• Journal of Power System Engineering
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• v.22 no.6
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• pp.28-35
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• 2018

The large-eddy simulation (LES) was carried out to evaluate the instantaneous vector and vorticity profiles of a small-size axial fan (SSAF) at the operating point of full-flowrate. The downstream flow of the SSAF exhibits a shorter axial flow when not fully developed, especially the stronger vortex appears at the edge near the flow end. On the other hand, the downstream flow of the SSAF exhibits a longer axial flow, and the weaker vortex appears at the edge near the flow end when the flow is sufficiently developed. Moreover, in the downstream of the SSAF, a periodic and intermittent flow pattern appears at the edge showing the axial flow, and the instantaneous vorticity contour lines showing the form of a circle group are distributed at specific intervals from the downstream region of the blade tip, which is considered to be the result of the intermittency phenomenon influenced by the number of blades and the number of revolutions.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.310-316
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• 2019

Fluidelastic instability is a key issue in steam generator tube bundles subjected in cross-flow. With a low flow velocity, a large amplitude vibration of the tube observed by many researchers. However, the mechanism of this vibration is seldom analyzed. In this paper, the mechanism of cross-flow effects on fluidelastic instability of tube bundles was investigated. Analysis reveals that when the system reaches the critical state, there would be two forms, with two critical velocities, and thus two expressions for the critical velocities were obtained. Fluidelastic instability experiment and numerical analysis were conducted to obtain the critical velocity. And, if system damping is small, with increases of the flow velocity, the stability behavior of tube array changes. At a certain flow velocity, the stability of tube array reaches the first critical state, a dynamic bifurcation occurs. The tube array returns to a stable state with continues to increase the flow velocity. At another certain flow velocity, the stability of tube array reaches the second critical state, another dynamic bifurcation occurs. However, if system damping is big, there is only one critical state with increases the flow velocity. Compared the results of experiments to numerical analysis, it shows a good agreement.

• Journal of Drive and Control
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• v.16 no.4
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• pp.1-8
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• 2019

The HPM (High-speed Power Matching) system is an electro-hydraulic control system. It directly controls the swash plate of the pump by selecting four-loop logic based on joystick signals, pump flow, and pressure signal to improve the efficiency and controllability of construction machines. In the NFC (Negative Flow Control) system, a typical pump control system using conventional open center type MCV, the loss is continuously generated by flow through the center bypass line even when the excavator is not in operation. Also, due to the slow response of the pump that indirectly controls the flow rate using the pressure regulator, peak pressure occurs at the start or stop of the operation. Conversely, the HPM system uses an MCV without center-by-pass flow path and the swash plate of a pump for the HPM is controlled by a high-speed proportional flow control valve. As a result, the HPM system minimizes energy loss in standby state of the excavator and enables peak pressure control through rapid electro-hydraulic control of a pump. In this paper, the concept of the HPM system algorithm is introduced and the hydraulic system efficiency is compared with the NFC system using the excavator SAT (System Analysis Tool).

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.4
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• pp.3980-3990
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• 1975

This study was carried out to develop a method of grain drying ststem that can be done by forcing the heated-air directly into the grains within the sack. The air duct was pushed into the central position of the grain-deposited sack and the heated-air was forced to flow in the radial direction. The system is referred here as the unit sack drying system. At a first step of this study, an air flow resistance tester was constructed to measure the resistance of air flow to grains in cooperated with some different sack materials, the sack materials, the tested were rice-straw bag, sack of polyethylene film, and jute sack In addition, unit sack drying system was constructed to investigate the drying characteristics of the dryer. on this dryer, two kind of terminal air ducts were attached and tested to examine its effects on uniform drying, and also, aseries of drying test was performed to trace the effect of increasing air flow rate on uniform drying. The results are as follows: 1) Resistance of air flow for each sack material was increased almost proportional to the increasing rate of air flow. Experimental data showed little significant differences of the air flow resistance among the materials. 2) From the comparison with air flow resistance of sack material and that of roughrice, it was indicated that airflow resistance of sack material was much higher than that of rice rough Therefore, in the unit sack drying sysle in which air flow is destined to face the sach material after leaving the grain, it was suggested that air flow would be inuniform to each part of grain within sack because of much higher air flow resistance of sack material than that of grain, and the fact would results inuniform grain drying. 3) Drying test on the unit sack drying system in cooperated with different type of terminal air ducts showed that high speed air is better for uniform drying than in high pressure. with the drying system which was assembled with the air ducts delivering higher speed air, there also involved a problem of significant inuniform drying. Therefore, any means to improve the inuniform drying should be undertaken for practical use. 4) A series of drying test with in creasing air flow rate resulted that increasing air flow rate in the unitsack drying system gave little effect on uniform drying, therefore, it is recommened to change its drying system for drying grain uniformly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.398-410
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• 1998

Two-phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and the liquid transportation system. The particular flow pattern depends on the conditions of pressure, flow velocity, and channel geometry. However, the research on drag reduction in two-phase flow is not intensively investigated. Therefore, experimental investigations have been carried out to analyze the drag reduction and void fraction by polymer addition in the two-phase flow system. We find that the polymer solution changes the characteristic of two-phase flow. The peak position of local void friction moves from tile wall of the pipe to the center of the pipe when polymer concentration increase. And then we predict that it is closely related with the frau reduction.

• Journal of Korean Society on Water Environment
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• v.23 no.3
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• pp.332-338
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• 2007

In this study the flow duration curves for Nakdong river basin are analyzed. The TANK model is used as a hydrologic simulation model whose parameters are estimated from 8-day intervals flow data measured by NIER Nakdong River Water Environment Laboratory. As a comparison result between generated natural and present river flow, the present river flow is higher than the natural river flow in the up- and mid-stream of Nakdong river, while the present river flow is lower than the natural river flow in the down stream of Nakdong river.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.1
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• pp.32-41
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• 2003

For the countermeasure of expected higher thermal load in miller cycle engine, coolant flows in the cylinder head of base engine with several coolant flow methods and drilled hole passages were measured by using PIV technique. And the cooling effect was evaluated by measurements of wall temperatures according to each coolant flow method. It was found that the series flow system was most suitable among the discussed 3 types of coolant flow methods since it had the best cooling effect in cylinder head by the fastest coolant flow velocity It was also found that for drilled water passage to decrease the large thermal load in exhaust valve bridge, nozzle type is more effective compared with round type of water passage, and its size has to be determined according to the coolant flow pattern and velocity in each cylinder.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.1-8
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• 2013

In nuclear power plant, the reactor cooling system has maintained high-Reynolds-number flow above 1E+07 to cool a heat generated by the reactor. To minimize uncertainty for flow calibration, it is necessary to simulate the high Reynolds' number flow. Y-connection is selected to connect four (4) parallel high flow circulation pumps for maintaining the high flow rate. This paper describes the characteristics for Y-connection by computer flow simulation. It was confirmed through the results that the pressure loss of the Y-connection was lower than that of T-connection. Also as the connection angle of Y-connection was small, as the pressure loss was low.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2064-2070
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• 1995

Characteristics of thermal flow stratification were studied experimentally by using the small scale pressurizer-surge line model. Thermal flow stratifications in the horizontal section of surge line were analyzed by the relation between the maximum temperature difference at any cross section in surge line and the Froude number representing the boundary conditions, i.e., in/out surge flow velocity and temperature difference of system. Thermal flow stratifications in outsurge flow decreased inversely proportional to the Froude number and did not exist for Fr>1. In insurge flow thermal flow stratifications disappeared near Fr=1.5, but resulted in the higher temperature difference than the case of outsurge flow.