• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.585-591
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• 2016

DOCR can be used to efficiently increase the reliability and to protect the bi-directional D/L(Distribution Lines). As more DG(Distributed Generation)s attempt to connect the bi-directional D/L, there is an increasing need for studies of how to use DOCR installed in the D/L. This paper investigates the operating principles of DOCR and presents the results an effect of sequence and fault impedance in L-L(Line to Line) fault. An advanced DOCR operating algorithm is proposed to reduce the mal-operation of conventional DOCR. The proposed algorithm is applied to the bi-directional power flow system and shows that it decreases the mal-operation of DOCR through the computer simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1512-1518
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• 2009

Recently, new dispersed power sources such as photovoltaics, wind power, fuel cell etc. are energetically interconnected and operated in the distribution systems, as one of the national projects for alternative energy. This paper deals with the optimal countermeasures for the mal-function of protective devices at primary feeder in distribution systems when new power sources like photovoltaic (PV) systems are interconnected, based on the symmetrical components of short circuit studies. When new power sources are considered to be interconnected to distribution systems, bi-directional power flow and interconnection transformer connection of new power sources may cause the operation problems of protective devices (mainly re-closer), since new power sources can change typical characteristics of distribution systems. Therefore, this paper shows an analysis skill of the mal-functional mechanism of protective relay and proposes the optimal solution for the mal-function problem using the symmetrical components of fault analysis. And, this paper also shows the effectiveness of proposed method by the simulation at the field distribution systems.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1195-1202
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• 2004

In this paper an experimental study was investigated for two-phase flow distribution in compact heat exchanger header. A test section was consisted of the horizontal bottom dividing header($\phi$: 5 mm, L: 80 mm) and 10 upward circular mini channels ($\phi$: 1.5 mm, L: 850 mm) using an acrylic tube. Three different types of tube intrusion depth were tested for the mass flux and inlet mass quality ranges of 50 - 200 kg/$m^2$s and 0.1 - 0.3, respectively. Air and water were used as the test fluids. The distribution of vapor and liquid is obtained by measurement of the total mass flow rate and the calculation of the quality. Two-phase flow pattern was observed, and pressure drop of each channel was measured. By adjusting the intrusion depth of each channel an uniform liquid flow distribution through the each channel was able to solve the mal-distribution problem.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.73-83
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• 2014

CFD(computational fluid dynamics) model is developed to simulate direct injection of ammonia gas phase from ammonia transporting materials into the SCR catalyst in the exhaust pipe of the engine with solid SCR. Configurations of one-hole and four-hole nozzle, circumferential type, porous tube type, and the effect of mixer configurations which commonly used in liquid injection of AdBlue are considered for complex geometries. Mal-distribution index related to concentration of ammonia gas, flow uniformity index related to velocity distribution, and pressure drop related to flow resistance are compared for different configurations of complex geometries at the front section of SCR catalyst. These results are used to design the injection system of ammonia gas phase for solid SCR of target vehicle.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.244-249
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• 2005

Flow distribution and pressure drop analysis for an inlet plenum of a Pebble Bed Modular Reactor (PBMR) have been performed using Computational Fluid Dynamics. Three-dimensional Navier-Stokes equations have been solved in conjunction with $k-{\epsilon}$ model as a turbulence closure. Non-uniformity in flow distribution is assessed for the reference case and parametric studies have been performed for rising channels diameter, Reynolds number and angle between the inlet ports. Also, two different shapes of the inlet plenum namely, rectangular shape and oval shape, have been analysed. The relative flow mal-distribution parameter shows that the flow distribution in the rising channels for the reference case is strongly non-uniform. As the rising channels diameter decreases, the uniformity in the flow distribution as well as the pressure drop inside the inlet plenum increases. Reynolds number is found to have no effect on the flow distribution in the rising channels for both the shapes of the inlet plenum. The increase in angle between the inlet ports makes the flow distribution in the rising channels more uniform.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.371-375
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• 2009

The distribution control of refrigerant flow is one of the basic technique to enhance system efficiency. However, if engineers forget to control the refrigerant flow speed in all operation range, refrigerant flow mal distribution becomes a noise source. The refrigerant flow noise should be checked and controlled at the lowest air flow mode which is the most silent mode and frequently used in night time.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.340-345
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• 2008

A computer program, which simulates the parall flow evaporator was developed. The program was having used to simulate the sample $650\;mm{\times}190\;mm$ frontal area, 25 mm flow depth and 3.0 mm fin pitch. It was shown that the cooling capacity of 3kW could be available from the sample. The present model, however, does not consider refrigerant mal-distribution in each pass, which is known to reduce the cooling capacity of the parallel flow heat exchanger.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.780-787
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• 2006

Several types of different header designs are numerically studied to have uniform distribution of two phase flow in the evaporator header having multi-channels. The different geometries include the inlet tube position into the header and the width of header. In the numerical calculation, two types of two-phase model such as homogeneous model and VOF(Volume Of Fluid) model are employed. In this study, the mal-distribution number, $M_d$, is newly defined to evaluate the averaged level of the flow distribution in the whole passes of the evaporator. As results, two phase flow in the header can be visualized using post-processing of numerical results. Furthermore, the optimum position of the inlet tube into the header and the width of header can be proposed for the better distribution of refrigerant(R-134a) flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.269-273
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• 2011

In present paper focused on the influence of the inlet-outlet area ratio of counter flow manifold on the flow distribution and pressure drop characteristics of a tubular heat exchanger. The characteristics of flow distribution and pressure loss can be obtained depending on the inlet-outlet area ratio. In this paper, a tubular heat exchanger can be designed with minimum flow mal-distribution and better characteristic of pressure loss by choosing the optimum inlet-outlet area ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.834-839
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• 2009

A three-dimensional computational fluid dynamics (CFD) analysis is performed to investigate flow characteristics in the anode channels and manifold of the internal reforming type molten carbonate fuel cell (MCFC). Considering the computational difficulties associated with the size and geometric complexity of the MCFC system, the polyhedral meshes that can reduce mesh connectivity problems at the intersection of the channel and the manifold are adopted and chemical reactions inside the MCFC system are not included. Through this study, the gas flow rate uniformity of the anode channels is mainly analyzed to provide basic insights into improved design parameters for anode flow channel design. Results indicate that the uniformity in flow-rate is in the range of ${\pm}$1% between the anode channels. Also, the mal-distributed inlet flow-rate conditions and the change in the size of the manifold depth have no significant effect on the flow-rate uniformity of the anode channels.