• Journal of Korean Society of Environmental Engineers
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• v.34 no.2
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• pp.103-108
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• 2012

A MILD (Moderate and Intense Low oxygen Dilution) combustor decreases NOx formation effectively during the combustion process and NOx formation is affected significantly by the exhaust gas entrainment rate toward fuel and air. The present study focused on the new MILD combustor, which has coaxial cylindrical tube. The outside tube of the new MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. The connection pipe is set between the outer side and the inner side tubes and coaxial air nozzle is inserted at the center of the connection pipe. A numerical analysis is accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of air nozzle exit velocity, nozzle diameter, nozzle exit position and exhaust gas side pressure. The entrainment rate is proportional to the square root of air nozzle exit velocity and negatively proportional to the pressure difference between the exhaust gas side and furnace side pressures. The effect of air nozzle exit position is not considerable on the exhaust gas entrainment.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.221-230
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• 2011

The cold spray process is an emerging technology that utilizes high velocity metallic particles for surface coating. Metallic powder particles are injected into a converging-diverging de Laval nozzle and accelerated to a high velocity by a supersonic gas flow. The cold spray process normally uses a circular nozzle that has a rather narrow spraying range. To overcome this fault, a slit nozzle was considered in this study. The slit nozzle is anticipated to reduce the coating process time because it has a wider coating width than the circular nozzle. However, the slit nozzle can reduce the coating efficiency because it does not allow as much gas and particle velocity as the circular nozzle. To improve the coating efficiency of a slit nozzle, the shape of the slit nozzle was modified. And the results of gas flow and particle behaviour according to the nozzlers shape were compared by the a numerical analysis. As a results, as Expansion Ratio(ER) of 7.5 was found to be the most optimal condition for enhancing the spraying efficiency when the ER was changed by the variation of nozzle neck and exit size.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.101-106
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• 2019

Carbon deposition on the turbine nozzle throat of a LOx/kerosene gas generator cycle(open cycle) engine causes performance reduction of the engine. Estimation methods for a turbine nozzle throat area are proposed. The discharge coefficient of the turbine nozzle was estimated with the turbine gas properties such as gas constant, specific heat ratio, and temperatures. The pressure ratio and temperature ratio of the turbine nozzle throat, was utilized to estimate the discharge coefficient also. Estimated discharge coefficient of turbine nozzle throat of KSLV-II 1st stage engine shows the carbon deposition effects on the turbine nozzle throat of a LOx/kerosene open cycle engine.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.6
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• pp.17-31
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• 1999

This paper is a review of the results of examining the flow characteristics of gas and particles with regards to pipe-type nozzle and converging nozzles depending on nozzle geometry. The nozzles used in this experiment are the pipe-type nozzle which can sufficiently mix the gas and particles, and the converging nozzle which can rapidly accelerate fluid . The particles used at the time of this experiment each measured 0.8, 30, 60 and 80${\mu}{\textrm}{m}$ in the diameter. The Phase Doppler Particle Analyzer was used to measure the velocity of each particle, and the Hot-wire probe was used to measure the spectrum in order to analyze the flow near the nozzle exit of the 0.8${\mu}{\textrm}{m}$ particle.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2127-2132
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• 2003

A computational study is performed to better understand the choke phenomenon of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Navier-Stokes equations are solved using a finite volume method. In order to simulate the effects of back pressure fluctuations on the critical nozzle flow, a forced sinusoidal pressure wave is assumed downstream the exit of the critical nozzle. It's frequency is 20kHz and amplitude is varied below 15% of time-mean back pressure. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thereby giving rise to applicable fluctuations of mass flow through the critical nozzle. The effect of the amplitude of the excited pressure fluctuations on the choke phenomenon is discussed in details.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.238-239
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• 2006

Nozzle geometry influences gas dynamics making sprayed particle behavior one of the most important parameters in cold spray process. Gas flows at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour, entrance geometry of nozzle and powder injection position at nozzle on the cold spray process. The process changes were observed through numerical simulation studies and the results were used to find a correlation with coating properties.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1167-1173
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• 2013

This study aimed to calculate the CFFs (critical flow functions) of a sonic nozzle bank with a 12-nozzle package within 1 s. Toward this end, the Helmholtz free energy of natural gas was formulated by using the AGA8-dc equation of state in a form without integral terms, and thereafter, thermodynamic properties such as the enthalpy, entropy, speed of sound, and heat capacity, which are used in CFF calculation, were derived in analytical form. As a result, the calculation time of CFFs was improved from 6.7 s in a previous study to 0.6 s per 12-nozzle package and kept almost constant regardless of the number of components in natural gas. Furthermore, it was confirmed that the calculated CFF values were in agreement with the results of a CFF international comparison test carried out under ISO management in 1998-1999.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.7
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• pp.911-917
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• 1999

The sonic nozzle is widely used as reference device for calibrating flowmeters In gas flow measurement and its use requires the Critical Flow Factor(CFF) based on the thermodynamic properties of the gas at the nozzle throat. ISO-9300 provides the calculating method of the factor. But since the CFF from this method show an error over ${\pm}0.5%$ In specific conditions and of ${\pm}0.1{\sim}{\pm}0.2%$ in common Natural Gas(NG) custody transfer condition. this method cannot be applied for gas flow measurement with sonic nozzle. Each research bodies or organizations of the world have joined in order to calculate the CFF more accurately. They have performed these works using their own method and compared the results with each other under the management of ISO. KOGAS have joined those works, because the high-pressure natural gas flow calibration facility of KOGAS will be constructed in late 1999, and then had necessities to calculate a CFF accurately. The calculation method of KOGAS was using the equation of state from AGA-8('94), high accuracy model of ideal gas properties and the solutions of thermodynamic equations. The evaluation results have had a very good consistency within ${\pm}0.05%$ in most NO custody transfer conditions compared to the speed of sound for methane and also shown that the CFF was within ${\pm}0.1%$ compared to the results of other works of the world.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.311-317
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• 2005

It has been the most progressive interruption technique to use the ablation gas from the surface of PTFE nozzle driven by arc plasma during switching process in $SF_6$ gas circuit breakers. This advanced interruption technique can reduce the required mechanical energy to compress and blow the gas for extinguishing the arc plasma between the electrodes due to using the ablation effect instead. In order to consider the phenomena during calculation of switching process, it is required to confirm the principles of ablation from PTFE nozzle as well as of arc plasma during switching process. In this study, we have calculated the switching process considered the ablation of PTFE nozzle driven by arc plasma using multidisciplinary simulation technique and compared the results with the data without the ablation effect. More $50\%$ difference of pressure rise inside expansion chamber has been found from the results and it should be indispensable for this type of computational work to consider and include the ablation effect of PTFE nozzle. Further study on turbulence and radiation will be followed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1406-1418
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• 2002

The direct simulation Monte Carlo(DSMC) method is employed to calculate the etch rate on Al wafer. The etchant is assumed to be Cl$_2$. The etching process of an Al wafer in a helicon plasma etcher is examined by simulating molecular collisions of reactant and product. The flow field inside a plasma etch reactor is also simulated by the DSMC method fur a chlorine feed gas flow. The surface reaction on the Al wafer is simply modelled by one-step reaction: 3C1$_2$+2Allongrightarrow1 2AIC1$_3$. The gas flow inside the reactor is compared for six different nozzle locations. It is found that the flow field inside the reactor is affected by the nozzle locations. The Cl$_2$ number density on the wafer decreases as the nozzle location moves toward the side of the reactor. Also, the present numerical results show that the nozzle location 1, which is at the top of the reactor chamber, produces a higher etch rate.