• 대한기계학회논문집
• /
• 제12권4호
• /
• pp.833-846
• /
• 1988

본 연구에서는 후래시현상과 가열이 동시에 존재하면서 증발을 일으키는 수직 증발관내에서의 유동양식에 대해서, 우선 전기 프로우브를 이용하여 관내의 유동양식 에 따른 전기적 신호를 얻고, 시진실험 방법(photographic experimental method)을 통 하여 이를 확인한다. 또한, 전기 프로우브를 통하여 얻은 신호는 적절한 해석과정을 통해 수직 증발관내의 유동에 따른 기공률을 측정하는데 적용된다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.811-814
• /
• 2002

Using a mathematical theory, we show that the optimality condition of a turbulent diffuser with maximum pressure recovery at the exit is zero shear stress along the wall. The optimal diffuser shape is designed through iterative procedures by using the $k-{\varepsilon}-{\nu}^{2}-f$ turbulence model for flow simulation. The Reynolds number based on the bulk mean velocity and the channel height at the diffuser entrance is 18,000. We also perform large eddy simulation to validate the shape design results and investigate the flow characteristics near the zero-skin friction wall. Results from large eddy simulation show that the skin friction is slightly higher than zero but is still very small as compared to that of the flat plate boundary layer flow Although the time-averaged wall shear stress is slightly above zero along the diffuser wall, instantaneous flow reversals occur intermittently. The streamwise mein velocity shows an asymptotic behavior of the half-power-law near the wall where the skin friction is close to zero.

• 한국추진공학회지
• /
• 제3권3호
• /
• pp.25-30
• /
• 1999

본 연구는 보론 카바이드를 함유한 고체 연료를 사용하여 고체 램제트에서 공기 유속량에 따른 연소효율과 입자 크기의 분포를 실험적으로 조사하였다. 입자 분포는 그레인 끝 부분과 노즐 입구에서 MALVERN 2600 HSD를 사용하여 측정하였다. 연소 효율은 공기 유속량이 적을수록 연소 효율이 높은 것으로 나타났으며, 일반적으로 입자 분포는 대략적으로 4, 15와 25$\mu\textrm{m}$, 경우에 따라 2$\mu\textrm{m}$ 보다 적은 크기에서 한 곳을 포함하여 3곳의 피크치 또는 4 곳의 피크치를 나타내는 분포를 보였다. 큰 입자는 주로 재순환 영역에서 표면에서의 입자들의 뭉침의 결과이다. 흡입 공기의 온도가 높으면 연소 효율이 좋았는데 이는 확산 영역에서 연소하는 큰 보론 카바이드 입자의 연소 촉진 결과로 보인다.

• 한국분무공학회지
• /
• 제25권2호
• /
• pp.60-67
• /
• 2020

Despite its benefit in engine thermal efficiency, gasoline-direct-injection (GDI) engines generate substantial particulate matter (PM) emissions compared to conventional port-fuel-injection (PFI) engines. One of the reasons for this is that the spray collapse caused by the spray-to-spray interaction forms the locally rich fuel-air mixture and increases the fuel wall film. Previous studies have investigated the spray collapse phenomenon through the macroscopic observation of spray behavior using laser optical techniques, but it is somewhat difficult to understand the interaction between sprays that is initiated in the near-nozzle region within 10 mm from the nozzle exit. In this study, the spray structure, droplet size and velocity data were obtained using an X-ray imaging technique from the near-nozzle to the downstream of the spray to investigate the spray-to-spray interaction and discuss the effects of spray collapse on local droplet size and velocity distribution. It was found that as the ambient density increases, the spray collapse was promoted due to the intensified spray-to-spray interaction, thereby increasing the local droplet size and velocity from the near-nozzle region as a result of droplet collision/coalescence.

• 소성∙가공
• /
• 제15권8호
• /
• pp.544-549
• /
• 2006

In this work, we have employed the strain gradient plasticity theory to investigate the effect of material size on the deformation behavior in metal forming process. Flow stress is expressed in terms of strain, strain gradient (spatial derivative of strain) and intrinsic material length. The least square method coupled with strain gradient plasticity was used to calculate the components of strain gradient at each element of material. For demonstrating the size effect, the proposed approach has been applied to plane compression process and micro rolling process. Results show when the characteristic length of the material comes to the intrinsic material length, the effect of strain gradient is noteworthy. For the microcompression, the additional work hardening at higher strain gradient regions results in uniform distribution of strain. In the case of micro-rolling, the strain gradient is remarkable at the exit section where the actual reduction of the rolling finishes and subsequently strong work hardening take places at the section. This results in a considerable increase in rolling force. Rolling force with the strain gradient plasticity considered in analysis increases by 20% compared to that with conventional plasticity theory.

• 펄프종이기술
• /
• 제46권3호
• /
• pp.1-10
• /
• 2014

Offset paper printing is a promising roll-to-roll technique for color printed materials. Although it is no doubt that understanding ink transfer mechanism in offset printing process is necessary to achieve high printing quality, investing the relationship between inks and substrates at the nip is difficult experimentally due to high printing speed. In this paper, rheological behavior and splitting point of the ink at the nip is studied using package software Ployflow and Flow 3D based on Navier-Stokes equation. Polydimethylsiloxane (PDMS) ink and IGT printability tester were used for an model ink and experiment to compare with that of simulation data, respectively. As a result, higher viscosity at state flow and pressure increased ink transfer due to higher possibility of presence of cavitation at the nip and increase in covering area ratio. These results have shown good agreements with experimental data compared by measuring density of print through.

• International Journal of Automotive Technology
• /
• 제2권1호
• /
• pp.17-23
• /
• 2001

Measurements of the initial values lead to an inverse and mathematically unprecisely formulated problem. A precise definition of an inverse problem is possible. It is to state a mathematical model of a physical process with clearly defined initial and exit values for the system behind the process. One can grasp the idea of an inverse problem by considering the tire as a copy of the objects of nature in a room with observations. Interpretation of nature is generally a result of an inverse problem. On one hand, the tire may be represented through the sensory organs and the nervous system as well as the experiences of the developer's existing apparatus of the projection of reality. On the other hand, it may be represented by a physical law or a model that can be confirmed or is to be refuted with the help of suitable measurements. During reconstruction of a measuring signal and the identification of a black box that can be assumed to be linear and causal, the tire becomes a first type Volterra integral equation of the convolution type. But measurements of the initial values are always fuzzy, the errors grow and the system behavior can no longer be forecasted. Thus, we have to deal with a chaotic system. This chaos produces fractals in a natural way. These are self-similar geometric structures. This self-similarity is clearly visible in the design.

• 한국표면공학회지
• /
• 제31권2호
• /
• pp.81-90
• /
• 1998

NiCrAly/YSZ(8wt% Y2O3-Zro2) functionally fraded thermal barrier coating (FGC) layers on a Co-base sureralloy (HAYNESS 188) substrate were fabricated using Ar shielded single torch air plasma spraying method. Functional grading were produced with the stepwise compositional change throughout layer thinkness. Microstructural observation revealed a sucessful fabrication of NiCrAly/YSZ FGC. From the results of the curvature measurement, adhesive stength measurement and thermal shock test for the FGC, it was concluded that the optimum enhance of functionally graded coating layer thinkcess and compositional pattern exit to enhance the properties of FGC, which is closely reated to the internal residual distribution with it.

• 한국수소및신에너지학회논문집
• /
• 제27권6호
• /
• pp.727-736
• /
• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• 한국분무공학회지
• /
• 제19권2호
• /
• pp.75-81
• /
• 2014

Swirl flow in the gun type burner has a decisive effect on the stabilization of the flame, improvement of the combustion efficiency, and also a reduction of NOx. This swirl flow is created by the spinner which is inside the airtube that guide the combustion air. Gun type burner has generally the inner devices composed nozzle adapter, spark gap ignitor, and spinner. These inner components change the air flow behavior passing through air tube. Meanwhile, turbulent characteristics of this air flow are important to understand the combustion phenomena in the gun type burner, because the mixture of fuel and air are depended on. However, nearly all of the studies have been analyzed the turbulent flow of simplified combustion formation without the inner devices. So, this study conducted the measurement using by hot-wire anemometer and analyzed turbulent flow characteristics of the swirl flow discharged from the air tube with inner devices. Turbulence characteristics come up in this study were turbulence intensity, kinetic energy and shear stress of the air flow with the change of the distance of axial direction from the exit of the air tube.