt and low oxide and slag formation. However, thermal stresses in the refractory lining caused by high temperature and flow of molten metal may cause premature erosion of the lining and failure of the inductor, and so it is difficult to repair the furnace. In addition, the furnace for steel melting often experiences shortened operating life and quicker needs for a repair cycle due to high temperature of molten metal and severe erosion of lining, so it is rarely used.
In order to solve these problems and make easy operation, it is important to improve the structure and to numerically simulate Joule heat generation and molten metal flow in the channel.
Song Hak Myong, a lecturer at the Mechanical Engineering Department, has designed a new type of channel of three-phase ICF for steel melting and investigated temperature distribution of the channel by a coupled simulation on the electromagnetism-heat-fluid using COMSOL Multiphysics 5.4.
ICF consists of molten metal bath and induction unit that is made up of iron core, inductor and channel. If one three-phase induction unit is fixed to the furnace body, it will lead to decrease in electrical unbalance and ease of furnace repair.
According to his simulation results, the optimal design parameters (with maximum S/N ratio) for three-phase ICF are as follows:
• Type of channel: Elliptic
• Dimensions of channel: 85×90 mm2
• Existence of protruding part: Yes
• Setting angle of channel: 30°
The local superheating temperature is relatively low (20.8–22.9K) and the maximum local superheating temperature is similar to the maximum local superheating temperature 33K in the channel of the twin channel induction furnaces.
It is one of the ways to prevent early erosion and expansion of refractory lining by local superheating in the channel and to increase its repair cycle.
The proposed method could be used for reducing manufacturing cost and regularizing operation through optimizing the parameters of induction furnace needed for aimed melting and flow.
If further information is needed, please refer to his paper “ Simulation on Temperature in Channel of Three-phase Induction Channel Furnace for Steel Melting Using COMSOL Multiphysics and Taguchi Method” in “International Journal of Metalcasting” (SCI).
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Jo Mar 23, 2024
As modern industrial processes become more complex with the development of technology, more advanced monitoring methodologies are required to keep high efficiency and safe operation. In order to improve monitoring performance, it is important to identify the operational phase of a process by evaluating all measurable variables comprehensively. Multiple operational characteristic that occurs in most industrial processes like chemical processes by their physical and chemical properties, variations in market requirement and product specification, catalyst degradation, etc. has become an important factor to be considered in process monitoring.
Since most multimode monitoring approaches with the mode-identification are only based on the similarity of process mean, the identification of transitions and faults is possible only after the cluster of process data should be formed or neighbour modes could be analyzed. Furthermore, mode-identification based approach seems to be inappropriate to monitoring of process with lots of modes not only because it requires a large amount of off-line data but also because its capability of adapting to unexpected states may not be acceptable.
Song Kwang Rim, a researcher at the Faculty of Automation Engineering, has proposed an online transition-identification based monitoring procedure for industrial process with multiple operational modes using process variability.
Firstly, he detected the change point in the dynamical behavior of multimode process by the log determinant of covariance matrix.
Second, based upon the analysis of the change behavior of process variability during transition and fault state, he developed new statistics to identify the transition.
Finally, he adopted an adaptive monitoring strategy to monitor multimode processes by the single model using the transition-identification.
Then, he conducted three case studies through TE benchmark to verify the usefulness and effectiveness of the proposed approach.
The result showed that the proposed approach has high ability to identify transitions and faults and to cope with the occurrence of new modes.
The details of this are found in his paper “Monitoring Industrial Processes with Multiple Operation Modes: a Transition-Identi¦cation Approach Based on Process Variability” in “Industrial & Engineering Chemistry Research” (SCI).
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Jo Mar 22, 2024
Numerical modeling and simulations of plasma is an indispensable means to overcome the technical limit in measuring plasma parameters, which has been performed by many researchers. Unlike conventional numerical modeling, lattice Boltzmann method (LBM) is a meso-scale scheme based on Boltzmann kinetic theory, which has some advantages such as relatively simple computational structure, easy handling on complex boundaries and possible parallel computation. Recently, the LBM has been widely used to simulate not only single phase flow but also multi-component and/or multi-phase thermal fluid transfer, electric and magnetic fields, acoustic fields and radiative transport. However, the previous models for plasma were limited to 2D schemes, so they were not enough to analyze 3D mechanism of arc dynamics.
Therefore, Kim Ju Song, a lecturer at the Faculty of Physical Engineering, has suggested a 3D lattice Boltzmann model to numerically simulate thermal fluid flow in non-transferred arc torch with swirl and validated its accuracy by comparing it with results in literature.
The Boltzmann model was built for local thermodynamic equilibrium. The boundary conditions were considered for both macro- and micro-parameters, and the curved boundaries were handled for the cathode and the anode.
The simulation results demonstrate that the maximal temperatures appear at positions downstream from cathode and the axial velocity profiles are remarkably different according to the swirl number and that the position in the maximal axial velocity shifts toward the cathode with increase in the swirl number.
For more information about it, please refer to his paper “Numerical Analysis for Argon Arc Plasma Jet Flow by Three-Dimensional Thermal Lattice Boltzmann Model” in “Bulletin of the Lebedev Physics Institute” (SCI).
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Jo Mar 20, 2024
Conventional approaches such as physical and chemical methods have been proposed for synthesis of metal nanoparticles. However, these are associated with the use of heavy equipment, huge amount of energy input, highly toxic and dangerous chemical compounds that cause biological hazards.
Apart from these, plant-mediated synthesis of metal nanoparticles seems to be very rapid, simple, dependable, non-toxic and ecofriendly.
Recently, great efforts have been made to use environmentally-friendly methods for the synthesis of silver (Ag) nanoparticles which have become a promising material in the recognition of ultrasensitive chemical and biological molecules owing to its low cost, high catalytic activity and noteworthy optical properties. Most plants used in green synthesis of Ag nanoparticles are medical herbs. The extracts of such medical herbs include several kinds of useful ingredients including polyphenol, protein and polysaccharide for reduction and stabilization of Ag nanoparticles.
Ri Yun Sik, a researcher at the Faculty of Materials Science and Technology, has investigated an eco-friendly route to the synthesis of Ag nanoparticles by extracts derived from Epimedium Koreanum Nakai leaves, which have been traditionally used as aphrodisiac and for low blood pressure, neurasthenia, infertility, impotence and amnesia, and their antibacterial properties and colorimetric sensing property on hydrogen peroxide.
As a result, he has found that the Ag nanoparticles he synthesized were small, nearly monodispersed and highly crystalline with face centered cubic structure and that these Ag nanoparticles show high antibacterial activity against bacteria such as E. coli and S. aureus. He has also proved that the degradation of Ag nanoparticles induced by catalytic decomposition of hydrogen peroxide causes a considerable change in the surface plasmon resonance absorbance with hydrogen peroxide concentration and that this sensor reaction has a very good sensitivity and a linear response over wide hydrogen peroxide concentration range of 10−6 to 10−1M hydrogen peroxide.
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Jo Mar 18, 2024
Nowadays, pearlite ductile cast irons are widely used for producing shafts, wheels and gears due to its good mechanical properties and excellent castability. Compared with carbon steels, ductile irons have relatively low melting temperatures, good fluidity and castability, and moderate shrinkage during solidification and cooling.
There are several heat treatment methods to improve the mechanical properties of ductile cast iron such as annealing, normalizing, quenching and tempering. These heat treatments could be partially replaced by adequate balances of alloying elements. It is an easy and economical way of obtaining different microstructures and good mechanical properties in ductile cast irons.
As the demand for pearlite ductile irons increases day by day, nickel, copper, and molybdenum are common alloying elements in as-cast pearlite ductile irons. In view of the international trend in the rising cost of nickel and molybdenum, there is a renewed interest in exploiting the strengthening effect of manganese and copper in ductile irons. Both manganese and copper are FCC metals and they are highly soluble in austenite. The use of alloying elements stabilizing the pearlite such as Cu and Mn can be considered as the most appropriate method to control the amount of pearlite in the matrix and enhance the mechanical properties.
Kim Yu Chol, a researcher at the Faculty of Materials Science and Technology, studied the effect of cheaper alloying elements like copper and manganese on the mechanical properties and microstructure of ductile cast iron, thus obtaining as-cast pearlite ductile cast iron with high tensile strength, good elongation and high hardness.
There was, practically, no free ferrite in the ductile cast iron alloyed with Mn and Cu. When the content of Mn was 0.53% and the additive amount of Cu was 0.6%, the pearlite content was 86%. At that time, the as-cast pearlite ductile cast iron had tensile strength of 720 MPa, elongation of 4.6% and hardness of HB 268.
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Jo Mar 16, 2024
A charge sensitive amplifier (CSA) is widely used as the preamplifier of an X-ray or gamma-ray detector. It is based on a low-noise high frequency field-effect transistor and a current feedback operational amplifier allowing the readout of fast charge pulses.
The pile-up of output pulses in a CSA is attributable to its long discharge time constant. A CR differentiator which shortens pulse width is used to remove pile-up. Due to the exponential decay of a CSA feedback circuit in combination with a differentiator circuit, undershoot occurs at the output of a shaping amplifier with the same time constant as the CSA. PZC circuit is inserted between the CSA and the shaping amplifier to eliminate undershoot. But this makes it difficult to decide the real differential time constant of the CR differentiator after elimination of undershoot and to process the signals like peak detection, time analysis, etc. An analog PZC circuit always has some uncertainties that result in pulse tail pile-up. This drawback can be overcome with a digital pole-zero, zero-pole compensation unit.
A digital PZC method also has some uncertainties. Although digital real time processing of pulses could, in principle, eliminate almost all pulse pile-up distortion in spectroscopy, it is not yet widespread.
Pae Won Sik, a researcher at the General Assay Office, has performed an analysis to search for the cause of undershoot after differentiation of input signals and designed a new PZC circuit with unchanged differential time constant by using a pot resistor. Then, he has conducted some simulations and experiments to verify its successful performance.
The results show that the proposed circuit effectively eliminates undershoot and significantly reduces pulse width, which leads to the improvement of pile-up cancelling, peak detection and time analysis.
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