• 한국유체기계학회 논문집
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• 제11권3호
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• pp.22-29
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• 2008

Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil and nuclear-fueled power plants to meet establishment of countermeasures against the global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power conversion system to capture the energy of ocean waves have been developed. However, suitable turbine type is not normalized yet because of relatively low efficiency of the turbine systems. The purpose of this study is to investigate the internal flow and performance characteristics of a cross-flow type hydro turbine, which will be built in a caisson for wave power generation. Numerical simulation using a commercial CFD code is conducted to clarify the effects of the turbine rotation speed and flow rate variation on the turbine characteristics. The results show that the output power of the cross-flow type hydro turbine with symmetric nozzle shape is obtained mainly from Stage 2. Turbine inlet configuration should be designed to obtain large amount of flow rate because the static pressure and absolute tangential velocity are influenced considerably by inlet flow rate.

• International Journal of Fluid Machinery and Systems
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• 제6권3호
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• pp.137-143
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• 2013

To improve annular jet pump (AJP) performance, new ways named constant rate of velocity/pressure change method (CRVC/CRPC) were adopted to design its diffuser. The design formulas were derived according to the assumption of linear velocity/pressure variation in the diffuser. Based on the two-dimensional numerical simulations, the effect of the diffuser profile and the included angle on the pump performance and the internal flow details has been analyzed. The predicted results of the RNG k-epsilon turbulence model show a better agreement with the experiment data than that of the standard and the realizable k-epsilon turbulence models. The AJP with the CRPC diffuser produces a linear pressure increase in the CRPC diffuser as expected. The AJP with CRPC/CRVC diffuser has better performance when the diffuser included angle is greater or the diffuser length is shorter. Therefore, the AJP with CRPC/CRVC diffuser is suitable for applications requiring space limitation and weight restriction.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.517-521
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• 2009

본 연구에서는 연소실의 축방향 압력과 속도변화를 도출할 수 있는 비정상 내탄도 해석모델을 개발하고 이를 바탕으로 산화제 변화에 따른 연소실 압력분포 변화를 해석할 수 있다. 개발 모델 검증을 위하여 연소실 전후단의 압력을 측정한 실험결과와 해석결과를 비교하여 실험과 해석결과가 유사함을 확인하였다. 하류방향으로 산화제 유량이 변하고 이는 연소실 압력 및 후퇴율, 연소가스 유속의 변화에 영향을 미침을 고찰하였다.

• 한국분무공학회지
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• 제4권3호
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• pp.32-41
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• 1999

In this research, internal-mixing twin-fluid atomizer using sonic energy is designed and manufactured. We are trying to intimate high efficiency twin-fluid atomizer to obtain good liquid atomization in the low pressure region. Define of geometric form of atomizer, characteristics of spray is influenced by position, depth and height variation of cavity resonator, variation of sound intensity and resonant sound frequency with liquid flow rate. The liquid atomization is promoted by multi-stage disintegration of mixing flow of gas with liquid and the optimum condition of position and depth of cavity resonator according to sonic energy is obtained from the condition at a=2.5mm and L=2mm. The velocity distribution of droplets shows negative value due to recirculation region at the center of axial, and as the radial direction distance is far, the velocity distribution of droplets decrease slowly after having a maximum value. However velocity and SMD show nearly uniform distribution at the down stream and as result compared to Nukiyama and Tanasawa's equation. atomization of mixing flow with air and liquid dispersing from the outlet of the nozzle is promoted by the effect of collision at the cavity resonator.

• 설비공학논문집
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• 제17권4호
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• pp.386-395
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• 2005

With the development of a living standard, the importance of indoor air conditioning system in all kinds of buildings and vehicles has increased. A lot of researches on energy losses in a duct and various kinds of flow pattern in branches or junctions have been carried out over many years, because the primary object of a duct system used in HVAC is to provide equal flow rate in the interior of each room by minimizing pressure drop. In this study, to get equal flow distribution in each branch, a blockage is applied to the rectangular duct system. The flow analysis for flow distribution of a rectangular duct with two branches was performed by CFD. By using SIMPLE algorithm and finite volume method, flow analysis is performed in the case of 3-D, incompressible, turbulent flow. Also, the standard $k-{\varepsilon}$ model and wall function method were used for analysis of turbulent fluid flow. The distribution diagrams of static pressure, velocity vector, turbulent energy and kinetic energy in accordance with variation of Reynolds number and blockages location in a rectangular duct show that flow distribution at duct outlets is improved by a blockage. In this rectangular duct system, mean velocity and flow rate distribution in two branch outlets are nearly constant regardless of variation of Reynolds number, and a flow pattern of the internal duct has a same tendency as well.

• 고려인삼학회:학술대회논문집
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• 고려인삼학회 1988년도 학술대회지
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• pp.87-91
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• 1988

고혈압 치료제를 투여한 19명의 고혈압환자에게 홍삼을 매일 3g씩 3개월간 투여하고 혈압과 생활상태를 조사하였다. 홍삼투여기간중에는 수축기 혈압이 현저히 감소하였으나, 이완기혈압과 심장박동에는 변화가 없었다. 환자 중 $89\%$가 생활상태가 현저히 개선되었는데 그중 불면, 갈증, 피로감, 기분, 성생활과 일반적인 상태등이 두드러졌다. 더욱이 이 기간 중에서 R-R 간격 변화계수가 개선되었다. 그러나 홍삼투여를 중단한 1개월 후에는 수축기 혈압과 생활상태를 나타내는 인자 등이 투여전의 상태로 다시 악화되었다. 이러한 결과로서 홍삼은 수축기 혈압을 저하시키며 고혈압 치료제를 투여한 환자에 있어서 생활상태를 개선시키는 것으로 사료된다.

• 한국수소및신에너지학회논문집
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• 제33권5호
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• pp.550-556
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• 2022

In this study, the flow uniformity was analyzed by performing numerical analysis on the 1 kWe internal manifold type solid oxide fuel cell stack according to the channel height of the separator. Also, it was examined by varying the fuel utilization rate and oxygen utilization rate. From the calculation results, we found that as the channel height of the separator decreased, the pressure drop increased exponentially. In addition, it was found that as the channel height of the separator decreased, the gas flow resistance inside the unit cell increased, and the flow resistance increased the pressure drop, thereby improving the flow uniformity inside the stack. Finally, the calculation results showed that as the fuel and oxygen utilization increased, the flow uniformity also improved.

• 한국추진공학회지
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• 제16권1호
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• pp.9-15
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• 2012

하이브리드 연소실의 국부 압력과 속도변화를 고려하는 비정상 내탄도 해석모델을 제안하고 이를 바탕으로 연소실 내 국부영역에서 내탄도 특성인자의 변화를 도출하였다. 해석 모델 검증을 위하여 연소실 전후단의 압력을 측정한 실험결과와 해석결과를 비교하여 실험과 해석결과가 유사함을 확인하고 연소 효율을 평가 하였다. 하류방향으로 산화제 유량이 변화하므로 이에 따른 연소실 국부영역의 압력, 온도, 연료의 후퇴율 및 연소가스의 유속 변화를 정량적으로 고찰하였다.

• 한국유체기계학회 논문집
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• 제9권2호
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• pp.19-24
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• 2006

Nano fountain-pen is a novel device to make the constant patterning in micro process using new designed probe. Fountain-pen nanolithography (FPN) is applied for constant supply of liquid in conjunction of patterns and surface variation in the micro process. In this study, nuo fountain-pen is composed with reservoir, micro channels, tip and scondary chamber. Instead of traditional method only using capillary force, liquid can be definitely and exactly injected with membrane pumping by the repulse force of tip. It is dfficult to perform experiments in the micro range so that we carried out a numerical analysis for internal flow, using a commercial code, FlUENT, The velocity, pressure and flow rate are obtained under laminar, unsteady, three-dimensional incompressible flow with no-slip condition, and results are graphically described.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.19-24
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• 2000

Stress corrosion crack growth is simulated after assuming a small axial surface crack inside a S/G tube. Internal pressure and residual stresses are considered as applied forces. Stress intensity factors along crack front, variation of crack shape and crack growth rate are obtained and discussed. It is noticed that the aspect ratio of the crack is not depend on the initial crack shape but depend on the residual stress distribution.