• 대한기계학회논문집B
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• 제35권5호
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• pp.503-511
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• 2011

수분류 스프레이 냉각은 $900^{\circ}C$ 이상의 고온에서 강판을 냉각하는데 매우 중요한 기술이다. 본 연구는 냉각수온이 고온 강판의 수분류 스프레이 냉각에 미치는 영향을 고찰하였다. 이 때의 열유속은 시편, 카트리지히터, 열전대의 조합으로 고안된 열유속게이지를 제작하여 엄밀하게 측정되었다. 스프레이는 fullcone 노즐로부터 생성되고 냉각실험은 일정한 스프레이 질량유속과 노즐과 표면 사이의 거리 조건에서 수행되었다. 냉각수온의 효과는 $5^{\circ}C$에서 $45^{\circ}C$까지 다섯 가지의 서로 다른 수온에 대한 수분류 스프레이 냉각의 열전달 현상을 비교 및 평가하였다. 여기서 열유속곡선과 열전달계수는 고온 강판의 냉각공정에서 실제 스프레이 냉각을 위한 기본 데이터로 활용될 수 있다.

• Transactions on Electrical and Electronic Materials
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• 제9권6호
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• pp.255-259
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• 2008

The magnetic field application effect on resistance of a high-$T_c$ superconducting (HTSC) element comprising a flux-lock type superconducting fault current limiter (SFCL) was investigated. The YBCO thin film, which was etched into a meander line using a lithography, was used as a current limiting element of the flux-lock type SFCL. To increase the magnetic field applied into HTSC element, the capacitor was connected in series with a solenoid-type magnetic field coil installed in the third winding of the flux-lock type SFCL. There was no magnetic field application effect on the resistance of HTSC element despite the application of larger magnetic field into the HTSC element when a fault happened. The resistance of HTSC element, on the contrary, started to decrease at the point of four periods from a fault instant although the amplitude of the applied magnetic field increased.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.346-350
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• 2001

PMSM drives are widely used in the industrial and residential applications because of high efficiency, high power density and high performance. For better performance of PMSM, however, torque ripples should be reduced. This paper investigates a reduction of torque ripple due to the unsinusoidal flux linkage produced by the shapes of stator slot and magnetic pole. To minimize torque ripple, a simple flux estimator is proposed. This method interatively compensates the distributed flux linkage from an error between the measured and estimated currents. The proposed algorithm is verified through simulation.

• 설비공학논문집
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• 제3권5호
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• pp.395-403
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• 1991

The purpose of this investigation was to characterize nucleate boiling and burn-out heat flux for rectangular free jet with saturated water impinging perpendicularly and upward against a flat uniform heat flux surface. Heat flux measured for Reynolds number based on rectangular nozzle width and for aspect ratio. The result of nucleate boiling heat transfer was presented nondimensional experimental equation including Nusselt, Boiling, Subcooling, Reynolds and Weber number. The effect of aspect ratio of heated surface in the burn-out heat flux had not appeared distinctly. But for the same aspect ratio, burn-out heat flux increased linearly with increment of nozzle exit velocity.

• Journal of Welding and Joining
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• 제11권2호
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• pp.13-20
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• 1993

The object of the research is to develop the flux for aluminum brazing. Five kinds of flux were applied to brazing joint with fin and tube structure using same filler metal. To estimate the performance of the developed flux, products analysis, differential thermal test, grain size test, observation of crystalline structure, tensile test, corrosion test were made. From the results of experiment, the following conculsions were obtained. 1. The optimum composition ratio (Wt) of AlF$_3$ and KF was 50-60% : 40-50% 2. The optimum melting point of the flux was 567-578$^{\circ}C$.

• Korean Chemical Engineering Research
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• 제52권3호
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• pp.294-301
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• 2014

This study focuses on analysis and comparison of entropy generation in various cross-sectional ducts along with fully developed laminar flow and constant uniform wall heat flux. The obtained results were compared in ducts with circular, semicircular, and rectangular with semicircular ends, equilateral triangular, and square and symmetrical hexagonal cross-sectional areas. These results were separately studied for aspect ratio of different rectangular shapes. Characteristics of fluid were considered at average temperature between outlet and inlet ducts. Results showed that factors such as Reynolds number, cross section, hydraulic diameter, heat flux and aspect ratio were effective on entropy generation, and these effects are more evident than heat flux and occur more in high heat fluxes. Considering the performed comparisons, it seems that semicircular and circular cross section generates less entropy than other cross sections.

• Journal of Mechanical Science and Technology
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• 제17권7호
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• pp.1063-1072
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• 2003

Direct immersion cooling has been considered as one of the promising methods to cool high power density chips. A fluorocarbon liquid such as FC-72, which is chemically and electrically compatible with microelectronic components, is known to be a proper coolant for direct immersion cooling. However, boiling in this dielectric fluid is characterized by its small value of the critical heat flux. In this experimental study, we tried to enhance the critical heat flux by increasing the nucleate boiling area in the heat spreader (Conductive Immersion Cooling Module). Heat nux of 2 MW/㎡ was successfully removed at the heat source temperature below 78$^{\circ}C$ in FC-72. Some modified boiling curves at high heat flux were obtained from these modules. Also, the concept of conduction path length is very important in enhancing the critical heat flux by increasing the heat spreader surface area where nucleate boiling occurs.

• 한국소음진동공학회논문집
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• 제26권7호
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• pp.875-880
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• 2016

A new hybrid permanent magnet biased magnetic levitation actuator (maglev) is developed. This new maglev actuator is composed of two C-core electromagnetic cores separated with two permanent magnets. Compared to the conventional hybrid maglev actuators, the new actuator has unique flux paths such that bias flux paths are separated with control flux paths. The control flux paths have minimum reluctances only developed by air gaps, so the currents to produce control fluxes can be minimized. The gravity load can be compensated with the permanent magnet bias fluxes developed at off-centered air gap positions while external disturbances are controlled with control fluxes by currents. The consumed power to operate this levitation system can be minimized. 1-D magnetic circuit model is developed for this model such that the flux densities and magnetic forces are extensively analyzed. 3-D finite element model is also developed to analyze the performances of the maglev actuator.

• Transactions on Electrical and Electronic Materials
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• 제8권5호
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• pp.222-225
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• 2007

In this paper, we compared the current limiting characteristics of both the hybrid type and the flux-lock type superconducting fault current limiters(SFCLs), which have a magnetic coupling structure between a primary winding and several secondary windings. The limiting impedances of two SFCLs were derived from each equivalent circuit considering the design parameters of SFCL such as the self-inductance of secondary winding and the resistance of $high-T_C$ superconducting(HTSC) element. Through the comparison for the limiting impedances of two SFCLs considering the dependence of the HTSC element's resistance on the applying voltage into the SFCL, the hybrid type SFCL was confirmed to have larger limiting impedance with smaller resistance of HTSC element than the flux-lock type SFCL. It was expected from the analysis that the hybrid type SFCL was more advantageous than the flux-lock type SFCL from the viewpoint of the fault current limiting level.

• Progress in Superconductivity
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• 제4권1호
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• pp.27-31
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• 2002

MgB$_2$samples have been prepared by a stoichiometry mixture of Mg and B inside stainless steel tubes(Commercial Stainless Steel Tube Enveloping Technique). XRD data show that there are no second phases like MgO. The transition temperature of specimens is 37.5 K with a sharp transition width of ΔTc within 1K. From magnetic hysteresis measurement, flux jump was shown up to 15K, which was higher than that of samples by other methods. We have concluded that the flux jump is mainly affected by impurities and second phases.