• Journal of Biomedical Engineering Research
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• v.21 no.5
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• pp.505-512
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• 2000

기계식 인공심장판막을 통한 혈액의 유동과 이 유동에 관련된 판첨의 거동특성을 수치해석기법을 이용하여 연구하였다. 혈액은 맥동류, 층류, 비압축성 유동으로 가정하였으며 유체-고체의 상호작용을 고려하기 위하여 혈액의 유동방정식과 고체의 운동방정식이 동시에 계산되었다. 심실과 대동맥에서의 압력파형을 경계조건으로 사용하였다. 연구의 결과로서 혈액유동과 판첨의 거동이 예측되었으며, 판막을 통한 3개의 제트가 발견되었으며 vortex가 판첨의 끝단에서 발생하여 하부로 흘러가는 것이 관찰되었다. 판첨의 닫힘 거동은 열림 거동에 비하여 2배정도 빠르게 진행되었으며 sinus에서 2개의 큰 vortex가 관찰되었다. 유체-고체 상호작용을 고려하는 본 연구방법은 향후 판막의 연구와 개발에 매우 유용할 것으로 판단된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.889-902
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• 2020

In this study, a numerical analysis was performed to confirm the formation of supersonic flow and the stabilization time satisfying the design condition in a Direct-connect supersonic combustor. The process was examined in which the high-pressure gas of vitiation air heater propagates downstream to the supersonic combustor and forms a supersonic flow field. It was confirmed through the analysis of pressure and temperature that the supersonic flow field satisfies the design points of Mach number 2.0 and 1,000 K, and requires a minimum of 4.0 ms for stabilization. These results indicate that the time required for the supersonic flow field stabilization should be taken into account when testing for the supersonic combustion experiment.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.853-860
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• 2019

In order to meet more severe environmental regulations, oxy-fuel circulating fluidized bed(CFB) boilers or ultra supercritical CFB boilers, which are a kind of process in that solid particles moves similar to fluid, have been developed in the world. In CFB power generation processes, the method to reduce or remove sulfur dioxide is in-situ desulfurization reaction via limestone directly injected into CFB boilers. However, the desulfurization efficiencies have continuously changed because limestones injected into CFB boilers are affected by various operation conditions (Bed temperature, pressure, solid circulating rate, solid holdup, residence time, and so on). In this study, a prediction method with physical and chemical properties of limestone and operation conditions of CFB boiler for in-situ desulfurization reaction in CFB boilers has developed by integrating desulfurization kinetic equations and hydrodynamics equations for CFB previously published. In particular, the prediction equation for in-situ desulfurization was modified by using experimental results from desulfurization reactions of various domestic limestones.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1075-1081
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• 2011

A leak-detection method has been developed by measuring the pressure variation between the inner and outer heattransfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1391-1397
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• 1992

Improved power law flow model was suggested for the calculation of wake flow characteristics around the three dimensional ship stern in case of the formation of bilge vortex in the direction of stern. In comparison with the power law and Coles flow model, the flow velocity calculated based on this study was delayed around the boundary of inner layer and outer layer in reverse flow. More accurate results was obtained with this improved power law flow model by the velocity calculation around ship stern. Accuracy was validated with the comparison of other calculation results and experimental datas.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.275-283
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• 2007

본 논문은 세관(ID<7 mm) 내 R-22와 R-134a의 증발 열전달과 유동양식에 대한 실험적 연구이다. R-22와 R-134a의 유동양식을 관찰하기 위해 내경 2와 8 mm의 파이렉스 튜브를 사용하였고, 열전달 계수는 내경 1.77, 3.35, 5.35 mm의 수평 평활동관에 대해서 측정하였다. 증발 유동양식에서 내경 2 mm의 환상류 영역이 내경 8 mm에 비해 저건도 영역에서 발생하는 것을 확인할 수 있었고, 내경 2 mm의 유동양식은 Mandhane의 선도와 많은 오차를 보였다. 세관(ID<7 mm) 내 증발 열전달 계수는 종래의 대구경관(ID>7 mm)에 비해 관직경에 대한 영향이 많이 나타나는 것을 알 수 있었다. 내경 1.77 mm의 열전달 계수는 내경 3.36 mm와 5.35 mm에 비해서 20내지 30% 정도 높은 것을 나타났다. 또한 종래의 열전달 상관식(Shah's, Jung's, Kandlikar's and Oh-Katsuda's correlation)과 비교한 결과, 실험 데이터는 상관식과 많은 이탈 정도를 보였다. 따라서 실험데이타를 기초로 세관내 R-22와 R-134a에 적용할 수 있는 증발 열전달 상관식을 새로이 제안하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.46-54
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• 1997

Based upon the results of numerical calculation, empirical scaling equations were made for supersonic under-expanded jets in both axisymmetric and two dimensional flows. The objective of the present study is to find a straightforward method that can predict the under-expanded supersonic jets issuing from various kinds of nozzles. The present empirical equations were agreed with the calculation results of total variation diminishing difference scheme. The supersonic under-expanded jets operating at a given pressure ratio could be well predicted by the present scaling equations.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11b
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• pp.300-304
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• 2003

수용성 안료인 RhB를 대상으로 GF/C에 고정한 $TiO_2$와 유동층 반응기를 이용하여 제거실험을 수행한 결과 다음과 같은 결론을 얻었다. 1. 고정화 $TiO_2$의 경우도 분말을 이용한 것과 같이 최적 광촉매 투입량이 나타났으며, 최적 투입량은 40.0 g/L이었고, 분말 $TiO_2$를 이용하는 광촉매 반응의 초기속도식과 같이 Langmuir - Hinshelwood 식으로 표현될 수 있었다. 분말 $TiO_2$를 이용한 경우보다 초기반응속도는 2.3배 느렸으나, 고정화 $TiO_2$의 경우 연속공정이 가능하고 촉매회수 공정이 필요하지 않으므로 반응속도만 더 높일 수 있으면 현장적용 가능성이 높다고 사료되었다. 2. 고정화 $TiO_2$의 최소유동을 위한 공기 공급량은 4 L/min, 최대 반응속도는 5 L/min에서 나타나 고정화 $TiO_2$를 충진한 유동층 반응기의 최적 공기 공급량은 최소유동화 속도 부근인 것으로 사료되었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.3
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• pp.171-181
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• 2017

Two-phase cross flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. The drag force acting on a tube bundle subjected to air/water flow is evaluated experimentally. The cylinders subjected to two-phase flow are arranged in a normal square array. The ratio of pitch to diameter is 1.35, and the diameter of the cylinder is 18 mm. The drag force along the flow direction on the tube bundles is measured to calculate the drag coefficient and the two-phase damping ratio. The two-phase damping ratios, given by the analytical model for a homogeneous two-phase flow, are compared with experimental results. The correlation factor between the frictional pressure drop and the hydraulic drag coefficient is determined from the experimental results. The factor is used to calculate the drag force analytically. It is found that with an increase in the mass flux, the drag force, and the drag coefficients are close to the results given by the homogeneous model. The result shows that the damping ratio can be calculated using the homogeneous model for bubbly flow of sufficiently large mass flux.

• The Journal of Engineering Geology
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• v.20 no.2
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• pp.191-202
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• 2010

In this study, the relationship between the settlements and the horizontal displacements according to embankment was analyzed at the marine sedimentary grounds for preparation of a site, and then the empirical equations of both the settlement and the horizontal displacement considering the embankment load and the thickness were proposed. To do this, the field and laboratory tests were performed at the improvement section where the pre-loading method was applied, and the field monitoring was performed using various sensors. Based on the results of the tests and monitoring, the ground deposits, soil characteristics and engineering properties were analyzed and the settlements and lateral movements were estimated by the Regression analysis. The ground deposits from the ground surface were composed of reclaimed soils, sedimentary soils and based rocks. The thickness of clay in the sedimentary soils layer was ranged from 3.9 m to 44.5 m. The embankment heights to improve the ground during pre-loading were constructed from 4.7 m to 7.8 m in each section. The settlements during embankment were ranged from 0.959 m to 2.217 m and the lateral movements were ranged from 0.048 m to 0.313 m. As the result of regression analysis, the equations of settlements and horizontal displacements according to embankments may be proposed as $s=0.02h^2+0.11h$ and ${\delta}=0.01e^{0.37h}$, respectively. The proposed empirical equations of the settlements and the horizontal displacements according to embankment on the marine sedimentary ground may be applied to the site where has a similar condition of study area.