• 동력기계공학회지
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• 제12권3호
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• pp.19-25
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• 2008

This paper deals with the heat transfer and pressure drop characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for condensing. The test section is a horizontal double pipe heat exchanger. Condensing heat transfer and pressure drop measurements were Peformed for 12.70 mm micro-fin tube and compared with the results in smooth tube. The local condensing heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-600a. The average condensing heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Hydrocarbon refrigerants have a higher pressure drop than that of R-22 with respect to refrigerant qualify and mass flux. Also, the condensing heat transfer coefficient and pressure drop of working fluids in smooth and micro-fin tube were compared. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 2.2 to 2.6 in all experimental conditions.

• 한국인터넷방송통신학회논문지
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• 제17권4호
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• pp.187-192
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• 2017

정확한 종방향 모드 전송선로 이론을 이용하여 비대칭 격자 구조형 방향성 결합기의 최대 전력전송 특성을 정확하게 분석하였다. 정확한 해석적 전송선로 수식과 대칭/비대칭 모드 사이의 간섭특성에 의존하는 결합효율을 정의하였으며, 전파 거리에 따른 TE 모드의 전력변화를 수치해석 하였다. 수치해석 결과, 비대칭 GADC에서 최대 전력전송은 전형적인 위상 정합조건 ${\Lambda}_{ph}$에서 발생하지 않았으며, 전파하는 중첩모드들의 삽입손실이 서로 같은 격자주기 ${\Lambda}_{eq}$에서 발생하였다. 더욱이, 격자의 비대칭 특성이 대칭 특성으로 변함에 따라 결합길이는 줄어들었으며, 전력전송 효율은 증가함을 보였다.

• 설비공학논문집
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• 제28권3호
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• pp.95-102
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• 2016

A boiling heat transfer is used in various industry such as power generation systems, heat exchangers, air-conditioning and refrigerations. In the boiling heat transfer system, the critical heat flux (CHF) is the important factor, and it indicated safety of the system. It has kept up studies on the CHF enhancement. Recently, it is reported the CHF enhancement, when working fluid used the nanofluid with high thermal properties. But it could be occurred nanoflouling phenomenon from nanoparticle deposition, when nanofluid applied the heat transfer system. And, it is reported that the safety and thermal efficiency of heat transfer system could decrease. Therefore, it is compared and analyzed to the CHF and the boiling heat transfer coefficient on effect of artificial nanofouling (coating) in oxidized multi-wall carbon nanotube nanofluids. As the result, the CHF of oxidized multi-wall carbon nanofluids and the CHF of artificial nanofouling in the nanofluids increased to maximum 99.2%, 120.88%, respectively. A boiling heat transfer coefficient in nanofluid increased to maximum 24.29% higher than purewater, but artificial nanofouling decreased to maximum -7.96%.

• 대한기계학회논문집B
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• 제41권6호
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• pp.415-421
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• 2017

환경규제의 강화에 따라 수처리 비용이 증가하는 추세이므로 폭기공정의 에너지 이용효율을 제고할 수 있는 소요동력에 대한 보다 정량적인 연구가 필요하다. 본 논문은 폭기공정의 물질전달 특성을 규명하기 위해 물질전달 계수와 기체 포집율 및 소요동력에 대한 상관관계식을 제시하였다. 소요동력이 커지면 기체 포집율은 감소하고 레이놀드 수는 증가하며, 혼합유동 선단 도달거리와 확산도가 증대되므로 물질전달 계수는 증가하였다. 물질전달 계수와 기체 포집율 및 소요동력의 상관관계 규명을 위해 제시한 실험식은 최대 약 ${\pm}10%$의 오차 범위에서 실험결과와 일치하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제17권1호
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• pp.120-128
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• 2017

This paper describes a neural stimulation system that employs an inductive coupling link to transfer power and data wirelessly. For the reliable data and power delivery, a self-referenced amplitude-shift keying (ASK) demodulator and a wide-range voltage regulator are suggested and implemented in the proposed stimulator system. The prototype fabricated in 0.35 um BCD process successfully transferred 1.2 Kbps data bi-directionally while supplying 4.5 mW power to internal MCU and stimulation block.

• KEPCO Journal on Electric Power and Energy
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• 제7권1호
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• pp.171-177
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• 2021

In terms of distribution planning, accurate electric load prediction is one of the most important factors. The future load prediction has manually been performed by calculating the maximum electric load considering loads transfer/switching and multiplying it with the load increase rate. In here, the risk of human error is inherent and thus an automated maximum electric load forecasting system is required. Although there are many existing methods and techniques to predict future electric loads, such as regression analysis, many of them have limitations in reflecting the nonlinear characteristics of the electric load and the complexity due to Photovoltaics (PVs), Electric Vehicles (EVs), and etc. This study, therefore, proposes a method of predicting future electric loads on distribution lines by using Machine Learning (ML) method that can reflect the characteristics of these nonlinearities. In addition, predictive models were developed based on actual data collected at KEPCO's existing distribution lines and the adequacy of developed models was verified as well. Also, as the distribution planning has a direct bearing on the investment, and amount of investment has a direct bearing on the maximum electric load, various baseline such as maximum, lowest, median value that can assesses the adequacy and accuracy of proposed ML based electric load prediction methods were suggested.

• 대한기계학회논문집B
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• 제22권1호
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• pp.50-60
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• 1998

As a method to develop an enhanced heat transfer fluid, the fine particles of a phase-change material were mixed with a conventional heat transfer fluid. Paraffin, which can be obtained easily in domestic market, was used for the phase-change material and water was used as a carrier fluid. Fine liquid particles of paraffin were formed in water as an emulsion by using an emulsifier, and they were cooled rapidly to become solid particle, resulting in paraffin slurry. The average diameter of produced solid particles was inversely proportional to the amount of the added emulsifier, which was theoretically proved. The produced paraffin slurry was tested thermally in heat transfer test section having a constant-heat-flux boundary condition. The test section was made of a circular stainless-steel pipe, which was directly heated by the power supply having a maximum of 50 Volts-500 Amperes. DSC(Differential scanning calorimeter) tests showed that two kinds of phase change were involved in the melting of paraffin, and it was explained in two different ways. A five- region-melting model was developed by extending the conventional three-region-melting model, and was used to obtain the local bulk mean temperatures of paraffin slurry in the heating test section. The local heat transfer coefficient showed a maximum where the bulk mean temperature of the paraffin slurry reached at the melting temperature of paraffin.

• 대한전기학회논문지:전력기술부문A
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• 제49권2호
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• pp.78-84
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• 2000

This paper introduces a method of determining the maximum real power transfer limit of interface lines, which connect two areas of a power system, using locally parameterized continuation algorithm. This method traces the path of power flow solutions as interface flow is gradually increased under a certain load demand condition and finds the steady state voltage stability limit, the interface flow limit. Voltage stability index is used to indicate how close the maximum limit is reached. Also, this study presents a procedure to determine the security-constrained interface flow limit using the above method. Contingency ranking index is proposed to identify the severity of contingencies. The case study is performed according to the suggested procedure.

• Nuclear Engineering and Technology
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• 제48권5호
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• pp.1206-1218
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• 2016

This article proposes a highly reliable power and communication system that guarantees the protection of essential instruments in a nuclear power plant under a severe accident. Both power and communication lines are established with not only conventional wired channels, but also the proposed wireless channels for emergency reserve. An inductive power transfer system is selected due to its robust power transfer characteristics under high temperature, high pressure, and highly humid environments with a large amount of scattered debris after a severe accident. A thermal insulation box and a glass-fiber reinforced plastic box are proposed to protect the essential instruments, including vulnerable electronic circuits, from extremely high temperatures of up to $627^{\circ}C$ and pressure of up to 5 bar. The proposed wireless power and communication system is experimentally verified by an inductive power transfer system prototype having a dipole coil structure and prototype Zigbee modules over a 7-m distance, where both the thermal insulation box and the glass-fiber reinforced plastic box are fabricated and tested using a high-temperature chamber. Moreover, an experiment on the effects of a high radiation environment on various electronic devices is conducted based on the radiation test having a maximum accumulated dose of 27 Mrad.

• Journal of Communications and Networks
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• 제18권6호
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• pp.926-937
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• 2016

In this paper, we study the feasibility of receiver diversity for application to downlink cellular networks, where low-energy devices are equipped with information decoding and energy harvesting receivers for simultaneous wireless information and power transfer. We compare several options that are based on selection combining and maximum ratio combining, which provide different implementation complexities. By capitalizing on the Frechet inequality, we shed light on the advantages and limitations of each scheme as a function of the transmission rate and harvested power that need to be fulfilled at the low-energy devices. Our analysis shows that no scheme outperforms the others for every system setup. It suggests, on the other hand, that the low-energy devices need to operate in an adaptive fashion, by choosing the receiver diversity scheme as a function of the imposed requirements. With the aid of stochastic geometry, we introduce mathematical frameworks for system-level analysis. We show that they constitute an important tool for system-level optimization and, in particular, for identifying the diversity scheme that optimizes wireless information and power transmission as a function of a sensible set of parameters. Monte Carlo simulations are used to validate our findings and to illustrate the trade-off that emerge in cellular networks with simultaneous wireless information and power transfer.