• New & Renewable Energy
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• v.18 no.2
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• pp.73-81
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• 2022

This study was aimed at designing a condenser, as a component of the organic Rankine cycle system for ships. The condenser was manufactured through press molding to achieve a bent shape to enhance the heat transfer performance, considering the shape of the heat transfer plate used in a brazing plate heat exchanger. The heat transfer plate was made of copper-nickel alloy. The required heat transfer rate for the condenser was 110 kW, and the maximum number of layers was set as 25, considering the characteristics of high-temperature brazing. Computational fluid dynamics techniques were used to perform the thermal fluid analysis, based on the ANSYS CFX (v.18.1) commercial program. The heat transfer rate of the condenser was 4.96 kW for one layer (width and length of 0.224 and 0.7 m, respectively) of the heat transfer exchanger. The fin efficiency pertaining to the heat transfer plate was approximately 20%. The heat flow analysis for one layer of the heat exchanger plate indicated that the condenser with 25 layers of heat transfer plates could achieve a heat transfer rate of 110 kW.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.10
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• pp.1409-1415
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• 2021

The Gysel divider has the advantage of easily setting the resistor in the circuit. If the line impedance in the Gysel divider is set differently, the input signal can be distributed to the two output ports at various distribution ratios. This paper proposes the Gysel divider that can change the power distribution to 1:3 or 3:1 by changing the line impedance. The impedance change of the line can be implemented by placing a floating copper plate on the bottom of the microstrip-line. When the floating copper plate and the ground plane are connected, the line operates as the microstrip-line, and when the floating copper plate and the ground plane are disconnected, the line operates as the coplanar-line. The proposed Gysel divider was fabricated at the center frequency of 1.5GHz. The fabricated 3:1 Gysel divider has a stable value S₁₁ of below -17dB, S₂₁/S₃₁ of 4.8±0.2dB, S₂₁(to high output port) of -1.39±0.12dB and S₃₁(to low output port) of -6.15±0.08dB over 1.3~1.7GHz.

• Korean Journal of Heritage: History & Science
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• v.52 no.1
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• pp.4-21
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• 2019

In this paper, 23 Silla gold earrings from the sixth and seventhand centuries, excavated from the Yeongnam region, were analyzed. Based on the silver content of the gold plate, they were classified into three types. The classifications included type I(20-50wt%), type II(10-20wt%) and type III (less than 10wt%). In the analysis process, the composition and morphological differences were identified on the surface of the gold plate. In the case of type I and II earrings, it was observed that the fine holes were concentrated in a relatively higher part of the gold content. The causes of the difference in the surface composition of the gold plate were divided into four categories: 1) surface treatment, 2) thermal diffusivity in the manufacturing process, 3) differences in composition of alluvial gold, and 4) the refining method of gold. It is possible that depletion gilding was attempted to increase the gold content while intentionally removing the other metals from the surface of the gold alloy in the portion where the gold deposit is relatively concentrated on the surface of the gold plating. The highest copper content was detected in the earring with the highest gold content of the analyzed earrings, and it was assumed that thermal diffusion had occurred between the gold plate and the metal rod during the manufacturing process rather than intentional addition. Copper was detected only in the thin ring earring type, and copper was not detected in the thick ring earring type or pendant type. It also proves that this earring has a high degree of tightness at higher temperatures, as there was an invisible edge finish on other earrings and horizontal wrinkles on the gold plate surface. In terms of the material of the gold plate, we examined whether the silver content of the gold plate was natural gold or added by alloy through analyzing the alluvial gold collected in the region. As a result of the analysis, it was found that on average about 13wt% of silver is included. This suggests that type II is natural gold, type III is refined gold, and type I seems to have been alloyed with natural gold. Here, we investigated the refining method introduced in the ancient literature, both at home and abroad, about the possibility of alloying silver after the refining process of type III earrings and then making pure gold. It was found that from ancient refining methods, silver which had been present in the natural gold was removed by reacting and combining with silver chloride or silver sulfide, and long-term efforts and techniques were required to obtain pure gold through this method. Therefore, it was concluded that the possibility of adding a small amount of silver in order to increase strength after making pure gold through a refining process is low.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.5
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• pp.64-69
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• 2014

This article presents machining experiments to assess the relationship between the profile accuracy and the workpiece hardness using a natural diamond tool on an ultra-precision diamond turning machine. The study is intended to secure a corner cube prism pattern for reflective film capable of high-quality outcomes. The optical performance levels and edge images of corner cubes having various hardness levels of the copper-coated layer on a carbon steel plate are analyzed. The hardness of the workpiece has a considerable effect on the profile accuracy. The higher the hardness of the workpiece, the better the profile accuracy and the worse the edge wear of the diamond tool.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.44-49
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• 1999

This paper is concerned with the theoretical and experimental study on the force conrtrol of a miniature robotic gripper. The gripper is an uniform flexible cantilever equipped with a distributed set of compact force sensor. As an actuator piezoelectric acturator, piezoelectric acturator is fixed with cupper plate at which the beam is clamped. The mathematical model of the assembled electro-mechaincal system is developed. The force sensor is described by a set of concentrated mass-spring system. The formulated equations of motion are applied to he study of a control problem where the gripper is commanded to grip an object The usefulness of the PID control technique is verified by experiment.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.266-271
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• 2003

The numerical study was carried out to effectively cool Induction motor applied to a washing machine. The outer rotor made of steel periodically spins up and down. The stator consists of the thin layered iron plates and copper coil. The effective cooling system is necessary to solve the reliability problem caused by the electric losses at the coil and the iron plate. Because the heat transfer rate of the natural convection in partially open space is generally low, thus it is necessary to enhance the heat transfer using rotating perforated plate. The flow phenomena around the motor are very complex due to the motor geometry and the outer rotor motion. The mixed convection takes place due to the slow rotation speed. The three dimensional flow simulation was performed using rotating reference frame technique and Boussinesq approximation but the radiation effect was neglected. It was found that the angle and direction of the cooling blades play an important role in the stator temperature.

• Fibers and Polymers
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• v.6 no.3
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• pp.235-243
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• 2005

A series of new metallized direct dyes based on benzidine congeners, 2,2'-dimethyl-5,5'-dipropoxybenzidine and 5,5'-dipropoxybenzidine, were evaluated for mutagenicity in Salmonella typhimurium strains TA98 and TA 100. All of the dyes examined were judged to be non-mutagenic with and without metabolic activation while toxicity was seen in some dyes at high doses. The study also suggested that the standard Salmonella mutagenicity plate-incorporated assay was an excellent method for evaluation of dyes for mutagenicity.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.167-168
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• 2007

고속 동도금 공정을 확립하기 위하여 선행실험으로 알카리계 동도금 용액을 이용하여 고속 동도금의 가능성을 실험하였다. 전류밀도와 극간거리, 유속의 조절을 통하여 최대 $17.6{\mu}m/min$. 속도의 도금속도를 확보하였으며, Hv 120 내외의 경도를 확보하였다. 고속 동도금을 실현하기 위해서는 높은 전류밀도를 필요로 하고, 낮은 용액 저항을 위해 극간거리는 짧게 유지하되, 빠른 유속을 필요로 하였다.

• Microbiology and Biotechnology Letters
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• v.36 no.3
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• pp.209-214
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• 2008

VBNC (Viable but nonculturable) state is an adaptive response of cells in adverse environments, which lead cell not grow on routine nutrient agar. In this study, we induced VBNC in Escherichia coli using copper and verify the characterization of it. After treatment of copper, we didn't detect any cells via plate cultivation, namely, colony forming unit (CFU) was zero. However, we identified the existence of VBNC by staining live cells with Live/Dead BacLight bacterial viability kit and counting them through flow cytometry. Then we isolated genomic DNA and RNA from VBNC-induced cells and analyzed the stability of them. Degradation of RNA is more severe than that of DNA and RNA is degraded as specific fragments. In addition, we showed the morphology of VBNC cell by Bio-Transmission Electron Microscope (Bio-TEM). VBNC cell showed impaired periplasmic space and inner and outer membrane were separated and the amount of cytosol were significantly decreased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.9-15
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• 2008

Mokumegane is one of the sophisticated metal craft techniques enabling wood grain surface effect. To embody the mokumegane, an ingot of well-bonded stacked metal plates has been required. Traditionally prepared mokumegane ingots were bonded using charcoal which enables reduction atmosphere, but sometimes end up with collapse of bonding interface due to the lack of reliable process control. We proposed a systematic vacuum direct bonding process for ingots. First, we confirmed copper//copper homogeneous plate bonding at $900^{\circ}C$ by applying uniaxial press of 2.5kg. We observed 80min required to obtain 90%-bonding ratio and the diffusion coefficient would be enhanced up to 100 times due to surface effect. Second, by considering enhanced diffusion behavior, we also obtained optimum bonding condition in copper/silver heterogeneous plates that ensures 90%-bonding ratio at $700^{\circ}C$ for 10min with apply uniaxial press. A 7-layered copper/silver ingot is prepared successfully, and eventually the prototype mokumegane cases for mobile phone were fabricated with these ingot.