• Journal of the Korean Institute of Gas
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• v.5 no.3 s.15
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• pp.1-8
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• 2001

This study was carried out for the purpose of determination of maintenance period and investigation of weak point due to freeze when the gas heater of KOGAS valve station Is not operated in winter season. 3-dimensional non-linear numerical simulation was conducted in order to predict the time and location which bath water in heater reaches to ice point. FLUENT V 5.0, commercial code, is used for thermal fluid flow analysis. We thought this was problem of heat conduction solving the energy equation and modeled gas heater by using the real geometry and scale for performing the 3-dimensional simulation. It was analyzed complex heat transfer phenomena considering convection due to air on surface, conduction in insulation material, natural convection of liquid in heater and heat loss through the pipe.

• Journal of the Korean Institute of Gas
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• v.23 no.6
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• pp.25-32
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• 2019

In many mass-consumption gas facilities, natural gas is not supplied through the pipeline of the gas corporation. LNG is supplied from the gas corporation through the tank lorry to be vaporized. In order to prevent human or property damage due to gas leakage at these facilities, a study was conducted to analyze the concentration of odorant injected at the initial and consumption points. An analysis was performed to confirm the change in odorant concentration according to the pipe position in the gas facility when a constant flow rate flowed. For this study the gas samples were taken with aluminium cylinders(4.5 L) which were created a vacuum at the pressure regulator in which the odorants was injected and the points using the gas. Odorant levels of the samples were analyzed by Gas chromatography(Main Body : Agilent 7890A, Detector : ANTEC 7090).We suggest that the small facilities using LNG need to make the management system by the types of facilities for maintaining the odorization system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.957-964
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• 2013

This research is on the methodology of flood risk assessment using flooding characteristic values. Necessity of design magnitude for flood control considering floods was judged by plotting peak flow with respect to frequency and duration, and flooding magnitude was defined with 6 flooding characteristic values which were proposed to be significant factors when assessing flooding magnitude. Precipitation data used in the assessment modeling were applied by combining all the possible precipitation events. After overlapping the simulated results with precipitation matrix by flooding characteristic values, contour map was drawn, and Flooding characteristic contour graph for possible rainfall events were suggested in respect of all possible precipitation. Flooding characteristic contour graph for possible rainfall events was confirmed that reducing of damage magnitude of each flood characteristic value was figured out easily. The flood risk assessment methods suggested in this study would be a good reference for urban drainage system design, which only focuses on pipe conduit.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.286-294
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• 2009

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.12
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• pp.929-936
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• 2013

The saturator and injection nozzle are important facilities on the dissolved air flotation process. To increase the formation of micro bubble, it is required to improve the air dissolving performance in the saturator and keep the pressure uniform from the saturator to the nozzle. This study aimed to evaluate the performance of the saturator and the hydraulic effect of the nozzle and the pipe structure. The air volume concentration, bubble size and bubble residual time were measured in the test. The saturator, which had mounted with the spray nozzle, showed a good performance for bubble formation. Also, the characteristics of micro bubble formation were influenced by pressure uniformity and flow velocity through the orifice in the nozzle.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.1969-1975
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• 2012

The air brake system used in heavy vehicle is very important from the point of safety due to its weight. In general, air brake system generates relatively long response time and large loss of pressure. It is known that the response time can be decreased by optimal design of brake system, i.e., by increasing the system pressure, minimizing the air line, and material of components. In this study, We developed experimental rigs for the measurement of braking response of heavy duty trucks and compared with the simulated results obtained from the net work fluid flow system analysis code (FLOWMASTER). The effect of several parameters such as, system pressure, diameter of pipe, chamber temperature on the brake response performance have been examined.

• Korean Journal of Food Science and Technology
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• v.47 no.4
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• pp.474-479
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• 2015

In this study, five different Gochujang (a traditional Korean sauce prepared using fermented red pepper paste) sauces were heated at $100^{\circ}C$ for 5 min using a continuous ohmic heating system. Ohmic heating yielded greater reduction in microbial counts (90-95% reduction) than did conventional heating (65-75% reduction). The sterilization effect of the continuous ohmic heater increased with increasing sample flow rate and decreasing Reynolds number inside the pipe. Low-viscosity samples had higher electrical conductivity and were better suited for ohmic heating than were high-viscosity samples. The color and texture were also satisfactorily maintained after ohmic heating. Compared with conventional heating, ohmic heating provided rapid and uniform heating, which is more suitable for aseptic thermal processing of viscous foods.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.93-105
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• 2017

This study presents direct shear tests, model tests, and numerical simulations to assess the effect of reduction of soil strength because of saturation during formation of ground cave-in caused by damaged sewer pipe lines. The direct shear test results show that the saturation affects the cohesion of soil significantly although it does not influence the friction angle of soil. To experimentally reproduce ground cave-in, the model tests were performed. As ground cave-ins were accompanied with extreme deformation, conventional finite element method has difficulty in simulating them. The present study relies on generalized interpolation material point method, which is one of meshless methods. Although there are differences between the model test and numerical simulation caused by boundary conditions, incomplete saturation, and exclusion of groundwater flow, similar ground deformation characteristics are observed both in the model test and numerical simulation.

• Journal of the Korean Solar Energy Society
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• v.29 no.2
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• pp.31-38
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• 2009

This study was conducted to forecast inner water temperature strata change by extracting deep water from a dam. For the methodology, the scope wherein the balance between the volume of low-temperature water intake through the virtual water intake opening as installed within the stored water area and the volume of water intake from the surrounding area is not destroyed was calculated through the CFD simulation technique using the computational fluid dynamics(CFD) interpretation method. This study suggested a supplementary method(diffuser) to avoid destroying the water temperature strata, and the effect was reviewed. In case of intake of the same volume, when the velocity of flow of water intake is reduced by increasing the pipe diameter, the destruction of water temperature strata can be minimized. When the area(height) where the intake of water is possible is low, a diffuser for interrupting the vertical direction inflow should be installed to secure favorable water intake conditions in case of water intake on the upper part. This study showed that there was no problem if the intake-enabled, low-temperature area was secured approximately 10m from the bottom when the scope that does not destroy the water temperature strata in case of water intake was forecast using the regression formula.