Jo May 9, 2025
Plasma technology has been widely used in various forms in the fields of functional materials, new materials synthesis, metal cutting, ozone generation, air purification, food, environmental, chemical, mechanical industries, etc. In particular, surface treatment of objects based on plasma has been studied by many researchers because it can improve several properties of the surface and broaden its application.
Dielectric barrier discharge is a very effective non-equilibrium plasma generation method that prevents the transition into spark and arc discharge that occurs in the discharge gap by inserting dielectric into the discharge space. Corona discharge is also an effective method of non-equilibrium plasma generation at atmospheric pressure. However, its discharge area is small and the power density is not high. Hence, if corona discharge and dielectric barrier discharge are properly combined, the discharge is more uniform and stable due to the corona effect at the corona electrode in the discharge space and high power density atmospheric pressure discharge can be realized.
The discharge formed by high frequency and high pressure after the insertion of dielectric into the corona discharge space is called dielectric barrier corona discharge (DBCD). Treatment of the surface of resin or cloth by DBCD can improve the surface properties by changing the adhesion, resistance, dyeing, painting, gloss, wear resistance, hydrophobicity, etc.
Kim Jin Hyok, a researcher at the Institute of Nano Science and Technology, has generated dielectric barrier corona discharge using quartz glass as dielectric in the atmosphere, treated the surface of Tetron fabric by passing it through the discharge space, and considered the change of its characteristics. At high frequency, high pressure power supply of 15 kHz and 18kV, he treated the Tetron fabric with varying discharge power, treatment speed and number of treatments, and measured the change of water penetration time to compare its surface characteristics.
As a result, he has found the following.
First, the higher the discharge power is, the shorter the water penetration time gets and the better the hydrophobicity becomes. When the slower the treatment speed is, i.e., the longer the treatment time for the unit area of the Tetron fabric is, the higher the treatment efficiency is, which leads to the shorter water penetration time. The more the number of treatment is, the better the surface properties become and the shorter the water penetration time gets.
From these characteristics, he determined the optimal surface treatment parameters by the Taguchi method. They are 900W of discharge power, 7cm/s of treatment migration rate and 4 rounds of treatment. Under these conditions, water penetration time is 9.2s.
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Jo May 6, 2025
A torque converter, equipped between engine and transmission, is a complex turbo-machine to transfer power from engine to transmission by means of interaction of moving fluid and blade cascades. A torque converter is widely used in vehicle transmissions and industrial power transmissions because of its outstanding automatic torque amplification, good acceleration performance and absorption of excessive vibration.
The design of blade cascades is the kernel part of a torque converter design. The blade cascades consist of complex surfaces and 3D curves, so it is very difficult to design and optimize them. There are two parts in the design of blade cascades: modeling of blade surface and its performance evaluation based on CFD analysis.
Kim Myong Hak, a researcher at the Robotics Institute, has proposed a practical torque converter design approach based on CFD analysis.
First, he built a 3D model of torque converter blades by ANSYS BladeGen and predicted their performance by CFD simulations. Second, he modeled the angle and thickness distribution curves at the core and shell of blades by Bezier curves, and improved the performance of the torque converter by controlling the control point of Bezier curves based on CFD simulation results. As a result, he established the methodology for designing torque converters with the required performance saving computation time and costs.
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Jo Apr 29, 2025
The exhaustion of fossil fuel resources and constant evil effect of the global warming due to greenhouse gas emission needs the introduction of new kinds of energy system. Now, hydrogen energy system is attracting a great deal of attention as a reasonable energy system that can solve almost all kinds of environmental problems.
Proton exchange membrane (PEM) water electrolysis is considered as a main option to integrate and to miniaturize hydrogen energy systems. An advantage of PEM water electrolysis is short start-up time, high current density, high pressurized hydrogen production possibility and no use of corrosive solutions like alkali.
The kinds and properties of an anodic porous transport layer (PTL) play an important role in water management and ohmic resistance reduction. Some materials such as porous carbon materials (carbon fiber or carbon paper) and metals (Ti or Ni) can be used as the PTLs of PEM water electrolyzers.
Jang Tae Il, a researcher at the Institute of Nano Science and Technology, has concluded that the hot-pressed carbon paper is a superior PTL for improving the conductivity of the catalyst coated layer (CCL), and intensified his research to use carbon paper as an anodic PTL.
First, he found that anti-oxidized and hydrophilically treated carbon paper could be used as anodic PTL. Then, during the formation of a micro protective layer (MPL) by protective agents, he conducted plasma treatment of the hydrophobized carbon paper followed by impregnation with the hydrophilic polymer Nafion solution before repeating immersion-drying processes several times and heat treatment at 140℃ for 30 min to use carbon paper as anodic PTL.
PEM water electrolyzer prepared with the hydrophilic anodic PTL displayed desirable performance; initial voltage at 1.2A·cm-2 of current density at 80℃ was 1.76±0.02V, and finally measured voltage 1.84±0.02V after 6 270h of testing.
For more information, please refer to his paper “Hydrophilic treatment of carbon paper for anodic porous transport layer in proton exchange membrane water electrolyzer” in “Reaction Kinetics, Mechanisms and Catalysis” (SCI).
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Jo Apr 28, 2025
Commercial pure titanium (Cp Ti) and Ti alloys have good mechanical properties, excellent biocompatibility, corrosion resistance and specific strength, and most suitable characteristics required for biomedical applications. So, they have been widely used in many biomedical applications including hip joints, dental implants, etc. Especially, the alloys with lower modulus are desired because the moduli of alloys are required to be much more similar to bone.
There are many kinds of Ti alloys applicable to biomedical applications. To evaluate the performance of Ti alloys, it is necessary to consider the multiple biomedical and mechanical properties comprehensively, not individually. Therefore, Ti alloy selection becomes a multi-attribute decision-making (MADM) problem for evaluating the multiple candidate Ti alloys in consideration of their multiple conflicting attributes and selecting the best one among them, and it could be solved using the MADM methods.
Many works have applied the multiple MADMs to solve the biomaterials selection problems. However, the previous works have the following shortcomings: (1) they do not reflect the preference-weights of each MADM in the integrated ranks, and (2) they determine only the integrated evaluation ranks of candidates, and do not determine the integrated evaluation values of candidates.
Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, has proposed a new integrated MADM methodology based on the integrated comprehensive evaluation index (ICEI) of candidates: ICEI-MADM.
The ICEIs are the preference-weighted averages of comprehensive evaluation indices (CEIs) of candidates obtained from individual MADMs, and the preference-weights are calculated by the normalized average correlation coefficients between rankings from the individual MADMs.
To demonstrate the effectiveness of the proposed method, he applied the method to the comprehensive evaluation of the performance of biomedical Ti alloys and the selection of the best of them.
For more information, please refer to his paper “Integrated multi-attribute decision-making methodology based on integrated comprehensive evaluation index: application to titanium alloy selection” in “Applied Physics A” (SCI).
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Jo Apr 26, 2025
The Interior Permanent-Magnet Brushless DC Motor (IPMBLDCM) without exciting winding and exciting source is widely used to replace traditional DC motors for subway locomotives. IPMBLDCM is gaining a great deal of interest for subway locomotive applications due to its high efficiency, simple control mode and small size.
PMBLDCM has a wide speed regulation range and its start current, start torque and starting time are small. Also, PMBLDCM generates enough torque and speed by the combination mode of motor/generator. From zero to base speed, it is dependent on applied voltage, and above the base speed, it is dependent on flux weakening by torque angle.
Cha Myong Song, a section head at the Faculty of Electrical Engineering, has proposed a winding design and lead angle control method for the maximum speed of an IPMBLDCM for subway locomotives.
The maximum speed of the IPMBLDCM is regulated by the linkage flux and armature reaction by lead angle control because permanent magnet magnetomotive force (mmf) cannot be regulated directly. The maximum speed of IPMBLDCM for the subway locomotive is 2.34 times the rated speed. As the speed regulation ratio is larger than 2, the maximum speed of motor must be ensured by lead angle and conductors per slot. If the lead angle is regulated, no-load speed is increased by changing linkage flux at no-load state and the rated speed is increased by armature reaction.
He simulated the relation between the speed, torque, output power and efficiency for the lead-angle and conductors per slot by means of Ansoft Maxwell/RMxprt. The simulation results verified that the speed, torque, output power and efficiency are constant in the range of 47°-68° and the maximum speed is 1948r/min. The experimental results indicated that the operation of the IPMBLDCM is stable at the maximum speed.
For more information, please refer to his paper “Winding Design and Lead-Angle Control for the Maximum Speed of an Interior Permanent-Magnet Brushless DC Motor” in “Journal of Electrical Power & Energy Systems” (SCI).
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Jo Apr 25, 2025
Low-pressure glow discharges (LPGD) are of topical interest for many applications such as lasers, plasma treatments and illuminators.
Simulations of LPGD have been reported in many works. Most of the numerical models for LPGDs used the monoatomic gases (especially argon) as background gases and failed to consider the excited species, which is essential for energy transport and chemical reaction mechanisms in plasma simulations and provides a more comprehensive understanding of the plasma dynamics.
Lattice Boltzmann Method (LBM) has several advantages such as simple calculation procedure, easy handling of complex geometries and simple implementation of parallel computation. In the last decades, the LBM has been utilized as an attractive method for fluid dynamics simulations such as multi-phase flows, multi-component flows and reactive flows.
In the applications of the LBM for plasma simulations, the coupling scheme of electrons and heavy species is important for the accuracy and stability of numerical simulations because of the huge difference between their parameters. For this combination, some interpolations and assumptions, which were used in previous studies, might lead to numerical errors.
Kim Yong Jun, a researcher at the Faculty of Physical Engineering, has proposed a mathematical model that uses the LBM to simulate the DC argon glow discharge.
He obtained the DC glow discharge through one- and two-dimension analyses, and compared them with the previous results.
The proposed model can be used as a mathematical model for simulating the nonequilibrium atomic (or molecular) plasmas with not only multi-components and multi-reactions, but also several electrode structures.
You can find more information in his paper “Lattice Boltzmann Simulation of Direct-current Glow Discharge at Low Pressure” in “International Journal of Modeling, Simulation, and Scientific Computing” (SCI).
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