• Tribology and Lubricants
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• 제27권6호
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• pp.338-343
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• 2011

Laser surface texturing (LST) methods are widely applied now to reduce friction and improve reliability of machine components such as thrust bearings, mechanical face seals and piston rings, etc. In this paper, the effect of dimple shapes on the lubrication characteristics of parallel thrust bearing are studied using a commercial computational fluid dynamics (CFD) code, FLUENT. Pressure and streamline distributions, variations of supporting load, leakage flow rate and friction force, are compared for three different dimple sectional shapes such as circle, pyramid and rectangle type. The lubrication characteristics are highly affected by dimple shapes and number of dimples. The pyramid type dimple shape can support the highest load while the rectangle type is the best in friction reduction.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.46-55
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• 2004

Thermal characteristics of the various cooling methods in electronic equipment are studied numerically. A common chip cooling system is modeled as a parallel channel with protruding heat sources. A two-dimensional model has been developed for the numerical analysis of compressible. viscous. laminar flow. and conjugate heat transfer between parallel plates with uniform block heat sources. The finite volume method is used to solve this problem. The assembly consists of two channels formed by two covers and one printed circuit board that is assumed to have three uniform heat source blocks. Various cooling methods are considered to find out the efficient cooling method in a given geometry and heat sources. The velocity and the temperature fields. the local temperature distribution along the surface of blocks. and the maximum temperature in each block are obtained. The results are compared to examine the thermal characteristics of the different cooling methods both quantitatively and qualitatively.

• 한국정밀공학회지
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• 제21권9호
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• pp.103-110
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• 2004

Pressure ripples yield noise and vibration in hydraulic pipelines, which are inevitably generated by a fluctuation of flow rate in the pump mechanism, and such noise and vibration deteriorate the stability and accuracy of hydraulic systems. To reduce the pressure ripples, accumulator and hydraulic attenuator are normally used. In this study, parallel pipeline with a bent-axis piston pump is introduced to a hydraulic pipe system as a method for reducing the pressure ripples and using the transfer matrix method, the dynamic characteristics of the pipe system are analysed and compared with experimental results. The results show that the phase interference using parallel pipeline with a bent-axis piston pump is effective to reduce the pressure ripples in the hydraulic pipelines.

• 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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• 제18권9호
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• pp.687-697
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• 2006

The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as mass flux, and quality are investigated, and the results are compared with the previous 30 channel results. The flow at the header inlet is annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted geometry, significant portion of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, different from the downward configuration, significant portion of the water flows through the rear part of the header. The effect of the protrusion depth is the same as that of the downward flow. As the protrusion depth increases, more water is forced to the rear part of the header. However, the effect of mass flux or quality is opposite to the downward flow case. As the mass flux or quality increases, more water flows through the frontal part of the header. Compared with the previous thirty channel configuration, the present ten channel configuration yields better flow distribution. Possible explanation is provided from the flow visualization results.

• 대한기계학회논문집B
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• 제26권1호
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• pp.159-169
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• 2002

The present study investigates in detail the combined effects of the Coriolis and centrifugal farce on the development of laminar flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a rotating curved region, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal farce due to the curvature of U-bend. When the values of Rossby number and curvature ratio are large, the flow field in a rotating U-bend can be represented by two dimensionless parameters ; the Dean number K$\_$LC/=Re/√λ and a body ratio F=λ/Po. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards, the directions of the two secondary flows are the same. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct with a larger f7c. On the other hand, in case of negative rotation, where two farces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces.

• 한국전산구조공학회논문집
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• 제22권6호
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• pp.639-646
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• 2009

고유동 강섬유보강 모르타르는 타설과정에서 특정한 섬유 방향성 분포를 가질 수 있으며, 이에 따라 재료의 인장거동 특성에 영향을 미칠 수 있다. 본 연구에서는 고유동 강섬유보강 모르타르의 타설단계에서의 유동에 따른 강섬유의 섬유 방향성 분포의 변화를 해석적으로 구하였다. 해석결과에 따르면 180mm 간격으로 나란히 놓여진 두 평판 사이에 흐르는 모르 타르의 전단흐름에 의한 섬유의 방향성 변화는 초기 150mm이내에서 크게 발생하는 것을 확인할 수 있었으며, 이후에서는 방향성 분포의 경향은 크게 변하지 않으며, 다만 흐름방향에 나란한 섬유의 밀도가 집중적으로 커지는 것을 볼 수 있었다. 섬유의 방향성과 섬유보강 복합체의 인장거동과 밀접한 관련성을 고려할 때, 이와 같은 방향성의 예측을 바탕으로 유동에 따른 고유동 강섬유보강 모르타르의 인장거동 변화의 예측이 가능할 것이다.

• 대한기계학회논문집
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• 제15권6호
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• pp.1948-1966
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• 1991

본 연구에서는 2상 횡유동을 받는 튜브군의 진동 메카니즘을 규명하기 위한 실험계획의 일환으로 실시된 실험으로부터 튜브군의 유체탄성 불안정성 상수에 관해 고찰하였다. 실험은 먼저 p/d=1.47 및 1.32 튜브군에 대해 수행되었는데, 이들 튜브 군의 결과는 참고문헌에 발표하였다. 본 논문은 후속 실험으로 수행된 p/d=1.22인 튜브군을 사용하여 유체탄성 불안정성 상수를 고찰한 참고문헌의 후속논문이다. 실 험은 액체상태로 부터 99% 보이드율(void fraction)까지 변화된 2상 유동에서 튜브가 유체탄성 불안정성 상태에 도달할 때까지 점진적으로 증가하였다.실험결과는 p/d= 1.32 alc 1.47 튜브군의 유체탄성 불안정성 결과들과 종합. 비교되었다.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1821-1833
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• 2021

The gas-liquid counter-current flow limitation (CCFL) is closely related to efficient and safety operation of many equipment in industrial cycle. Air-water countercurrent flow experiments were performed in a tube with diameter of 25 mm to understand the triggering mechanism of CCFL. A parallel electrode probe was utilized to measure film thickness whereby the time domain and frequency domain characteristics of liquid film was obtained. The amplitude of the interface wave is small at low liquid flow rate while it becomes large at high liquid flow rate after being disturbed by the airflow. The spectral characteristic curve shows a peak-shaped distribution. The crest exists between 0 and 10 Hz and the amplitude decreases with the frequency increase. The analysis of visual observation and characteristic of film thickness indicate that two flooding mechanisms were identified at low and high liquid flow rate, respectively. At low liquid flow rate, the interfacial waves upward propagation is responsible for the formation of CCFL onset. While flooding at high liquid flow rate takes place as a direct consequence of the liquid bridging in tube due to the turbulent flow pattern. Moreover, it is believed that there is a transition region between the low and high liquid flow rate.

• 한국해안·해양공학회논문집
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• 제29권3호
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• pp.139-146
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• 2017

해안선 변동을 제어하기 위해 설치되는 잠제의 효과를 이해하기 위해 해안선과 평행한 단일 잠제 주변 연안의 흐름변화 특성을 수리실험을 통해 연구하였다. 잠제와 입사파 파라미터에 따른 잠제 후면의 흐름패턴을 관측하기 위해 LSPIV(Large-Scale Particle Image Velocimetry) 이미지 분석 기법을 적용하였고, 잠제 주변의 역학적 특성을 파악하기 위해 평균수면 및 파고분포를 관측하였다. 수리실험을 통해 흐름패턴은 잠제에 의한 파고(파랑응력) 분포변화와 그에 따라 발달하는 잠제 후면과 측면 쇄파유도류 및 평균수면상승효과의 상호작용에 의해 변화됨을 알 수 있었다. 잠제 주변의 분기 또는 수렴하는 흐름패턴에 따라 각각 해안선 변동을 침식 또는 퇴적반응으로 구분하는 Ranasinghe et al.(2010)의 경험식과 수리실험 결과를 비교하여, 전반적으로 경험식에 부합하는 흐름패턴을 확인할 수 있었다. 그러나 일부 실험결과에서 기존의 경험식을 적용하여 구분하기 어려운 침식과 퇴적이 혼재된 반응을 유도하는 흐름패턴도 관찰할 수 있었다.