• Journal of Power System Engineering
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• v.13 no.5
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• pp.25-33
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• 2009

In the present study, the numerical investigation has been carried out to see the effects of water mist sprays on the fire suppression mechanism. The special-purposed program named as FDS was used to simulate the interaction of fire plume and water mists. This program solves the fire-driven flows using LES turbulence model, the mixture fraction combustion model, the finite volume method of radiation transport for a non-scattering gray gas, and conjugate heat transfer between wall and gas flow. The computational domain was composed of a rectangular space dimensioned as $L{\times}W{\times}H=4.0{\times}4.0{\times}2.5\;m^3$ with a mist-injecting nozzle installed 1.0 m high from the fire pool. In this paper, two types of nozzles were chosen to compare the performance of the fire suppression. Numerical results showed that the nozzle, type A, with more orifices having smaller diameters had poorer performance than the other one, type B because the flow injected through side holes deteriorated the primary flow. The fire-extinguishing time of type A was 2.6 times bigger than that of type B.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.93-97
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• 2005

Air interlacing serves to protect the yarn against damage, strengthens inter-filament compactness or cohesion, and ensures fabric consistency. The air interlacing nozzle is used to introduce intermittent nips to a filament yarn so as to improve its performance in textile processing. This study investigates the effect of interlacing nozzle geometry on the interlacing process. The geometries of interlacing nozzles with multiple air inlets located across the width of a yarn channels are investigated. The basic interlacing nozzle is the yarn channel, with a perpendicular single air inlet in the middle. The yarn channel shapes are cross sections with semicircular or rectangular shapes. This paper presents three doubled sub air inlets with main air inlet and one of them is slightly inclined doubled sub air inlets with main air inlet. The compressed air coming out from the inlet hits the opposing wall of the yarn channel, divides into two branches, flows trough the top side of yarn channel, joins with the compressed air coming out from the sub air inlet and then creates two free jets at both ends of the yarn channel. The compressed air moves in the shape of two opposing directional vortices. The CFD-FASTRAN was used to perform steady simulations of impinging jet flow inside of the interlace nozzles. The vortical structure and the flow pattern such as pressure contour, particle traces, velocity vector plots inside of interlace nozzle geometry are discussed in this paper.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1892-1897
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• 2003

A new thermal inkjet printer head on SOI wafer with virtual valve was proposed. It was composed of two rectangular heaters with same size. So we could call it T-jet(Twin jet). T-jet has a lot of merits. It has the advantage of being fabricated with one wafer and is easy to change the size of chamber, nozzle, restrictor and so on. However, above all, It is the best point that T-jet has a virtual valve. And it was manufactured on SOI wafer. The chamber was formed in its upper silicon whose thickness was 40um. The chamber's bottom layer was silicon dioxide of SOI wafer and two heaters were located underneath the chamber's ceiling. And the restirctor was made beside the chamber. Nozzle was molded by process of Ni plating. Ni was 30um thick. Nozzle ejection test was performed by printer head having 56 nozzles in 2 columns with 600NPI(nozzle per inch) and black ink. It measured a drop velocity of 12m/s, a drop volume of 30pl, and a maximum firing frequency of 12KHz for single nozzle ejection. Throwing out the ink drop in whole nozzles at the same time, it was observed that the uniformity of the drop velocity and volume was less than 4%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.485-494
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• 2000

The purpose of this paper is to investigate a critical heat flux(CHF) during forced convective subcooled and saturated boiling in free water jet system impinged on a rectangular heated surface. The surface is supplied with subcooled or saturated water through a rectangular jet. Experimental parameters studied are a width of heated surface, a height of supplementary water and a degree of subcooling. Incipient boiling point is observed in the temperature of 6${\~}8^{\circ}C$ of superheat of test specimen. CHF depends on jet velocity for various boiling-involved coolant system. CHF also is proportional to the nozzle exit velocity to the power of n, where n is 0.55 and 0.8 for subcooled and saturated boiling, respectively. CHF is enhanced with a higher jet velocity, higher degree of subcooling and smaller width of a heated surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1115-1122
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• 2002

The present experiment investigates the effects of pore density f of aluminum foam heat sinks, the jet-to-jet spacing X and the nozzle plate-to-target surface spacing H of 3$\times$3 square impinging arrays on the averaged Nusselt number. The performance of the aluminum foam heat sinks and the rectangular plate heat sink is evaluated in terms of the enhancement factor. /equation omitted/. The multiple impinging jet with X/d=4.0 displays higher Nusselt numbers than single impinging jet for 12.0$\leq$H/d$\leq$20.0. With the variation of the jet-to-jet spacing, the aluminum foam heat sink of 10 PPI show higher Nusselt numbers than the 20 and 40 PPI aluminum foam heat sinks. Further, the 10 PPI aluminum foam heat sink demonstrates 26% higher enhancement factor than the rectangular plate heat sink in the range of 7000$\leq$Re$\leq$11000.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.12 no.4
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• pp.264-274
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• 1983

Two-dimensional jet flows into a couple of confined rectangular enclosures such as an Ondol flue channel and their flow distributions were analyzed by numerical graphics : rectangular space in one enclosure is vacated and the other has 8 rectangular small posts. Both enclosures have a protruded inlet nozzle and on outlet on its center line. Steady state incompressible laminar viscous flow was assumed. The primitive forms of Navier-Stokes equations and continuity equation in a cartesian coordinate system were solved numerically by the Marker and Cell method for Reynolds numbers of 5, 10, 20, 30 and 40. From the numerical graphics it was found that the flow regions in both enclosures were devided into tow parts ; one part was the jet flow localized in a narrow center region of the enclosure and the other part was the very slow recirculating flow occupying the rest of the flow region in the enclosures. However there were a little differences in the shapes of jet flow in both enclosures for Reynolds numbers of 5 and 10 and also in the shapes of recirculating flows in both enclosures for all Reynolds number. Also it was found that waving flow appeared right before the outlet at Reynolds number of 20 and more.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.66-72
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• 1997

Circular-to-rectangular transition ducts are used as exhaust components of high performance fighter aircraft with vectored thrust nozzles. Three-dimensional incompressible Navier-Stokes solver is used to analyze the transition duct. Cross sections of transition duct are defined by superelliptic equation. The grid system is generated by Non-Uniform Rational B-Spline, after generating surface grid by blending the cross sections. Good agreement between the results of the computational simulation and the experimental data is observed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.355-365
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• 1991

New definition for the interaction of flames is introduced and interacting turbulent diffusion flames issuing from two rectangular nozzles are investigated on the basis of the definition. Theoretical study through numerical model is carried out and experiment for validation is conducted. The characteristics of interaction due to the variation of major parameters such as nozzle spacing, Reynolds number and nozzle aspect ratio are studied. Results show that strong interaction occurs for small nozzle spacing, small Reynolds number and large aspect ratio. In order of their magnitude, the intensity of interactions on the individual transport mechanism is momentum, heat and mass. It is also found that interaction makes flames longer, tilted and finally merged. Increase of velocities and temperature, decrease of oxygen concentration and depression of turbulence are occurred in the region between flames.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.53-58
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• 2020

This study analyzed the surface roughness of the fine particle spraying process in the plane and the surface roughness by the factors in the fine particle spraying process on the helical surface is analyzed. Finally, the surface fine particle spraying process and the helical curved surface fine particle Analyze the difference in injection conditions of the injection process. Key process variables are particle type, nozzle diameter, and pressure. The remaining conditions are fixed values of. A total of 32 experiments were conducted, each with different process variables. Rectangular and cylindrical specimens were fabricated and a corresponding jig was prepared for use in the experiment. Analyses conducted by using ANOVA enabled comparisons of the effects of each process variable on the experiment.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.2
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• pp.51-60
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• 2003

An experimental research program is being undertaken to develop a regeneratively-cooled experimental thrust chamber of liquid rocket engine using liquefied natural gas and liquid oxygen as propellants. Prior to firing test using a regenerative cooling with liquefied natural gas in this program, several firing tests were conducted with water as a coolant. Experimental thrust chambers with a thrust of about 10tf were developed and their firing test facility was built up. Injector used in the thrust chamber was of shear-coaxial type appropriate for propellants of gas and liquid phase and cooling channels are of milled rectangular configuration. Periodical variation of the soot deposition and discoloration was observed through an eyes' inspection on the inner wall of a combustion chamber and a nozzle after each firing test, and an intuitive concept of the periodical variation of mixture ratio near the inner wall of a combustion chamber and a nozzle at once was brought about and analyzed quantitatively. Thermal heat flux to the coolant was calculated and modified with the periodical variation model of mixture ratio, and the increment of coolant temperature at cooling channels was compared with measured one.