• 설비공학논문집
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• 제13권10호
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• pp.1017-1024
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• 2001

The optimum shape of header part in a PFHE (parallel-flow heat exchanger) is studied. The optimal values of each geometric parameter are proposed according to their order of influence with varying the four important parameters (the injection angle of working fluid ($\Theta$), the shape of inlet(S), the location of inlet ($y_c/D_{in}$) and the height of the protruding flat tube ( $y_{b/}$ $D_{in}$ )). The optimal geometric parameters are as follows:$\Theta= -21^{\circ}C,\; S=Type\; A \;an\;y_b/D_{in}$/=0. The heat transfer rate of the optimum model, compared to that of the reference model, is increased by about 55%. The optimal geometric parameters ran be applicable to the Reynolds number ranging from 5,000 to 20,000.0.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.197-202
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• 2007

In this study, the cooling characteristics of a liquid cooler using thermoelectric module was experimentally investigated. The experiment was conducted for various inner structures of liquid cooler (4 cases), hot fluid flow rates (0.15-0.25 L/min), number of T.E module (2, 4, 6 set), and the cooling water flow rates (200-600 cc/min) for both parallel and counter flow types. Among the results, better cooling performance geometry was selected. And experiment was also carried out to examine further enhancement of cooling performance by inserting coils (pitches: 0.2, 3, 6 mm) into the hot-fluid channel. Present results showed that the short serpentine type(case2) indicated the best cooling performance. In the case of coil pitch of 3 mm, the best cooling performance was shown, more than 10% increase of the inlet and outlet temperature difference, compared with the case of the cooler without coil. Consequently, the inserted coil pitch should be properly selected to improve cooling performance.

• Nuclear Engineering and Technology
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• 제38권5호
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• pp.449-454
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• 2006

Neutron imaging technique was used to investigate the water distribution and movement in Polymer Electrolyte Membrane Fuel Cell (PEMFC) at HANARO, KAERI. The Feasibility tests were performed in the first and second exposure rooms at the neutron radiography facility (NRF) at HANARO in order to check the ability of each exposure room, respectively. The feasibility test apparatus was composed of water and pressurized air before making up the actual test apparatus. Due to the low neutron intensity in the second exposure room, the exposure time was too long to investigate the transient phenomena of PEMFC. Although the exposure time was improved to 0.1 sec in the first exposure room, it was difficult to discriminate detail water movement at the channel due to the high noise level. Therefore, the experimental setup must be optimized according to the test conditions. Water discharge characteristics were investigated under different flow field geometries by using feasibility test apparatus and the neutron imaging technique. The water discharge characteristics of a 3-parallel serpentine are superior to those of a 1-parallel serpentine, but water at Membrane Electrode Assembly (MEA) was not removed, regardless of the flow field type.

• 설비공학논문집
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• 제25권9호
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• pp.516-521
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• 2013

In the present study, the performances of a fin-tube evaporator and three PF evaporators for a heat pump dryer were experimentally investigated. Among the tested evaporators, the PF3 type evaporator showed the highest values of heat transfer capacity and dehumidification performance, while the fin-tube evaporator had the lowest values. PF3 showed better performance compared to PF1 and PF2, due to the large pin pitch, which leads to more draining for dehumidified water. Also, the $45^{\circ}$ inclined PF evaporator presented better performance than that of the $90^{\circ}$ inclined PF evaporator, owing to its easier draining characteristics. The effect of air velocity was revealed to be quite large. When the air velocity increased by 20%, the heat transfer capacity and dehumidification performance increased 43%/11%, 48%/13% and 54%/23% for PF1, PF2 and PF3, respectively.

• 대한화학회지
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• 제21권5호
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• pp.330-338
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• 1977

고체의 소성변형을 설명하기 위하여 다음과 같은 가정을 하였다. (1) 고체의 소성변형은 크게 두 가지 기구 즉 dislocation 운동과 grain boundary 운동에 의하여 일어난다. (2) Dislocation 운동에 있어서 유동 단위들은 역학적 모형으로 나타내면 다종의 Maxwell 단위들의 평행연결형으로 되고 grain boundary 유동단위들도 다종의 Maxwell 단위들의 평행연결로 표현된다. 이를 물리적으로 설명하면 같은 부류의 유동단위들은 모두 같은 shear plane에서 같은 shear rate로 흐름을 의미한다. (3) Grain boundary 유동단위들과 dislocation 유동단위들 같은 서로 직렬 연결되어 있다. 이는 물리적으로 고체내에서 stress는 균일하게 작용하나 shear rate는 shear plane 의 종류(dislocation 운동면과 grain boundary 운동면)에 따라 달리 나타남을 의미한다. (4) Dislocation 유동단위들과 grain boundary 운동단위들의 운동은 그들의 흐름을 방해하는 장애물 근방의 원자 또는 분자들이 확산해 나가므로써 가능하게 된다. 이러한 가정하에 반응속도론을 적용하여 shear rate와 shear stress를 구하는 일반식을 도출하였다. 본 연구에서는 실제로 중요한 네가지 경우에 대하여 상기 도출한 일반식을 고찰하였다.

• 동력기계공학회지
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• 제19권4호
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• pp.5-10
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• 2015

Dust collector is one of the most widely used equipment among the method of separating particles, it filters exhaust gas having various kinds of dusts through several filters installed on parallel. This research investigated the moving characteristic of Honeycomb-type carbon filter in pressure drop of smoking collector's ventilation system. It also compared pressure transmission coefficient through pressure drop according to flow velocity change.

• 대한설비공학회지:설비저널
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• 제6권4호
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• pp.255-261
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• 1977

This study was concerned with the performance of solar air heater using parallel channels. Heat transmission model was developed and fabricated to increase the economic feasibility for solar heating system by using the cheap zinc plate. The prformance was discussed as a function of mass flow rate, and plate, inlet and outlet temperatures. Experimental results show that heat transmission model is sufficient for the analysis of thermal characteristics of air heater and collection efficiency is better than the domestic water heater, as the range 32-49 percent. Collection efficiency in the 2 layers of glass cover is better than that in 1 layer, so it is considered better to use the 2 layers of glass cover during the cold winter season in Korea.

• 설비공학논문집
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• 제17권1호
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• pp.1-7
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• 2005

The heat transfer characteristics of an internal heat exchanger for $CO_2$ refrigeration cycle are numerically investigated. The numerical model is verified using the published experimental results for the concentric tube type internal heat exchanger. The Hardy-Cross Method gives very good agreement between the calculation and experimental results on the heat transfer rates and exit temperatures. Also, appropriate combination of heat transfer correlations is found. The operating parameters of the heat exchanger are calculated at transcritical region of $CO_2.$ The heat transfer rate of the counter flow type heat exchanger shows the $32\%$ greater than that of the parallel flow type heat exchanger. The increase of heat exchanger length enhances the heat transfer rate. The thermodynamic characteristics and heat transfer coefficient of $CO_2$ in the internal heat exchanger are estimated.

• Nuclear Engineering and Technology
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• 제41권1호
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• pp.135-142
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• 2009

In this investigation, we prepared a 1 and 3-parallel serpentine single PEMFC, which has an active area of $100\;cm^2$ and a flow channel cross section of $1{\times}1mm$. Distribution and transport of water in a non-operating PEMFC were observed by varying flow types and the flow rates (250, 400, and 850 cc/min). This investigation was performed at the neutron imaging facility at the CO1d Neutron RAdiography facility (CONRAD), HMI, Germany of which the collimation ratio and neutron fluence rate are 250, $1{\times}10^{6}n/s/cm^2$, respectively. The neutron image was continuously recorded by a scintillator and lens-CCD coupled detector system every 10 seconds. It has been observed that although the distilled water was supplied into the cathode channel only, the neutron image showed a water movement from the cathode to the anode channel. The water at the cathode channel was completely discharged as soon as the pressurized air was supplied. But the water at the anode channel was not easily removed by the pressurized air except for the 3-parallel serpentine type with 850cc/min of air flow rate. Moreover, the water at the MEA wasn't removed for any of the cases.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제7권3호
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• pp.67-72
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• 2018

축류 팬(axial fan)은 팬이 회전하면서 작은 압력 상승을 만들어 다량의 공기를 불어주는 유체 기계로써 최근 축류 팬의 소음 저감이 중요하게 인식되고 있다. 본 연구는 팬 주위의 유동 소음을 해석하는 MPI 병렬프로그램 방법 및 최적화 기법에 대해 다룬다. 이때 수억 개 이상의 격자에서 수만 포인트의 소음원을 해석하기 위해서 2차원 도메인 분할 방법을 사용해서 MPI 병렬화를 하였다. 이때 대규모 계산 시 MPI 프로세스 간의 통신이 많이 발생하여 성능이 심각하게 느려지는 현상이 발생한다. 이를 극복하기 위해 MPI 일방향 통신을 적용하였다. 뿐만 아니라 통신 및 메모리 최적화 방법을 통해 최대 2.97배 향상시켰다. 마지막으로 KISTI 타키온2 슈퍼컴퓨터를 활용하여 전체 시뮬레이션 실험에서 유동 계산 시 6,144코어에서 최대 12배, 소음 계산 시 128코어에서 최대 6배의 성능향상을 달성하였다.