• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.1
• /
• pp.69-81
• /
• 1999

In this research computational methods for the droplet atomization and spray wall impingement are studied for the non-evaporating diesel fuel spray. The TAB(Taylor Analogy Breakup) model and Wave model are compared with experiments in order to describe droplet atomization process. The Watkins model and O'Rourke model are compared to simulate the spray wall impingement. As a result, It is found that the application of the Wave model has a good agreement with the experimental data in the case of high pressure injection. With regard to wall Impingement phenomena, it is found that the Watkins model is appropriate to the high temperature cylinder wall condition, while the O'Rourke model is appropriate to cold starting problem.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.23 no.2
• /
• pp.288-298
• /
• 1999

In spark ignited engines, the electrical spark not only sets the time for the onset of combustion but also is able to greatly influence the character of the initial flame growth and the subsequent combustion, and thereby can influence engine performance. The relative importance of the ignition energy is particularly high under lean or high residual gas or exhaust gas recirculation (EGR). In this study, a modeling of flame Initiation and its development is proposed. Submodels consist in representing of cylinder pressure and temperature, heat transfer to cylinder wall, and flame kernel heat transfer to ambient air and to spark plug electrodes. The breakdown process and the subsequent electrical power input initially control the kernel growth while intermediate growth is mainly dominated by diffusion or conduction. Then, the flame propagates by the chemical energy, and laminar and turbulent flame velocity.

• Journal of Ocean Engineering and Technology
• /
• v.16 no.5
• /
• pp.56-60
• /
• 2002

본 논문은 고온 고압의 유류 수송용 이중배관의 팽창에 대한 해석적 방법에 대한결과고찰과 해석, 그리고 설계시 응용이 가능한 현상에 대해 논하였다. 고온의 유류수송시 온도를 유지할 목적으로 내부의 수송 배관과 외부의 케이싱 배관사이에 절연체가 쓰여진다.이런 이중배관의 팽창을 조사할 수 있는 간단한 해석적 방법이 개발되었다. 본 논문에서는온도의 분포, 입력, 토질의 저항, 수송배관과 케이싱 배관과의 상호작용 등이 고려되어졌으며, 이 해석적 방법은 심해의 이중배관 해석에 적합하게 개발되었다. 계산의 결과 분석에서고온의 영향이 고압보다 현저한 것이 밝혀졌다.

• Proceedings of the KIEE Conference
• /
• 2004.07d
• /
• pp.2260-2262
• /
• 2004

After steam turbines in power plant drives generator and maintains it at rated speed using high temperature and high pressure steam energy, they regulate the output of generator when synchronized in parallel with the power system. By the way, as the steam flow into turbine can not be reduced fast even though the electrical load is lost, the turbine gets into dangerous situation due to the increase of its speed. At this time, the duty of the turbine governor is "how to limit the speed within its overspeed trip setpoint and escape from danger." For the purpose of it, there are various ways known. Some overspeed protection methods for steam turbines now being operating in korea are introduced in this paper.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1069-1072
• /
• 2003

Ultraviolet-nanoimprint lithography (UV-NIL) is a promising nanoimprint method for cost-effectively defining nanometer scale structures at room temperature and low pressure. Nanostamp fabrication technology is a key technology for UV-NIL because fabricating a high resolution nanostamp is the first step for defining high resolution nanostructures in a substrate. We used quartz as an UV transparent stamp material for the UVNIL. A $5{\times}5{\times}0.09$ inch stamp was fabricated using the quartz etch process in which Cr film was used as a hard mask for transferring nanostructures into the quartz. In this paper, we describe the quartz etching process and discuss the results including SEM images.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1458-1462
• /
• 2003

High temperature and high pressure heavy water flows through the pipes in atomic power plants. The curved parts of pipes are critical parts in that they change the direction of steam flow, and these parts are especially affected by severe wear. Therefore, most pipes in atomic power plants are tested by non-destructive examination by workers who use ultrasonic sensors to measure the wall thickness of pipes. But not only are these pipes located in a very dangerous environment, but the space is also very limited. For the safety of workers, it is necessary to design a device that uses a mobile robot that can inspect curved pipes. This paper presents the design and construction of a small device that can generate the necessary contact forces between ultrasonic sensors and pipe walls in a limited space. And a mobile robot is used in place ortho worker for successful non-destructive examination.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.8 s.173
• /
• pp.159-164
• /
• 2005

The Hot Embossing Lithography(HEL) as a method fur the fabrication of the nanostructure with polymer is becoming increasingly important because of its simple process, low cost, high replication fidelity and relatively high throughput. In this paper, we carried out experimental studies and numerical simulations in order to understand the viscous flow of the polymer (PMMA) film during the hot embossing process. To grasp the characteristics of the micro patterning rheology by process parameters (embossing temperature, pressure and time), we have carried out various experiments by using the nickel-coated master fabricated by the deep RIE process and the plasma sputtering. During the hot embossing process, we have observed the characteristics of the viscoelastic behavior of polymer. Also, the viscous flow during the hot embossing process has been simulated by the continuum based FDM(Finite Difference Method) analysis considering the micro effect, such as a surface tension and a contact angle.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.487-492
• /
• 2001

The Multi-bubble sonoluminescence(MBSL) provides a unique environment, that is, very high temperature$(5,000\sim20,000K)$ and high pressure$(500\sim10,000\;atm)$. However, the mechanism for the MBSL has been elusive. Recently, it has been suggested that the mechanism be continuous and also of discrete peaks that are caused by molecular transitions. In this article, this mechanism has been examined for the Ar/water system by the combined hydrodynamics and molecular transition.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.5 no.4
• /
• pp.338-346
• /
• 1981

Honing, lapping, polishing and superfinishing are applied for a precision machining to finish the metal surface, but these precision machining are micro-cutting by hard and micro-abrasive grains. Frictional machining is the new method to finish mirrorlike surface without using those abrasive grains. The frictional machining produces high pressure and high temperature instantly by compressing a tool material against the metal surface in sliding motion. The metal surface is given plastic deformation and plastic flow by the above mentioned frictional motion, but the surface roughness of the metal surface is influenced by physical and chemical reaction in surrounding atmosphere. Therefore, the atmosphere around the metal optimum atmosphere in the frictional machining. The part 1 of the study was performed in liquid atmospheres. Diesel oil, lubricant, grease, lard oil, bean oil and cutting fluid were used as such atmospheres. Medium carbon steel SM 50 C was used as a workpiece and ceramic tip was applied as a frictional tool. The result of the experiment showed characteristic machining conditions to generate the best surface roughness in each atmospheres.

• Journal of ILASS-Korea
• /
• v.2 no.4
• /
• pp.1-6
• /
• 1997

In the case of analyzing the combustion phenomena in a small high speed DI diesel engine, one demands the experimental results of the impinging spray on the wall as a basic characteristics. In the experiments presented here, diesel fuel oil was injected into a high pressure chamber in which compressed air at room temperature was charged. The single spray was impinged on a flat wall. The growth of the spray was photographed with transmitted light or scattered light. The effect of the spray axis angle to the wall on the impinging spray was revealed. Finally, the experimental results was presented, that is, the radius and height of the impinging spray was influenced by above mentioned variable.