• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.1
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• pp.105-115
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• 2014

A numerical analysis on the smoke behavior and evacuee safety has been performed with computational fluid dynamics. The purpose of this study is to build computational processes for an evacuation and prevention of a fire disaster of a 3 km-length tunnel in Korea. To save computational cost, 1.5 km of the tunnel that can include a few cross-passing tunnels is considered. We are going to assess the fire safety in a road tunnel according to the smoke level, which consists of the smoke density and the height from the floor. The smoke density is obtained in detail from three-dimensional unsteady CFD analysis. To obtain proper temperature distributions on the tunnel wall, one-dimensional conduction equation is considered instead of an adiabatic wall boundary or a constant heat flux. The tunnel considered in this study equips the cross passing tunnels for evacuees every 250 m. The distance is critical in both safety and economy. The more cross passing tunnels, the more safe but the more expensive. Three different jet fan operations can be considered in this study; under- and over-critical velocities for normal traffic condition and 0-velocoty operation for the traffic congestion. The SE (smoke environment) level maps show a smoke environment and an evacuating behavior every moment.

• Spatial Information Research
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• v.18 no.4
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• pp.1-11
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• 2010

Unlike the previous studies which have focused on 2-dimensional urban characteristics, this paper presents statistical models explaining urban heat island(UHI) effect by 3-dimensional urban morphologic information and addresses its policy implications. 3~dimensional informations of Columbus, Ohio arc captured from LiDAR data and building boundary informations are extracted from a building digital map, Finally NDV[ and temperature data are calculated by manipulating band 3, band 4, and thermal hand of LandSat images. Through complicated data processing, 6 independent variables(building surface area, building volume, height to width ratio, porosity, plan surface area) are introduced in simple and multiple linear regression models. The regression models are specified by Box-Tidwell method, finding the power to which the independent variable needs to raised to be in a linearity. Porosity, NDVI, and building surface area are carefully chosen as explanatory variables in the final multiple regression model, which explaining about 57% of the variability in temperatures. On reducing UHI, various implications of the results give guidelines to policy-making in open space, roof garden, and vertical garden management.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.5
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• pp.482-490
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• 2007

When a molten corium is relocated in a lower head of a reactor vessel, the ERVC (External Reactor Vessel Cooling) system is actuated as coolant is supplied into a reactor cavity to remove a decay heat from the molten corium during a severe accident. To achieve this severe accident mitigation strategy, the two-phase natural circulation flow in the annular gap between the external reactor vessel and the insulation should be formed sufficiently by designing the coolant inlet/outlet area and gap size adequately on the insulation device. For this reason, one-dimensional natural circulation flow tests and the simple analysis were conducted to estimate the natural circulation flow under the ERVC condition of APR1400. The experimental facility is one-dimensional and scaled down as the half height and 1/238 channel area of the APR1400 reactor vessel. The calculated circulation flow rate was similar to experimental ones within about ${\pm}$15% error bounds and depended on the form loss due to the inlet/outlet area.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.185-194
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• 1984

The finite analytic method is extended to solve the steady two dimensional Navier-Stokes equation of stream functions and vorticity in polar coordinate system. The method is applied to calculate laminar flows in a sector cavity where the motion is induced by the rotation of the outer wall. Numerical solutions are obtained in the range of Reynolds number 0 to 5000 and aspect ratios 0.50, 1.20, 1.60 and 1.92. The finite analytic method is verfied to be accurate and fast convergent at high Reynolds numbers. It is promising as a numerical method of viscous flows and heat transfer. Flows in sector cavities show different flow structures and formation of secondary vortex with aspect ratios and Reynolds numbers in comparison with rectangular cavities.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.6
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• pp.289-296
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• 2017

This study aimed to analyze the deck floor heating system of an outdoor swimming pool in terms of the thermal capacity/output and the surface temperature distribution based on the outdoor temperature, to design for anti-freezing during winter. Through the transient heat transfer simulation with PHYSIBEL and theoretical equations, the surface temperature distribution of the floor heating system at two outdoor conditions in Jeju, were calculated and evaluated. The results indicate that the specific thermal output required for maintaining $4^{\circ}C$ surface temperature at the design outdoor temperature of $0.1^{\circ}C$, was about $90W/m^2$. This performance analysis can be applied for future design criteria, including optimizations of system capacity and size.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.9
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• pp.772-779
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• 2007

In this paper, thermo-flow characteristics of an outer-rotor type BLDC motor are numerically analyzed using three-dimensional turbulence modeling. On the rotor of the BLDC motor, cooling blades and cooling holes are existed for the enhanced cooling performances. Rotating the blades and holes generates axial air flow streaming into inner rotor side and passing through stator slots, which cools down stator by forced convection. Operating tests are performed and the numerical temperature fields are found to be in good agreement with experimental results. A new design of the BLDC motor has also been developed and major design parameters such as the arrangement of cooling holes, the area of cooling holes and cooling blades, and the cooling blade angle, are analyzed for the enhanced convective heat transfer rate. It is found that the convective heat transfer rate of the new BLDC motor model is increased by about 8.1%, compared to that of the reference model.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.47-54
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• 2012

The steady three-dimensional numerical analysis on the thermal flow using standard k-${\varepsilon}$ turbulence model was carried out to investigate the air cooling effect of a cooler on the cabin for a commercial vehicle. Here, the heat exchanging method of this cabin cooler uses the cooling effect of a thermoelectric module. In consequence, the air system resistance of a cooler within the cabin is about 12.1 Pa as a static pressure, and then the operating point of a virtual cross-flow fan considering in this study is formed in the comparatively low flowrate region. The discharging air temperature of a cooler is about $14{\sim}15^{\circ}C$. Moreover, the air cooling temperature difference obtained under the outdoor cabin temperature of $40^{\circ}C$ shows about $7{\sim}9^{\circ}C$ in a driver resting space and about $9{\sim}14^{\circ}C$ in the front of a driver's seat including the space of a driver's foot.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.4
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• pp.165-171
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• 2018

In this study, the shape of the flow control structure within a DVR was designed for heat dissipation of the CPU. The proposed design consists of three thin metal plates, which directly controls the air flow inside the DVR box and forces the air to pass through the CPU, thereby efficiently dissipating heat from the CPU. The shape of the structure was determined using parametric studies. To verify the design result, we carried out a three-dimensional time dependent numerical analysis using a commercial fluid dynamics analysis package FlowVision. As a result of experiments with a real DVR equipment, it is confirmed that the temperature of the CPU is significantly reduced compared to the initial model.

• Progress in Superconductivity and Cryogenics
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• v.19 no.4
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• pp.45-50
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• 2017

This paper presents a conceptual design and analysis for a 1-kW-class high-temperature superconducting rotating machine (HTSRM) rotor. The designed prototype is a small-scale integration system of a HTSRM and a HTS contactless rotary excitation device (CRED). Technically, CRED and HTSRM are connected in the same shaft, and it effectively charges the HTS coils of the rotor field winding by pumping fluxes via a non-contact method. HTS coils in rotor pole body and toroidal HTS wire in CRED rotor are cooled and operated by liquid nitrogen in cryogen tank located in inner-most of rotor. Therefore, it is crucial to securely maintain the thermal stability of cryogenic environment inside rotor. Especially, we critically consider not only on mechanical characteristics of the rotor but also on cryogenic thermal characteristics. In this paper, we conduct two main tasks covering optimizing a conceptual design and performing operational characteristics. First, rotor parameters are conceptually designed by analytical design codes. These parameters consider to mechanical and thermal performances such as mechanical strength, mechanical rigidity, and thermal heat losses of the rotor. Second, mechanical and thermal characteristics of rotor for 1-kW-class HTSRM are analyzed to verify the feasible operation conditions. Hence, three-dimensional finite element analysis (3D-FEA) method is used to perform these analyses in ANSYS-Workbench platform.

• Journal of the Korean Solar Energy Society
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• v.33 no.2
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• pp.70-77
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• 2013

Recently the radiant panel heating and cooling system has been regarded as an alternative of low temperature heating and high temperature cooling by applying the renewable energy sources to the heating and cooling of buildings. Especially this system can be used as HVAC system alternatives in super high-rise buildings for energy saving and thermal comfort. Also it can be possible to reduce the plenum space because the minimum ventilation air will be supplied into the space. This study focused on the evaluation the basic characteristics of thermal output in prefabricated steel wall panel system for radiant heating and cooling. In order to evaluate the thermal output according to both various supply water temperatures and supply water flow rates, three-dimensional dynamic heat transfer analysis was performed. As results, for the heating mode, thermal output increased by 26% with the supply temperature increasing by $5^{\circ}C$. The surface temperature of panels range within $1{\sim}3^{\circ}C$. For the cooling mode, thermal output decreased by 18.2% with the supply temperature increasing by $2^{\circ}C$. The surface temperature of panels range within $0.5{\sim}1^{\circ}C$ and it was shown the even temperature distribution.