• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.274-280
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• 2014

Polysulfone (PSf) hollow fiber membranes were prepared via the nonsolvent induced phase separation technique. The cosolvent of ${\gamma}$-butyrolactone (GBL) was added to the polymer solution containing a mixture of PSf and N,N-dimethylacetamide (DMAc). Water was utilized as a precipitation nonsolvent. The morphology of prepared membranes was investigated using a field emission scanning electron microscopy. The fabricated membrane showed a typical asymmetric structure such as the dense layer on the porous support layer by the addition of GBL to the polymer solution. As the concentration of GBL increased, the asymmetric porous structure was shown to be more intensified. It was thought that the added GBL played a role of enhancing the liquid-liquid phase separation of the polymer solution, since the cosolvent of GBL might change the thermodynamic solubility parameter of the doping solution. Permeation properties through the prepared hollow fiber membranes were characterized by measuring the pure water flux and the solute rejection using $0.05{\mu}m$ polystyrene latex (PSL) beads. Experimental results revealed that the use of PEG as the internal coagulant enhanced the pure water flux up to 130 times compared to the use of EG while the rejection of the PSL beads decreased only 5%.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.12-16
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• 2002

The clear sky radiative forcings of aerosols were evaluated over East Asia. We first investigated optical characteristics of aerosol using sky radiation measurements. An algorithm of Nakajima et al. (1996) is used for retrieving aerosol parameters such as optical thickness, ${\AA}$ngstr$\"{O}$m exponent, single scattering albedo, and size distribution from sky-radiation measurements, which then can be used for examining spatial and temporal variations of aerosol. Obtaining aerosol radiative forcing at TOA and surface, a radiative transfer model is used with inputs of obtained aerosol parameters and GMS-5 satellite-based cloud optical properties. Results show that there is a good agreement of simulated downwelling radiative flux at the surface with observation within 10 W m$^{-2}$ rms errors under the clear sky condition. However, a relatively large difference up to 40 W m$^{-2}$ rms error is found under the cloudy sky condition. The computed aerosol radiative forcing at the surface shows downward flux changes ranging from -100 to -170 W m$^{-2}$ per unit aerosol optical thickness at 0.7 $\mu$m. The different values of aerosol radiative forcing among the stations is mainly due to the differences in single scattering albedo ($\omega$$_{0.7}$) and asymmetric parameter (g$_1$) related to the geographical and seasonal variations.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.313-313
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• 2006

In this study, we describe a new double layered nanoporous membrane suitable for virus filtration. One layer is an 80 nm thick film having cylindrical pores with diameters of 15 nm and a narrow pore size distribution. This layer is prepared by using a thin film of the mixture of a block copolymer and a homopolymer, and mainly acts to separate viruses. The support layer (${\sim}150\;microns\;thick$) is a conventional micro-filtration membrane with a broad pore size distribution. This asymmetric membrane showed very high selectivity and flux for the separation of human rhinovirus type 14 (HRV 14) which has a diameter of ${\sim}30\;nm$ and is a major pathogen of the common cold in humans.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.673-675
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• 2015

This paper presents a design of a high speed 2-phase 6/5 switched reluctance motor (SRM) for an air-blower application. This type of motor is suitable for the applications that require high speed and only one directional rotation as air-blower. The desired air-blower is unidirectional application, and requires a wide positive torque region without torque dead-zone. In order to get a wide positive torque region without torque dead-zone during phase commutation, asymmetric inductance characteristic with non-uniform air-gap is considered. The proposed motor can be operated at any rotor position. The proposed 6/5 SRM uses short flux path technique that achieved by means of winding configuration and lamination geometry. The purpose of short flux path is to reduce the core loss and the absorption MMF in the stator. The proposed 2-phase 6/5 SRM is verified by finite element method (FEM) analysis and Matlab-Simulink. In order to verify the design, a prototype of the proposed motor was manufactured for practical system.

• Journal of Magnetics
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• v.21 no.2
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• pp.173-178
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• 2016

Six-step commutation control widely used in brushless DC (BLDC) motor can be applied to consequent pole permanent magnet (CPPM) belt starter generator (BSG) with trapezoidal back electromotive force (EMF) in the starter state. However, rotor position detection with three Hall sensors in BLDC motor can hardly be employed in CPPM BSG due to asymmetric flux distribution in each pole side of CPPM BSG. This paper presents a low-cost rotor position detection method for CPPM BSG in which six Hall sensors are proposed to be used based on the analysis of flux distribution by 3D FEA. In the method, the six Hall sensors are divided into three groups and two signals in each group are combined through performing logic operations. In addition, offset angle between back EMF and the related Hall signal can be compensated by moving the Hall sensors. Experiments of a 2 kW CPPM BSG prototype have also been performed to verify the proposed method.

• Membrane Journal
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• v.2 no.1
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• pp.59-66
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• 1992

The experimental studies were carried out on ultrafiltration of PEG #6000 and dextran 70T macromole¬cules. using an asymmetric cellulose acetate membrane in a cross flow plane type cell. Effects of pressure difference. feed concentration were studied on permeate flux and observed rejection for both the macromole¬cules. and the concentration polarization layer resistance $R_{b1}$ on permeate flux was analysed. The concentration polarization layer resistance $R_{b1}$ was correlated with the average macromolecule concen¬tration $C_{b1}$ in polarization layer. The resulting dimensionless correlation was expressed as : $\frac{R_{b1}}{{R_m}}=\alpha[\frac{\rho_{b1}}{C_{b1}}]^\beta$

• Environmental Engineering Research
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• v.23 no.3
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• pp.316-322
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• 2018

In this study, the effects of polymer concentration and additive in the formation of asymmetric nanofiltration (NF) membrane were evaluated. The membrane fabrication was carried out via dry/wet phase inversion technique. A new formulation of dope solution with polymer concentration ranging between 17 wt% to 21 wt% and the present of additive was developed. The results show that the permeate flux gradually decreases as polymer concentration increased, until $2.5969L/m^2h$ and increased the rejection up to 98.7%. Addition of additive, polyethylene glycol 600 increased dyes rejection up to 99.8% and decreased the permeate flux to $3.6501L/m^2h$. This indicates that the addition of polyethylene glycol additive led towards better membrane performance. The morphological characteristics of NF membrane were analysed using a Scanning Electron Microscopy.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.10
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• pp.693-698
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• 1999

Vacuum interrupters have a special asymmetric electrode structure to generate an magnetic field and consequently to increase the interrupting ability. Accordingly 2-dimensional analysis has a large analysis error because radial flux can not be considered. In this paper, in order to analyse the electric field distribution of a vacuum interrupter with arc shield more accurately, 3-dimensional finite element method(FEM) is used. The induced electric potentials of floating shield was increased with the gap distance, which is because the relative position of shield is closer to the fixed contact so that the capacitance distribution inside interrupter is varied. The calculated results also show that the induced potential of shield causes electric field distortion so that the maximum value of electric field in a vacuum interrupter with arc shield is higher than that without one.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.12
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• pp.2230-2235
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• 2011

The purpose of this paper is to provide the unbalanced magnetic force and vibration mode comparison between two large interior permanent magnet machines(IPM) with different pole-slot combination considering stator and rotor eccentricity. Due to the punching tolerance, the mixed eccentricity of air-gap is inevitable. It will generate the asymmetric magnetic flux density in air-gap, which makes the unbalanced magnetic pull and vibration. The study is focused on the unbalanced magnetic force and their harmonic components according to eccentricity conditions such as static, dynamic and mixed. When the high vibration is produced especially resonance, the obtained results provide clues what eccentricity condition occurs in the machine.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.153-154
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• 2011

본 논문은 비대칭 2상 SRM의 센서리스 속도제어를 위한 초기각 검출 및 초기 기동방식과 자속관측기를 적용한 센서리스 제어에서 전동기의 온도 및 파라미터 변동에 의한 자속 오차 성분으로 인해 발생하는 위치 추정오차를 보상하기 위한 새로운 보상기를 제안한다. 제안된 방식은 전압펄스 인가로 초기각을 검출하고 검출된 초기 위치정보를 바탕으로 동일한 전압펄스 인가를 통해 비여자상이 여자상이 되는 회전자 위치를 검출하여 상여자를 교체하는 초기기동을 통해 자속관측기를 적용한 센서리스 제어로 안정적으로 진입하도록 한다. 이 때, 제안된 추정위치 보상기를 통해 추정된 센서리스 위치를 순시적으로 보상한다.