Jo Aug 19, 2025
The separation of acid gases from gas mixtures and waste gases is very important for environmental protection. Acid gases which can form an acidic solution when mixed with water include carbon dioxide (CO2), hydrogen sulfide (H2S), and sulfur dioxide (SO2).
Sulfur dioxide (SO2) is generated mainly from combustion of sulfur-containing fossil fuels such as coal or oil. It is also produced from some production processes such as fertilizer production, aluminum smelting and steel production. Sulfur dioxide is a major component of acid rain because it reacts with water vapor in the atmosphere to produce sulfuric acid (H2SO4).
Therefore, there have been many attempts to remove SO2. Among them, membrane-based gas separation is of great importance in the chemical industry due to its simplicity, ease of operation, reduced energy consumption and compact structure.
Ri Chang Ryop, a researcher at the Institute of Nano Science and Technology, has conducted a mass transfer simulation to remove sulfur dioxide (SO2) using tubular membranes, and proposed a general mass transfer model to predict the absorption of SO2 into N,N-dimethylaniline solvent.
He solved the governing equations including continuity and momentum equations by computational fluid dynamics (CFD) methods. In order to obtain the concentration distribution of SO2 in the membrane, he investigated the effect of parameters on the performance of the membrane by simulating the behavior of the vapor and liquid phases.
The simulation results showed that the removal of SO2 increased with decreasing gas velocity at the membrane surface.
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Jo Aug 18, 2025
Non-destructive testing will estimate the size, shape and state of defects without damaging the structures. Non-destructive testing methods include eddy current inspection (ECT), ultrasonography, X-ray inspection, etc. Ultrasonography shows good accuracy and reproducibility, but it needs direct contact with specimens and special liquids, which means complicated procedure and high cost. X-ray inspection has the disadvantage that operators can be exposed to irradiation. Although eddy current technology has the advantages of relatively simple structure, no contact with test specimens, low cost and fast testing, it still has a disadvantage. If sine wave is used as an excitation current, the increase in power can cause the excitation coil to be severely heated and damaged, and increasing frequency limits the depth to detect defects.
Pulsed eddy current (PEC) technique can overcome these limitations. PEC technique is widely used for contactless inspection of large areas of pressure body or tube made of ferromagnetic materials.
What is important in detecting internal defects of nonmagnetic materials by PEC technology is to increase the excitation power and the sensitivity. However, some parameters such as pulse amplitude and width cannot be increased constantly. Differential signals of defective and non-defective parts must be obtained to identify defects. The key to designing PEC probes is to optimize the magnetic field near defects to the maximum.
Jo Kwang Myong, a researcher at the Faculty of Mechanical Science and Technology, has built a finite element model of a concentric sensor and obtained the type of a relatively sensitive sensor, and, on this basis, he developed a sensor. In addition, he has made a differential sensor in the same way and compared it with the concentric sensor.
From the internal defects located 3mm below the surface in a stainless steel plate of 4mm in thickness, he determined the structural dimensions of a concentric sensor for maximum signals and manufactured it for a test. The concentric sensor determined the presence or absence of defects, but not their exact size or depth. In the meanwhile, the same test by the differential sensor showed that its signal strength is very high with a significant change in the depth of defects and it can fully process them without amplifying the signals.
His study demonstrates that differential sensors are effective in detecting the internal defects of nonmagnetic materials.
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Jo Aug 17, 2025
The excitation field circuits of synchronous generators are typically isolated under normal operating conditions. The field winding is subjected to mechanical and thermal stress cycles due to the increase in rotation speed and temperature. In addition to the normal stress, the field winding can be exposed to abnormal mechanical or thermal stress due to overspeed, vibrations, excessive field currents, poor cooling or stator negative sequence currents. This may result in the breakdown of insulation between the field winding and the rotor core at the points where the stress has the highest value.
When the excitation system is isolated, a single ground fault in the field winding or its associated circuits, causes a negligible fault current, which does not lead to any immediate danger. However, if a second ground fault occurs, high fault currents and severe mechanical unbalances may quickly arise, leading to serious damage. In some cases, the field current, flowing through the rotor core, could generate enough heat to melt it.
It is essential, therefore, that the first insulation failure has to be detected, and the generator has to be removed from service to check the insulation health.
Jong Chol Min, a section head at the Faculty of Electrical Engineering, has proposed an on-line rotor ground fault location method for synchronous machines with static excitation, and conducted computer simulations to validate its effectiveness. In addition, he has proposed a new algorithm for estimating the ground fault resistance value in rotor windings in order to improve the accuracy of location.
This novel technique has two important advantages. First, it does not need any additional injection source to detect faults. Second, the new algorithm locates the fault position under normal operating conditions.
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Jo Aug 15, 2025
With the recent increase in gold production, low-grade, fine-grained gold ores difficult to cyanide and refractory gold ores containing harmful impurities such as sulfur, arsenic, copper, etc. have become the major resources for gold production.
In order to effectively extract gold from the refractory gold ore, oxidative pretreatment must be conducted prior to leaching to oxidize the sulfide bearing gold particles and convert their physical and chemical properties.
There are several pretreatment methods, each with their own advantages and disadvantages. Hydrothermal oxidation pretreatment of refractory gold ores is an effective one, which has been widely used in recent years, due to its high rate of desulfurization, little environmental pollution and high reaction rate.
Sin Hyok, a researcher at the Faculty of Chemical Engineering, has investigated the thermodynamic process of nitric acid oxidation and the factors affecting gold extraction when pyrite-and-arsenopyrite-based gold concentrates are pretreated by mechanochemical activation and nitric acid oxidation.
He has found the following.
The factors affecting gold extraction are nitric acid concentration, mechanical activation time and liquid-solid ratio. The decomposition of pyrite and arsenopyrite in nitric acid medium proceeds from above 1mol/L of nitric acid concentration at room temperature, and the mechanical activation starts decomposition from above 0.5mol/L.
After pretreatment using mechanical activation and nitric acid oxidation, the cyanidation leaching rate for gold concentrates is over 87%.
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Jo Aug 14, 2025
Semiconducting BaTiO3 ceramics are widely used in electronic information, automatic control, biological technology, energy management and traffic control as an important control component. The barium titanate (BaTiO3) shows high intrinsic resistivity of more than 1010Ω·cm when prepared in the oxidizing atmosphere. Therefore, the chemically unmodified BaTiO3, because of its large energy gap, is an electrical insulator. However, when polycrystalline BaTiO3 ceramics are doped with higher valence cations such as Y3+, La3+, Nb5+ or Ta5+, they show semiconducting properties and positive temperature coefficient of resistance (PTCR) effect.
SiO2 and Mn additions assist homogenization of the microstructure during sintering, improving the performance of PTCR under transient loads. In terms of electrical properties, the variation of permittivity with temperature is significantly affected by SiO2 additions: with increasing SiO2, the permittivity increases below Tc.
SiO2 has long been added to BaTiO3 as a sintering aid, but it has not been reported to significantly affect the electrical properties of PTCR thermistors.
Kong Myong Il, a researcher at the Semiconductor Institute, has investigated the effects of SiO2 addition on PTCR characteristics of Y-doped BaTiO3 ceramics prepared by solid-state reaction method.
He has found through the experiments that the optimum SiO2 content was 2mol.
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Jo Aug 13, 2025
At present, most injection molding designers depend on their old experiences in mold design. Due to the diversity and complexity of plastic workpieces and the limited experience of designers, it is difficult to precisely design good-quality products at low cost and in a short period.
Computer Aided Engineering (CAE) analysis techniques are useful for the manufacturing and design of injection molds. The operational tests of injection molds by CAE techniques makes it possible to predict the quality status of plastic products in the forming process of injection molding dies before injection molding. The simulation and analysis using Moldflow instead of operational tests of injection molds at the time of injection mold design help predict the potential defects of injection molds to modify and improve their structure.
Choe Tong Ju, a researcher at the Robotics Institute, has applied CAE simulation analysis to the injection molding of a container into a Hermetia illucens box, and proposed an improved design scheme of die structure.
First, he simulated the flow of plastic melt in the forming chamber. Then, he predicted the best gate position, packing pressure, temperature change, air bubble and weld line position by using the Moldflow software.
Applying the Moldflow to die design helps reduce the cost and the cycle of new product updating by predicting the defects that may occur during the injection process.
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