• 전력전자학회논문지
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• 제3권4호
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• pp.307-314
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• 1998

근접부하의 동작주파수의 차이에 의해 발생하는 간섭가청잡음을 제거하기 위해서 다부하를 갖는 유도가열기를 위한 새로운 고역률 이중 하프브릿지 직렬공진 인버터를 제안한다. 이 회로는 하나의 인버터로 두 개의 유도가열요소를 독립적으로 전대역 출력제어를 할 수 있고 영전압 스위칭 특성 때문에 최소 스위칭 손실을 갖는다. 모드분석을 통해서 제안된 회로의 동작을 설명할 것이다. 요구되는 냉각능력을 평가하기 위해서 몇 개의 손실식을 유도함으로써 손실분석을 행하였다. 역률제어기능을 갖고 시스템의 크기를 축소하기 위해서 적절한 설계가이드를 제시하였다. 이렇게 설계된 값들을 사용하여 각 유도가열요소가 2.8kW 전력소모를 갖는 proto-type 회로를 구성하고 제안된 회로의 동작을 확인하기 위해서 실험을 행하였다.

• Journal of the Korean Wood Science and Technology
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• 제45권1호
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• pp.1-11
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• 2017

건축물에서 냉방과 난방에 많은 양의 에너지가 소요되고 있다. 건축은 $CO_2$ 발생을 줄이고 에너지 소비 저감을 위하여 냉 난방 부하를 최소화할 필요성이 있다. 그리고 최근 주거문화는 친환경적이고 실내 쾌적성을 중시하는 방향으로 변화하면서 단독주택의 수요가 증가하고 있다. 국내 단독주택의 구조는 크게 조적조, 콘크리트조, 목조 주택으로 구분할 수 있다. 따라서 본 논문은 세 가지 구조방식(조적, 콘크리트, 목조)으로 구성된 동일 면적 단독주택의 냉 난방 부하와 에너지 요구량을 분석하였다. 구조방식별 벽체, 지붕, 바닥 레이어를 구성하였고, 각 레이어의 열관류율(U-value)은 목조 벽체와 같이 스터드를 고려해주기 위하여 PHPP 계산법을 이용하였다. 또한 스터드 유무에 따른 차이를 비교 분석하기 위하여 목조 벽체에서 스터드를 고려하지 않은 경우(비 스터드)를 분석하였다. 분석은 엑셀을 기반으로 자체 개발한 냉 난방 부하 산출 프로그램(CHLC)과 ECO2를 이용하였다. 냉 난방 부하와 에너지 요구량 결과, 목조 구조가 가장 높은 결과를 보였고 콘크리트 구조는 두 번째로 높은 값을 유지하는 것을 확인하였다. 두 구조방식은 에너지소비 측면에서 불리하다고 판단하였다. 결론적으로, 동일한 조건에서의 조적 구조는 다른 구조방식에 비하여 냉 난방 부하 및 에너지 요구량에 있어 유리하며, 목조 구조에서 스터드로 인한 열교를 제외한다면 에너지소비를 줄일 수 있다고 판단되었다.

• Wind and Structures
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• 제27권1호
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• pp.11-27
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• 2018

The straight-cone steel cooling tower is a novel type of structure, which has a distinct aerodynamic distribution on the internal surface of the tower cylinder compared with conventional hyperbolic concrete cooling towers. Especially in the extreme weather conditions of strong wind and heavy rain, heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind, but existing studies mainly focus on the impact effect brought by wind-driven rain to structure surface. In addition, for the indirect air cooled cooling tower, different additional ventilation rate of shutters produces a considerable interference to air movement inside the tower and also to the action mechanism of loads. To solve the problem, a straight-cone steel cooling towerstanding 189 m high and currently being constructed is taken as the research object in this study. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed with continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind sped and rainfall intensity on flow field mechanism, the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower cylinder is analyzed. On this basis, the internal pressures of the cooling tower under the most unfavorable working condition are compared between four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the 3D effect of equivalent internal pressure coefficient is the most significant when considering two-way coupling between wind and rain. Additional load imposed by raindrops on the internal surface of the tower accounts for an extremely small proportion of total wind load, the maximum being only 0.245%. This occurs under the combination of 20 m/s wind velocity and 200 mm/h rainfall intensity. Ventilation rate of shutters not only changes the air movement inside the tower, but also affects the accumulated amount and distribution of raindrops on the internal surface.

• 동력기계공학회지
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• 제20권4호
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• pp.63-68
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• 2016

In this study, through portion of the blind control which the user can adjust the deration and the main loads, night for energy reduction during the review of the energy difference between the cooling and heating load periods in order to present the best operation schedules of the blind control. The result, Cooling period, the venetian blind is installed the day or the day and night CASE adjusted to $0^{\circ}$ was identified as optimal for the operating schedule. Heating period, the day, without installed the blinds, the Venetian blind is installed only at night CASE adjusted to $0^{\circ}$ or $45^{\circ}$ angle of the slats, which have been identified as optimal for the operating schedule.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.397_398
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• 2009

Demonstrations to deploy high temperature superconducting (HTS) cable to the real gird are actively carried out throughout the world. Power utilities have an interest in the inherent advantage of the HTS cable system, and achieve the expected results from the series of verification test. To embody the reliability in the phenomenon occurred commonly in three-phase system, we simulate the load unbalance. A 22.9 kV large scale HTS cable system with the specification of 100 m-long, 50 MVA capacity has been tested with up to 30% unbalance rate. To evaluate the effect of AC loss increase due to the unbalanced load, the cooling loads are measured by the calorimetry method. In this paper, the correlation between AC loss and load unbalance is described and investigated precisely.

• 한국태양에너지학회 논문집
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• 제24권2호
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• pp.33-38
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• 2004

Outside wall systems we lost much energy from the dew of thermal bridge and unsuitable adiabatic construction. The air vent wall system can make reduce cooling loads from the outside wall in summer. The basic concept is connected with buoyant force by the difference of density. An external surface of a wall absorbs solar radiation, and transfers it to the air in the cavity. The warmed air gets buoyant force. So the warmed air is released through the top opening and cooler outside air replaces the space in the cavity. So because of the cavity and the openings, the cooling load reduction by natural ventilation is believed to be considerable. The purpose of this study is finding optimal length of air cavity by numerical analyses.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.354-362
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• 2002

In this paper, the heat transfer characteristics of a self-oscillating heat pipe are experimentally investigated for the effect of various working fluid fill charge ratios and heat loads. The characteristics of temperature oscillations of the working fluid are also analysed based on chaotic dynamics. The heat pipe is composed of a heating section, a cooling section and an adiabatic section, and has a 0.002m internal diameter, a 0.34m length in each turn and consists of 19 turns. The heating and the cooling portion of each turn has a length of 70mm. A series of experiments was carried out to measure the temperature distributions and the pressure variations of the heat pipe. Furthermore, heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients are calculated for various operating conditions. Experimental results show the efficacy of this type of heat pipe.

• 대한기계학회논문집B
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• 제24권3호
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• pp.346-353
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• 2000

In this paper, heat transfer characteristics of a loop type capillary heat pipe were experimentally investigated for the effect of several fill charge ratios of working fluid and heat loads. This type of heat pipe consists of a heating section, a cooling section and an adiabatic section. The heat pipe used has a 0.002m internal diameter, a 0.34m length in one turn and consists of 19 turns. Heating and cooling sections each have a length of 70mm. Experiments were performed to measure the temperature distributions and the pressure variation of the heat pipe. Heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients were calculated for various operating conditions of heat pipe and it was found that heat transfer characteristics of this type heat pipe were very excellent. As shown by this experimental study, this type of heat pipe operates by oscillatory flow caused by pressure and temperature oscillations.

• 설비공학논문집
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• 제25권7호
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• pp.392-397
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• 2013

To fulfill the demands concerning energy efficiency for zero energy buildings, various technologies of architects and engineers are required. This study aims to estimate the thermal performance of heat source equipment in which part load characteristics are considered in an office building. Overestimation of heat source equipment was reviewed through literature survey, and heating and cooling loads depending on the capacity and division of the equipment were analyzed through a simulation program (DOE-2.1E). The conclusions gained from this study are as follows; 1) The more the division of equipment, the less the heating and cooling energy consumption. 2) When a large item of equipment is divided into two small items of equipment, the optimum application rate showed as 5:5 for chiller, and 7:3 for boiler, respectively.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권11호
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• pp.557-562
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• 2003

To develop a stable and compact small-sized superconducting magnetic energy storage (SMES) system, which provides electric power with high quality to sensitive electric loads, we fabricated a SMES coil and tested it. Because such a large-sized superconducting coil quenches far away from its critical current, the recovery current is frequently used as a stability criterion in the coil fabrication. Therefore, we first investigated the recovery current characteristics of the large current conductor, which was used in our SMES coil fabrication. The test results indicate that the recovery currents measured in the conductor are nearly identical to those based on the single wire. This implies that the recovery current is affected by the conductor's cooling condition rather than its size and current capacity. In the SMES coil test the first quench occurred at 1250 A, which is equivalent to the stored energy of about 2 MJ. It corresponds to the quench current density of about $130A/mm^2$ This value is much higher in comparison with that reported in the other work. In addition, the first quench current of the coil agrees well with the measured recovery current of the conductor having similar cooling condition with it. This means that to determine the recovery current of a conductor is, first of all, important in the design and fabrication of a large-sized superconducting coil.