• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.215-223
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• 1999

Characteristics of radiation field in the steam generator(S/G) water chamber of a PWR were investigated and the anticipated effective dose rates to the worker in the S/G chamber were evaluated by Monte Carlo simulation. The results of crud analysis in the S/G of the Kori nuclear power plant unit 1 were adopted for the source term. The MCNP4A code was used with the MIRD type anthropomorphic sex-specific mathematical phantoms for the calculation of effective doses. The radiation field intensity is dominated by downward rays, from the U-tube region, having approximate cosine distribution with respect to the polar angle. The effective dose rates to adults of nominal body size and of small body size(The phantom for a 15 year-old person was applied for this purpose) appeared to be 36.22 and 37.06 $mSvh^{-1}$) respectively, which implies that the body size effect is negligible. Meanwhile, the equivalent dose rates at three representative positions corresponding to head, chest and lower abdomen of the phantom, calculated using the estimated exposure rates, the energy spectrum and the conversion coefficients given in ICRU47, were 118, 71 and 57 $mSvh^{-1}$, respectively. This implies that the deep dose equivalent or the effective dose obtained from the personal dosimeter reading would be the over-estimate the effective dose by about two times. This justifies, with possible under- or over- response of the dosimeters to radiation of slant incidence, necessity of very careful planning and interpretation for the dosimetry of workers exposed to a non-regular radiation field of high intensity.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.223-232
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• 2001

To study the stabilization characteristics of diffusion flame formed in the wake of a cylindrical bluff body with fuel injection, the flame stability limits, length and temperature of recirculation zone of flame, turbulence intensity distribution near the recirculation zone of flame were measured and analyzed. The length of recirculation zone is independent on main fuel injection quantity, but it is dependent on fuel injection angles, air stream velocity, and auxiliary fuel injection into recirculation zone. For diffusion flame, in general, the flame stabilization is deteriorated with increase of he length of recirculation zone, but if the turbulence generator is installed, the flame stabilization is improved with increase of the length of recirculation zone. The temperature of recirculation zone is dependent on fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators, and it dependent on fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators, and it has a maximum value at the condition of each theoretical mixture. In general, the more temperature of recirculation zone is low, the more flame is stable. But when the turbulence generator is installed, the more temperature of recirculation zone is low, the more flame is unstable. The turbulence intensity in the wake of bluff body is increased with increase of diameter or blockage ratio of grid. The more turbulence intensity is increased by installation of turbulence generator, the more flame is unstable. Finally, It is clear that the stabilization characteristics of diffuser flame can be controlled by some parameters such as fuel injection angles, auxiliary fuel injection into recirculation zone, turbulence generators.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.72-80
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• 2014

This study proposed a wind power generation system utilizing outdoor air on the rooftop and indoor ventilation, which would increase according to the building height, as a way to help to save energy consumption in a building by using wind power energy of the new renewable energy sources. The study measured the distribution of air currents and power generation according to the usage factor of exhaust pipes in the kitchen and bathroom and identified the elements to consider when applying a wind power generation system to buildings in order to use outdoor air on the rooftop increasing according to the height and the indoor ventilation produced in the facility vertical shafts inside the buildings by installing a wind power generation system on the rooftop. (1) The study measured the ventilation velocity of the kitchen hood and bathroom ventilation fan by changing the zone areas by the households according to the usage factor of [${\alpha}$]=33~100%. As a result, the kitchen ventilation pipe generated the ventilation wind of 3.0m/s or more at the usage factor of [${\alpha}$] 66% or higher, and the bathroom ventilation pipe generated ventilation velocity lower than 3.0m/s, the blade velocity of the wind power generator, even after the usage factor rose to [${\alpha}$]=100%. (2) As the old bathroom ventilation pipe generated the ventilation velocity of 3.0m/s, the blade velocity of the wind power generator, even with the rising usage factor [${\alpha}$], the application of an outdoor air induction module increased the ventilation velocity by 2.9m/s at the usage factor of [${\alpha}$]=33%, 3.8m/s at the usage factor of [${\alpha}$]=66%, and 3.6m/s at the usage factor of [${\alpha}$]=100%. Thus the ventilation velocity of 3.0m/s, the blade velocity of the wind power generator, or higher was secured. (3) The findings prove that the applicability of a wind power generation system using outdoor air on the rooftop and indoor ventilation is excellent, which raises a need for various efforts to increase the possibility of its commercialization such as securing its structural stability according to momentary gusts on the rooftop and typhoons in summer and making the structure light to react to the wind directions of outdoor air on the rooftop according to the seasons.

• Applied Chemistry for Engineering
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• v.30 no.1
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• pp.62-67
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• 2019

This study was focused on the design and the performance analysis of integral Hot BoP for recovering waste heat from high-temperature exhaust gas in 2 kW class solid oxide fuel cell (SOFC). The hot BoP system was consisted of a catalytic combustor, air preheater and steam generator for burning the stack exhaust gas and for recovering waste heat. In the design of the system, the maximum possible heat transfer was calculated to analyze the heat distribution processes. The detail design of the air preheater and steam generator was carried out by solving the heat transfer equation. The hot BoP was fabricated as a single unit to reduce the heat loss. The simulated stack exhaust gas which considered SOFC operation was used to the performance test. In the hot BoP performance test, the heat transfer rate and system efficiency were measured under various heat loads. The combustibility with the equivalent ratio was analyzed by measuring CO emission of the exhaust gas. As a result, the thermal efficiency of the hot BoP was about 60% based on the standard heat load of 2 kW SOFC. CO emission of the exhaust gas rapidly decreased at an equivalent ratio of 0.25 or more.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.151-162
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• 2020

This paper presents an acoustic inversion method for estimating the bubble size distribution. The estimation error of the attenuation coefficient represented by a Fredholm integral equation of the first kind is defined as an objective function, and an optimal solution is found by applying the Levenberg-Marquardt (LM) method. In order to validate the effectiveness of the inversion method, numerical simulations using two types of bubble distribution are performed. In addition, a series of experiments are carried out in a water tank (1.0 m × 0.54 m × 0.6 m), using bubbles generated by three different generators. Images of the distributed bubbles are obtained by a high-speed camera, and the insertion losses of the bubble layer are measured using a source and a hydrophone. The image is post-processed to glance a distribution characteristics of each bubble generator. Finally, the size distribution of bubbles is estimated by applying the inversion method to the measured insertion loss. From the inversion results, it was observed that the number of bubbles increases exponentially as the bubble size decreases, and then increases again after the local peak at 70 ㎛ - 120 ㎛.

• Journal of the Korean Applied Science and Technology
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• v.35 no.4
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• pp.985-994
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• 2018

Bio-heavy oil for power generation is a product made by mixing animal fat, vegetable oil and fatty acid methyl ester or its residues and is being used as steam heavy fuel(B-C) for power generation in Korea. However, if the fuel supply system of the fuel pump, the flow pump, the injector, etc., which is transferred to the boiler of the generator due to the composition of the raw material of the bio-heavy oi, causes abrasive wear, it can cause serious damage. Therefore, this study evaluates the fuel characteristics and lubricity properties of various raw materials of bio-heavy oil for power generation, and suggests fuel composition of biofuel for power generation to reduce frictional wear of generator. The average value of lubricity (HFRR abrasion) for bio-heavy oil feedstocks for power generation is $137{\mu}m$, and it varies from $60{\mu}m$ to $214{\mu}m$ depending on the raw materials. The order of lubricity is Oleo pitch> BD pitch> CNSL> Animal fat> RBDPO> PAO> Dark oil> Food waste oil. The average lubricity for the five bio-heavy oil samples is $151{\mu}m$ and the distribution is $101{\mu}m$ to $185{\mu}m$. The order of lubricity is Fuel 1> Fuel 3> Fuel 4> Fuel 2> Fuel 5. Bio-heavy oil samples (average $151{\mu}m$) show lower lubricity than heavy oil C ($128{\mu}m$). It is believed that bio-heavy oil for power generation is composed of fatty acid material, which is lower in paraffin and aromatics content than heavy oil(B-C) and has a low viscosity and high acid value, resulting in inhibition of the formation of lubricating film by acidic component. Therefore, in order to reduce friction and abrasion, it is expected to increase the lubrication of fuel when it contains more than 60% Oleo pitch and BD pitch as raw materials of bio-heavy oil for power generation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.18 no.2
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• pp.101-108
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• 1982

In this paper the result of heat transfer analysis around the square heat source of interior solid by using the F. E. M is reported. Calculation for temperature distribution and each element was used by F. E. M. the solid is sub-divided into system of equal size triangular shape. These values of temperature distribution will valuable for design of jet engine and steam generator and the results gained are as follow; 1. Calculation by F. E. M is identified with the experiment. 2. Temperature distribution on the horizontal surface is $\theta$=0.698 in model 4 and the other hand $\theta$=0.401 in model 6 for X=16cm. In intermediates surface between heat source and bottom surface, the influence of L is more greater than that of height in the temperature difference. 3. Temperature distribution on the vertical surface for model 2 is resulted strong influence by K. In the case of Y=4cm is identified with $\theta$=0.0790 for K=7 and also $\theta$=0.0036 for K=0.3. In the difference of temperature distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.235-240
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• 2020

This study evaluated the improvements for circuits of a combat vehicle distribution box to reduce the noise generated in electromagnetic compatibility (EMC) testing. An analysis of the distribution boxes that failed the standard revealed the conducted noise generated from the converter and semiconductor switching elements on the circuit board. The distribution box transfers power from the generator and battery to the cooling system of a combat vehicle to keep turning the air conditioner on and off. Two methods were proposed to overcome this problem: a passive filter was added to the circuit board for the first method, and the converter and switching elements were replaced with the relays for the second method. Both methods were effective in reducing noise, but a greater improvement was obtained from the second method. The second method was applied to a combat vehicle system and was found to be suitable according to the EMC standards.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.4
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• pp.434-439
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• 2010

This study fabricated a simulation facility which reduced the structure of a current distribution line to 50:1 in order to analyze the induced lightning shielding effect of a 22.9kV-Y distribution line according to ground resistance capacity, grounding locations, etc. When installing an overhead ground wire, the standard for grounding a distribution line with a current of 22.9kV-Y requires that ground resistance in common use with the neutral line be maintained less than $50\Omega$every 200m span. The reduced line for simulation had 7 electric poles and induced lightning was applied to the ground plane 2m apart from the line in a direction perpendicular to it using an impulse generator. If induced voltage occurred in the line and induced current flowed through the line due to the applied current, the induced voltage and current of the 'A' phase were measured respectively using an oscilloscope. When all 7 electric poles were grounded with a ground resistance of less than $50\Omega$ respectively, the combined resistance of the line was $7.4\Omega$. When an average current of 230A was applied, the average induced voltage and current measured were 1,052V and 13.8A, respectively. Under the same conditions, when the number of grounding locations was reduced, the combined resistance as well as induced voltage and current showed a tendency to increase. When all 7 electric poles were grounded with a ground resistance of less than $100\Omega$, the combined resistance of the line was $14.9\Omega$. When an average current of 236A was applied, the average induced voltage and current of the 'A' phase calculated were 1,068V and 15.6A, respectively. That is, in this case, only the combined resistance was greater than when all 7 electrical poles were grounded, and the induced voltage and current were reduced. Therefore, it is thought that even though ground resistance is slightly higher under a construction environment with the same conditions, it is advantageous to ground all electric poles to ensure system safety.

• Geophysics and Geophysical Exploration
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• v.26 no.1
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• pp.8-17
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• 2023

Various sources, such as wind, waves, ships, and gas leaks from the seafloor, forms bubbles in the ocean. Underwater bubbles cause signal scattering, considerably affecting acoustic measurements. This characteristic of bubbles is used to block underwater noise by attenuating the intensity of the propagated signal. Recently, researchers have been studying the large-scale release of methane gas as bubble plumes from the seabed. Understanding the physical properties and distribution of bubble plumes is crucial for studying the relation between leaked methane gas and climate change. Therefore, a water tank experiment was conducted to estimate the distribution of bubble plumes using seismic imaging techniques and acoustic signals obtained from artificially generated bubbles using a bubble generator. Reverse time migration was applied to image the bubble plumes while the acquired acoustic envelope signal was used to effectively estimate bubble distribution. Imaging results were compared with optical camera images to verify the estimated bubble distribution. The water tank experiment confirmed that the proposed system could successfully image the distribution of bubble plumes using reverse time migration and the envelope signal. The experiment showed that the scattering signal of artificial bubble plumes can be used for seismic imaging.