• Journal of the Korean Society of Visualization
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• v.12 no.3
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• pp.15-20
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• 2014

Direct numerical simulation (DNS) dataset of a turbulent boundary layer (TBL) with a step change from smooth to rough surface is analyzed to examine spatially developing flow characteristics. The roughness elements are periodically arranged two-dimensional (2-D) spanwise rods with a streamwise pitch of ${\lambda}=8k$ ($=12{\theta}_{in}$), and the roughness height is $k=15{\theta}_{in}$, where ${\theta}_{in}$ is the inlet momentum thickness. The step change is introduced $80{\theta}_{in}$ downstream from the inlet. For the first time, full images from the DNS data with the step change from the smooth to rough walls is present to get some idea of the geometry of turbulent coherent structures over rough wall, especially focusing on their existence and partial dynamics over the rough wall. The results show predominance of hairpin vortices over the rough wall and their spanwise scale growth mechanism by merging.

• Journal of Welding and Joining
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• v.34 no.5
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• pp.13-18
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• 2016

Toshiba has developed a laser peening system for PWRs(pressurized water reactors) as well after the one for BWRs(boiling water reactors), and applied it for BMI(bottom-mounted instrumentation) nozzles, core deluge line nozzles and primary water inlet nozzles of Ikata Unit 1 and 2 of Shikoku Electric Power Company since 2004, which are Japanese operating PWR power plants. Laser pulses were delivered through twin optical fibers and irradiated on two portions in parallel to reduce operation time. For BMI nozzles, we developed a tiny irradiation head for small tubes and we peened the inner surface around J-groove welds after laser ultrasonic testing (LUT) as the remote inspection, and we peened the outer surface and the weld for Ikata Unit 2 supplementary. For core deluge line nozzles and primary water inlet nozzles, we peened the inner surface of the dissimilar metal welding, which is of nickel base alloy, joining a safe end and a low alloy metal nozzle. In this paper, the development and the actual application of the laser peening system for PWR power plants will be described.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.5
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• pp.559-564
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• 2015

Distribution basins are used widely in the water treatment process. Uniform distribution at the distribution basin is an important because it affect precipitation efficiency of sedimentation basin. Generally distribution basin has a free surface water and is consisted of a weir. Study result, when inflow of distribution basin is less, amount of overflow is much at the nearest weir from the inlet. But when inflow is much, amount of overflow is much at the far weir from the inlet. The difference of distribution amount at the pipe is affected by the curvature and length of the pipe. The magnitude of the effect is determined by the relative energy loss and the flow state of the distribution basin. Optimization of the response surface method for minimizing an amount of deviation of the distribution is a very useful technique to determine the optimal ratio of the valve opening.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.323-328
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• 2005

The objective of this study is to analyze the cooling performance of an air- cooling system for telecommunication equipment. Temperature variation and capacity were measured in an actual unit for telecommunication equipment. In addition, the cooling performance was measured by installing a silicon rubber heater as a heat source in a cabinet. The standard thermal load for telecommunication equipment was approximately 293 W, and the maximum temperature of the heated surface was $64.5^{\circ}C$. The average and maximum temperatures of the heated surface were proportional to the inlet air temperature. When the heat load increased from 293 W to 400 W, the maximum temperature of the heated surface was higher than $64.5^{\circ}C$ even though the inlet air temperature decreased from 25 to $11^{\circ}C$.

• Journal of computational fluids engineering
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• v.7 no.3
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• pp.44-52
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• 2002

An analytic methodology was developed for free surface motions between liquid metal coolant and cover gas in order to calculate the phenomena of gas entrainment in hot pool surface through IHX EMP and reactor core. The methodology was setup by applying the first order VOF convection model to CFX4 general purpose fluid dynamics analysis code. The methodology was validated by applying it to an experimental apparatus designed for free surface motions of KALIMER reactor. The distributions of free surface calculated by the present methodology were almost coincident with the experimental data. The developed methodology was applied to the KALIMER reactor of full power operating condition. The shapes of the free surface were nearly uniform. From the results, it was found that the altitude of the free surface from the IHX inlet nozzle of KALIMER reactor is high enough not to affect to free surface motions of generating gas bubbles from the turbulent shear flows such as hydraulic jump and water falls.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.9
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• pp.709-717
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• 2009

Heat transfer rate is a very important factor for the performance of a steam reformer because a steam reforming reaction is an endothermic reaction. Coaxial cylindrical reactor is the reactor design which can improve the heat transfer rate. Temperature, fuel conversion and heat flux in the coaxial cylindrical steam reformer are studied in this paper using numerical method under various operating conditions. Langmuir-Hinshelwood model and pseudo-homogeneous model are incorporated for the catalytic surface reaction. Dominant chemical reactions are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming (DSR) reaction. Although coaxial cylindrical steam reformer uses 33% less amount of catalyst than cylindrical steam reformer, its fuel conversion is increased 10 % more and its temperature is also high as about 30 degree. There is no heat transfer limitation near the inlet area at coaxial-type reactor. However, pressure drop of the coaxial cylindrical reactor is 10 times higher than that of cylindrical reactor. Operating parameters of coaxial cylindrical steam reformer are the wall temperature, the inlet temperature, and the Gas Hourly Space Velocity (GHSV). When the wall temperature is high, the temperature and the fuel conversion are increased due to the high heat transfer rate. The fuel conversion rate is increased with the high inlet temperature. However, temperature drop clearly occurs near the inlet area since an endothermic reaction is active due to the high inlet temperature. When GHSV is increased, the fuel conversion is decreased because of the heat transfer limitation and short residence time.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.25-34
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• 2008

In this paper, three-dimensional multiblade row unsteady Navier-Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in low pressure stage of a Vaneless Counter-Rotating Turbine. The hot streak is circular in shape with a diameter equal to 25% of the high pressure turbine stator span. The hot streak center is located at 50% of the span and the leading edge of the high pressure turbine stator. The tip clearance size studied in this paper is 2.0mm(2.59% high pressure turbine rotor height, and 2.09% low pressure turbine rotor height). The numerical results show that the hot streak is not mixed out by the time it reaches the exit of high pressure turbine rotor. The separation of colder and hotter fluid is observed at the inlet of low pressure turbine rotor. Most of hotter fluid migrates towards the rotor pressure surface, and only little hotter fluid migrates to the rotor suction surface when it convects into the low pressure turbine rotor. And the hotter fluid migrated to the tip region of the high pressure turbine rotor impinges on the leading edge of the low pressure turbine rotor after it goes through the high pressure turbine rotor. The migration of the hotter fluid directly results in very high heat load at the leading edge of the low pressure turbine rotor. The migration characteristics of the hot streak in the low pressure turbine rotor are dominated by the combined effects of secondary flow and leakage flow at the tip clearance. The leakage flow trends to drive the hotter fluid towards the blade tip on the pressure surface and to the hub on the suction surface, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the low pressure turbine rotor is intensified due to the effects of the leakage flow. And the numerical results also indicate that the leakage flow effect trends to increase the low pressure turbine rotor outlet temperature at the tip region.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.43-48
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• 2001

In this study, the characteristics of the surface around a hole on inlet and outlet of product which are manufactured by face mill or end mill cutting with a hole or a pocket in its surface, are investigated. Furthermore, experiment for optimization of process conditions to minimize the change of characteristics of milling cut surface after a hole cutting operation, is implemented. Applying the results in this study to surface manufacturing of mold products whose surface is uneven or metal products made by diecasting, reducing the number of sequence process to obtain fine surface is expected.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.1044-1051
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• 2005

The isothermal characteristics of a rectangular parallelepiped sodium heat pipe were inves­tigated for high-temperature applications. The heat pipes was made of stainless steel of which the dimension was $140\;m\;(L)\;{\times}\;95m\;(W)\;{\times}\;46 m\;(H)$ and the thickness of the container was 5 mm. Both inner surfaces of evaporator and condenser were covered with screen meshes to help spread the liquid state working fluid. To provide additional path for the working fluid, a lattice structure covered with screen mesh wick was inserted in the heat pipe. The bottom surface of the heat pipe was heated by an electric heater and the top surface was cooled by circulating coolant. The concern in this study was to enhance the temperature uniformity at the bottom surface of the heat pipe while an uneven heat source up to 900 W was in contact. The temperature distribution over the bottom surface was monitored at more than twenty six locations. It was found that the operating performance of the sodium heat pipe was critically affected by the inner wall temperature of the condenser region where the working fluid may be changed to a solid phase unless the temperature was higher than its melting point. The maximum temperature difference across the bottom surface was observed to be $114^{\circ}C$ for 850 W thermal load and $100^{\circ}C$ coolant inlet temperature. The effects of fill charge ratio, coolant inlet temperature and operating temperature on thermal performance of heat pipe were analyzed and discussed.