• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.643-651
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• 1998

Turbulent unsteady flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms the mean and turbulence components of the axial velocity and the entrance length are obtained as a major characteristics of the developing turbulent unsteady flows. An inviscid flow theory is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed so far. The local turbulence intensi-ty is found to be a little smaller in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large the hydraulic diameter.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.637-643
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• 2000

The shrouded corotating disk flow has a simple figure on geometric basis, but has various and complicated forms of flow. this complicated flows can be variously applied to not only information storage device, but also turbomachinery which is greatly influenced by centrifugal force. This study measured its velocity to measure inner flow field with unique flow field univluenced, using LDV and subminiature hot-wire. The result of experiment shows that distribution limits of solid body rotation region, dimensionless velocity gradient and distribution limits of disk surface boundary layer(Ekman layer) are changed by the gap of disks and rotating speed. Circulating vortex which is near the shroud is effected by the gap of disks and rotating speed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.118-124
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• 2012

The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.151-152
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• 2005

Both $Al_2O_3$ and AlN nanopowders with diameters from ${\mu}m$ to mm were bead-milled and surface-modified by stabilizing agent. The size of bead-milled nanoparticles compared with the primary powder was effectively decreased and was dependent on milling time and bead size. The results of dispersion stability analysis indicated that chemical bonding between nanoparticles and surfactant is more effective than chemical adsorption to prepare the stable transformer oils containing nanoparticles. In this study, the thermal conductivity of the transformer oils containing nanoparticles was measured by transient hot-wire and laser flash methods.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.33-39
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• 2002

Unsteady behaviors of counterflow flame were studied experimentally in opposing jet counterflow burner using diluted methane. To generate the unsteadiness on the flame, the counterflow diffusion flame was perturbed by velocity changes made by the pistons installed on both sides of the air and fuel stream. The velocity changes were measured by Hot wire and Laser Doppler Velocimetry, and the flame behaviors were observed by High speed ICCD and ICCD. In this investigation, the spatial irregularity of the strain rate caused the flame to extinguish from the outside to the axis during the extinction, and we found the following unsteady phenomena. First, the extinction strain rates of unsteady cases are much larger than those of the steady ones. Second, the extinction strain rates become larger as the slope of the change of the strain rate increases. Third, the unsteady extinction strain rates become smaller with the increase of the initial strain rate.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.370-370
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• 2009

이종접합태양전지는 구조적 대칭성 때문에 웨이퍼 두께가 감소하여도 보우잉이 일어나지 않는 특징이 있으며, 산요에서 개발한 이종접합태양전지의 효율이 22% 이상을 보이고 있다. 이종접합태양전지에서 비정질 실리콘과 실리콘 웨이퍼의 계면에 따라 이종접합태양전지의 특성이 크게 변화한다. 본 연구에서는 패시베이션 층으로 사용되는 비정질 실리콘을 hot wire chemical vapor deposition(HWCVD)을 사용하여 이종접합태양전지에 적용하였으며 기존의 plasma-enhanced chemical vapor deposition을 이용한 비정질 실리콘을 적용한 이종접합태양전지와 비교하였다. 패시베이션 특성을 확인하기 위해 quasi-steady state photoconductance로 minority carrier lifetime을 측정하였고, 태양전지 특성평가로는 암전류특성 및 광전류특성을 사용하였다. HWCVD를 사용하여 패시베이션한 태양전지의 경우 16.1%의 효율을 보였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1077-1086
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• 2001

An experimental study is performed to investigate the characteristics of vortex shedding behind a circular cylinder with serrated fins using hot-wire anemometer. Strouhal numbers which are calculated using outer diameter of a circular cylinder with serrated fins are higher than that of a circular cylinder. Fin thickness and pitch are closely related with vortex shedding frequency and play increasing or decreasing vortex shedding after transient Reynolds number. Strouhal numbers using effective diameters which are proposed in this paper agree with that of a circular cylinder. After transient Reynolds number, a trend of Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.31-39
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• 1996

The effect of rear-spoiler attached at rear end of automobile trunk on the aerodynamic characteristics of a MIRA reference car model was experimentally investigated. For different shapes and positions(G/H) of the rear-spoiler, the aerodynamic forces on the automobile were measured at various flow speed(ReL). The effect of rear-spoiler on the wake structure behind the automobile was also investigated using flow visualization and hot-wire anemometer. The rear-spoiler modifies the near wake structure and decreases aerodynamic drag and increases driving stability compared with those of the conventional automobile without rear-spoiler. From the experimental results, rear-spoiler of airfoil shape installed at the position of G/H=0.084 shows the best aerodynamic performance.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.2
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• pp.183-196
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• 1997

Gas flow field within the cylinder which is called a tumble flow is important factor in improving lean combustion stability. In this study, steady state flow tests were performed to quantify tumble ratio of flowfields generated by a tumble intensifying valve(TIV). In addition, velocity and fluctuation profiles in an intake port and flowfields in th cylinder were inspected using a hotwire anemometer and a laser light sheet method with various TIV configurations. These experimental results show that installated TIV has a great effect on flow field distribution in an intake port and test effects enhance a tumble flow in the cylinder.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.594-601
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• 1997

Propeller fans are commonly equipped in outdoor units of air-conditioners to provide effective cooling in a dried heat exchanger. A new design technique was developed to satisfy requirements of aerodynamic and aeroacoustic performance, which employs the intersection method of two cylinders for mean camber line. Three proto-types of propeller fan including Palm-Shaped, Highly-Swept(PSHS) fan (proto 3)were not only to provide low lift forces for dipole sound, but also to reduce the organized tip vortices interacting with the fan guide causing narrow-banded rotating instabilities. Cross-correlation technique was applied to study flow noise source characteristics for three proto-type fans designed. The cross-correlations between a microphone at far field and a hot-wire sensor at near field show that flows near hub region of proto 3 fan are less organized and the flow structures especially at high flow rate coefficients for proto 3 fan are less correlated with noise generated than other proto-types fans.