• Journal of the Korean institute of surface engineering
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• v.46 no.1
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• pp.9-15
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• 2013

The effect of the additionally applied electrical current on the adhesion strength between electroless Cu and polyimide films was investigated. Peel tests were performed after applying electrical current within the range from 0.1 to 100 mA for the duration from 1 to 30 minutes. Sample with more than 1 mA of additional electrical current for 1 minute showed higher adhesion strength than that without additional electrical current. However, samples with 10 mA of additional electrical current for more than 10 miniutes showed the degradation of adhesion strength. Ra and RMS values of the peeled polyimide surface were proportional to the adhesion strength though there were no significant changes in the morphology of the peeled surfaces with varied amount and time-length of additional electrical current. Applying electrical current could increase the density of chemical bonding, which results in increase of the adhesion strength between copper and polyimide. However, in the case of applying additional electrical current for excessive amount or time, the degradation of the adhesion strength owing to the formation of copper oxide at the interface could occur.

• Journal of the Korean institute of surface engineering
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• v.51 no.6
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• pp.415-420
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• 2018

The possibility of an improvement in heat dissipation performance of aluminum alloy heat sink for shipboard LED luminaries through plasma electrolytic oxidation (PEO) was investigated. Four different PEO coatings were produced on aluminum alloy 5052 in silicate based alkaline solution by varying current density ($50{\sim}200mA/cm^2$). On voltage-time response curves, three stages were clearly distinguished at all current densities, namely an initial linear increase, slowdown of increase rate, and steady state(constant voltage). It was found that the increase in current density caused the breakdown voltage to increase. Two different surface morphologies - coralline porous structure and pancake structure - were confirmed by SEM examination. The coralline porous structure was predominant in the coatings produced at lower current densities (50 and $100mA/cm^2$) while under high current densities(150 and $200mA/cm^2$) the pancake structure became dominant. The coating thickness was measured and found to be in a range between about $13{\mu}m$ and $44{\mu}m$, showing increasing thickness with increasing current density. As a result, $100mA/cm^2$ was proposed as an effective process parameter to improve the heat dissipation performance of aluminum alloy heat sink, which could lower the LED operating temperature by about 30%.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.4
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• pp.137-144
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• 2008

This study deals with on-line fault detection and diagnosis(FDD) for heat exchangers of a variable speed refrigeration system(VSRS) based on current information. The current residual which is the difference between real detected current from current sensors and estimated current from no fault model was utilized to diagnose faults of the heat exchangers. Comparing to the conventional FDD of constant refrigeration system based on temperature and pressure information, the suggested FDD method shows better robustness to the VSRS which has a feedback control loop. Moreover the suggested method can be expected more precise and faster diagnosis of faults about heat exchangers. Throughout some experiments, the validity of the method was verified.

• Journal of Welding and Joining
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• v.27 no.2
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• pp.44-50
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• 2009

The characteristics of arc pressure, current density and heat flux distribution are important factors in understanding physical arc phenomena, which will have a marked effect on the penetration, size and shape of a weld in TIG welding. The purpose of this study is to find out the effect of the heat flux on the melting efficiency and penetration shape in TIG welding using the results of the previous investigators. The conclusions obtained permit to draw a proper method which derived the heat flux distributions by arc pressure distribution measurements, but previous researchers calculated heat flux and current distribution with the heat intensity measurements by the calorimetry. Heat flux of Ar gas arc was concentrated at the central part and distributed low from the arc axis to the radial direction, that of He mixing arc was lower than that of Ar gas, and it was wide distributed to radial direction. That showed a similar characteristic with the Nestor's by calorimetry calculated values. Throughout heat flux drawn in this study was discussed melting efficiency and penetration shape on Ar gas and He mixing gas arc.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.6
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• pp.484-495
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• 2017

In HVDC thyristor valves, more than 95% of heat loss occurs in snubber resistors and valve reactors. In order to dissipate the heat from the valves and to suppress the electrolytic current, water with a high heat capacity and a low conductivity of less than 0.2 uS/cm must be used as a refrigerant of the heat sink. The cooling parts must also be arranged to reduce the electrolytic current, whereas the pipe that supplies water to the thyristor heat sink must have the same electric potential as the valve. Corrosion is mainly caused by electrochemical reactions and the influence of water quality and leakage current. This paper identifies the refrigerants involved in the ionization, electrical conductivity, and corrosion in HVDC thyristor valves. A method for preventing corrosion is then introduced. The design of the heat sink with an excellent heat radiation is also analyzed in detail.

• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.32-36
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• 2010

Superconducting current leads are indispensible for reducing power loss when subjecting current into superconducting magnets. HTS(High-Tc superconducting) current leads are divided into two types; one is bulk type and the other is tape type. In this paper, conceptual design on the HTS current leads which adopts tape type for nuclear fusion magnets is carried out using magnetic field analysis and thermal analysis. When large current flows through superconducting current leads, strong self magnetic field is generated and applied to the superconducting tapes. This phenomenon leads to the critical current decrease of the superconducting tape. Therefore, we analyzed magnetic field distribution of current leads and found the proper arrangement with respect to the various HTS tapes. In addition to the magnetic field analysis, heat leak through the current leads was also calculated to know which HTS tape is superior than others in thermal aspect. Magnetical field analysis and calculation of heat leak are performed to design 2 kA class HTS current leads.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.20 no.3
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• pp.203-224
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• 2016

The heat and mass transfer characteristics of the unsteady hydromagnetic natural convection flow with Hall current and Soret effect of an incompressible, viscous, electrically conducting, heat absorbing and optically thin radiating fluid flow past a suddenly started vertical infinite plate through fluid saturated porous medium in a rotating environment are taken into account in this paper. Derivations of exact analytical solutions are aimed under different physical properties. The velocity, concentration and temperature profiles, Sherwood number and Nusselt number are easily examined and discussed via the closed forms obtained. Soret effect and permeability parameter tends to accelerate primary and secondary fluid velocities whereas hall current, radiation and heat absorption have reverse effect on it. Radiation and heat absorption have tendency to enhance rate of heat transfer at the plate. The results obtained here may be further used to verify the validity of obtained numerical solutions for more complicated transient free convection fluid flow problems.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.862-863
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• 2007

In this article, we researched the characteristics of heat transfer of the bimetal for over-current protection device. Bimetal consists of two metals which have a different thermal expansion coefficient. To analyze the heat transfer characteristics, by using a bimetal which has a single metal, we analyzed the temperature distribution when bimetal acts a switch. As usual, heat source is applied to the bimetal. But, in the over-current protection switch, the current become heat source. So, by using the current as source, we performed the magnetic analysis and thermal analysis together.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.4
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• pp.16-23
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• 2020

An electric vehicle operates at high currents and requires real-time monitoring of the entire system for ensuring efficiency and safety of the vehicle. Current sensors are applied to drive the motors, inverters, and battery control systems, and are the key components to ensure constant monitoring of the magnitude and waveforms of the operating current. In this study, a heat treatment process condition to influence the performance of Permalloy current sensors was developed; the correlation between the output capacity, low-temperature characteristics, and high-temperature characteristics of the current sensor was studied; and the process was optimized to meet the required output accuracy and temperature characteristics.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.54-58
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• 2014

High-temperature superconducting (HTS) rotating machines always require an electric current of from several hundreds to several thousand amperes to be led from outside into cold region of the field coil. Heat losses through the current leads then assume tremendous importance. Consequently, it is necessary to acquire optimal design for the leads which would achieve minimum heat loss during operation of machines for a given electrical current. In this paper, conduction cooled current lead type of 10 MW-Class HTS rotating machine will be chosen, a conceptual design will be discussed and performed relied on the least heat lost estimation between conventional metal lead and partially HTS lead. In addition, steady-state thermal characteristic of each one also is considered and illustrated.