• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.260-269
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• 2000

Oil-film flow visualizations and three-dimensional flow measurements have been conducted in the downstream region of a butterfly-type valve used in air-conditioning systems, with the variation of a disk open angle. The flow visualizations in the flow symmetry plane show that there are a pair of counter-rotating separation/recirculation zones as wall as two jet-like near-wall flows. These flow disturbances are strongly depends on the disk open angle. Based on the flow visualization, a qualitative flow model is suggested in the near-field and downstream region of the valve disk. For a small disk open angle, the mean velocities and turbulent intensities have relatively small values in the near-field of the valve disk, but they do not show uniform distributions even in some downstream region. With an increment of the disk open angle, mean velocity variations and turbulent intensities are greatly increased in the immediate downstream region, but uniform distributions are quickly resumed as departing from the valve disk. The mass flow rate remains nearly constant for the disk open angles less than 30 degrees, meanwhile it strongly depends on the disk open angles between 45 and 75 degrees. The pressure loss is found to be about zero for the disk open angles less than 45 degrees, but is substantially increased for those larger than 75 degrees.

• Journal of computational fluids engineering
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• v.21 no.3
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• pp.24-30
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• 2016

In the water purification plant, the mixture of water and chemical from the mixing basin enters the flocculation basin. The rotating flocculators are generally used for the efficient flocculation of dregs. In this paper, the performance of flocculators of a vertical paddle type, widely used in the typical flocculation basins, and a hydro-foil type, recently disseminated in the field, are compared with each other by use of the numerical method. Also the characteristics and the efficiency are analyzed with CFD techniques. The strain rate and the eddy viscosity are compared for two types to predict the mixing efficiency, and the maximum speed and its location are pursued from the computed data. The hydrofoil type shows that the eddy viscosity is enhanced 1.66 to 3.03 times larger than that of vertical paddle type, and also produced 1.87 to 1.95 times larger flocs for each stage. However, the rapid rotation of hydrofoil may chop the floc to small size due to the higher turbulence intensity. From the result of computation, the strong and weak points of each type have been analyzed for the decision making.

• Progress in Superconductivity and Cryogenics
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• v.2 no.2
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• pp.44-48
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• 2000

The high temperature superconducting bulk can be used as the rotor of an ac motor. This paper presents the fabrication and test results of a ac motor with HTS bulk rotor. The rotor of a conventional squirrel cage induction motor was replaced with cylinder type YBCO bulk. Height and outer diameter of the HTS bulk was 15mm and 46mm, respectively. Eddy current brake using aluminium disk was used to measure the torque of the HTS motor. No load test, locked rotor test and load test were performed to examine the characteristics of the HTS motor. Test results show the motor can rotate at synchronous speed without any special starting circuit. Maximum output power of the constructed HTS motor was 408W.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.10
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• pp.1011-1017
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• 2012

We report the development of an optical micro-nanolithography method by using a roll-type mask. It includes phase-shift lithography and photolithography for realizing various target dimensions. For sub-wavelength resolution, a structure is achieved using the near-field exposure of a photoresist through a cylindrical phase-mask, allowing high-throughput continuous patterning. By using a film-type metal mask, continuous photolithography was achieved, and this method could be used to control the period of resultant patterns in real time by changing the rotating speed of the cylinder mask. As an application, we present the fabrication of a transparent electrode in the form of a metallic mesh by using the developed roll-type photolithography process. As a result, a transparent conductor with good properties was achieved by using a recently built cylindrical phase-shift lithography prototype, which was designed for patterning on 100-mm2 substrates.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.337-339
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• 1998

This paper deals with the design and fabrication of a novel superconducting power supply system, and characteristics have been analyzed through experiments. Superconducting power supply consists of rotating and static parts, and superconducting magnet. In this experiment, the current-pumping characteristics have been analyzed with superconducting sheets placed in parallel within the static part of the machine. In addition, in order to observe the 3-dimensional flux distribution in the superconducting sheet, several hall-sensors were placed in it. With the flux distribution acquired, the effect of the flux on the superconducting sheet during the process of current pumping have been analyzed. Also, general operational characteristics of the superconducting power supply system have been investigated on the basis of the current and voltage data and magnetic field values acquired through the experiments. In this experiment, maximum pumping current has been achieved to about 1280 amps.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.12
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• pp.771-777
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• 2000

This paper deals with the design and fabrication of a novel superconducting power supply system, and characteristics have been investigated through experiments. Superconducting power supply consists of rotating and static parts, and superconducting magnet. In this experiment, superconducting foils were placed in parallel within the static part of the machine, pumping currents were measured with respect to rotor speeds and excitation currents. In addition, in order to observe the rotating flux distribution in the superconducting foils, several hall-sensors were placed in it. With the flux distribution acquired, effect of the flux on the superconducting foil during the process of current pumping has been discussed. Also, the general operational characteristics of the superconducting power supply system have been investigated on the basis of the current and voltage data, and magnetic field values acquired through the experiments.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.244-246
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• 1999

This paper deals with the design and fabrication of a novel superconducting power supply system, and characteristics have been analyzed through experiments. Superconducting power supply consists of rotating and static parts, and superconducting magnet. In this experiment, the current pumping characteristics have been analyzed with superconducting sheets placed in parallel within the static part of the machine. In addition, in order to observe the rotating flux distribution in the superconducting sheet, several hall-sensors were placed in it. With the flux distribution acquired, the effect of the flux on the superconducting sheet during the process of current pumping have been analyzed. Also, general operational characteristics of the superconducting power supply system have been investigated on the basis of the current and voltage data, and magnetic field values acquired through the experiments.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.776-783
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• 2020

As the refueling of a sodium-cooled fast reactor is conducted by rotating part of the reactor head without opening it, the monitoring of existing obstacles that can disturb the rotation of the reactor head is one of the most important issues. This paper deals with the ultrasonic ranging technique that directly monitors the existence of possible obstacles located in a lateral gap between the upper internal structure and the reactor core in a prototype generation IV sodium-cooled fast reactor (PGSFR). A 10 m long plate-type ultrasonic waveguide sensor, whose feasibility has been successfully demonstrated through preliminary tests, was employed for the ultrasonic ranging technique. The design of the sensor's wave radiating section was modified to improve the radiation performance, and the radiated field was investigated through beam profile measurements. A test facility simulating the lower part of the upper internal structure and the upper part of the reactor core with the same shapes and sizes as those in the PGSFR was newly constructed. Several under-water performance tests were then carried out at room temperature to investigate the applicability of the developed ranging technique using the plate-type ultrasonic waveguide sensor with the actual geometry of the PGSFR's internal structures.

• Journal of The Korean Astronomical Society
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• v.41 no.4
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• pp.83-98
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• 2008

In an attempt of clarifying the connection between the photospheric abundance anomalies and the stellar rotation as well as of exploring the nature of "normal A" stars, the abundances of seven elements (C, O, Si, Ca, Ti, Fe, and Ba) and the projected rotational velocity for 46 A-type field stars were determined by applying the spectrum-fitting method to the high-dispersion spectral data obtained with BOES at BOAO. We found that the peculiarities(underabundances of C, O, and Ca; an overabundance of Ba) seen in slow rotators efficiently decrease with an increase of rotation, which almost disappear at $v_esin\;i{\gtrsim}100km\;s^{-1}$. This further suggests that stars with sufficiently large rotational velocity may retain the original composition at the surface without being altered. Considering the subsolar tendency(by several tenths dex below) exhibited by the elemental abundances of such rapidly-rotating (supposedly normal) A stars, we suspect that the gas metallicity may have decreased since our Sun was born, contrary to the common picture of galactic chemical evolution.