• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1756-1766
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• 2003

Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed.

• Tribology and Lubricants
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• v.16 no.2
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• pp.75-83
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• 2000

The present paper proposes a new type of an electro-rheological squeeze film damper (ER SFD) of which the damping capacity can be controlled by the application of electric field. The new ER .SFD- is sealed with slotted rings having electrodes at the inside of the constant gap. The ER SFD can provent the problem of electric short which might be occurred in a previous ER SFD. Reynolds lubrication equation for a Newtonian fluid and the end leakage equation for ER fluids are numerically solved to get the pressure distributions and the damping coefficients of the ER SFD. The results show that the damping coefficients greatly increase with increasing the yield shear stress of ER fluid. In addition, the unbalance response analysis of a flexible rotor supported on the new ER SFD implies that the rotor system can be operated with the minimum of rotor amplitude and force transmissibility by controlling the yield shear stress of ER fluids properly.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.294-301
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• 2005

The instabilities in rocket engines and gas turbine combustors due to the interaction between the fluid flow (acoustics) and the heat transfer (thermal energy) are called thermoacoustic or combustion instabilities. Almost all analysis assumes constant hot section temperature for Modern mathematical analysis of acoustic oscillations in Rijke type devices. However, it is impossible to predict whether a system is stable or not because the flame or heater response model can have a dramatic effect on predicted growth rates. In this study, A standard ${\kappa}-{\varepsilon}$ turbulent model and hybrid combustion model(eddy breakup model and chemical reaction) were used. After steady solution was gotten, unsteady calculation is simulated by perturbating on pressure boundary. As a result, we obtained the relationship of equivalence ratio and frequency by numerical simulation, and they are comparable to the experimental result. In addition, in spite of these results, there are limitations of using turbulent and combustion model in simulation method of thermoacoutic instability

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.191-196
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• 2009

Experiments were conducted in a constant pressure combustion chamber using schlieren system to investigate the effects of carbon dioxide/nitrogen/helium diluents on cellular instabilities of syngas-air premixed flames at room temperature and elevated pressures. Laminar burning velocities and Markstein lengths were calculated by analyzing high-speed schlieren images at various diluent concentrations and equivalence ratios. Experimental results showed substantial reduction of the laminar burning velocities and of the Markstein lengths with the diluent additions in the fuel blends. Effective Lewis numbers of helium-diluted syngas-air flames increased but those of carbon dioxide- and nitrogen-diluted syngas-air flames decreased in increase of diluents in the reactant mixtures. With helium diluent, the propensity for cells formation was significantly diminished, whereas the cellular instabilities for carbon dioxide-diluted and nitrogen-diluted syngas-air flames were not suppressed.

• Journal of ILASS-Korea
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• v.5 no.4
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• pp.33-39
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• 2000

The behavior of the 2-stage spray was studied by using the schlieren method with the high pressure common-rail injection system. The spray injected 2 times with the interval of $0.3ms{\sim}1.5ms$ between the 1st and the 2nd spray in a modeled combustion chamber of constant volume bomb. In this case, the quantity of injected fuel of 1st and 2nd also changed. The schlieren photograph shows that the 2nd spray goes further away than the 1st spray when the quantity of the 1st spray is less than that of the 2nd spray. The dispersion of the vapour to the combustion chamber is not affect in a 10% of 1st spray quantity. When the 1st spray quantity is more than the 2nd spray, the vapour scattering of spray is good.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.482-487
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• 2001

Leaf type foil bearings have been used successfully in many aerospace applications such as air cycle machines, turbocompressors and turboexpander. These applications are characterized by light loads, constant speeds and low to moderate temperatures. But, as system on start-up or shutdown, sliding contact between the shaft and foil surfaces cause wear. So, in present study, to understand pressure-flow characteristics and deformation of foil bearing, flow/structure interaction analysis was used. and using this method, 2D and 3D calculation was peformed for shape of foil bearing to know circumferential direction flow and leakage flow characteristics of axial direction.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.170.1-170
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• 2001

This paper developed the model for electro hydraulic force control system by identification method via ARMAX model. Implementation of Identification is performed on Pin-On-Disk type tribotester. The wear mechanism is an important mechanic property to select a material´s life and a optimum work condition. Pin-on-disk type tribotester is popular wear analysis experimental equipment and its mechanism is that adding a force on a rotating disk to simplify two surface contact´s wear experimental condition. Material´s rotating velocity and eccentricity rotation makes disturbance and it affects adding constant force. To get a high performance of force adding part, DDV(Direct Drive Valve) which has pressure control loop is used. To obtain a tribotester´ s ARMAX model, prediction error method(PEM) is used in case force adding part and rotating part is ...

• Journal of ILASS-Korea
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• v.13 no.2
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• pp.65-72
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• 2008

It is recognized that alternative fuel such as dimethyl ether (DME) has better combustion polluting characteristics than diesel fuel, even though the cetane number of DME is almost the same as that of diesel. Characteristics of DME spray were observed experimentally under various ambient conditions using a constant volume chamber and a common-rail injection system. N-dodecane and LPG fuel sprays were also observed under same conditions of DME spray. Using spray images from backlight scattering and Mie scattering, characteristics of fuel sprays such as penetration and spray volume were visualized and quantitatively measured. The measurements showed that the penetration of early period decreased remarkably, because evaporation of alternative fuels became prosperous by the influence of flash boiling phenomenon under the condition of the low temperature and pressure compared with n-dodecane. The penetration of DME and LPG spray received the influence of temperature more largely in comparison with low density, because the specific surface area increased by atomizing in high density.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.69-72
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• 2003

The purpose of this study is the development of hybrid horizontal electrokinetic(EK) remediation system on rifle range soil under unsaturated conditions. In order to remediate soil polluted by multi-species heavy metals, in pi]of scale, a series of EK remediation tests are carried out. PVC and PDB(Plastic Drain Board) electrode systems that connected with the power supply of constant voltage and vacuum pressure of 0.5kgf/$\textrm{cm}^2$ are installed, The test results showed that the pH distribution in the sample is below 8, which is maintained until the test is finished, because of the injection of flushing solution. The final concentration, which is normalized by initial concentration, is ranged about 50 to 90%.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.329.1-329.1
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• 2014

In this paper, we report electrical, optical and structural properties of Al-doped zinc oxide (AZO) thin films deposited at different substrate temperatures and pressures. The films were prepared by radio frequency (RF) magnetron sputtering on glass substrates in argon (Ar) ambient. The X-ray diffraction analysis showed that the AZO films deposited at room temperature (RT) and 20 Pa were mostly oriented along a-axis with preferred orientation along (100) direction. There was an improvement in resistivity ($3.7{\times}10^{-3}{\Omega}-cm$) transmittance (95%) at constant substrate temperature (RT) and working pressure (20 Pa) using the Hall-effect measurement system and UV-vis spectroscopy, respectively. Our results have promising applications in low-cost transparent electronics, such as the thin-film solar cells and thin-film transistors due to favourable deposition conditions. Furthermore our film deposition method offers a procedure for preparing highly oriented (100) AZO films.