• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.1113-1114
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.339-340
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.595-596
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• 2008

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.673-674
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1363-1364
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• 2011

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1194-1197
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• 2005

Micro nozzle is employed as a dynamic passive valve in micro fluidic devices. Micro nozzle array is used in micro droplet generation in bio-medical applications and propulsion device for actuating satellite and aerospace ship in vacuum environments. Aperture angle and the channel length of the micro nozzle affect its retification efficiency, and thus it is needed to produce micro nozzle precisely. MEMS process has a limit on making a micro nozzle with high-aspect ratio. Reactive ion etching process can make high-aspect ratio structure, but it is difficult to make the complex shape. Focused ion beam deposition has advantage in machining of three-dimensional complex structures of sub-micron size. Moreover, it is possible to monitor machining process and to correct defected part at simultaneously. In this study, focused ion beam deposition was applied to micro nozzle production.

• Journal of computational fluids engineering
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• v.18 no.3
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• pp.26-33
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• 2013

In the present study, unsteady flow simulations of a variable geometry nozzle were conducted using a two-dimensional flow solver based on hybrid unstructured meshes. The variable geometry nozzle is used to achieve efficient performances of aircraft engines at various operating conditions. To describe the motion of the variable geometry nozzle, an algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements. A ball-vertex spring analogy was used for inviscid elements. The aerodynamic data were obtained for a range of nozzle pressure ratios, and the validations were made by comparing the present results with available experimental data. The unsteady nozzle flows were simulated with an oscillating diverging section and a converging-diverging section. It was found that the nozzle performances are influenced by the nozzle exit flow characteristics, mass flow rate, as well as unsteady effects. These unsteady effects are shown to behave differently depending on the frequency of the nozzle motion.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.1
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• pp.56-63
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• 2021

The feedwater ring is an assembly in steam generator internal piping, which distributes feedwater into the secondary side of the steam generator. It consists of an assembly of carbon steel piping, pipe fittings and J-nozzles which are inserted into the top of the feedwater ring and welded to the diameter of the ring. The feedwater ring at the attachment region of the J-nozzle may be susceptible to flow accelerated corrosion (FAC) due to flow turbulence which increases local fluid velocities. If a J-nozzle becomes a loose part, it can cause damage to tubing near the tube sheet. In this paper, the structural stress analysis for a wall thinned feedwater ring and integrity evaluations under assumed loading conditions are carried out in compliance with ASME B&PV SecIII, NB-3200.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.54-60
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• 2008

The atomization characteristics of the dual air supplying twin-fluid nozzle were investigated experimentally using PIV and PDA systems. The two-fluid nozzle is composed of three main parts: the feeding injector to supply fluid that is controlled by a PWM (pulse-width modulation) mode, the adaptor as a device with the ports for supplying the carrier and assist air and the main nozzle to produce the spray. The main nozzle has the swirl tip with four equally spaced tangential slots, which give the injecting fluid an angular momentum. The angle of the swirl tip varied with 0$^{\circ}$ 30$^{\circ}$, 60$^{\circ}$ and 90$^{\circ}$, and the ratios of carrier air to assist air and ALR(total air to liquid) were 0.55 and 1.23, respectively. The macroscopic behavior of the spray was investigated using PIV system, and the mean velocity, turbulent intensity and SMD distributions of the sprays were measured using PDA system. As the results, the mean axial velocity at the spray centerline decrease with the increase of the swirl angle. The turbulent intensities of the axial and radial velocity were increased with the increase of the swirl angle. The mean SMD (Sauter mean diameter) of the radial direction along the axial distance shows the lowest value at the swirl angle of 60$^{\circ}$.

• 한국전산유체공학회:학술대회논문집
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• 2000.10a
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• pp.54-59
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• 2000

A numerical study of axisymmetric rocket main nozzle flow has been accomplished. The CSCM upwind flux difference splitting method with an iterative time marching scheme having second order accuracy in time and space has been used to simulate unsteady flow characteristics in an axisymmetric rocket main nozzle. Though the pressure vary at nozzle inlet with the lapse of time, Mach No. and the density were not changed significontly compared with the temperature. Specific heat ratio $\gamma$=1.134 predicted higher temperature at nozzle throat and exit and nondimensional thrust coefficients at exit than specific heat ratio $\gamma$=1.4 did.