• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.747-754
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• 2005

Because the liquid-vapor interfacial shear stress affects seriously the liquid flow and the maximum heat transport rate of the grooved wick heat pipe, an accurate modeling for the pressure drop characteristics of the liquid flow is required. A novel method for calculating the liquid pressure drop and the velocity profile of an open channel flow in a microchannel with an arbitrary cross-section is suggested and validated by experiments. An experimental apparatus for the Poiseuille number of the liquid flow in open rectangular microchannels with the hydraulic diameters of 0.40mm, 0.43mm, 0.48mm is used in order to reproduce real situations in the grooved wick heat pipe. Analytic results from the suggested method are compared with the experimental data and they are in a close agreement with each other.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.136-141
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• 2000

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally studied in 760 mm long and 100 mm wide test sections with 2.0 and 3.0mm gaps. The resulting data have been compared to previous transition models. For the transition from bubbly to slug flow the superficial velocity of gas increased as the gap width increased. The comparison of experimental data to the transition model developed by Taitel and Barnea showed relatively good agreement for the bubbly-to-slug transition in the case of 2mm gap width. For the criteria of Mishima and Ishii to be applicable to the slug-to-churn transition the distribution parameter should be well defined for narrow channels. Even though the gap width of narrow channels increased the superficial gas velocity did not change for the transition form chum to annular flow regime. For the chum-to-annular transition the model of Taitel and Barnea showed discrepancies with experimental data, especially in the channel with larger gap.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.229-234
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• 2001

An adiabatic counter-current vertical two-phase flow of air and water in narrow rectangular channels with offset strip fm was investigated experimentally. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.06 m/s and 0 to 2.5 m/s ranges, respectively. Two-phase flow regimes were classified by examining the video images of flow patterns in transparent test sections of 760 mm long and 100 mm wide channel with gaps of 3.0 and 5.0 mm. The channel average void fraction was measured by the quick-closing valve method. Unlike the flow regimes in the channels without fin, where bubbly, slug, chum, and annular flow were identified, only bubbly and chum flow regimes were found for the channels with offset strip fin. However the existence of fin in the channels showed negligible effects on the void fraction. Instead counter-current flow limitations were found to happen at lower air superficial velocity once offset strip fin was introduced in narrow rectangular channels.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.667-673
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• 2017

We investigated the temperature uniformity in an anode-supported solid oxide fuel cell, using the open source computational fluid dynamics (CFD) toolbox, OpenFOAM. Numerical simulation was performed in three different flow paths, i.e., co-flow, counter-flow, and cross-flow paths. Gas flow in a porous electrode was calculated using effective diffusivity while considering the effect of interconnect rib. A lumped internal resistance model derived from a semi-empirical correlation was implemented for the calculation of electrochemical reaction. The result showed that the counter-flow path displayed the most uniform temperature distribution.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.6
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• pp.441-446
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• 2007

An experimental study on the countercurrent two-phase flow in narrow rectangular channels has been peformed. Countercurrent flow limitation (CCFL) was investigated using air and water in 760mm long, 100mm wide, vertical test sections with 1 and 3mm channel gaps. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.125 and 0 to 3.5m/s ranges, respectively. As the gap width of rectangular channel increased the CCFL water superficial velocity decreased for the given air superficial velocity. Slight increase of the air superficial velocity resulted in the abrupt decrease of water velocity when $j_g=2{\sim}4m/s$. The critical superficial velocity of air, at which the downward flow of water was no longer allowed, also decreased with the increase of gap width. The experimental results were compared with the previous correlations, which were mainly for round tubes, and the qualitative trends were found to be partially acceptable. However the quantitative discrepancies were hardly neglected. New correlation of CCFL was developed and showed good agreement with the experimental data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.269-273
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• 2011

In present paper focused on the influence of the inlet-outlet area ratio of counter flow manifold on the flow distribution and pressure drop characteristics of a tubular heat exchanger. The characteristics of flow distribution and pressure loss can be obtained depending on the inlet-outlet area ratio. In this paper, a tubular heat exchanger can be designed with minimum flow mal-distribution and better characteristic of pressure loss by choosing the optimum inlet-outlet area ratio.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2012.04a
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• pp.58-61
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• 2012

엔진나셀 화재를 둔각물체에서 분사된 연료제트 화염으로 모사하여 화염안정화 및 소화특성을 조사하기 위해 실험과 수치해석을 수행하였다. 연료제트는 공기유동에 동측류인 경우와 대향류인 경우에 사각의 둔각물체에서 분사하였고, 소화약제는 이산화탄소와 질소를 사용하여 공기유동에 희석시켜주었으며 연료로는 메탄을 사용하였다. 본 실험의 결과를 해석하고 보충하기 위하여 LES(Large Eddy Simulation)을 기반으로 하는 FDS(Fire Dynamics Simulator)를 이용하여 비반응 유동장에서의 혼합특성과 둔각물체 후류의 유동특성을 살펴보았다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.503-511
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• 2013

The humidifying supply gas is important in terms of the performance efficiency and membrane life improvement of a PEM fuel cell. A planar membrane humidifier is classified as a cross-flow and counter-flow type depending on the flow direction, and heat and mass transfer occur between the plate and the membrane. In this study, the changes in heat and mass transfer for various inlet temperatures and flow rates are compared according to the flow direction by using the sensible and latent ${\varepsilon}$-NTU method. The obtained results indicate that the counter flow shows higher heat and mass transfer performance than the cross flow at a low flow rate, and the difference in performance decreases as the flow rate increases. Furthermore, changes in the mass transfer performance decrease considerably with a nonlinear increase in the inlet temperature, and variations of the heat transfer performance are small.

• Journal of Energy Engineering
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• v.9 no.3
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• pp.178-183
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• 2000

본 연구에서는 유동과 냉각수를 이용하는 아이슬러리 제조관정을 관찰하고, 이 시스템의 가장 큰 문제점인 관내동결 특성을 파악하였다. 시험수로는 수도수(city water)를 이용하였다. 시스템을 순환하는 시험수가 제빙관내에서 $0^{\circ}C$ 이하의 과냉각 조건이 형성되어 제빙관을 빠져 나오면서 축냉조에 설치된 충격판상에서 과냉각 해소가 일어났다. 이때 유동과냉각수는 내부에너지를 방출하면서 그 일부가 얼음 입자로 상변화되었고, 나머지는 실험장치를 계속순환하였다. 제빙관에서 시험수와 브라인의 열교환 방식을 대향류와 평행류 두 조건에서 시험수의 과냉각도는 Reynolds 수가 증가함에 따라 감소하는 경향을 보였고, 이들 결과 값으로부터 각각의 관계식을 유도하였다. 또한 브라인의 냉각속도가 0.29~0.53[$^{\circ}C$/min] 범위에서 시험수의 과냉각도는 브라인 냉각속도에 종속되지 않았다.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.39-45
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• 2004

The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal Performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The Present work showed that the flow velocity range for Possible collision between the tube wall and the particles was higher with heavier density solid particles. in audition. the solid particle periodically hitting the tube wall broke the thermal boundary laver. and increased the rate of heat transfer.