• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.386-391
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• 2006

This study presents experimental results of sloshing phenomenon done on rectangular box. A simple harmonic excitation was done on the box. Two kinds of filling ratio, 20% and 30% of height, were tested. A total of 15 pressure sensors were installed to monitor the impact pressure. Each test was repeated for 20 times to ensure the repeatability. The high speed camera captured the flaw filed and the corresponding pressure were synchronize with video signal so that the video image can help the interpretation of the impact pressure. The two filling ratio made difference in the flaw characteristic and impact pressure. The use of high speed camera made it possible to understand the bubble generation mechanism. The pressure time histories were presented.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2290-2298
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• 2020

The damage of first wall material in fusion reactor due to the bubbles caused by plasma has been studied by introducing a relation between the von Mises equivalent stress and the temperature field. The locations and shapes of the bubbles and the synergetic effect between the different bubbles under steady operational conditions have been studied using the finite elements method. Under transient heat loads, plastic deformations have been found to occur, and are significantly enhanced by the presence of the bubbles. The calculated concentration locations of von Mises equivalent stress are well consistent with the observed crack positions of the tungsten surface in many test experiments. Our simulations show that the damage of the bubbles is not severe enough to lead to catastrophic failure of the tungsten armor; however, it can cause local and gradual detachment of tungsten surface, which provides a reasonable explanation for the observed pits and rough or hairy surface morphology etc. Considering the transient heat loads, the lower bound of the security thickness of the tungsten tile is estimated to be greater than 2 mm.

• Journal of Electrochemical Science and Technology
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• v.12 no.3
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• pp.358-364
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• 2021

In this study, an anion exchange membrane water electrolysis (AEMWE) cell was operated for ~1000 h at a voltage bias of 1.95 V. Impedance spectra were regularly measured every ~ 100 h, and changes in the ohmic and non-ohmic resistance were traced as a function of time. While there was relatively little change in the I-V curves and the total cell resistance during the long-term test, we observed various electrochemical phenomena in the cell: 1) initial activation with a decrease in both ohmic and non-ohmic resistance; 2) momentary and non-permanent bubble resistance (non-ohmic resistance) depending on the voltage bias, and 3) membrane degradation with a slight increase in the ohmic resistance. Thus, the regular test protocol used in this study provided clear insights into the performance degradation (or improvement) mechanism of AEMWE cells.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.7
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• pp.509-517
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• 2013

The purpose of this study is to assess the applicability of device-type stream coagulation process which combines physiochemical, biological processing for efficient improvement of water quality in small, middle-sized urban streams. The stream purification facility of this study is compose of pressure flotation type Micro Bubble Process(MBP) to remove TSS and TP and conduit line type Attached Microbial Pipe System(AMPS) to remove BOD. Test conditions of each device were set by floating stay time and change of ultra fine bubble injection amount of MBP, and change of AMPS stay time. Also, removal efficiency of pollution sources of each process were assess by change of season. As result of continuous operation of each process, MBP showed a maximum of TSS 83.69%, TP 95.15% process efficiency and AMPS showed a maximum of 52.95% TBOD5 removal efficiency. Also as result of circular operation of each process, MBP showed a maximum of TSS 69.75%, TP 70.17% process efficiency and AMPS showed a maximum of 68.58% TBOD5 removal efficiency. Therefore, it is considered that this stream coagulation process is effective in improving the water quality of streams in urban areas.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.6
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• pp.515-522
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• 2019

Since Liquefied Natural Gas (LNG) is normally carried at 1.1 bar pressure and at -163℃, special Cargo Containment System (CCS) are used. As LNG carrier is becoming larger, typical LNG insulation systems adopt a method to increase the thickness of insulation panel to reduce sloshing load and Boil-off Rate (BOR). However, this will decrease LNG cargo volume and increase insulation material costs. In this paper, silica aerogel, glass bubble were synthesized in polyurethane foam to increase volumetric efficiency by improving mechanical and thermal performance of insulation. In order to increase dispersibility of particles, ultrasonic dispersion was used. Dynamic impact test, quasi-static compression test at room temperature (20℃) and cryogenic temperature (-163℃) was evaluated. To evaluate the thermal performance, the thermal conductivity at room temperature (20℃) was measured. As a result, specimens without ultrasonic dispersion have a little effect on strength under the compressive load, although they show high mechanical performance under the impact load. In contrast, specimens with ultrasonic dispersion have significantly increased impact strength and compressive strength. Recently, as the density of Polyurethane foam (PUF) has been increasing, these results can be a method for improving the mechanical and thermal performance of insulation panel.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.183-191
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• 2005

This study is designed to compare the performance of established samplers (personal air sampler and MiniVOL portable air sampler) commonly used in the air environment or work environment with that of the sampler made by remodeling the air bubble generator for aquarium fishes. Sampling method used in this study is the filter collection method for PM10 and total suspended particles (TSP), the liquid collection method for sulfur dioxide ($SO_2$) and nitrogen dioxide ($NO_2$), and the solid collection method for toluene, respectively. There is not a significant difference in the average concentration of TSP between the Gilian personal air sampler (1st, $0.316{\pm}0.095$; 2nd $0.191{\pm}0.090$; 3rd, $0.185{\pm}0.073mg/m^3$) and the remodeled sampler (1st, $0.317{\pm}0.106$, 2nd $0.201{\pm}0.050$; 3rd $0.189{\pm}0.081mg/m^3$). There are also not significant differences in the average concentration of PM10 among the Gilian personal air sampler ($0.058{\pm}0.006mg/m^3$), the remodeled sampler ($0.052{\pm}0.008mg/m^3$) and the MiniVOL portable air sampler ($0.054{\pm}0.007mg/m^3$). The average concentration of the SO2 by the established sampler and the remodeled one is $3.79{\pm}0.21ppb$ and $3.45{\pm}0.15ppb$, respectively. In addition, there are not sigmficant differences in the average concentration of the NO2 between the Gilian personal air sampler (1st, $0.325{\pm}0.068$; 2nd $0.341{\pm}0.206$; 3rd, $2.971{\pm}0.078{\mu}g/m^3$) and the remodeled sampler (1st, $0.300{\pm}0.062$; 2nd $0.332{\pm}0.144$, 3rd, $2.968{\pm}0.085{\mu}g/m^3$). There are not significant differences in the average concentration of toluene between the Gilian personal air sampler (1st, $0.499{\pm}0.072$; 2nd $0.598{\pm}0.112$; 3rd $2.284{\pm}0.077{\mu}g/m^3$) and the remodeled sampler (1st, $0.463{\pm}0.133$; 2nd $0.603{\pm}0.082$; 3rd $2.353{\pm}0.115{\mu}g/m^3$). From these results, we can conclude that the performance of the remodeled sampler is not different from that of established samplers. There is possibility that the remodeled sampler can be used as a alternative device for Gilian personal air sampler in area and personal air sampling.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.6
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• pp.922-930
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• 2004

An experimental investigation was performed to study on the generation of air bubble and air core with swirling flow in a horizontal cicular tube. To determine some characteristics of the flow, 2D PIV technique is employed for velocity measurement in water. The experimental rig is manufactured from an acryl tube. The test tube diameter of 80mm, and a length of 3000mm. The used algorithm is the gray leve cross-correlation method(Kimura et al. 1986). An Ar-ion laser is used and the light from the laser(500mW) passes through a probe to make two-dimensional light sheet. In order to make coded images of the tracer particles on one frame, an AOM(Acoustic-Optical Modulator) is used. The maximum axial velocities showed near the test tube wall at y/D =0.1 and y/D =0.9 along the test tube. The higher Reynolds number increase, the lower axial velocities are showed in the center of the test tube. The air bubbles are generated from Re =10,000 and developed into air core from the recirculating water pump rpm equal 30Hz. The pressure and temperature are measured across the test tube at X/D=3.33.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.447-450
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• 2012

An analysis of chill-down process was performed for 30 tonf Turbopump-Gas generator coupled tests. The chill-down process must be fulfilled before liquid rocket engine test using cryogenic propellant. Cavitation, damage and/or combustion instability due to bubble of propellant must be eliminated by chill-down process in a test specimen, especially cryogenic pump. The analysis of test data obtained by 30 tonf TP-GG coupled tests was performed in order to be based on the test process of KSLV-II liquid propellant rocket engine which will be developed. To macroscopically understand the process of chill-down from the viewpoint of test procedure the temperatures of important part and total time of chill-down process were analyzed.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.22-29
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• 2003

New high-speed depressurized circulating water channel was designed by using the CFD code. Flow in the channel has free surface and pressure in the test section can be depressed. In this study, Flow separation and bubble occurrence were considered in designing the contraction nozzle shape for better flow uniformity Tn the test section. To supplement velocity defect due to the free surface, nozzle injection system more effective in high-speed flow was installed instead of drum system. Necessary power and injection techniques were proposed. And guide vane arrangement was analyzed to reduce the flow resistance and keep quiet free surface from ´surging´. Wave absorber was devised to reduce the wave resistance and to prevent the entrainment of air to the diffuser.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.181-184
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• 2009

In this study, flow visualization method to simulate internal flows of solid rocket motor in a water tunnel is introduced. The tunnel provides excellent visualization of vortex flows and has been used to propellant grain design of the solid rocket motor. A water tunnel is suggested for the research and the visualization test using dye, hydrogen bubble generator and PIV has been studied and discussed.