• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.32-41
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• 1999

Natural gas is an attractive fuel in view of environment benefits due to its flow carbon-to-hydrogen ratio. However, its compositions and properties are varied depending upon production regional groups. Therefore, study on the combustion characteristics of natural gas engines with a variety of compositions has been demanded for the efficient application of gas engines. This study aims to investigate the effects of gas composition on engine combustion characteristics. It was found that , by controlling an engine with fixed fuel nozzle area, power and heat release were subject to Wobbe Index. And at fixed excess air ratios, power and heat release were subject to low heating value of unit mixture . In addition, in case of constant nozzle area, combustion duration was found to be inversely proportional to CP(Combustion Potential), and the condition of fixed excess air ratios showed no change in combustion duration, regardless of CP.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.135-138
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• 2002

High-speed ejection of burnt gases from the resonator cavity is essential for performance optimization of the chemical laser system. Additionally, to maintain the population of lasing species at a level for maximum optical power, the pressure within the cavity must be of order of 10 torr. In the present study, a small-scale ejector was designed and built for parametric study of its performance. High-pressure air was used as a motive gas. Measurements include schlieren visualization and pressure distribution trace near the ejector nozzle and along the diffuser downstream of the ejector. preliminary tests showed performance of the ejector is a function of parameters including mass flow rate and stagnation pressure of the motive gas, ejector nozzle area ratio, throat area of the diffuser downstream of the ejector.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.42-52
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• 1997

The basic principle of underwater ram-jet as a unique marine propulsion concept showing vary high cruise speed range(e. g. 80-100 knots) is the thrust production by the transfer of the potential energy of compressed gas to the operating liquid through kinetic mixing process. This paper is aimed to investigate the propulsive efficiency of the nozzle flow in underwater ram-jet at the speed of 80 knots for the buried type vessel. The basic assumption of the theoretical analysis is that mixture of water and air can be treated as incompressible gas. For an optimized nozzle configuration obtained from the performance analysis, preliminary data for performance evaluation are obtained and effects of nozzle inner wall friction, ambient temperature, ambient pressure, water density, gas velocity, bubble radius, flow velocity, diffuser area ratio, mass flow ratio and water velocity gradient are investigated.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.530-533
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• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.841-848
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• 1997

Combustion of gaseous fuel combustor in a high temperature vitiated air stream was studied with computer simulation. It is for application to afterburner of gas turbine engine which the exact mechanism is not yet clarified. As the jet velocity from fuel nozzle is very high and the geometry of combustor is three dimensional complex structure, many time and money are required to have good results. To consider this demerit, it is simplified to 2-dimensional and modified with the nozzle hole area to same area of annual status. As the thickness of annual is too thin, it is to divide with the many grids for reasonable results. Accordingly, new method which injected fuel mass, momentum and energy are added to source terms of each governing conservation equation as a source terms is introduced like as two phase analysis. Reaction rate is determined by taking into account the Arrhenius reaction based on a single step reaction mechanism. It is focused to temperature and product concentration distribution at each equivalence ratio of inlet hot product.

• Journal of Energy Engineering
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• v.13 no.1
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• pp.34-39
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• 2004

The process of energy separation in a low pressure vortex tube with compressed air as a working medium is studied in detail. Experimental data of the temperature of the cold and hot air leaving the vortex tube are presented. The variation of the maximum wall temperature along the inner surface of a vortex tube and the temperature distribution in a vortex tube provide useful information about the location of the stagnation point of the flow field at the axis of the vortex tube Analysis of the results enabled to find the optimum ratio of nozzle area and the optimum shape of an orifice. From this optimum geometric setup of a low pressure and big vortex tube the effectiveness of energy separation was better than a high pressure and small vortex tube.

• Journal of Biosystems Engineering
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• v.29 no.1
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• pp.21-28
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• 2004

Spraying is one of the most efficient methods for pesticide and insecticide control. Generally, orchard sprayers(aircarrier sprayer) are used for such applications. However, when an orchard sprayer is used, only 20% of total amount of spray deposits on the target. The rest of spray are not only wasted but are also potential sources of environmental pollution. The research far the development of electrostatic spraying system for orchard sprayer was conducted to develop the new pesticide application technology for the reduction of environmental pollution and f3r the production of safe agricultural products. The spray characteristics for nozzles with the different charging methods were tested and the effect of electrostatic charge was analyzed, in the laboratory experiments. The results of this study indicate that the capacitive type of electrostatic spraying nozzle exhibits a large current deposition of water sprays on the sample target. The covering area ratio by conventional spraying system was 10.2%, while that of electrostatic sprays with pulse induction charging method gave the increased covering area ratio by 4.3 times.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3549-3558
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• 2023

The jet pump can be used in a test device of a nuclear reactor for high flow amplification as it reduces inlet flow requirement and thereby size of the process components. In the present work, a miniature jet pump was designed to meet high flow amplification greater than 3. Subsequently, experiments were carried out using a test setup for design validation and performance evaluation of the jet pump for different parameters. It was observed that a minimum pressure of 0.6 bar (g) was required for the secondary fluid inside the jet pump to ensure cavitation free performance at high amplification. Spacing between the nozzle tip and the mixing chamber entry point had significant effect on the performance of the jet pump. Variation in primary flow, temperature and area ratio also affected the performance. It was observed that at high flow amplification, the analytical solution differed significantly from experimental results due to very large velocities encountered in the miniature size jet pump.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.85-96
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• 2003

For a design of rocket engine nozzle, chemical equilibrium analysis which shares the same numerical characteristics with frozen flow analysis can be used as an efficient design tool for predicting maximum thermodynamic performance of the nozzle. 10 this study, a chemical equilibrium flow analysis code was developed for the design of hydrocarbon fueled rocket engines. 10 oder to understand the thermochemical characteristics occurring in a nozzle through the expansion process, such as recombination of chemical components and the accompanying energy recovery, chemical equilibrium flow analysis was carried out for the KSR-III rocket engine nozzles together with frozen flow and non-equilibrium flow analyses. The performance evaluation based on the present KSR-III nozzle flow analyses has provided an understanding of the thermochemical process in the nozzle and additionally, it has confirmed that the newly designed nozzle shape modified to have a reduced exit area ratio is an adequate design for obtaining an increased ground thrust.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.291-295
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• 2011

Thermo-structural analysis was performed for a radiation-cooled nozzle extension of thrust chamber. A Niobium alloy that is known to be a high-performance refractory alloy was used. Since area ratio of the nozzle extension is larger than that of nozzle divergence part, its size also becomes larger. For this reason, it is important to minimize the thickness of nozzle extension to reduce its weight. For the purpose of weight minimization, the thickness of nozzle extension was varied from 1.0 mm to 0.4 mm and structural stability was evaluated for each case. Analysis results showed that nozzle extension with thickness of 0.4 mm is structurally stable for the operation condition. The effect of combustion-included vibration will be additionally considered in the future.