• 대한기계학회논문집B
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• 제23권1호
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• pp.92-103
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• 1999

The fuel spray behavior in the intake port of an electronic control port irijection gasoline engine has a strong influence on engine performance, exhaust emission and fuel consumption. Thus, in this study, fuel spray behavior and flow characteristics of the air assist gasoline spray injected into a suction flow in a simulated rectangular intake port have boon investigated. Macro-behavior of spray characteristics was investigated by means of visualization and the measurements of SMD and velocity were made by PDPA. For analysis the flow field with droplets size, droplets are classified five droplets size groups. As a result, the normal distance of suction flow increasing, the relatively large droplets distribution and SMD increase because small droplets easily follow suction flow. Near impinging wail, after impinging against the wall, secondary atomized small droplets of D < $30{\mu}m$ bound from the wall. And the increasement of suction flow progress to the large droplets of D > $100{\mu}m$ distribution. Therefore, SMD are apparently increased near impinging wall, Z/d = 9.0.

• 한국가시화정보학회지
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• 제3권1호
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• pp.78-89
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• 2005

An experimental study was carried out to investigate the effect of local ultrasonic forcing on a turbulent boundary layer. Stereoscopic particle image velocimetry (SPIV) was used to probe the characteristics of the flow. A ultrasonic forcing system was made by adhering six ultrasonic transducers to the local flat plate. Cavitation which generates uncountable minute air-bubbles having fast wall normal velocity occurs when ultrasonic was projected into water. The SPIV results showed that the wall normal mean velocity is increased in a boundary layer dramatically and the streamwise mean velocity is reduced. The skin friction coefficient (C$_{f}$) decreases 60$\%$and gradually recovers at the downstream. The ultrasonic forcing reduces wall-region streamwise turbulent intensity, however, streamwise turbulent intensity is increased away from the wall. Wall-normal turbulent intensity is almost the same near the wall but it increases away from the wall. In the vicinity of the wall, Reynold shear stress, sweep strength and production of turbulent kinetic energy were decreased. This suggests that the streamwise vortical structures are lifted by ultrasonic forcing and then skin friction is reduced.

• 한국가시화정보학회지
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• 제10권3호
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• pp.16-20
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• 2012

In the past decades, extensive studies on convection heat transfer on internal flow have been conducted by using high specific surface area, by increasing heat transfer coefficient and swirl flow, and by improving the transport properties. In this study, we applied a tangential slot swirl generator to improve heat transfer in a horizontal circular copper tube. The Al-Mg particles (approximately $100{\mu}m$ to $130{\mu}m$) were employed for this experimental work. The copper tube was heated uniformly by winding a heating coil with a resistance of 9ohm per meter for heat transfer. Using Al-Mg particles, experiments were performed in the Reynolds number range of 5,000 to 13,130, with and without swirl. Experimental data transfers or comparisons between Nusselt numbers with and without swirl along the test tube and Reynolds numbers are presented. The Nusselt number is improved by increasing Reynolds numbers or swirl intensities along the test tube.

• 한국가시화정보학회지
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• 제6권2호
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• pp.3-8
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• 2008

A new 3D-PTV algorithm(a Volume PTV) based upon a hybrid fitness function has been constructed. A coherency fitness function is introduced using the information of space and time to sort out the correct particle pairs between the two camera images. The measurement system consists of two-high-definition-cameras($1k{\times}1k$), a Nd-Yag laser and a host computer. The developed algorithm has been employed to investigate the flow features of the cylinder wake. The Reynolds numbers with the cylinder diameter(d=10 mm) are 360, 540, 720, 900, 1080 and 1260. Two-dimensional displacements of the particles of each camera's image and neighbouring constraints were introduced to reduce the calculation loads. More than 10,000 instantaneous 3D vectors have been obtained by the constructed algorithm. The constructed algorithm could recover more than $80{\sim}90%$ of the particle numbers in the image condition.

• 한국가시화정보학회지
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• 제16권2호
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• pp.16-22
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• 2018

This study investigates dynamic wetting behaviors of a water droplet placed on surfaces with different wettability and nano-structures. Hydrophobic and hydrophilic properties on as-received silicon wafers were prepared by fabricating thin films of hydrophobic polymer and hydrophilic nanoparticles via layer-by-layer coating. Dynamic advancing contact angle of droplets on the prepared surfaces was measured at various moving velocities of triple contact line with a high-speed video camera. As advancing velocity of triple contact line increased, dynamic advancing contact angle on the as-received silicon and hydrophobic surfaces sharply increased up to $80^{\circ}$ in the range of order of mm/sec whereas the SiO2 nanoparticle-coated hydrophilic surface maintained low contact angles of about $30^{\circ}$ and then it gradually increased in the velocity range of order of hundred mm/sec. The improved dynamic wetting ability observed on the nanostructured hydrophilic surface can benefit the performance of various phase-change heat transfer phenomena under forced convective flow.

• 대한기계학회논문집B
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• 제31권11호
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• pp.957-962
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• 2007

The flow around a rotating circular cylinder near a plane wall is investigated by the measurement of the lift acting on the cylinder and by the flow visualization using the hydrogen bubble technique in the circulating water tank. The experimental parameters are the rotating direction of the cylinder, the space ratios H/D($H/D=0.05{\sim}0.5$) between cylinder and plane wall and the velocity ratios ${\alpha}({\alpha}=0{\sim}{\pm}2.0)$. In the case of clockwise, the lift on the rotating circular cylinder was increased with the reduction of the space ratios and with the velocity ratios, the upper separation point was more shifted in the rotating direction with them. In the case of anticlockwise, the absolute value of the lift on the rotating circular cylinder was increased with the space ratios and with the velocity ratios, the lower separation point was more shifted in the rotating direction with them.

• 한국가시화정보학회지
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• 제4권2호
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• pp.69-75
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• 2006

The microbubbles were used in various fields, such as turbulent control, drag reduction, material science and life science. The X-ray PTV using X-ray micro-imaging technique was employed to mea-sure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}$=2.7mm) were tested. Due to the different refractive indices of water and air, phase contrast X-ray images clearly show the exact size and shape of over-lapped microbubbles. In all of the working fluids tested (deionized water, tap water, 0.01 and 0.10M NaCl solutions), the measured terminal velocity of the microbubbles rising through the solution was proportional to the square of the bubble diameter. The rising velocity was increased with increasing mole concentration. The microbubble can be useful as contrast agent or tracer in life science and biology. The X-ray PTV technique should be able to extract useful information on the behavior of various bio/microscale fluid flows that are not amenable to analysis using conventional methods.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2530-2535
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• 2008

The Visualizations of the flowfield through tube banks with in-line and staggered arrangements were investigated by PIV. Strouhal numbers, velocity vectors and velocity profiles around the cylinders with in-line and staggered arrangements were observed at the pitch ratio $P_t/D=2.0$ and Reynolds number of $Re=4.0{\times}10^3$. As the results The flow patterns through tube banks were almost a straight line in case of the in-line arrangement while it was almost 八 type in case of the staggered arrangement in the direction of the wake. The average velocity in the rear region of the tube banks with the staggered arrangement was far smaller than that with the in-line arrangement. The Strouhal number in the last rank was far smaller than that in the front ranks in both of the in-line and staggered arrangements. The wake of each cylinder changed with time and with the position of the cylinder.

• 비파괴검사학회지
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• 제27권6호
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• pp.563-575
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• 2007

This contribution contained the classical work of an open-hole tensile plate to demonstrate the performance of grating shearography and to compare with the results obtained by other full-field measurement techniques, The isotropic plate with an open-hole has often appeared in the previous contributions introducing novel full-field method and system. Grating shearography directly provided six quantitative measurands about the specimen's surface kinematics by using a single measurement set: three in-plane strains, in plane rotation, and two out-of-plane slopes. The quasi-plane wavefront of grating metrology led to high signal-to-noise ratio (SNR) and thus neither fitting nor filtering was applied, and the small shearing distance of $101{\mu}m$ could be used. The small shearing distance provided the outstanding spatial resolution of $80{\mu}m$ and sensitivity appropriate for experimental mechanics. Finally, the grating shearography enabled the visualization of the complex surface deformation around the hole and also detected parasitic flexions of the specimen in the micrometer regime during the tensile test.

• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 1997년도 International Symposium on Fire Science and Technology
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• pp.518-525
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• 1997

A series of measurements and visualization to investigate the interaction of water sprays with pool fires is presented. Fire source is a small-scale pool burner with methanol, ethanol and gasoline. Measurements of temperatures, $O_2$, $CO_2$, and CO concentrations along the plume centerline are carried out to observe pool fire structures without water sprays. Visualization by the Ar-ion laser sheet shows flow pattern of droplets of the sprays above the pool fires. It is observed that in the case of methanol and ethanol, water sprays continuously penetrate into the center of fuel surfaces. The gasoline pool fire allows intermittent penetration of water sprays because of pulsating characteristics of the gasoline flame. To evaluate the cooling effect of the fuel surface by the sprays, the temperature was measured at the fuel surface. As soon as the mists reach the fuel surface of methanol and ethanol, the temperatures of the fuel surface decrease rapidly below the boiling point, and then the fires are extinguished. Due to the application of mist upon the gasoline fire, though the fuel temperature decrease abruptly at the time of the injection, such a rapid decrease do not continue till the extinction point.