• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.1
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• pp.7-14
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• 1995

As a part of the multidisciplinary oceanographic study for the productivity enhancement in Deukryang Bay, temperature and salinity were observed from 1992 through 1993. From the results, only the data in summer of two years are compared. Owing to the contrary meteorolgical conditions in both summers both of temperature and salinity had the patterns of horizontal distributions quite different from each other. In 1992 with low precipitation, there was a tendency of temperature increase and salinity decrease from the bay mouth towards the bay head. In 1993 when the air temperature was abnormally low, isotherms and isotherms tended to be parallel to the local u3s of the bay where the warmer and less saline water distributed along the western coast. Reduced solar radiation and increase in the relative importance of the distribution of properties along the current that was parallel to the axis of the bay could be responsible for this result. Vertical structures of both temperature and salinity were dependent on the stirring effect of tidal current. Stratification was destroyed during the spring tide while it was formed during the neap tide.

• Journal of the Korean Institute of Gas
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• v.10 no.3 s.32
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• pp.54-59
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• 2006

A safety device with shut-off function was developed for preventing intentional accidents that might happen by separating of cutting hoses connected to pressure regulators used in residential LP gas facility. For the verification of function and field adaptability, the safety device with shut-off function was tested in the state of joining the device to the regulator and a field test was carried out at home. This study shows that, at the inlet pressure of 0.07-1.56 MPa, the device shuts off the gas within the 5m length of hose regardless of the installation condition of the regulator. The shut-off flow rate increases in the order of perpendicular upward, horizontal and perpendicular downward. From the results of the field tests carried out at home for 5 months, there appears no problem using a gas range or a boiler. If the developed shut-off device is commercialized and distributed in the market the intentional accidents occurred by cutting or separating hoses can be prevented remarkably.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.3
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• pp.85-90
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• 2006

The purpose of this research is to design an imitation boiler similar to the waste heat boiler installed on a plasma melting furnace in order to acquire a capability of a thermal design as to the circulation of heat and the discharge of noxious gas inside a boiler and to improve the efficiency of a waste heat boiler using the CFD (Computation Fluid Dynamics) program. The position of corrosion and the generation of a clinker inside a boiler due to temperature changes, combustion gas flows, and corrosive gases inside a boiler are examined to design the structure of an efficient boiler and recycle energy. As a result of this research, the boiler installed on a plasma melting furnace met the conditions of design by cooling the combustion gases discharged after the second combustion from an exhaust port, originally at 1,200 degrees Celsius, down to around 450 degrees Celsius. On the other hand, the circulation of corrosive gases (SOx and HCL) may lead to the generation of corrosion or a clinker in the upper and lower parts of an exhaust port more easily than any other parts of a boiler. Accordingly, the corrosion on the inside and outside walls of a boiler may result in a shortened lifespan of a boiler and an inability to recycle waste heat in an efficient manner. A prevention against corrosion at high and low temperatures needs to be considered in detail.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.319-332
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• 2015

The pressure wave formed by the piston effects of the train proceeds within the tunnel when a train enters the tunnel with a high speed. Depending on the condition of tunnel exit, the compression waves reflect at a open end, change to the expansion waves, transfer to tunnel entrance back. Due to interference in the pressure waves and running train, passengers experience severe pressure fluctuations. And these pressure waves result in energy loss, noise, vibration, as well as in the passengers' ears. In this study, we performed comparison between numerical analysis and field experiments about the characteristics of the pressure waves transport in tunnel that appears when the train enter a tunnel and the variation of pressure penetrating into the train staterooms according to blockage ratio of train. In addition, a comparative study was carried out with the ThermoTun program to examine the applicability of the compressible 1-D model(based on the Method of Characteristics). Furthermore examination for the adequacy of the governing equations analysis based on compressible 1-D numerical model by Baron was examined.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.740-746
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• 2017

Infrared signatures emitted from hot exhaust gases generated by the internal combustion engine and generator of naval ships and from the metal surfaces of the funnel have become the targets of infrared homing missiles, which is the main cause of a reduced survivability of naval ships. The infrared signatures from the exhaust gas and the metal surface of a funnel can be reduced by installing an infrared signature suppression (IRSS) system on a ship. The IRSS system consists of three parts: an eductor that generates turbulent flow of the exhaust gas, a mixing tube that mixes the exhaust gas with ambient air, and a diffuser that forms an air film using the pressure difference between the inside and outside air. As a basic study to develop an IRSS system using domestic technology, this study analyzed the model test conditions of an IRSS system developed by an overseas engineering company and installed on a domestic naval ship, and a numerical heat-flow analysis was conducted based on the results of the aforementioned analysis. Numerical heat-flow analysis was performed using a commercial numerical-analysis application, and various turbulence models were considered. As a result, the temperature and velocity of the exhaust gas at the educator inlet and diffuser outlet and that of the metal surface of the diffuser were measured, and found to agree well with the measurement results of the model test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5425-5433
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• 2014

This study examined the effects of the key parameters on the power efficiency of the waste heat power plant using the EES program to obtain data for the design of the 20kW Kalina power plant. The parameters include the ammonia mass fraction, vapor pressure, heat source temperature, and the cooling water temperature. According to the analyses, a lower ammonia mass fraction and a higher vapor pressure increase the efficiency, in general. On the other hand, this study shows that there is a specific region with a very low ammonia mass fraction, where the efficiency decreases with ammonia mass fraction. Regarding the vapor pressure at the turbine inlet, the power efficiency increases with increasing vapor pressure. In addition, it was found that the influence of the vapor pressure on the efficiency increases with increasing ammonia mass fraction. Finally, the optimal condition for the maximum power efficiency is defined in this study, i.e., the maximum efficiency was 15% with a 25bar vapor pressure, $160^{\circ}C$ heat source temperature, $10^{\circ}C$ cooling water temperature, and 0.4 ammonia mass fraction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.510-517
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• 2016

Supersonic jet technology using high pressures has been popularly utilized in diverse industrial and engineering areas related to working fluids. In this study, to consider the effects of a shock wave caused by supersonic jet flow from a high pressure pipe, the SST turbulent flow model provided in the ANSYS FLUENT v.16 was applied and the flow characteristics of the pressure ratio and Mach number were analyzed in accordance with the working fluids (air, oxygen, and hydrogen). Before carrying out CFD (Computational Fluid Dynamics) analysis, it was presumed that the inlet gas temperature was 300 K and pressure ratio was 5 : 1 as the boundary conditions. The density function was derived from the ideal gas law and the viscosity function was derived from Sutherland viscosity law. The pressure ratio along the ejection distance decreased more in the lower density working fluids. In the case of the higher density working fluids, however, the Mach number was lower. This shows that the density of the working fluids has a considerable effect on the shock wave. Therefore, the reliability of the analysis results were improved by experiments and CFD analysis showed that supersonic jet flow affects the shock wave by changing shape and diameter of the jet, pressure ratio, etc. according to working fluids.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.227-236
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• 2016

In the present experimental study, the effect of gas- and liquid-injected methods on the formation of bubble and liquid slug at the merging micro T-junction of a square microchannel with dimensions $600{\mu}m{\times}600{\mu}m$ was investigated. Nitrogen and water were used as test fluids. The superficial velocities of the liquid and gas were in the range of 0.05 - 1 m/s, and 0.1 - 1 m/s, respectively, where the Taylor flow was observed. The bubble length, liquid slug length, bubble velocity, and bubble generation frequency were measured by analyzing the images captured using a high-speed camera. Under similar inlet superficial velocity conditions, in the case of gas injection to the main channel at the merging T-junction (T_gas-liquid), the lengths of the bubble and liquid slug were longer, and the bubble generation frequency was lower than in the case of liquid injection to the main channel at the merging T-junction (T_liquid-gas). On the other hand, in both cases, the bubble velocity was almost the same. The previous correlation proposed using experimental data for T_liquid-gas had predicted the present experimental data of bubble length, bubble velocity, liquid slug length, and bubble generation frequency for T_gas-liquid to be ~24%, ~9%, ~39%, ~55%, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.123-130
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• 2012

A cooling system is indispensable for the fossil and nuclear power plants which produce electricity by rotating the turbines with hot steam. A cycle of the typical cooling system includes pumping of seawater at the intake pump house, exchange of heat at the condenser, and discharge of hot water to the sea. The cooling type of the nuclear power plants in Korea recently evolves from the conventional surface intake/discharge systems to the submerged intake/discharge systems that minimize effectively an intake temperature rise of the existing plants and that are beneficial to the marine environment by reducing the high temperature region with an intensive dilution due to a high velocity jet and density differential at the mixing zone. It is highly anticipated that the future nuclear power plants in Korea will accommodate the submerged cooling system in credit of supplying the lower temperature water in the summer season. This study investigates the approach flow patterns at the velocity caps and discharge flow patterns from diffusers using the 3-D computational fluid dynamics code of $FLOW-3D^{(R)}$. The approach flow test has been conducted at the velocity caps with and without a cap. The discharge flow from the diffuser was simulated for the single-port diffuser and multi-ports diffuser. The flow characteristics to the velocity cap with a cap demonstrate that fish entrainment can significantly be minimized on account of the low vertical flow component around the cap. The flow pattern around the diffuser is well agreed with the schematic diagram by Jirka and Harleman.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.2
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• pp.77-83
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• 2012

Numerical analyses through Computational Fluid Dynamics have been performed to investigate the seawater flow field characteristics for various shrouds used in horizontal axis tidal current turbine systems. Seawater flow characteristics are largely influenced under constant tidal current velocity by the shroud geometry and there is considerable difference in fluid velocity distributions around the shrouds. Especially the location and magnitude of maximum seawater flow velocity directly affect turbine performance for power generation. For the cylinder-diffuser type shroud system whose cylinder and diffuser parts have the same length accelerated flow region is formed in the overall cylinder part while maximum velocity in the nozzle-diffuser type whose nozzle and diffuser parts have the same length with symmetry, locally appears near the minimum sectional area. In case of cylinder-diffuser type shroud fluid velocity increases rather high compared with current velocity. And fluid velocity at the centerline gradually increases from the entrance, and then decreases rapidly after reaching a peak close to the middle of the cylinder part unlike the nozzle-diffuser while there is not much variation near the rear of the shroud. These results of the seawater flow characteristics with various shroud geometries can be applied to optimal design for the development of efficient tidal current power generation systems.