• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.241-246
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• 1995

An experimental investigation was performed under steady flow condition to assess hydrodynamic performance of floating-type monoleaflet polymer valves (MLPV) with different leaflet thickness. The St. Jude Medical valve (SJMV) was also used for comparison tests. Pressure drops of MLPVs are larger than those for other types of polymer valves and mechanical valves. Furthermore, the thicker is the leaflet thickness of a polymer valve, the larger arc the corresponding press drop. The velocity profiles for MLPV reveal a large reversed flow region downward to the valve position. The maximum wall shear stresses of MLPVs at a flow rate of 30 l/min are in the range $54-130\;dyn/cm^2$, and the corresponding maximum. Reynolds shear stresses are in the range of $100-500\;dyn/cm^2$, respectively. Both arc beyond the allowable limit clinically. In contrast, floating-type monoleaflet polymer valves show better hydrodynamic performance in leakage volume. From the designing point of view, it can be concluded that the optimum thickness of leaflet for better hydrodynamic performance is one of the important parameters.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.127-130
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• 1997

Phase-contrast(PC) methods have been used for quantitative measurements of velocity and volume flow rate. In addition, phase contrast cine magnetic resonance imaging (MRI) combines the flow dependent contrast of PC MRI with the ability of cardiac cine imaging to produce images throughout the cardiac cycle. In this method, the through-plane velocity has been encoded generally. However, the accuracy of the flow data can be reduced by the effect of flow direction, finite slice thickness, resolution, pulsatile flow pattern, and so on. In this study we calculated the error caused by misalignment of tomographic plane and flow directon. To reduce this error and encode the velocity for more complex flow, we suggested 3 directional velocity encoding method.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1265-1268
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• 2009

In this paper, the effect of a flow barrier and bypass on the cooling performance for a straight fin heat sink is presented. Both side directions and upward direction of bypass are controlled using various ducts which have different width and heights. In addition, a flow barrier is used to control flow toward heat sink. Through experiments, the distance from leading edge of a heat sink to a flow barrier is varied for various bypasses under fixed volume flow rate condition. This study shows possibility to improve cooling performance when bypass and a flow barrier exist.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.172-177
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• 2000

In this numerical work, three dimensional supersonic laminar flow and heat transfer of a blunt body(sphere-cone) at Mach 5 is simulated. The effects of angle of attack and the spin rate on the now and heat transfer are analysed. To solve the three dimensional compressible Wavier-Stokes equation, a finite volume method with the modified LDFSS scheme is employed for spatial discretization, and a point SGS implicit method is used for time integration. It is found that the heat transfer rate increases at the windward side and decreases at the leeward side with the angle of attack. The heat transfer rate at all surfaces slightly increases with the spin rate.

• 산업융합연구
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• 제21권7호
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• pp.83-92
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• 2023

유전체 전위장벽방전방식에 의한 플라즈마 젯의 블렛 형상은 인가되는 유량과 전기장의 크기에 따라 달라지고 이러한 변화는 DBD 플라즈마 젯의 밀도차이에 의한 스펙트럼 분포의 차이로 나타난다. 발생된 플라즈마 젯의 스펙트럼의 분석을 통한 활성종의 발생과 강도의 차이는 장치를 활용하는데 있어서 중요한 요소이다. 본 논문에서는 Ar가스를 이용한 대기압 볼륨 DBD방식의 플라즈마 젯 발생장치를 제안된 설계방법에 따라 구성하였다. 플라즈마 젯의 발생을 위한 유량의 의존도를 규명하기 위한 Ar가스의 유동해석을 시뮬레이션을 통해 확인하였고 프로토타입 시스템에서는 MFC를 통한 유량제어를 통해 최적의 플라즈마 젯 불렛형상을 발생시키고 발생된 플라즈마 젯의 특성을 분석하기 위해 스펙트로미터를 이용한 플라즈마 젯의 특성을 분석하였다. 제안된 시스템의 설계방법을 통한 장치에서 최적의 플라즈마 젯 형상 확립방법과 EOS 상에서 활성종에 대한 결과를 확인하였다.

• Korea-Australia Rheology Journal
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• 제13권1호
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• pp.47-54
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• 2001

Prediction of the maximum packing volume fraction with non-spherical particles has been one of the important problems in powder technology. The sphericity of fly ash particles depending on the particle diameter was measured by means of a CCD image processing instrument. An algorithm to predict the maximum packing volume fraction with non-spherical particles is proposed. The maximum packing volume fraction is used to predict the slurry viscosity under well dispersed conditions. For this purpose, Simha's cell model is applied for concentrated slurry with wide particle size distribution. Also, Usui's model developed for aggregative slurries is applied to predict the non-Newtonian viscosity of dense fly ash - water slurry. It is certified that the maximum packing volume fraction for non-spherical particles can be successfully used to predict slurry viscosity. The pressure drop in a pipe flow is predicted by using the non-Newtonian viscosity of dense fly ash-water slurry obtained by the present model. The predicted relationship between pressure drop and flow rate results in a good agreement with the experimented data obtained for a test rig with 50 mm inner diameter tube. Base on the design procedure proposed in this study, a feasibility study of fly ash hydraulic transportation system from a coal-fired power station to a controlled deposit site is carried out to give a future prospect of inexpensive fly ash transportation technology.

• 한국진공학회지
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• 제19권4호
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• pp.243-248
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• 2010

진공용 기체 유동측정 표준기로 사용하고자 소닉노즐을 ISO 9300에서 제시한 사양에 맞추어 목직경 0.03 mm와 0.2 mm의 소닉 노즐을 제작하였다. 한국표준과학연구원에서 진공용 유량측정 장치로 개발된 정적형 유량계를 이용하여 제작된 2종의 소닉노즐의 유출계수를 확장불확도 3% 이내로 교정하였다. 교정된 소닉노즐의 유량 측정범위는 약 0.6~1,800 cc/min 범위를 갖는 것으로 나타났으며, 사용유동 조건에 해당되는 레이놀드 수(Reynolds number) 범위는 26~12,100으로 확인되었다. 이러한 결과는 교정된 소닉노즐을 이용하여 진공공정에서 필요한 극 미세 유량의 정밀측정을 가능하게 한 새로운 연구결과로 판단된다. 교정된 소닉노즐을 이용하여 진공펌프의 배기속도 측정결과는 기 구축된 정적법을 이용한 배기속도 측정결과와 1% 이내의 오차범위내로 매우 잘 일치함을 보였다. 교정된 소닉노즐은 향후 반도체 및 디스플레이 공정에 사용되는 다양한 건식 진공펌프들의 배기속도를 현장에서 간단하게 평가할 수 있는 현장 성능평가 장치에 활용할 예정이며, 현재 공정현장에서 배기속도 측정에 널리 사용중인 MFC를 대체할 수 있을 것으로 예상된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.302-307
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• 2004

The major flow-induced vibration mechanisms such as fluid-elastic and turbulence excitation can cause the various types of wear of the steam generator tubes in unclear power plant. It is generally accepted that the tube wear due to vibration is affected by the presence of gap clearance between tube and support plate. Connors showed that the tube wear depth could be estimated by using the relationship between wear volume and sliding distance for contact time. Au-Yang predicted the wear depth by using the nonlinear characteristics of normal work rate to contact time. In this study the effect of gap size on the steam generator tubes wear is analyzed by deriving the wear depth versus normal work rate relationship from these previous results.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.75-83
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• 2001

This paper presents the evaluation of combustion characteristics of sing-hole plasma jet ignitions in comparison with conventional spark ignition for variable of swirl velocity. Plasma jet plugs are three types according to ejecting directions : center of chamber, positive and negative swirl flow direction. Experiments are carried out for equivalent ratio 1.0 of LPG-air mixture in a constant volume cylindrical vessel. Not only the flame propagation is photographed at intervals, but the pressure variation in the combustion chamber is also recorded throughout the entire combustion process. The results show that the plasma jet ignitions and spark ignition enhance the overall combustion rate by increasing the swirl velocity. The dependence of the combustion rate swirl velocity leade to the conclusion that the placma jet plug, which ejects plasma jet to the cwnter of combustion chamber is the most desirable ignitor than other plugs.

• 한국지열·수열에너지학회논문집
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• 제12권4호
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• pp.40-46
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• 2016

In order to improve air quality of indoor environment, studies of the underfloor air distribution (UFAD) system for application in buildings are actively in progress based on temperature and air flow distribution. However, although the age of air is the major evaluation parameter, there has been very little study on this parameter for the UFAD system. In this study, we investigated the age of air to reach the air diffuser, which is installed at the bottom of the interior by the UFAD system. Computational fluid dynamics simulations showed no regular pattern to the maximum value of the age of air in accordance with air flow rate and the velocity at air diffuser. These factors can be deduced from air movement by considering that air emitted from air conditioners was rotated according to the bottom shape of the floor, and then, the age of air in the rotation center was increased. The average age of air of internal interior was reduced considerably as the flow velocity at the underfloor air diffuser was increased from 0.5 m/s to 1.0 m/s However, the age of air was not substantially affected with change in the air volume. Moreover, when the flow velocity at the underfloor air diffuser was higher than 1.0 m/s, the age of air showed no significant difference with change in air volume or height of measurement. These results imply that indoor air quality is more substantially influenced by flow velocity than air volume, and the appropriate flow velocity is 1 m/s or more.