• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.623-629
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• 2004

Rapid development of electronic technology requires small size, high density packaging and high power of electronic devices, which result in more heat generation by the electronic system. Present cooling technology may not be adequate for the thermal management in the current state-of-the-art electronic equipment. Forced convective heat transfer in a channel filled with pin-fin array is studied experimentally in this paper as an alternative cool-ing scheme for a high heat-dissipating equipment. Various configurations of the pin-fin array are selected in order to find out the effect of spacing and diameter of the pin-fin on the heat transfer and pressure drop characteristics. In the low porosity region, interfacial heat transfer and pressure drop seem to show different trend compared to the conventional heat transfer process.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.290-291
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• 2023

모빌리티 기술의 발전으로 자율주행 및 센서 데이터 처리를 위한 신뢰할 수 있는 고성능 저장 시스템의 수요가 증가하고 있다. SSD(Solid State Drive)는 빠른 데이터 처리 속도의 장점뿐만 아니라 외부 충격에 강한 내구성과 저전력의 특징 때문에 모빌리티 환경의 저장 시스템으로 사용되고 있다. 그러나 고온에 장시간 노출되면 NAND 플래시 메모리 소자에 손상이 발생할 수 있는 특성 때문에 모빌리티 내부 SSD의 온도를 관리해야 한다. 본 논문에서는 SSD의 외부 및 내부의 온도를 측정하여 저장장치가 고온에 장시간 노출되지 않도록 쿨링 시스템을 설계하고 실험을 통하여 적정 온도를 유지할 수 있는 최적화 방법을 제안한다. 또한 실험을 통해 쿨링 시스템이 SSD의 내부와 외부에 미치는 온도 변화를 측정하여 제안하는 시스템의 효과를 증명한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.735-737
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• 2017

An Off grid or remote solar electric systems are an energy supply to our home or to our companies without the utility of Grid at all. Off grid solar systems are very important for those who live in remote locations especially for developing countries where getting the electric grid is extremely expensive, inconvenient or for those who doesn't need to pay a monthly bill with the electric bill in general. The main critical components of any solar power system or renewable energy harvesting systems are the energy storage systems and its charge controller system. Energy storage systems are the essential integral part of a solar energy harvesting system and in general for all renewable energy harvesting systems. To provide an optimal solution of both high power density and high energy density at the same time we have to use hybrid energy storage systems (HESS), that combine two or more energy storage technologies with complementary characteristics. In this present work, design and simulation we use two storage systems supercapacitor for high power density and lithium based battery for high energy density. Here the system incorporates fast-response supercapacitors to provide power to manage solar smoothing and uses a battery for load shifting. On this paper discuss that the total energy throughout of the battery is much reduced and the typical thermal stresses caused by high discharge rate responses are mitigated by integrating supercapacitors with the battery storage system. In addition of the above discussion the off grid solar electric energy harvesting presented in this research paper includes battery and supercapacitor management system, MPPT (maximum power point tracking) system and back/boost convertors. On this present work the entire model of off grid electric energy harvesting system and all other functional blocks of that system is implemented in MATLAB Simulink.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.361-364
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• 2009

KEPRI has studied planar type SOFC stacks using anode-supported single cells and kW class co-generation systems for residential power generation. A 1kW class SOFC system consisted of a hot box part, a cold BOP part and a water reservoir. A hot box part contains a SOFC stack made up of 48 cells with $10{\times}10cm^2$ area and ferritic stainless steel interconnectors, a fuel reformer, a catalytic combustor and heat exchangers. Thermal management and insulation system were especially designed for self-sustainable operation. A cold BOP part was composed of blowers, pumps, a water trap and system control units. When a 1kW class SOFC system was operated at $750^{\circ}C$ with hydrogen, the stack power was 1.2kW at 30 A and 1.6kW at 50A. Turning off an electric furnace, the SOFC system was operated using hydrogen and city gas without any external heat source. Under self-sustainable operation conditions, the stack power was about 1.3kW with hydrogen and 1.2kW with city gas respectively. The system also recuperated heat of about 1.1kW by making hot water. Recently KEPRI developed stacks using $15{\times}15cm^2$ cells and tested them. KEPRI will develop a 5 kW class CHP system using $15{\times}15cm^2$ stacks by 2010.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.772-776
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• 2008

The Korea Electric Power Research Institute (KEPRI) has been developing planar solid oxide fuel cells (SOFCs) and power systems for combined heat and power (CHP) units. The R&D work includes solid oxide fuel cell (SOFC) materials investigation, design and fabrication of single cells and stacks, and kW class SOFC CHP system development. Anode supported cells composed of Ni-YSZ/FL/YSZ/LSCF were enlarged up to $15{\times}15\;cm^2$ and stacks were manufactured using $10{\times}10\;cm^2$ cells and metallic interconnects such as ferritic stainless steel. The first-generation system had a 37-cell stack and an autothermal reformer for use with city gas. The system showed maximum stack power of about $1.3\;kW_{e,DC}$ and was able to recover heat of $0.57{\sim}1.2\;kW_{th}$ depending on loaded current by making hot water. The second-generation system was composed of an improved 48-cell stack and a prereformer (or steam reformer). The thermal management subsystem design including heat exchangers and insulators was also improved. The second-generation system was successfully operated without any external heat source. Under self-sustainable operation conditions, the stack power was about $1.3\;kW_{e,DC}$ with hydrogen and $1.2\;kW_{e,DC}$ with city. The system also recuperated heat of about $1.1\;kW_{th}$ by making hot water. Recently KEPRI manufactured a 2kW class SOFC stack and a system by scaling up the second-generation 1kW system and will develop a 5kW class CHP system by 2010.

• Journal of the Korean Association of Geographic Information Studies
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• v.21 no.1
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• pp.115-127
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• 2018

This study aims to propose management strategies of ventilation paths for improving urban thermal environments. For this purpose, Gimhae-si in Gyeongsangnamdo was selected as a study area. We analyzed hot spots and cool spots in Gimhae by using Landsat 8 satellite image data and spatial statistical analysis, and finally derived the vulnerable areas to thermal environment. In addition, the characteristics of ventilation paths including wind direction and wind speed were analyzed by using data of the wind resource map provided by Korea Meteorological Administration. As a result, it was found that a lot of hot spots were similar to those with weak wind such as Jinyoung-eup, Jillye-myeon, Juchon-myeon and the downtown area. Based on the analysis, management strategies of ventilation paths in Gimhye were presented as follows. Jinyoung-eup and Jillye-myeon with hot spot areas and week wind areas have a strong possibility that hot spot areas will be extended and strengthened, because industrial areas are being built. Hence, climate-friendly urban and architectural plans considering ventilation paths is required in these areas. In Juchon-myeon, where industrial complexes and agricultural complexes are located, climate-friendly plans are also required because high-rise apartment complexes and an urban development zone are planned, which may induce worse thermal environment in the future. It is expected that a planning of securing and enlarging ventilation paths will be established for climate-friendly urban management. and further the results will be utilized in urban renewal and environmental planning as well as urban basic plans. In addition, we expect that the results can be applied as basic data for climate change adaptation plan and the evaluation system for climate-friendly urban development of Gimhye.

• Proceedings of the KIEE Conference
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• summer
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• pp.120-122
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• 2004

This paper analyse impacts of Community Energy System (CES) on the grid during transition periods for integrating of the CES and the grid. In the near future, CES might be one of major energy supply structures. The basic concept of CES is that it supplies electrical and thermal energy to the local customer loads through the islanded power network separated from the grid. Therefore, the interconnection with the grid occurs only when the energy supply from the CES generators does not meet the demand of the local load. For avoiding impacting the grid during the transition operation modes of CES, it is necessary to thoroughly analyse the influences on the grid during those periods. In order to show them, in this paper, we model the CES with 2.34 WVA DG and simulate the impacts on the grid due to interconnection of CES The simulation results show that, in order to reduce bad influences of CES on the grid, CES need the efficient load management and generation control schemes during the transition periods.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.2
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• pp.99-104
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• 2014

Active vibration control methods are required in the high speed rotor systems supported by magnetic bearings. A prediction control technique is one of the control methods. Gain and phase angle are primarily chosen with analyzing the responses for a certain rotor speed. The feasibility of this technique has been reported for only analytical simulations. Therefore this paper constructs the test rig supported by ball bearings with a magnetic bearing type actuator and develops a prediction control system by using LabVIEW and Compact RIO. Finally as rotating speeds are modulated, the gains and phase angles for the speeds are determined with vibration control of the test rig. This leads that the prediction control technique may be applied to the rotor system with the magnetic bearing.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.137-143
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• 2014

An investigation on lightning characteristics and damage to wind turbines was performed on Jeju and Gangwon regions. The lightning data from January 2010 to September 2013 detected by IMPACT ESP were collected and analyzed in detail. Hangyeong and Seongsan wind farms of Jeju province and Taebaek, Changjuk, Taegisan and Gangwon wind farms of Gangwon province were selected for this study. Lightning rates and lightning damage events at the six wind farms were compared with each other. Lightning maps for the two regions were drawn using lightning frequency data. As a result, lightning frequency of Gangwon region was higher than that of Jeju region, while lightning strength of Gangwon was weaker than that of Jeju. Lightning rates were assessed to be good for all of the six wind farms. No lightning damage to wind turbines occurred at the two wind farms of Jeju, while some lightning damage to wind turbines took place at the four wind farms of Gangwon.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.475-479
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• 1999

Langasite ($La_{3}Ga_{5}SiO_{14}$) was found to have wide application as a promising piezoelectric material. It has high thermal stability of the frequency and large electromechanical coupling factor. For the further development of new compounds with langasite type structure, powders in the La-Al-Si-O system were synthesized by a modified Pechini process. The evolution of the crystalline phase during calcination was studied using TG-DTA, XRD and TEM for the precursor powders. Decomposition proceeded via dehydration and removal of excess solvents at low temperatures ($T<500^{\circ}C$), followed by the crystallization of lanthanum aluminum silicate ($T>800^{\circ}C$) and phase transformation to $LaAlO_{3}$ phase ($T>1200^{\circ}C$). Transmission electron microscopy (TEM) of the calcined powders showed diffuse hollow rings corresponding to an amorphous phase at $800^{\circ}C$ and clear diffraction patterns corresponding to a crystalline phase from the P321 space group ($T<1200^{\circ}C$) and the R3m ($T<1200^{\circ}C$).