• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.604-610
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• 2007

To investigate effects of the inflow area on pool boiling heat transfer in a vertical annulus, the inflow area at its bottom has been changed from 0 to $1060.3mm^2$. For the test, a heated tube of 34 mm diameter and water at atmospheric pressure have been used. To elucidate effects of the inflow area on heat transfer results of the annulus are compared to the data of a single unrestricted tube. The change in the inflow area at the bottom of the annulus results in much variation in heat transfer coefficients. When the inflow area is $113.1mm^2$ the deterioration point of heat transfer coefficients gets moved up to the higher heat fluxes because of the convective flow at the bottom regions.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.860-869
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• 2005

Local pool boiling on the outside and inside surfaces of a 51 mm diameter tube in horizontal direction has been studied experimentally in saturated water at atmospheric pressure. Much variation in local heat transfer coefficients was observed along the tube periphery. On the outside surface the maximum and the minimum are observed at ${\theta}=45^{\circ}$ and $180^{\circ}$, respectively. However, on the inside surface only the minimum was observed at ${\theta}=0^{\circ}$. Major mechanisms on the outside surface are liquid agitation and bubble coalescence while those on the inside surface are micro layer evaporation and liquid agitation. As the heat flux increases liquid agitation gets effective both on outside and inside surfaces. The local coefficients measured at ${\theta}=90^{\circ}$ can be recommended as the representative values of both outside and inside surfaces.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.654-659
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• 2020

The reliability of the spent fuel pool instrument is very important for the security of nuclear power plant, especially during the earthquake. The effect of the fluid force on the vibration characteristics of the flexible tube of the spent fuel pool instrument needs comprehensive analysis. In this paper, based on the potential flow theory, the hydrodynamic pressures acting on the flexible tube were obtained. A mathematical model of a flexible tube was constructed to obtain the dynamic response considering the effects of seismic load and fluid force, and a computer code was written. Based on the mathematical model and computer code, the maximum stresses of the flexible tube in both safe shutdown earthquake and operating basis earthquake events on the spent fuel pool with three typical water levels were calculated, respectively. The results show that the fluid force has an obvious effect on the stress and strain of the flexible tube in both safe shutdown earthquake and operating basis earthquake events.

• Ocean and Polar Research
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• v.24 no.2
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• pp.135-146
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• 2002

The upper ocean in the western equatorial Pacific warm pool during TOGA-COARE IMET IOP was simulated using a one-dimensional turbulence closure ocean mixed-layer model, which considered recent observations, such as the remarkable enhancement of turbulent kinetic energy near the ocean surface. The shoaling/deepening of the mixed layer and warming/cooling subsurface water in the model were in reasonable agreement with the observations. There was a significant improvement in simulating the cooling trend of the sea surface temperature under a westerly wind burst with heavy rainfall over previous simulations using bulk mixed-layer models. By contrast the simulated sea surface salinity (SSS) departed significantly from the observed SSS, especially during a westerly burst and the subsequent restratification period, which might be due to 3-D control processes, such as downwelling/upwelling or advection.

• Nuclear Engineering and Technology
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• v.29 no.3
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• pp.240-250
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• 1997

Liquid sodium is widely used as a coolant of LMR(Liquid Metal Reactor) because of its physical and nuclear properties. However, the liquid sodium is very chemically reactive with oxygen and water so that the study on the sodium fire plays an important role in the LMR safety analysis. In this study, a sodium fire model is suggested to analyze the sodium pool fire where both the flame and the reaction products are considered. And also, sodium pool fire analysis computer code, SOPA, is developed. The sensitivity study on the experimental parameters such as the thermal radiation from flame to atmospheric gas, the vessel cooling and the duration of sodium spill was performed. The results showed good agreements with experimental data in the literature.

• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1285-1292
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• 2009

The effects of the narrowed upside gap on nucleate pool boiling heat transfer in a vertical annulus were investigated experimentally. For the study, a stainless steel tube with a diameter of 25.4 mm and saturated water that kept an atmospheric condition were used. The ratio between the gaps measured at the upper and the lower regions of the annulus ranged from 0.18 to 1. Two different lengths of the modified gap also were investigated. The change in heat transfer due to the modified gap became evident as the gap ratio decreased and the length of the gap increased. As the gap ratio became less than 0.51, a significant decrease in heat transfer was observed compared to the plain annulus. The longer gap size resulted in an additional decrease in heat transfer. The major cause for the tendency was attributed to the formation of lumped bubbles around the upper region of the annulus followed by the increased flow friction between the fluid and the surface around the modified gap.

• Nuclear Engineering and Technology
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• v.35 no.3
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• pp.191-205
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• 2003

Effects of the width and location of a flow disturbing circular plate, installed at a vertical tube surface, on nucleate pool boiling heat transfer of water at atmospheric pressure have been investigated experimentally. Through the tests, changes in the degree of intensity of liquid agitation have been analyzed. The plate changes the fluid flow around the tube as well as heat transfer coefficients on the tube surface. It is identified that the plate width changes the rate of the circulating flow whereas its location changes the growth of the active agitating flow. Moreover, the flow chugging was observed at the downside of the plate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.749-755
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• 2006

To improve pool boiling heat transfer in an vertical annulus with closed bottoms, the length of an outer tube has been changed from 0.2m to 0.6m. For the test, a heated tube of 19.1mm diameter and water at atmospheric pressure have been used. Annular conditions are made using glass tubes fabricated around the heated tube. The gap size of the annulus is 3.65mm. To elucidate effects of the outer tube length on heat transfer results of the annulus are compared with the data of a single unrestricted tube and the annulus with wider gap size of 6.35mm. Throughout the tests much higher heat transfer coefficients are observed for the annulus of 3.65mm gap size comparing to the other two cases. The change in the outer tube length results in much variation in heat transfer coefficients. Moreover, with shortening the length of outer tube the possibility of the CHF occurrence can be removed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.930-937
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• 2000

A series of data sets for the heat transfer coefficient versus wall superheat has been obtained experimentally using various combinations of tube diameters ($9.7{\sim}25.5mm$), surface roughness ($15.1{\sim}60.9nm$), and tube orientations (horizontal and vertical) to obtain effects of tube diameters on nucleate pool boiling heat transfer for the saturated water at atmospheric pressure. In addition, the results are compared with the well known Cornwell and Houston's correlation for horizontal tubes to identify the deviation of the present experimental data from the correlation and the applicability of it to vertical tubes. The experimental results show that the heat transfer coefficient decreases as the tube diameter increases for both horizontal and vertical tubes and they are in good agreement with the Cornwell and Houston's correlation within ${\pm}20%$ scatter range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.327-334
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• 2008

Effects of tube inclination on pool boiling heat transfer have been studied for the saturated water at atmospheric pressure. For the analysis, seven inclination angles varying from the horizontal to the vertical and two tube diameters(25.4 and 30.0 mm) are tested. According to the results, inclination angles result in much change on heat transfer. For the same wall superheat(about $5.3^{\circ}C$) the ratio between two heat fluxes for the $45^{\circ}$ inclined and the vertical has the value of more than five when the tube diameter is 25.4mm. As the inclination angle is increasing from the horizontal to the vertical direction heat transfer is gradually increasing because of the increase in liquid agitation. However the detailed tendency depends on the ratio between the tube length and the diameter.