• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.65-72
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• 2021

700 W class laboratory model Hall thruster, which can be used for the orbit control or station keeping of small satellites, was developed. The size of the discharge channel was determined using a scaling law, and the magnetic field was designed to be symmetric with respect to the midline of the discharge channel and to be maximized outside the discharge channel. Base pressure of a vacuum chamber was maintained below 2.0×10^-5 Torr during experiments, and the thrust was measured by a thrust stand. The anode flow rate and coil current were varied with the fixed anode voltage at 300 V. Under the operation condition at 2.36 mg/s anode flow rate and 2.4 A coil current, performance was optimized as 38 mN thrust, 1,540 s total specific impulse, and 50 % anode efficiency at 620 W anode power.

• Tribology and Lubricants
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• v.39 no.2
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• pp.72-75
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• 2023

Silicon carbide (SiC) is used as a substrate material for power semiconductors; however, SiC chemical mechanical polishing (CMP) requires considerable time owing to its chemical stability and high hardness. Therefore, researchers are attempting to increase the material removal rate (MRR) of SiC CMP using various methods. Mixed-abrasive CMP (MAS CMP) is one method of increasing the material removal efficiency of CMP by mixing two or more particles. The aim of this research is to study the mathematical modeling of the MRR of MAS CMP of SiC with SiO₂ and TiO₂ particles. With a total particle concentration of 32 wt, using 80-nm SiO₂ particles and 25-nm TiO₂ particles maximizes the MRR at 8 wt of the TiO₂ particle concentration. In the case of 5 nm TiO₂ particles, the MRR tends to increase with an increase in TiO₂ concentration. In the case of particle size 10-25 nm TiO₂, as the particle concentration increases, the MRR increases to a certain level and then decreases again. TiO₂ particles of 25 nm or more continuously decreased MRR as the particle concentration increased. In the model proposed in this study, the MRR of MAS CMP of SiC increases linearly with changes in pressure and relative speed, which shows the same result as the Preston's equation. These results can contribute to the future design of MAS; however, the model needs to be verified and improved in future experiments.

• Progress in Superconductivity and Cryogenics
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• v.25 no.3
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• pp.49-55
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• 2023

This paper presents the design of a re-liquefaction system as a BOG (boil-off gas) handling process in liquid hydrogen transport vessels. The total capacity of the re-liquefaction system was assumed to be 3 ton/day, with a BOR (boil-off rate) of 0.2 %/day inside the cargo. The re-liquefaction cycle was devised using the He-Brayton Cycle, incorporating considerations of BOG capacity and operational stability. The primary components of the system, such as compressors, expanders, and heat exchangers, were selected to meet domestically available specifications. Case studies were conducted based on the specifications of the components to determine the optimal design parameters for the re-liquefaction system. This encompassed variables such as helium mass flow rate, the number of compressors, compressor inlet pressure and compression ratio, as well as the quantity and composition of expanders. Additionally, an analysis of exergy destruction and exergy efficiency was carried out for the components within the system. Remarkably, while previous design studies of BOG re-liquefaction systems for liquid hydrogen vessels were confined to theoretical and analytical realms, this research distinguishes itself by accounting for practical implementation through equipment and system design.

• The Korean Journal of Pesticide Science
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• v.16 no.1
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• pp.11-20
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• 2012

As increasing the use of pesticides both in number and amount to boost crop production, consumer concerns over food quality and safety with respect to residual pesticides are also continuously increasing. However, there is still lacking of information that can effectively help to remove residual pesticides in foods. In recent years, contaminant removal by gas (or) glow discharge plasma (GDP) attracts great interests on environmental scientists because of its high removal efficiency and environmental compatibility. It was shown to be effective for the removal of some organophosphorus pesticides, phenols, benzoic acid, dyes, and nitrobenzene on solid substrate or in aqueous solution. This work mainly focuses on the removal of wide range of residual pesticides from fresh fruits and vegetables. As for preliminary study, the experiments were carried out to investigate whether GDP can be used as an effective tool for degrading target pesticides or not. With this objective, 60 selected pesticides drop wised onto glass slides were exposed to two types of GDP, dielectric barrier discharge plasma (DBDP) and low pressure discharge plasma (LPDP), for 5 min. Then, they were washed with 2 mL MeCN which were collected and used for determination of remaining concentration of pesticides using LC-MS/MS. Among selected pesticides, degradation of 18 pesticides (endosulfan-total was counted as one pesticide) by GDP could not be examined because control treatments, which were left in ambient environment, of those pesticides recovered less than 70% or even did not recover. However, majority of tested pesticides (42) were degraded by both types of GDP with satisfactory recovery (>80%) of control sample. Pesticides degradation ranged from 66.88% to 100% were achieved by both types of plasma except clothianidin which degradation in LPDP was 26.9%. The results clearly indicate that both types of gas discharge plasma are promising tools for degrading wide range of pesticides on glass substrate.

• Tunnel and Underground Space
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• v.22 no.3
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• pp.173-180
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• 2012

In this study, diagonal ventilation circuits that are advantageous in air flow direction control were studied. Based on the results of the study, it could be seen that air volumes in diagonal ventilation circuits could also be calculated using numerical formulas or programs if the air volumes and air flow directions to be infused into diagonal branches are determined in advance as with other serial/parallel circuits. To apply the results, design plans for high level radioactive waste repositories applied with diagonal ventilation circuits and parallel ventilation circuits. To compared the each design plans and obtain expected operation results, ventilation network simulations were conducted through the Ventsim program which is a ventilation networking program. Based on the results, in the case of diagonal repositories that was expected to cause great increases in resistance, fan pressure was 1570 pa, total flux was 84 $m^3/s$, fan efficiency was 76.4%, fan power consumption was 181.2 kW and annual fan operating costs were 178,710,838 and thus maximum around 8% differences were shown in pressure and flux values and a difference of around 1.5% was shown in terms of operating costs.

• Korean Journal of Food Science and Technology
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• v.30 no.5
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• pp.1146-1151
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• 1998

To prevent deterioration of the jujube wine quality by using heat sterilization while commercial production, ultrafiltration and microfiltration were applied. The permeate flux and physicochemical properties of jujube wine determined by MF and UF membrane ($0.2\;{\mu}m$ pore size and 50 K dalton cut off) were investigated. The permeate flux increasing caused the increased operating pressure. The Hunter L value of jujube wine treated MF and UF was increased and that of b value was decreased. The turbidity of jujube wine treated MF and UF was largely decreased. And the values of pH, ethanol, total acid and soluble solid were decreased or were at the same level comparing with untreated jujube wine. Retention percentage of sugar and organic acid was more than 80% and was not influenced by operating pressure. Results of sensory evaluation indicated that the color of UF was superior to un-treatment and commercial ones. And the flavor and taste were not significantly different with untreated jujube wine. The quality deterioration of commercial jujube wine could be improved by MF and UF. According to the sensory evaluation, there was also not difference between MF and UF for preference test. Therefore, the quality of jujube wine could be improved by MF having better separation yield efficiency than UF.

• Composites Research
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• v.26 no.6
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• pp.363-372
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• 2013

Numerical simulation for Resin Transfer Molding manufacturing process is attempted by using the eXtended Finite Element Method (XFEM) combined with the level set method. XFEM allows to obtaining a good numerical precision of the pressure near the resin flow front, where its gradient is discontinuous. The enriched shape functions of XFEM are derived by using the level set values so as to correctly describe the interpolation with the resin flow front. In addition, the level set method is used to transport the resin flow front at each time step during the mold filling. The level set values are calculated by an implicit characteristic Galerkin FEM. The multi-frontal solver of IPSAP is adopted to solve the system. This work is validated by comparing the obtained results with analytic solutions. Moreover, a localization method of XFEM and level set method is proposed to increase the computing efficiency. The computation domain is reduced to the small region near the resin flow front. Therefore, the total computing time is strongly reduced by it. The efficiency test is made with a simple channel flow model. Several application examples are analyzed to demonstrate ability of this method.

• Membrane Journal
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• v.22 no.6
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• pp.461-469
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• 2012

This study was carried out to find the optimum chemical cleaning (CIP) conditions for ceramic microfiltration membrane process of Y drinking water treatment plant. B train consists of coagulation as pretreatment process with membrane was chemically cleaned 9 times more than that of A train with ozonation and coagulation. The frequent CIP of B train was due to improper CIP method suggested by membrane manufacture as well as different membrane fouling between A and B train resulting from the different pretreatment processes. That is, recovery rate of CIP was overestimated because the rate was calculated based on normalized trans membrane pressure (TMP) rather than normalized permeability. And also, iron oxide fouling was ineffectively removed by citric acid. By using a mixture of 1% citric acid and 0.1 N sulfuric acid as reagent for acid CIP step, the recovery rate of CIP was the highest while CIP efficiency by 0.1 N sulfuric acid was the lowest. When sulfuric acid concentration increased from 0.1 N to 0.3 N in mixture, total recovery rate of CIP was not increased due to the decreased CIP efficiency in alkali CIP step by 0.3% NaOCl although its rate in acid CIP step was increased. It was proved through the experiment result of CIP sequence changes that an acid followed by alkali CIP was more effective than that of the reverse method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.443-449
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• 2017

The imbalance of air supply and the exhaust on subway platforms has led to the installation of platform screen doors in underground subway stations. This imbalance causes the accumulation of pollutants on the platform and loss of comfort due to the lack of ventilation. In this study, a floor exhaust system was optimized using computational fluid dynamics (CFD) and an optimization program. The optimized floor exhaust system was manufactured and tested experimentally to evaluate the particle collection efficiency. CFX 17.0 and HEEDS were used to analyze the flow field and optimize the principal dimensions of the exhaust system. As a result of the three-step optimization, the optimized floor exhaust system had a total height of 1.78 m, pressure drop of 430 Pa, and particle collection capability of 61%. A fine dust particle collection experiment was conducted using a floor exhaust system that was manufactured at full scale based on the optimized design. The experiment indicated about 65% particle collection efficiency. Therefore, the optimized design can be applied to subway platforms to draw in exhaust air and remove particulate matter at the same time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.506-512
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• 2018

The fine dust generated in the home and restaurant business occupies a low ratio of about 4% of the total fine dust emissions. However, at the foodservice business, the rate of change of the pollutant concentration is very high, so that the temporary fine dust concentration can be measured up to 60 times. The pollutants generated from non-industrial combustion plants consist of particulate fine dust and gaseous organic compounds. To remove these pollutants, cleaning dust collection system, which is an effective system for simultaneous removal of gaseous and particulate matter, is applied. This is a method of increasing the probability of diffusion capture of the Brownian motion by pressurized liquid injection method using the atomizing nozzle. The dust removal efficiency of the fine dust collecting system was analyzed by nozzle spraying air pressure condition and angle using the manufactured fine dust removing system. As a result, it was confirmed that the efficiency of removal of fine dust and gaseous organic compounds was more than 90%. The developed system is expected to be highly usable in the future because it can remove particulate dust from the existing plant hood system without any installation cost.