• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1106-1113
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• 2001

This paper presents experimental works on the ultrasonic influence during melting of ice and paraffin and compared the paraffin's result with ice's results. The experiments was carried out under two setting conditions.: 1) Heater without ultrasonic vibration, 2) heater with ultrasonic vibration. Experimental observations show that the ultrasonic vibration enhances significantly the phase-change process (melting) so that the melting time is reduced about 16∼25% compared to those of molting process without ultrasonics in the melting of both ice and paraffin. But the influence of ultrasonics was not significant to affect the reduction of the power consumption. In the case of paraffin, the reduction rate of power consumption was about 20%, but the reduction of the power consumption was increased about 0∼12%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.7
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• pp.603-611
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• 2006

A variety of schemes were sought for a mitigation of thermal stratification phenomenon in the branch piping of domestic nuclear power plant. Several mechanisms of thermal stratification occurrence were introduced in this paper. A number of factors were selected to find out the schemes for thermal stratification mitigation and the computational analysis were performed. The length of vertical branch piping, the diameter, the radius of curvature of the elbow, the direction of connection between main piping and branch piping, the slope of branch piping, the leakage flow rate, the installation of additional valve, the change of the 1st valve position and another branch piping connected with branch piping were mentioned as factors in this paper.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.7
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• pp.560-566
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• 2012

Numerical study has been carried out to investigate heat transfer and pressure drop characteristics for streamlined shape tubes. The flow and thermal fields are investigated with varying diameter ratio of the tube ranging from 0.4 to 2.5 and Reynolds number ranging from 10,000 to 30,000. The results show that heat transfer per unit fan power is maximum at $D_2/D_1=0.8$. Furthermore, the heat transfer per unit fan power of streamlined shape tubes was compared with circular tube. The heat transfer per unit fan power of streamlined shape tube was larger than that of circular tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.2
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• pp.126-130
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• 2009

The present study describes an investigation into the characteristics of combustion oscillation and its suppression instability of a silo type gas turbine combustor in commercial power plant. Combustion oscillation is occurred the combustor in near full load during operation. As a result of FFT analysis of the combustion dynamics, the frequency of the oscillation is analyzed as the 1'st longitudinal mode of acoustic resonance of the combustor. For suppress of the instability, combustion tuning with adjust of fuel valve schedule is carried out, which changes equivalent ratio of each burners. As the result, the oscillation is successfully reduced with meeting the level of NOx emission regulation.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.217-218
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• 2014

전력 계통에 연계하는 신재생에너지 분산형 전원의 보급량이 지속적으로 늘어나면서 저압 계통의 공통 연계점에 다수대의 PCS(Power Conditioning System)가 집중적으로 설치되는 사례가 증가하고 있다. 최근 일본전기공업회(JEMA)는 계통 사고나 계획 정전 등으로 변전소 차단기가 개방되었을 때, 복수대 PCS의 능동방식이 서로 간섭을 일으켜 정해진 시간 내에 단독운전 검출기능이 작동하지 않게 되는 상황을 방지하기 위해 표준형 단독운전 능동적 방식을 공표하였다. 본 논문에서는 일본 단독운전 검출방식의 표준으로 지정된 스텝주입이 있는 주파수피드백 방식의 원리와 특징을 살펴보고, 이를 적용하여 연계 보호기능의 안전성 확보와 분산형 전원 보급에 기여하는 효과에 대해 소개하였다.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.425-426
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• 2015

본 논문에서는 실시간 시뮬레이터를 이용하여 1MW PCS(Power Conditioning System)의 불평형 비간섭 전류제어(Unbalanced Current Control under Unbalanced Condition) 알고리즘을 검증하였다. 3상 불평형 발생 시, 기존의 전류제어는 전압의 불안정으로 인해 전류의 목표 값이 흔들리는 현상을 보인다. 하지만, 3상 불평형 비간섭 제어는 불평형 상황 전압과 전류를 정상과 역상 성분으로 나누고, 이를 독립적으로 제어함으로써 더욱 우수한 성능을 가진다. 본 논문은 1MW PCS의 HILS(Hardware-In-the-Loop Simulation) 환경을 구축하여 실시간 시뮬레이터에서 실제 출력되는 전류의 불평형을 확인하고, 이를 개선하는 것을 검증하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.6
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• pp.248-255
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• 2016

In this study, the degree of performance changes between the guaranteed performance and the performance after a certain operating start time is calculated by using the performance test of gas turbine CHP. The reason of the performance degradation will then be analysed. For some results of the CHP plant performance tests the comprehensive electric power output was 8,380 kW lower than the guaranteed performance, and the gas turbine's output was reduced to about 250 kW whenever ambient temperatures rose to $1^{\circ}C$. Also, causes of the performance degradation of gas turbines are ambient temperature rise, temperature aging and air compressor's efficiency drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.251-257
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• 2000

District heating and cooling systems offer highly efficient energy utilization and maintenance by centralizing heat management. More pumping power, however, is required because the water has to travel long distance from heat source to the users. In the present study, a trace of drag reduction additives is added to the District Cooling system to achieve a significant drag reduction and save pumping power. Water-soluble polymers, surfactants, and environment-friendly degradable polymers are used as effective drag reducing additives. Time dependent percent drag reductions are compared for various additive solutions at 100 wppm concentration for different water velocity. Without as an anionic surfactant, copolymer was most effective in percent drag reduction. It is found that there exists an optimal condition when copolymer is mixed with SDS. An environment-friendly degradable polymer, xanthan gum, is found to be a significant drag reduction additive. Ice slurry systems, can give less pressure drops compared with chilled water system for certain condtions. Drag reduction additives were also effective for the ice slurry system.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.87-92
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• 2016

This research dealt with performance characteristics of OTEC system applying an ejector and additional pump. Each system using five kinds of working fluids was analyzed, and primary parameters with respect to entrainment ratio were examined: Turbine gross power, evaporation capacity, pump work, efficiency and volume flow ratio. The primary results were as following. The efficiency of ejector-pump OTEC system was dependent on entrainment of the ejector. The degree of efficiency change was different from applied working fluid, and amount of pump work was turned out to be primary factor affected system efficiency. Meanwhile, optimized entrainment ratio was different from applied working fluid since their different vapor density. System efficiency at optimized entrainmet ratio of each working fluid was around 5%, showing minor difference each other.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.3
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• pp.302-308
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• 2011

The HVAC(Heating Ventilation and Air Conditioning) system is only controlled by turn on/turn off operations with AC 380V input. Therefore, the efficiency of the system is reduced and accoustic noise problem occurs. Also, the blower is shut down at the AC power failure. In this paper, the inverter system with UPS function for the A/C(Air Conditioning) blower is proposed. Proposed inverter system which is powered from the AC and DC voltage can control speed, operation mode, and soft-start time using CAN communication. In case of the CAN communication failure, RS-232 communication could be used to control the hardware directly by the engineer that can solve existing problems. To verify the validity of proposed inverter system, simulations and experiments are carried out.