• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.72-83
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• 2017

A thermo-fluid dynamic analysis was performed through the numerical simulation of a missile canister. Calculation was made in a fixed analytical volume and fully evaporated water was used as a coolant. To analyze the interaction among the hot gas, coolant, and mixture flow, Realizable $k-{\varepsilon}$ turbulence and VOF(Volume Of Fluid) model were chosen and parametric study was performed with the change of coolant flow rate. It could be found that the pressure on the canister top nonlinearly increased with the increase of coolant flow rate. Temperature and coolant distribution were closely related to the flow behavior in canister. Temperature on the canister bottom indicated a decrease being proportional to coolant flow rate in early times but after a specific time, the temperature increased with the tendency being reversed. In addition, the early part of temperature showed a fluctuating phenomenon because of the overall circulatory flow of mixture gas.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.5
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• pp.37-44
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• 1998

Lean burn combustion is an important concept for improving the fuel consumption and exhaust emissions. However, the lean burning is associated with increased cycle-to-cycle combustion variations due to the ignition instabilities and redu- ced flame propagation rates. Engine stability under lean mixture conditions could be improved by increasing flame speed through enhanced flow characteristics and by securing ignitability with improvement of ignition systems. The effects of flow motion and ignition characteristics on the combustion performances were investigated in a 4-valve SI engine. Flow motions of tumble-swirl were varied with a swirl control valve attached at the inlet ports, while ignition energy and its distribution were controlled in a high -frequency ignition system by changing spark duration and spark frequency. The improvement of lean burn performance by the optimum flow motion and ignition characteristics is discussed.

• Journal of ILASS-Korea
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• v.23 no.4
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• pp.159-168
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• 2018

Thrust throttling in a liquid rocket engine can be implemented via several ways such as high pressure drop injector, dual manifold, multiple chamber, pintle injector, and gas injection. Thrust throttling using gas injection controls thrust by usually injecting inert gas into propellant through an aerator to reduce the propellant's bulk density. In this study, the outside-in aerator was used in the propellant line to create two phase flow. Closed-type, open-type, and screw-type bi-swirl coaxial injectors were utilized for investigating throttling characteristics such as pressure drop, mixture density, and discharge coefficient according to gas-liquid mass ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.94-97
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• 1997

We investigated the sheet resistance properties of tungsten nitride thin films deposited by RF and DC sputtering system. It deposited at various conditions that determine the sheet resistance. The properties of the sheet resistance of these films were measured under various conditions. Sheet resistance analysed under the flow rate of the argon gas and contents of nitrogen from nitrogen-argon gas mixtures. We found that these sheet resistance were largely depend on the temperature of substrate, gas flow rate and RF power. Very high and low sheet resistance of tungsten films obtained by DC sputtering. As the increase of contents of nitrogen gas obtained from nitrogen-argon gas mixture, tungsten nitride thin films deposited by the reactive DC sputtering and the sheet resistance of these films were increased.

• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.139-146
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• 2001

The experimental study was carried out for the diffusion flame characteristics of second stage combustor with the variations of temperature and supplying rate of hot exhaust gas from first stage combustor. It also examined the flame structure and NOx formation of the second stage combustor in which the fuel(natural gas) is supplying into the mixture of oxygen hot exhaust gas from first stage combustor. The results show that the increasement of temperature and flow rate of exhaust gas lead to increase the NOx up to 30ppm with 19% $O_2$ condition

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.9-12
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• 2015

NbN thin films were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an $Ar-N_2$ gas mixture. Total sputtering gas pressure was fixed while varying $N_2$ flow rate from 1.4 sccm to 2.9 sccm. X-ray diffraction pattern analysis revealed dominant NbN(200) orientation in the low $N_2$ flow rate but emerging of (111) orientation with diminishing (200) orientation at higher flow rate. The dependences of the superconducting properties on the $N_2$ gas flow rate were investigated. All the NbN thin films showed a small negative temperature coefficient of resistance with resistivity ratio between 300 K and 20 K in the range from 0.98 to 0.89 as the $N_2$ flow rate is increased. Transition temperature showed non-monotonic dependence on $N_2$ flow rate reaching as high as 11.12 K determined by the mid-point temperature of the transition with transition width of 0.3 K. On the other hand, the upper critical field showed roughly linear increase with $N_2$ flow rate up to 2.7 sccm. The highest upper critical field extrapolated to 0 K was 17.4 T with corresponding coherence length of 4.3 nm. Our results are discussed with the granular nature of NbN thin films.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.165-171
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• 1999

Diamond-like carbon(DLC) films were synthesized using the rf-plasma CVD technique with the addition of small amounts of nitrogen and oxygen to a gas mixture of $CH_4$ and $H_2$. The gas flow ratio of $CH_4$ to $H_2$ was 2.4:1, and 3% , 13.6% of nitrogen were added to the gas mixture of $CH_4$ and $H_2$ for the deposition of DLC films. The film stress tended to decrease as the nitrogen concentration increased from 3% to 13.6%, probably due to the decrease of the number of the interlink between carbon atoms. The residual stress tended to slightly decrease when 3% of oxygen was added. Scratch tests were performed to investigate the adhesion between the DLC films and the Ti intelayer after pretreating the TiN surface with direct hydrogen plasma. The adhesion was enhanced by adding nitrogen and oxygen to the $CH_4$ and $H_2$ gas mixture. The adhesion for the 3% nitrogen addition was better than that for the 13.6% nitrogen addition. The Vicker's hardness of the DLC films was measured to be 1100Hv.

• Journal of Surface Science and Engineering
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• v.18 no.1
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• pp.5-11
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• 1985

Titanium was deposited onto AISI-430 stainless steel by chemical vapor deposition from $TiI_4\;and\;H_2$ gas mixture. Effects of temperature, flow rate of the gas, and $TiI_4$ partial pressure on the deposition rate were thoroughly investigated. The deposition rate of Ti was found to be constant at the given temperature and was increased with increasing temperature. The rate is controlled by surface reaction at the flow rate of gas higher than 500 ml/min, whereas at the flow rate lower than that by diffusional process. It is also interesting to note that the reaction mechanism changes at 1050$^{\circ}C$, at temperatures lower than 1050$^{\circ}C$ the activation energy is 56.9 Kcal/mol, whilst at temperatures higher than that is 8.3 Kcal/mol.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.42-48
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• 2007

An inert gas atomized NiTiZrSiSn bulk metallic glass feedstock was sprayed onto the copper plate using vacuum plasma spraying process. In order to change the in-flight particle energy, that is, thermal energy, the hydrogen gas flow rate in plasma gas mixture was increased at the constant flow rate of argon gas. Coating and single pass spraying bead were produced with the least feeding rate. Regardless of the plasma gas composition, fully melted through unmelted particle could be observed on the overlay coating. However, the frequency of the unmelted particle number density was increased with the decrease of the hydrogen gas flow rate. The amorphous phase fraction within coating was also affected by the number density of the unmelted particle.

• Membrane Journal
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• v.4 no.4
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• pp.197-204
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• 1994

In this study, permeation characteristics of pure $CH_4,\;CO_2$ and $CH_4/CO_2$ gas mixture were examined by permeation experiments through hollow fiber membrane module and experimental results were compared with simulation results. Permeation rate of pure gas increased with increaseing temperature in Arrhenius type. Activation energy was 6.61 kJ/mol for $CO_2$ and 25.26 kJ/mol for $CH_4$. In the permeation experiment of gas mixture, permeate flow rate and $CO_2$ concentration in permeate decreased and $CH_4$ concentration in reject increased with the increase of cut. Separation factor was in the range of 20~40 at 5~20 atm and 20% cut and it increased with pressure and against temperature Experimental values corresponded to numerical values with the deviation of 8% in permeate flow rate and $CO_2$ concentration in permeate and 15% in $CO_2$ concentration in reject.