• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2017-2022
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• 2004

There are multistage preheaters in the power generation plan to improve the thermal efficiency of the plant and to prevent the components from the thermal shock. The energy source of these heaters comes from the extracted two phase fluid of working system. These two-phase fluid can cause the so-called Flow Accelerated Corrosion(FAC) in the extracting piping and the bubble plate of the heater for example, in case of point Beach Nuclear Power Plant and in the Wolsung Nuclear Power Plant. The FAC is due to the mass transport of the thin oxide layer by the convection. FAC is dependent on many parameters such as the operation temperature, void fraction, the fluid velocity and pH of fluid and so on. Therefore, in this paper velocity was calculated by FLUENT code in order to find out the root cause of the wall thinning of the feedwater heaters. It also includeed in the fluid mixing analysis model are around the number 5A feedwater heater shell including the extraction pipeline. To identify the relation between the local velocities and wall thinning, the local velocities according to the analysis results were compared with distribution of the shell wall thicknes by ultrasonic test.

• Microbiology and Biotechnology Letters
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• v.26 no.1
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• pp.1-6
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• 1998

The characteristics of $CO_2$ fixation by Chlorella HA-1 cultured in bubble columns were studied to achieve high photosynthetic rates per basal area. The influence of experimental conditions such as the diameter of a bubble column and gas flow rate, on photosynthesis of Chlorella HA-1 was investigated. The maximum productivity and the overall $CO_2$ fixation rate obtained in a 0.15 L bubble column was 1.09 g dry biomassa-day and 1048 g CO$_2/\m^2$-day, respectively. Light limitation has been observed in the bubble columns having a diameter larger than 3.5 cm.. As the reactor volume increased, the decrease of the $CO_2$ fixation rate was remarkable. High gas flow rate was helpful to mitigate the light limitation problem.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.184-189
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• 1997

A prompt fission gas release model incorporating the resistance to gas flow in the gap was developed and the effects of gap resistance and failure location on prompt fission gas release from the cladding breach were assessed. The process of prompt fission gas release from the plenum and gap into the coolant was modeled in accordance with three major phenomena: (1) transient gas flow in the gap, (2) the growth of the fission gas bubble while it is still attached to the breach, and (3) the detachment of the fission gas bubble from the breach and mixing with the coolant. The cumulative mass release fraction by the present model was calculated for the case of Young-Gwang 3 & 4 nuclear fuel rod as a typical example. The results showed that the release behavior of prompt fission gas with time was different from the frictionless model which has frequently been used in a simplified approach, and that the location of cladding failure was another key factor for the prompt fission gas release process due to the resistance in the gap.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4213-4227
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• 2023

Computer Automated Radioactive Particle Tracking (CARPT) technique has been successfully utilized to measure the velocity profiles and mixing parameters in different multiphase flow systems where a single radioactive tracer is used to track the tagged phase. However, many industrial processes use a wide range of particles with different physical properties where solid particles could vary in size, shape and density. For application in such systems, the capability of current single tracer CARPT can be advanced to track more than one particle simultaneously. Tracking multiple particles will thus enable to track the motion of particles of different size shape and density, determine segregation of particles and probing particle interactions. In this work, a newly developed Multiple Radioactive Particle Tracking technique (M-RPT) used to track two different radioactive tracers is demonstrated. The M-RPT electronics was developed that can differentiate between gamma counts obtained from the different radioactive tracers on the basis of their gamma energy peak. The M-RPT technique was validated by tracking two stationary and moving particles (Sc-46 and Co-60) simultaneously. Finally, M-RPT was successfully implemented to track two phases, solid and liquid, simultaneously in three phase slurry bubble column reactors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.69-75
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• 2009

This paper studies the aerodynamic performance that the vent mixer-new conceptual supersonic mixer-showed with its geometric characteristics. The hole is 2 mm with 2 mm's distance from the wall in case 1 and with no distance in case 2. In case 3 die hole is 1 mm. Case 1 and case 2 showed the same total pressure recovery ratio, of which the case 3 was lower than that. While cases 1-3 had the same reattachment length, the shear layer was thicker in cases 1 and 2 than in case 3. Within the recirculation zone, cases 1 and 2 had lower pressure loss and higher velocity gradient difference than case 3-they enhance mixing between air and fuel. Separation bubble which is developed by the inflow into the recirculation zone has a significant effect on the total pressure recovery ratio in the combustor. Also separation bubble influences pressure distributions and recirculation flows in the recirculation zone. Therefore, inflow rate of air into the recirculation zone mainly affects the performance of vent mixer.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.219-231
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• 2004

The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. This study focuses on the hydrodynamic behavior of bubble plumes, which is the major mechanism of destratification and their combined effect of adjacent plumes on destratification efficiency. By introducing 2-phase Computational Fluid Dynamics(CFD) technique, we could suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. Lab experiments were also carried out to verify CFD model in thermally stratified fresh water which quite differs from former researches using salts. This study showed that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is lower than 1.5 times the depth, the combined effect is stronger; as Plume Number(PN) is increased, the efficiency is strongly affected by spacing. If the distance is shorter than the depth of water, the efficiency increases linearly in proportion to PN. Otherwise, the efficiency increases non-linearly. These findings suggest that the combined effect should be more quantitatively taken into consideration for design and operation of air-diffuser destratification system, and recommend that the optimal destratification efficiency will be when plume number is 1000 and the spacing between neighboring diffusers is 1.5 times the depth.

• Clean Technology
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• v.27 no.1
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• pp.39-46
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• 2021

A road structure washing vehicle equipped with a 4 HP, 80 LPM ultrafine bubble generator was used to clean a tunnel wall and the surface of the surrounding structure, consisting of concrete and tiles, in a heavy traffic area around an apartment complex in the city. Ultrafine bubbles were generated by supplying air at 2 to 3 LPM and using a specially designed nozzle, whereas fine bubbles made by an impeller in a gas-liquid mixing self-priming pump were produced with an average diameter of 165.4 nm and 6.81 × 107 particles mL-1. Using a high pressure washer gun that can perform high-pressure cleaning at 150 bar and 30 LPM, ultrafine bubbles were used to wash dust adsorbed on the surface of the road structures. The experimental analysis was divided into before and after washing. The samples were analyzed by applying ISO 8502-3 to measure surface contamination of dust adsorbed on the surface. Using the transparent tape attached to the surface, the removal rate was calculated by measuring the weight of the dust, and the number of particles was calculated using the gravimetric method and the software, ImageJ. The results of the experiment showed that the number of dust particles adsorbed on the tile wall surface before and after washing were 3,063 ± 218 particles mL-1 and 20 ± 5 particles mL-1, respectively, with weights of 580 ± 82 mg and 13 ± 4 mg. Particles on the surface of the concrete structure before and after washing were 8,105 ± 1,738 particles mL-1 and 39 ± 6 particles mL-1, respectively, with weights of 1,448 ± 190 mg and 118 ± 32 mg.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.467-470
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• 2011

In this study, two different kind of impeller, commercial hand blender and manual type were used to investigate the most effective mixing method for simulant gel propellant. Ionized Water, Carbopol 941 and NaOH were used to produce the simulant gel for temperature of $25^{\circ}C$ and $50^{\circ}C$. The amount of bubbles produced during mixing of simulant gel at $50^{\circ}C$ were higher than that of simulant gel at $25^{\circ}C$. After 24 hours, bubbles of simulant gel made at $50^{\circ}C$ disappeared rapidly with respect to the bubbles of gel made at $25^{\circ}C$. Bubbles from blender did show notable amount even after 24 hours. Among mixing type, it was found that the pitched paddle impeller was the best candidate for the production of simulant gel.

• Transactions of Materials Processing
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• v.31 no.5
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• pp.290-295
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• 2022

Recently, the use of high-tech ceramic parts in functional electronic parts, automobile parts and semiconductor equipment parts is increasing. These ceramics materials are required to have high reproducibility, reliability, large size and complex shapes. The researchers initiated the work to develop a new shaping method called gel casting, which allows high performance ceramic materials with a complex shape to be produced. The manufacturing process parameters of gel casting include uniform mixing of the initiator, bubble removal, and slip injection. In this study, we analyzed the dispersion and gelation characteristics according to the change in the additive content of the alumina slurry in the gel casting process. The alumina slurry for gel casting was prepared by mixing a solvent, a monomer and a dispersant through a ball mill. Alumina powder and a gelation initiator were added to the mixed solution, and ball milling was performed for 24 hours. A viscosity of 6,435 cps and a stable zeta potential value were obtained under the conditions of alumina powder content of 55 vol% and dispersant 2.0 wt%. After curing for 12 hours by adding aps 0.1wt%, TEMED 0.2wt%, and Monomer 3, 5wt%, it was possible to separate from the molding cup, confirming that the gelation was completed.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.901-906
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• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.