Computational Fluid Dynamics Simulation of Mass Tra...

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.

Development of PEC Sensor for Detecting Stainless S...

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.

Rotor Ground Fault Location Method for Synchronous ...

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.