• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.1029-1040
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• 2021

For the structural integrity evaluation of pressurized water reactor (PWR) steam generator (SG) tubes subjected to transient hydraulic loading, determination of the tube-to-tube gap velocity and static pressure distributions along the tubes is prerequisite. This paper addresses both computational fluid dynamics (CFD) and analytical approaches for predicting the tube-to-tube gap velocity and static pressure distributions during blowdown following a feedwater line break (FWLB) accident at a PWR SG. First of all, a comparative study on CFD calculations of the transient velocity and pressure distributions in the SG secondary sides for two different models having 30 or no tubes is performed. The result shows that the velocities of sub-cooled water flowing between any adjacent two tubes of a tubed SG model during blowdown can be roughly estimated by applying the specified SG secondary side porosity to those of the no-tubed SG model. Secondly, simplified analytical approximate solutions for the steady two-dimensional SG secondary flow velocity and pressure distributions under a given discharge flowrate are derived using a line sink model. The simplified analytical solutions are validated by comparing them to the CFD calculations.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1384-1387
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• 2007

We have investigated the sputtering and secondary electron emission characteristics of MgO protective layer according to the $O_2$ partial pressure. The MgO layer have been deposited by electron beam evaporation method and have varied the $O_2$ partial pressure as 0, $5.2{\times}10^{-5}$, $1.0{\times}10^{-4}$, and $4.1{\times}10^{-4}$ Torr. It has been known that the secondary electron emission coefficient and the number of defect energy levels increased as the $O_2$ partial pressure increases. So we have investigated the property of sputtering yield according to the $O_2$ partial pressure. We have known that the sputtering yield deceases as the $O_2$ partial pressure increases by using the FIB system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.784-795
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• 1995

This paper represents the results of the experiments of the three-dimensional flow and the aerodynamic loss caused by the three-dimensional flow within the plane bucket blades. To research the secondary flow and the aerodynamic loss, the large-scale plane bucket blade of lst-stage in the low pressure steam turbine is made of FRP. The detailed investigation of the secondary flow and the aerodynamic loss using 5-hole pressure probe within turbine cascade has been carried out in the low speed wind tunnel. The limiting streamlines of the suction and endwall surface have been visualized by the oil film method. The flow visualization of the secondary flow has been performed by the laser light sheet technique and image processing system. By using the method mentioned above, it is possible to observe the evolution of the pitchwise mass-averaged flow deviation angle and total pressure loss coefficient, the secondary flow, and the aerodynamic loss through the cascade.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.580-585
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• 2003

The present study addresses experimental results to investigate the details of the near field flow structures produced in the under-expanded, dual, coaxial, swirling, jet. The sonic/supersonic swirling jets are emitted from the sonic inner nozzle and the outer annular nozzle produce the co-swirling and counter swirling against the primary swirling jet, respectively. The interactions between both the secondary annular swirling and primary inner supersonic swirling jets are quantified by the pitot impact and static pressure measurements and visualized by using the Schliern optical method. The experiment is performed for different swirl intensity and pressure ratio. The results obtained show that the secondary co-swirling jet significantly changes the inner under-expanded swirling jet, such as the recirculation zone, pressure distribution, through strong interactions between both the swirling jets and the effects of the secondary counter-swirling jet is similar to the secondary co-swirl jet case.

• Geomechanics and Engineering
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• v.34 no.1
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• pp.69-86
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• 2023

To overcome the dilemma of the [BQ] method's inability to predict mountain tunnel support loads, this study is based on the Hoek-Brown criterion and previous results to obtain the connection equations from GSI scores to each parameter of the Hoek-Brown criterion and the link between the [BQ] scores and the GSI system. The equations were embedded in the Hoek-Brown criterion of FLAC6.0 software to obtain tunnel construction forecasts without destroying the in-situ stratigraphy. The feasibility of the secondary development of the Hoek-Brown criterion was verified through comparative analysis with field engineering measurements. If GSI > 45 with a confining pressure of less than 10 MPa, GSI has little effect on the critical softening factor while we should pay attention to the parameter of confining pressure when GSI < 45. The design values for each parameter are closer to the FLAC3D simulation results and the secondary development of the Hoek-Brown criterion meets the design objectives. If the Class V surrounding rock is thinned with shotcrete or the secondary lining is installed earlier, the secondary lining may act as the main load-bearing structure. The study may provide ideas for rapid prediction of mountainous tunnels in China.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1231-1237
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• 2004

Determination of geometric design parameters of a second-throat type annual supersonic ejector is described. Tested geometric parameters were primary nozzle area ratio, cross-sectional area of second-throat, L/D ratio of second-throat and primary flow injection angle. Varying these four geometric parameters, we build a test matrix made of 81 test conditions, and experimental apparatus was fabricated to accommodate them. For each test condition, the stagnation pressure of primary flow and the static pressure of the secondary flow were measured simultaneously along with their transition to steady operation and finally to unstarting condition. Comparing the performance curve of every case focused on starting pressure, the unstarting pressure and the minimum secondary pressure, we could derive correlations that the parameters have on the performance of the ejector and presented the optimal design method of the ejector. Additional experiments were carried out to find effects of temperature and mass flow rate of the secondary flow.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.14-19
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• 2004

Boiler is a hazardous equipment to have potential explosion ail the time. And not only it has malfunction at explosion. it lead to people death but also secondary accident such as explosion and fire. Therefore, this equipment should not be broken for keeping its own function. And also, high level of safety should be kept in the process of the use not to be malfunctioned. A large scale of accident due to boiler explosion can be preventive in advance. Boiler fracture is occurred by instant expansion (approximately 1700 time) from quick evaporation of rater in boiler, due to pressure decrease in boiler Emitting energy from it is tremendous and it is so dangerous because of its high temperature. Secondary explosion such as fire is also a main hazard occurring at fuel supply place. If any devices with high pressure is broken, then not only boiler vessel but also components of it are spread with high speed, causing secondary accident. This study is to analyze integrally accident cause of fire and flue tube boiler to have occurred pressure fracture actually, to show countermeasures to prevent accident loss from the fire and flue tube boiler.

• Nuclear Engineering and Technology
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• v.56 no.10
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• pp.4263-4279
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• 2024

The small modular PWR (SMPWR) usually adopts integral design. Under severe accident, the system responses are different from those large PWRs. It is necessary to study the severe accident behavior of the SMPWR. A MELCOR model is developed for SMPWR and its steady-state results are in good agreement with the design values. Severe accidents induced by secondary pipeline break accidents are simulated, and no pressure relief measures are taken to keep the primary loop under high pressure. The mitigation effects of passive containment air cooling system (PAS) and passive cavity injection system (PCIS) are evaluated under different cases. The results show that under high pressure conditions, PCIS can effectively cool the lower head. The earlier the PCIS operates, the more significant the mitigation effect can be. In addition, PAS can effectively reduce the peak pressure and temperature in the containment. This study can provide a reference for the formulation of severe accident management guidelines on SMPWRs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.640-647
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• 2002

An experimental investigation or the sonic and supersonic air ejector systems has beer conducted to develop design and prediction programs for practical ejector system. Five different primary nozzles have been employed to operate the ejector systems in the ranges of low and moderate operating pressure ratios. The ejector operating pressure ratio for the secondary chamber pressure to be minimized has a strong influence of the ejector throat ratio. The pressure inside the ejector diffuser is not dependent on the primary nozzle configurations employed but only a function of the ejector operating pressure ratio. Experimental results show that a supersonic ejector system is more desirable for obtaining high vacuum pressure of the secondary chamber than a sonic ejector system.

• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.481-490
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• 2004

Steady state flow calculations are executed for turbo-pump inducers of modern design to validate the performance of Tascflow code. Hydrodynamic performance of inducers is evaluated and structure of the passage flow and leading edge recirculation are also investigated. Calculated results show good coincidence with experimental data of static pressure performance and velocity profiles over the leading edge. Upstream recirculation, tip leakage and vortex flow at the blade tip and near leading edge are main sources of pressure loss. Amount of pressure loss from the upstream to the leading edge corresponds to that of whole pressure loss through the blade passage. The viscous loss is considerably large due to the strong secondary flow. There appears more stronger leading edge recirculation for the backswept inducer, and this increases the pressure loss. However, blade loading near the leading edge is considerably reduced and cavitation inception delayed.