• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.1
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• pp.28-35
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• 1995

The fluid flow for a energy transfer is essential for the design and operation of power plants, petrochemical plants and ships including a process. When the operating conditions of a plant are changed or any transitional event occured, the flow controls of a fluid must be performed to follow the new operating state or mitigate the results of a event. Generally these flow controls to accommodate the new operating state of a plant are made by the use of various valves. The refore the design of valves and the related techniques are very important to the system and component designs. However the system and component design are not familiar with the practical theory of the valve since the derivative procedures of the flow equations in a valve are difficult and it is not easy to found the theoretical foundamentals and informations about the design of a valve from the present references. In this study the flow equations applicable to a valve for liquid are theoretically derived in detail. And the definition of valve reynolds number and its boundary values between the tubulent and laminar flow is described compared with the values of a circular pipe flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.7
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• pp.608-615
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• 2012

In this study, we analyzed the system impedance of Unmanned Aerial Vehicle avionics bay and Environmental Control System(ECS), and estimated the proper air flow rate to be supplied avionics equipments. As the result of estimation, we evaluated the performance of ECS after analysing the flow balance rate and the air flow rate about each outlet port, and simultaneously decided the flow balance rate after evaluating the thermal substantiality by the thermal analysis of avionics bay. In order to verify the property of analysis result, we conducted the flow balance test using the actual avionics equipments and finally deduced the flow rate to be met system requirements of avionics equipments. Also, as the analysis results, we verified the satisfaction of system requirements at midium altitude condition and proved the performance characteristics of an Environmental Control System(ECS).

• Journal of Power Electronics
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• v.7 no.4
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• pp.286-293
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• 2007

This paper proposes a distribution voltage control method when a voltage increase condition occurs due to reverse power flow from the clustered photovoltaic (PV) system. This proposed distribution voltage control is performed a by distribution-unified power flow controller (D-UPFC). D-UPFC consists of a hi-directional ac-ac converter and transformer. It does not use any energy storage component or rectifier circuit, but it directly converts ac to ac. The distribution model and D-UPFC voltage control using the ATP-EMTP program were simulated and the results show the voltage increase control in the distribution system.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.2
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• pp.331-336
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• 2013

The purpose of this study is to visualize the characteristics of ER fluids as preceding step of developing 3 port ER valves. As the strength of the electric field increases, more clusters in flow are made and these clusters are thought to be the reasons of the load flow rate being increased and the outlet flow rate being decreased. The ER Valves and load and outlet flow rate check method are considered to be applied to the fluid power control system. Using the manufactured pressure control valve, a one-link manipulator with FHA in robot system is driven. As a result, it is experimentally confirmed that the pressure control valve using ER fluids is applicable to use in driving actuator. If it applies characteristics of the ER fluids, it will be able to apply in the control system for the ER Valve which occurs from industrial controller(PLC).

• The KIPS Transactions:PartD
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• v.11D no.2
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• pp.415-422
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• 2004

Automation systems improve the productivity of works which relate to product design, facilities management, fault processing and quality evaluation. In these systems, the description language for monitoring and control process is called new control language. These are five flow control languages : IL, ST, FBD, SFC and LD. IL and ST are based on left form. FBD, SFC and LD are based on graphic form. Generally, a software which monitors and controls a system is allowed to use just one flow control language. It is impossible to use more than two languages for simulation in the same system environment. In this paper, we analyzed the characteristics of flow control languages and the process of programming in the legacy system. In addition, for the Integrated processing of languages, we propose Extended ST based on the high-level ST language. Based on this research, we implement a graphical language editor and EST-IL convertor. The graphical language editor makes sequence rules, and converts graphical language into EST. EST-IL convertor has a function to convert EST into IL which is similar to assembly language. As the result of this paper, we present a scheme which integrates all the flow control language processing based on IL.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.8
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• pp.577-584
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• 2007

A variable-flow-rate balancing valve has been developed and optimized to apply to a distributor in a hot-water heating system. Fluid dynamic performance of the system was evaluated by comparing the results with the previous pressure difference control valve (PDCV) system. In view of the variations of pressure drop and flow rate according to the sequential closing of the control valves, the present system which is named "smart system distributor", is very stable without a certain flow rate concentration. The level of pressure drop variation is also low as compared with the previous system with a PDCV. In view of the occurrence of cavitation, the present system is quite superior to the previous system because the instantaneous pressures at all sections are much higher than the vapor pressure. On the other hand, the previous system has a possibility of cavitation when one or more control valves are closed.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.7-12
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• 2009

A nuclear fuel test loop(after below, FTL) is installed in the IRI of an irradiation hole in HANARO for testing the neutron irradiation characteristics and thermo hydraulic characteristics of a fuel loaded in a light water power reactor or a heavy water power reactor. There is an in-pile section(IPS) and an out-pile section(OPS) in this test loop. When HANARO is operated normally, the fuel loaded into the IPS has a nuclear reaction heat generated by a neutron irradiation. To remove the generated heat and to maintain the operation conditions of the test fuel, a main cooling water system(MCWS) is installed in the OPS of the FTL. The MCWS is composed of a main cooler, a pressurizer, two circulation pumps, a main heater, an interconnection pipe line and instruments. The interconnection pipeline is a closed loop which is connected to an inlet and an outlet of the IPS respectively. The MCWS is under a cold function test during a start-up period. This paper describes the system flow network analysis results of the flow control of a main cooling water system in the HANARO fuel test loop. It was confirmed through the results that the flow was met the system design requirements.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.473-474
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• 2013

In this paper, a power flow control of PV hybrid module system with ESS is proposed. Photovoltaic(PV) hybrid module system is consist of individual converter, central inverter, and energy storage system(ESS). Because PV power can be changed in particular hours and environment condition, the power management control for ESS is required. In this paper, the power flow control method for PV hybrid module system with ESS is proposed. The validity of proposed control method is verified by simulations and theoretical analysis.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.342-344
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• 2006

The modem enormous electric power system has made power system analysis much more complex and difficult. For effective analysis of the power system, model reduction and aggregation is required. In this paper, a new aggregation method is presented to aggregate the coherent generators in the large scale power system while matching the power flow. In order to demonstrate the effects of this aggregation method, it is applied to a small scale power system. A multi-variable control technique of $H_{\infty}$ control is also applied to enhance the dynamic stability of the aggregated power system.