• 한국결정성장학회지
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• 제30권6호
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• pp.237-243
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• 2020

본 연구에서는 STS-316 플레이트와 구리(Cu) 브레이징으로 구성된 접합 판형 열교환기(BPHE, Brazed Plate Heat Exchanger)의 내식성과 열효율 성능 향상을 위해 실란계 코팅을 적용하고자 하였다. 코팅 재료에 따른 부식 및 접촉각을 평가하여 선정된 코팅재료를 열교환기에 적용하였으나, 전열 성능 평가 결과 코팅하지 않은 열교환기에 비해 열효율이 떨어지는 결과가 나타났다. 이는 접합 판형 열교환기 내부의 유로에 코팅제의 고착화 및 표면의 잔여 코팅제가 열저항으로 작용하여 열전달을 방해는 것으로 분석되었다. 이는 내부에 미세한 유로가 존재하는 판형 열교환기의 구조적인 특성에 기인한 것으로, 판형 열교환기 제작 공정에서 사전에 유로 표면에 코팅 후 제작하는 것이 전열성능을 향상 시킬 수 있을 것으로 판단된다.

• 대한건축학회논문집:계획계
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• 제35권6호
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• pp.27-37
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• 2019

This study focused on the possibility of reducing the cooling load through the change of micro climate in the outdoor space during summer season. This study proposes an efficient planning model by comparing the effects of urban heat island mitigation through wind path planning, outdoor space vegetation, and exterior material change by using the basic model of the street-oriented block housing proposed in the previous research by the same author. As a result, the most effective wind path planning strategy in the street-oriented block housing was the change of the air flow through the mass height adjustment. When the tall building masses were staggered and arranged in a balanced manner, the overall wind environment could be improved. The greater the height difference between low and high masses, the better the air flow was shown. It was also important to arrange the building masses so that the inlet of the main wind was open and to allow the external space to connect to the adjacent block to create a continuous flow. The change of outdoor space vegetation and flooring, and the formation of wind paths through the opening of lower part also showed the effect of heat island reduction. In addition, the change of PMV in summer was the biggest influence of shadow by tall building mass. Attention should be paid to the fact that high-albedo exterior materials are adversely affected by multiple reflections in dense street-oriented block housing. The use of albedo of the exterior material showed that it is necessary to pay attention to apply in the high density block housing. This is attributed to the rise of the temperature due to the absorption of energy into the low-albedo flooring, where the high-albedo exterior causes multiple reflections.

• Journal of Advanced Marine Engineering and Technology
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• 제31권3호
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• pp.272-281
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• 2007

A numerical simulation on nitrogen gas flow in a long parallel plate microchannel was performed to obtain the effect of compressibility and rarefaction on gaseous flow in microchannels. The simulation was based on steady. two dimensional compressible Navier-Stokes and energy equations with noslip and first order slip boundary conditions. The channel was $1.2{\mu}m$ deep and $3000{\mu}m$ long. The Reynolds numbers were in the range of order from $10^{-2}$ to $10^{-1}$. So the flow was assumed to be laminar. The computations were performed on various pressure ratios. The outlet pressure was fixed to atmospheric pressure. The outlet Knudsen number was 0.0585, consequently the flow was in the slip flow regime. The computations were performed with the assumption of isothermal channel walls. The results were compared with the experimental data. The agreement was good.

• 한국가구학회지
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• 제18권2호
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• pp.161-165
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• 2007

An experiment was conducted to observe the safranine flow depth in longitudinal direction of Populus tomentiglandulosa. Longitudinal flow of safranine was considered from bottom to top end of the tree. Vessel and wood fiber were considered for the measurement of safranine flow depth. It was found that sapwood conducted safranine 12.25% higher in longitudinal direction compared with heartwood. Vessel was found the main avenue for safranine flow. Vessel conducted safranine 41.94% higher than that of wood fiber. Safranine penetrated through vessel and fiber forming a curved meniscus.

• 신재생에너지
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• 제3권3호
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• pp.14-19
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• 2007

A flow channel model of a bipolar plate with varying cross-sectional area was newly designed for improving performance and efficiency of a PEM fuel cell stack. As a result, the varying cross-sectional area model showed poor uniformity in velocity distribution, however, maximum velocity in the flow path is about 30% faster than that of the uniform cross-sectional area model. The proposed varying cross-sectional area model is expected to diffuse operating fluids more easily into diffusion layer because it has relatively higher values in pressure distribution compared with other flow channel models. It is expected that the implementation of the varying cross-sectional area model can reduce not only the mass transport loss but also the activation loss in a PEM fuel cell, and open circuit voltage of a fuel cell can thus be increased slightly.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.879-882
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• 2002

To control the vibration and sound of structure, it is important to analyze the dynamic action of structure. And through those analysis, the vibration source and the flow path is understood. To grasp that, when the two-dimension plate structure is shaken by a harmonic point excitation with the natural frequency using the finite element method, this paper presents the relation between vibration power flow and mode shape. As those results present to vector flow, the vibration power flow is visualized.

• 유공압시스템학회논문집
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• 제5권4호
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• pp.10-16
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• 2008

In this paper, the authors benchmark a servo valve model for the fuel supply system of Auxiliary Power Unit (APU) in the KHP helicopter. This valve is directly driven with a torque motor, and the size of small gap controlled by a flapper can make change of flow rate under given pressure drop between inlet and outlet. CFD analyses using a commercial code, ANSYS-CFX 10 are performed for the series of three-dimensional models at various openness conditions. The computational results on simplified models show that CFD can play a fine roll in the design of flow path as well as in the estimation of flow force due to its precision and good repeatability. Consequently, the CFD analysis helps valve designers to understand its flow characteristics from the basis of physical fundamentals.

• 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.

• 제어로봇시스템학회논문지
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• 제22권3호
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• pp.210-216
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• 2016

This paper presents a novel collision avoidance technique for mobile robots based on omni-directional vision simultaneous localization and mapping (SLAM). This method estimates the avoidance path and speed of a robot from the location of an obstacle, which can be detected using the Lucas-Kanade Optical Flow in images obtained through fish-eye cameras mounted on the robots. The conventional methods suggest avoidance paths by constructing an arbitrary force field around the obstacle found in the complete map obtained through the SLAM. Robots can also avoid obstacles by using the speed command based on the robot modeling and curved movement path of the robot. The recent research has been improved by optimizing the algorithm for the actual robot. However, research related to a robot using omni-directional vision SLAM to acquire around information at once has been comparatively less studied. The robot with the proposed algorithm avoids obstacles according to the estimated avoidance path based on the map obtained through an omni-directional vision SLAM using a fisheye image, and returns to the original path. In particular, it avoids the obstacles with various speed and direction using acceleration components based on motion information obtained by analyzing around the obstacles. The experimental results confirm the reliability of an avoidance algorithm through comparison between position obtained by the proposed algorithm and the real position collected while avoiding the obstacles.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.311-317
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• 2005

Measurements of the leakage flow in the shrouded cavity were performed in axial compressor cascades at $Re=2.6{\times}10^5$. This paper describes the effects of the leakage flow tangential velocity on kinematics of the leakage flow in the shrouded cavity and consequent overall loss and exit flow turning at stator blade row downstream. Flow data and flow visualization images consistently indicate that leakage flow circumferentially migrates 2, 4 and 5 blade passages in the direction of rotation for ${\upsilon}_y/c=0.09$, 0.35 and 0.45, respectively where ${\upsilon}_y$ is the leakage tangential velocity and c is the mainstream velocity. The leakage flow contracts to a jet across the seal-tooth resulting in an increase in the leakage axial velocity-doubling the leakage axial velocity in upstream cavity compared to that in the downstream cavity. Consequently, two flow regions are distinguished before and after the seal-tooth. As increasing the leakage tangential velocity, the overall loss downstream of stator blade row decreases and the exit flow turning in the range of span. from the hub endwall to 15% increases while the decreases in the flow turning from 15% to 30% span is observed.