• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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• pp.886-892
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• 2008

The development of fluid mechanics is briefly reviewed and the importance of fluid flows to heat and mass transfer in nature as well as to science and engineering is outlined. This paper presents the experimental results of air flow in the rectangular tunnel which has four different exhaust outlets, each distance of which from the inlet is 0, 30, 60 and 90mm respectively. This experiment is conducted by using the olive oil as the tracer particles and the kinematic viscosity of the air flow is $1.51{\times}10^{-5}\;m^2$/s. The flow is tested at the flow rate of 1.3 $m^3$/h and the velocity of 0.3 m/s. PIV technology can be used to make a good description of the smoke flow characteristics in the tunnel.

• Journal of Ship and Ocean Technology
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• 제4권1호
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• pp.11-20
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• 2000

Reynolds-averaged Navier-Stokes equations are numerically solved using a secondorder finite difference method for the analysis of turbulent flows around single and tandem hydrofoils advancing under the free surface. The location of the free surface, not known a priori, is computed from the kinematic free surface condition and the computational grid is conformed at each iteration to the free surface deformation. The eddy viscosity model of Baldwin-Lomax is employed for the turbulence closure. The method is validated through the comparision of the numerical results with the experimental data for a single hydrofoil of a Joukowski foil section. A computational study is also carried out to investigate the effect of the submergence depth and the Froude number on the lift and the drag of the hydrofoil. For tandem hydrofoils, computations are performed for several separation distances between the forward and aft foils to see the interference effect. The result shows clearly how the lift and drag change with the separation distance.

• 에너지공학
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• 제24권2호
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• pp.79-83
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• 2015

Hydrogen has long been recognized as a fuel having some unique and highly desirable properties, for application as a fuel in engines. Hydrogen has some remarkably high values of the key properties for transport processes, such as kinematic viscosity, thermal conductivity and diffusion coefficient, in comparison to those of the other fuels. Such differences together with its extremely low density and low luminosity help to give hydrogen its unique diffusive and heat transfer characteristics. The thermodynamic and heat transfer characteristics of hydrogen tend to produce high compression temperatures that contribute to improvements in engine efficiency and lean mixture operation.

• 에너지공학
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• 제24권2호
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• pp.84-90
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• 2015

Hydrogen has some remarkably high values of the key properties for transport processes, such as kinematic viscosity, thermal conductivity and diffusion coefficient. Hydrogen, as an energy medium, has some distinct benefits for its high efficiency and convenience in storage, transportation and conversion. Hydrogen has much wider limits of flammability in air than methane, propane or gasoline and the minimum ignition energy is about an order of magnitude lower than for other combustibles. Statistical thermodynamics provides the relationships that we need in order to bridge this gap between the macro and the micro. Our most important application will involve the calculation of the thermodynamic properties of the ideal gas.

• Tribology and Lubricants
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• 제10권1호
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• pp.78-88
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• 1994

For the study of chemical and mechanical properties of the synthetic and mineral oil added with two different Zn-DTPs, base and formulated oils were analyzed and compared. Kinematic viscosity and total acid number (TAN) were tested at high temperature for formulated oils. Also the oils added with different alkyl groups of Zn-DTP were tested for thermal stability and TAN changes. The 4-ball machine was used to test for the mechanical properties, such as the coefficient of friction and wear. The worn areas after sliding test were analyzed with microscope and EDX, too. From the study, mineral and synthetic oil have different effects according to the various added ratio of the primary and secondary alkyl groups of Zn-DTP. Also the temperature of test oil affected the anti-wear and friction property of the formulated oils. For synthetic oil, the primery alkyl group of Zn-DTP made better friction properties than that of secondary, while, for mineral oil, secondary alkyt group was better only at low temperature for mineral oil.

• 신재생에너지
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• 제3권2호
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• pp.17-23
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• 2007

대두유로부터 생산된 바이오디젤과 바이오디젤 혼합 연료유를 대상으로 지방산메틸에스터 함량과 화학적 분석을 통해 산화 특성과 오일의 수명 예측 연구를 수행하였다. 바이오디젤, 경유, BD5, BD20은 산화가 진행될수록 산가(Acid number), 동점도(Kinematic Viscosity) 및 밀도(Density)는 증가하였다. 산가 측정결과의 활용에 의해 임의의 온도조건에서 정확한 사용수명을 예측하기 위하여 화학속도론에 의거하여 각각의 연료에 대한 사용수명식을 도출하였다. 도출된 사용수명식으로부터 바이오디젤이 가장 빠르게 산화가 진행되었고 바이오디젤 혼합량이 증가할수록 사용수명이 단축되는 것을 확인할 수 있었다.

• 설비공학논문집
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• 제12권8호
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• pp.717-724
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• 2000

It is important to investigate characteristics of flow of refrigerant/oil mixture circulating in a refrigeration system. Therefore the oil concentration in refrigerant/oil mixture should be measured exactly by the adequate measuring instrument. In this paper, the oil concentration was measured by density monitoring system(DMS) in the liquid-line of a inverter-driven heat pump. Experimental result follows ; the main factor that have an effect on oil concentration refrigerant/oil mixture circulating in a refrigeration system is the momentum and kinematic viscosity of refrigerant/oil mixture compressed by scroll compressor.

• Journal of Magnetics
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• 제12권2호
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• pp.84-88
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• 2007

A micropump with spiral-type magnetic micromachine was fabricated. When a rotating magnetic field was applied, the machine rotated and pumped a surrounding liquid. We experimentally examined the basic properties of this pump. We found that the pressure and the flow rate could be controlled by the rotating frequency, and this pump could work under wide range kinematic viscosity. In addition, we proposed a disposable pump system using the machine. When a plate installed a fluid channel and the machine was set on a stage for generating a rotating magnetic field, the machine worked as the pump.

• 한국응용과학기술학회지
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• 제30권1호
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• pp.35-48
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• 2013

바이오디젤은 식물성유지, 동물성유지 그리고 폐식용유를 전이에스테르화 반응을 시켜 만들어진 것으로 경유를 대체할 수 있는 연료이다. 본 연구에서는 다양한 원료의 식물성유지 (대두유, 폐식용유, 유채유, 면실유, 팜유)로부터 얻어진 바이오디젤의 연료 특성을 알아보았다. 다양한 식물성유지 원료로부터 얻어진 바이오디젤은 지방산메틸에스테르 함량, 동점도, 인화점, 필터막힘점, 글리세린 함량을 분석하였다. 바이오디젤의 품질기준과 시험방법은 한국 표준과 유럽 표준인 EN14214에 따라 시험하였다. 대두유, 폐식용유, 유채유, 면실유 바이오디젤은 불포화지방산이 많이 포함되어 있는 반면에 팜유 바이오디젤은 포화지방산이 많이 함유되어 있다. 저온특성, 동점도, 산화안정도와 같은 바이오디젤의 연료 특성은 지방산메틸에스테르의 구성 성분과 관련이 깊다.

• 한국방재학회 논문집
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• 제6권1호
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• pp.83-95
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• 2006

본 연구는 강우시 소하천 수로구간에서 유사농도의 연직분포를 유사량 측정기 (ASM-IV)로 실측하여 그 특성을 분석하고자 한다. 이를 위해 충남 연기군 서면에 위치한 월하천 시점부분의 수로구간을 연구대상으로 선정하였다. 실측된 부유사농도의 분석자료는 상하류구간에서 각각 1시간 11분 30초 및 40분 32초 동안에 2초 간격으로 측정된 2,145개 및 1,216개중 16개씩의 시간구간 자료가 사용되었다. 분석한 결과, 상류구간의 실측치 Rouse 수는 $0.00129{\sim}0.02394$로 분포하고, 평균값은 0.01129로 나타났으며, 하류구간에서는 $0.00118{\sim}0.00822$, 평균값은 0.00436으로 하류의 값이 상류의 값보다는 훨씬 작게 분포하는 것으로 나타났다. 계산치 Rouse 수는 상류구간의 경우 $0.065115{\sim}0.065295$, 평균값은 0.06521로 나타났고, 하류구간의 경우에는 $0.057315{\sim}0.059109$, 평균값은 0.05795로 하류구간이 상류구간보다 약간 작은 값을 갖으나, 실측치 비교에서의 차이보다는 적게 나타났다. 그러나 실측치와 계산치의 비교에서는 상류구간보다 하류구간에서 더 큰 차이를 갖는 것으로 나타났는데, 이 오차는 하류구간의 침강속도 산정시 높은 수온에 대한 동점성계수 값을 본 연구에서 유도한 경험식으로 계산한 것도 원인중의 하나에 포함될 것이다.