• Journal of Environmental Science International
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• v.20 no.8
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• pp.929-942
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• 2011

A novel conductivity technique was developed to detect penetration depth of the vessel fluid into the feedpipe. For a given reactor geometry, critical agitator speeds were experimentally determined at the onset of feedpipe backmixing using Rushton 6 bladed disk turbine (6BD) and high efficiency axial flow type 3 bladed (HE-3) impellers. The ratio of the feedpipe velocity to the critical agitator speed ($v_f/v_t$) was constant for either laminar or turbulent feedpipe flow regimes. Compared to the results of fast competitive reaction, feedpipe backmixing had to penetrate at least one feedpipe diameter into the feedpipe to significantly influence the yield of the side product. However, higher $v_f/v_t$ than that for L/d = 0 (position at the feedpipe end) of the conductivity technique is recommended to completely eliminate feedpipe backmixing in conservative design criteria. The conductivity technique was successful in all feedpipe flow conditions of laminar, transitional and turbulent flow regimes.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.152.1-152
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• 2001

This paper presents a high performance and cost effective way by using an FPGA circuit to implement torque controller so that the SRM can operate at high speed. In order to increase the operating speed, we need to implement both the torque and the current controllers by using an FPGA. However, it is difficult to implement all of the torque controller in the FPGA. Moreover, implementation of a time critical part is sufficient for improving the performance. One of the time critical part is the switching angle control. In this study, torque controller which calculate the switching on and commutation angles is implemented in PC because these angle are a function of rotor velocity which is varied slowly, and switching angle controller ...

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1521-1527
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• 2009

This study is aimed to analyze the floe patterns and thermal characteristics by computer simulation under the variations of fire strength for the logitudinal tunnel, from which flow and heat distributions are predicted in the longitudinal tunnel. Through the results of numerical computations, followings are found; one is that the volume flow rate is discontinuously increasing as closer to fire location, and the other is that a critical design to get the faster flow rate is required because of existence of backlayer flow for the high fire strength in view of safety for the people in fire of the tunnel.

• Nuclear Engineering and Technology
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• v.29 no.4
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• pp.348-359
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• 1997

This paper reviews cooling aspects of the diverter system in Tokamak fusion devices with primary emphasis on the critical heat flux (CHF) issues for oater-cooled designs. General characteristics of four (4) coolant options for diverter cooling gases, oater, liquid metal, and organic liquid - are discussed first, focusing on the comparison of advantages and disadvantages of those options. Then results of recent studies on the high-heat-flux CHF of water at subcooled high-velocity conditions are reviewed to provide a general idea on the feasibility of the water-cooled diverter concept for future Tokamak fusion reactors. Water is assessed to be the most viable and practical coolant option for diverters of future experimental Tokamaks.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.273-277
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• 2004

This paper deals with the dynamic stability and vibration of a non-uniform cantilevered pipe conveying fluid. The present model consists of two segments with different cross-sections. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The critical flow velocities and stability maps of the pipe are obtained by changing step ratios, mass ratios and internal damping parameters of the pipe. Finally, the vibrational modes associated with flutter are shown graphically.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.67-74
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• 2006

The paper presents gravitational effect on eigenvalue branches and flutter modes of a vertical cantilevered pipe conveying fluid. The eigenvalue branches and modes associated with flutter of cantilevered pipes conveying fluid are fully investigated. Governing equations of motion are derived by extended Hamilton's principle, and the related numerical solutions are sought by Galerkin's method. Root locus diagrams are plotted for different values of mass ratios of the pipe, and the order of branch in root locus diagrams is defined. The flutter modes of the pipe at the critical flow velocities are drawn at every one of the twelfth period. The transference of flutter-type instability from one eigenvalue branches to another is investigated thoroughly.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.300-303
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• 2008

In the present study, the simple form of the heat transfer equation were suggested to estimate the temperature variation inside the oil pipe in order to determine the thickness of the insulating materials to retain the working oils below the critical temperature. The conservation of the thermal energy at arbitrary time were modeled to one dimensional unsteady equation with the empirical formula or data. The calculating results for non-insulation case showed that the temperature were very sensitive to the thermal convection by the velocity of the external wind. For insulation case, the insulation material which has higher density and specific heat, lower thermal conductivity should be chosen with more brighter coloring outside the pipe in order to retain the working oils below the critical temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.613-616
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• 2001

This SF6 gas is widely used in industrial of insulation field. In this paper, N2 is mixed to improve pure SF6 gas characteristics. Electron transport coefficients in SF6-N2 mixture gases are simulated in range of E/N values from 70 to 400 [Td] at 300K and 1 Torr by using Boltzmann equation method. The results of this method, which are like electron drift velocity, ionization coefficient, attachment coefficient, effective ionization coefficient, and critical EIN, can be important data to present characteristic of gas for insulation. Specially critical E/N is a data to evaluate insulation strength of a gas and is presented in this paper for various mixture ratios of SF6-N2 mixture gases.?⨀␍?܀㘱〮㜳㬓M敤楣楮攠慮搠桥污瑨

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1041-1047
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• 2004

This paper deals with the dynamic stability and vibration of a discontinuous cantilevered Pipe conveying fluid. The present model consists of two segments with different cross-sections. Governing equations of motion are derived by extended Hamilton's principle, and the numerical scheme using finite element method is applied to obtain the discretized equations. The critical flow velocities and stability maps of the pipe are obtained by changing ratios of second area moment of inertia and mass ratios. Finally, the vibrational modes associated with flutter are shown graphically.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.552-557
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• 1997

Based on the bubble coalescence adjacent to the heated wall as a flow structure for CHF condition, Chang and Lee developed a mechanistic critical heat flux (CHF) model for subcooled flow boiling. In this paper, improvements of Chang-Lee model are implemented with more solid theoretical bases for subcooled and low-quality flow boiling in tubes. Nedderman-Shearer's equations for the skin friction factor and universal velocity profile models are employed. Slip effect of movable bubbly layer is implemented to improve the predictability of low mass flow. Also, mechanistic subcooled flow boiling model is used to predict the flow quality and void fraction. The performance of the present model is verified using the KAIST CHF database of water in uniformly heated tubes. It is found that the present model can give a satisfactory agreement with experimental data within less than 9% RMS error.