• 한국전기전자재료학회논문지
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• 제16권10호
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• pp.931-937
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• 2003

The principle of the superconducting vortex flow transistor (SVFT) is based on control of the Abrikosov vortex flowing along a channel. The induced voltage is controlled by a bias current and a control current, instead of external magnetic field. The device is composed of parallel weak links with a nearby current control line. We explained the process to get an I-V characteristic equation and described the method to induce the external and internal magnetic field by the Biot-Savarts law in this paper. The equation can be used to predict the I-V curves for fabricated device. From the equation we demonstrated that the current-voltage characteristics were changed with input parameters. I-V characteristics were simulated to analyze a SVFT with multi-channel by a computer program.

• 대한기계학회논문집A
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• 제31권5호
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• pp.594-600
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• 2007

Rapid mold heating has been recent issue to enable the injection molding of thin-walled parts or micro/nano structures. Induction heating is an efficient way to heat a conductive workpiece by means of high-frequency electric current caused by electromagnetic induction. Because the induction heating is a convenient and efficient way of indirect heating, it has various applications such as heat treatment, brazing, welding, melting, and mold heating. The present study covers an experimental investigation on the rapid heating using the induction heating and rapid cooling using a vortex tube in order to eliminate an excessive cycle time increase. Experiments are performed in the case of a steel cup mold core with various heating and cooling conditions. Temperature is measured during heating and cooling time, from which appropriate mold heating and cooling conditions can be obtained.

• 대한기계학회논문집B
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• 제21권1호
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• pp.49-56
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• 1997

Heat-transfer enhancement is seeked through modifications of fin surface. Real life plate-fin heat exchangers have complex three-dimensional geometries. Fins can have arrays of dimples and are attached to rows of penetrating tubes. To isolate the effect of surface modification, we model the real flow by a two-dimensional channel flow with a dimple on one side. The flow is analysed by solving the incompressible Navier-Stokes equation by a finite volume method on a generalized boundary-fitted coordinate. Results show a trapped vortex inside the dimple for all cases computed. Local maximum of Nusselt number occurs near the downstream end of the dimple, due to such a vortex. Location of the vortex does not change with respect to the wall temperature change, but moved downstream when Reynolds number increases. This, together with the results that in all cases vortex core is somewhat downstream of the dimple center, suggests that the mean flow above continuously feeds the kinetic energy to the recirculating flow. Heat transfer enhancement and pressure losses are studied through analysing the relevant dimensionless parameters like, Nusselt number and friction factor. In all cases computed, dimpled channel flow experiences less pressure loss than two-dimensional Poiseuille flow.

• 대한기계학회논문집B
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• 제35권3호
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• pp.263-268
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• 2011

본 연구는 볼텍스 형태를 대신하는 원심형태의 비 막힘형 2엽 수중 슬러리 펌프 임펠러를 개발하기 위해 수행하였다. 이를 위해 먼저 펌프 설계에 있어 중요한 변수로 입구면 날개각(blade angle)과 날개 길이 각(blade length angle) $\alpha$를 선정하여 이들이 펌프의 효율에 미치는 영향을 살펴보기 위해 상용 코드인 ANSYS CFX and BladeGen을 사용하여 해석을 수행하였다. 그 결과 입구면 임펠러 날개 형상은 $\beta$값이 $30^{\circ}$ 로 일정한 값을 가질 때 가장 높은 효율을 가지게 됨을 알 수 있었으며, $\alpha$값은 효율에 비례하는 특징을 가짐을 관찰할 수 있었다.

• 한국자동차공학회논문집
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• 제18권1호
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• pp.93-98
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• 2010

An object of this study is to confirm the opening amount of the throttle valve that is begun the temperature separation of vortex tube for various engine speed and load condition in a common rail diesel engine. The vortex tube located at downstream of the exhaust manifold is a device separating the incoming exhaust gas to hot and cold stream. To find optimum separation efficiency of vortex tube, the opening amount of throttle valve has been investigated for various engine speed and load conditions. Engine speed was found that the influence of engine speed was dominant compared with that of engine load. As engine speed was increased, the throttle opening amount starting temperature separation was reduced.

• 한국의류산업학회지
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• 제18권1호
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• pp.113-119
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• 2016

The evolution of spinning technology was focused on improving productivity with good quality of yarns. More detail spinning technology according to mixing of various kinds of fibre materials on the air vortex spinning system is required for obtaining good quality yarns. This paper investigated the physical properties of air vortex yarns compared with ring and compact yarns using PTT/tencel/cotton fibres. It was observed that unevenness of air vortex yarns was higher than those of ring and compact yarns, which resulted in low tenacity and breaking strain of air vortex yarns. Initial modulus of air vortex yarns was higher than those of ring and compact yarns. Yarn imperfections of air vortex yarns such as thin, thick and nep were much more than those of ring and compact yarns. These poor yarn qualities of air vortex yarn were attributed to the fasciated yarn structure with parallel fibres in the core part of the air vortex yarn. However, yarn hairiness of air vortex yarns was less and shorter than those of ring and compact yarns. Thermal shrinkage of air vortex yarns were higher than that of ring yarns, which was caused by sensible thermal shrinkage of PTT fibres on the bulky yarn surface and core part of air vortex yarns.

• 신재생에너지
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• 제10권4호
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• pp.9-15
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• 2014

In this study pressure and shaft torque pulsation were measured with variation of head and flow during the model test for a 15 MW Francis Turbine. Pressure pulsations were measured at the inlet of the spiral casing and 4 points in the cone of the diffuser and shaft torque pulsation at the upper position of the turbine. The maximum amplitude of pressure pulsation appeared 2.03% of the maximum rated head with the frequency of 25% of the rated revolution and at the guide vane opening of $10^{\circ}$. Shaft torque pulsation appeared 0.01% of the rated shaft torque, fairly low value. Air was admitted through the cone and pressure pulsation gradually decreased with increase of air flow and kept nearly constant after 5% of the rated flow. A new Francis turbine of which specific speed is 115 m-kW had been designed to rehabilitate the old one and the model test was performed at EPFL. The commercial code, STAR-$CCM^+$ was used for numerical simulation of flow.

• 동력기계공학회지
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• 제19권4호
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• pp.36-42
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• 2015

TMixed convective flow in a bottom heated and top cooled rectangular channel can be significantly affected by the channel aspect ratio, Prandtl number, Reynolds number, Rayleigh number and angle of inclination. In such a mixed convection, the flow pattern plays an important role in various technological processes. In this study, a numerical investigation is carried out to explore mixed convection in a three-dimensional rectangular channel with bottom heated and top cooled uniformly. The three-dimensional governing equations are discretized using the finite volume method. In the range of low Reynolds number($0{\leq}Re{\leq}9.6{\times}10^{-2}$), the effects of the aspect ratio($2{\leq}AR{\leq}12$) and Gr/Re are presented and discussed. The longitudinal roll number in the channel is increased with increasing aspect ratio, and the roll number induced, regardless of the aspect ratio number, is even in the range of aspect ratios between 2 and 12, New vortex flow structure containing inclined longitudinal rolls is found, which is affected by aspect ratio and Reynolds number. The ratio Gr/Re is used to check the relative magnitudes of forced and natural convection in the mixed convective flow of high viscous fluid.

• 한국전산유체공학회지
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• 제20권4호
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• pp.7-13
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• 2015

Vortex tube is a thermal static device that separates compressed air into hot and cold streams. In general, the cooling efficiency of vortex tubes is lower than that of traditional air conditioning equipment and vortex tubes are mainly used for industrial spot cooling applications because of their quick responses. In this study, conical frustums are employed in the nozzle chamber to improve the cooling performance. Conical frustums can be used to decrease the ineffective mass fraction that directly passes through the cold exit without energy separation. The shape optimization of conical frustums has been performed using full factorial design. It is found that the height of frustums has the largest main effects on the cooling performance. Computational results show that the cooling performance can be increased by about 10% within the considered range of the design parameters. This is because the ineffective mass fraction toward the cold exit is decreased by about 20%.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.546-549
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• 2003

The principle of the superconducting vortex flow transistor (SVFT) is based on control of the Abrikosov vortex flowing along a channel. The induced voltage is controlled by a bias current and a control current, instead of external magnetic field. The device is composed of parallel weak links with a nearby current control line. We explained the process to get an I-V characteristic equation and described the method to induce the external and internal magnetic field by the Biot-Savarts law in this paper. The equation can be used to predict the I-V curves for fabricated device. From the equation we demonstrated that the current-voltage characteristics were changed with input parameters. I-V characteristics were simulated to analyze a SVFT with multi-channel by a Matlab program.