• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.276-285
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• 1991

The transient heat transfer characteristics in the radiant heating panel were predicted by numerical analysis. Thermal behaviors of panel, such as temperature distributions in panel and convective and radiative heat fluxes in panel surface with respect to time were obtained. Heating hours per day, rate of energy supplied and maximum temperature differences at panel surface were also compared for several important parameters. The performance and thermal comfort of heating panel were studied and compared for various operating and design conditions such as pipe pitch, pipe location, pipe diameter and flow rate of hot water for the purpose of producing useful data, which can be used for the test and decision of efficient operating condition of the conventional heating systems or the optimal design of the new panel heating systems.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.201-211
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• 2001

The influence of aerated oil on high-speed journal bearing is examined by classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of aerated oil in fluid-film bearing. Convection to the walls, mixing with supply oil and re-circulating oil, and some degree of journal misalignment are considered. The considered Parameters for the study of bubbly lubrication are oil aeration level, air bubble size, shaft misalignment and shaft speed. The results show that deliberate oil aeration can more clearly bring on the increasing load capacity under high-speed operation of plain journal hearing than previous normal speed operation. And the load capacity may be increased more by oil aeration under the conditions of shaft misalignment and the increasing speed.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.84-90
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• 1999

The shape of weld nuggest in arc spot welding of 304 stainless steel was found by searching thermal history of a weld joint through a three-dimensional finite element model. The problem consists of one in which the finite element mesh is growing continuously in time in order to accomodate metal transfer in arc spot welding using element rebirth technique. The analysis was performed on the basis of experimental results. The finite element program MARC, along with a few user subroutines, was employed to obtain the numerical results. Temperature-dependent thermal properties, stir effect in weld pool, effect of phase transformation, and the convective and radiative boundary conditions are included in the model. Numerically predicted shape of weld nuggest is compared with the experimentally observed shape.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.29 no.2
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• pp.77-100
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• 2024

Circulation, tides, currents, harmful algal blooms, water quality, and hypoxic conditions in Jinhae-Masan Bay have been extensively studied. However, these previous studies primarily focused on short-term variations, and there was limited detailed investigation into the physical mechanisms responsible for ocean circulation in the bays. Oceanic processes in the bays, such as pollutant dispersal, changes on a seasonal time scale. Therefore, this study aimed to understand how the circulation in Jinhae-Masan Bay varies seasonally and to examine the effects of tides, winds, and river discharges on regional ocean circulation. To achieve this, a three-dimensional ocean circulation model was used to simulate circulation patterns from 2016 to 2018, and sensitivity experiments were conducted. This study reveals that convective estuarine circulation develops in Jinhae and Masan Bays, characterized by the inflow of deep oceanic water from the Korea Strait through Gadeoksudo, while surface water flows outward. This deep water intrusion divides into northward and westward branches. In this study, the volume transport was calculated along the direction of bottom channels in each region. The meridional water exchange in the eastern region of Jinhae Bay is 2.3 times greater in winter and 1.4 times greater in summer compared to that of zonal exchange in the western region. In the western region of Jinhae Bay, the circulation pattern varies significantly by season due to changes in the balance of forces. During winter, surface currents flow southward and bottom currents flow northward, strengthening the north-south convective circulation due to the combined effects of northwesterly winds and the slope of the sea surface. In contrast, during summer, southwesterly winds cause surface seawater to flow eastward, and the elevated sea surface in the southeastern part enhances northward barotropic pressure gradient intensifying the eastward surface flow. The density gradient and southward baroclinic pressure gradient increase in the lower layer, causing a strong westward inflow of seawater from Gadeoksudo, enhancing the zonal convective circulation by 26% compared to winter. The convective circulation in the western Jinhae Bay is significantly influenced by both tidal current and wind during both winter and summer. In the eastern Jinhae Bay and Masan Bay, surface water flows outward to the open sea in all seasons, while bottom water flows inward, demonstrating a typical convective estuarine circulation. In winter, the contributions of wind and freshwater influx are significant, while in summer, the influence of mixing by tidal currents plays a major role in the north-south convective circulation. In the eastern Jinhae Bay, tidally driven residual circulation patterns, influenced by the local topography, are distinct. The study results are expected to enhance our understanding of pollutant dispersion, summer hypoxic events, and the abundance of red tide organisms in these bays.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.68-78
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• 1997

A numerical study on the transient vapor flow and heat transfer is performed to investigate the ideal switching operation of heat source in a high temperature heat pipe. The cylindrical 2-dimensional compressible laminar vapor flow is assumed for the vapor space and the conjugate heat transfer for the heat pipe wall, wick and vapor space is calculated. The different boundary conditions such as constant heat flux, convective or radiative boundary at the outer wall are used respectively to compare the influence of boundary conditions on the transient operation. The transient temperature profile and the internal flow of the entire pipe for the switching operation are described as a result. The results show that the transient time is not significantly affected by the boundary conditions at the outer wall in present study. During the transition, two independent flows are observed temporarily on the right side and left side of the heat pipe. It is also found that the trend of temperature variation in the vapor region is different from the variation in the wick and wall region.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.187-197
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• 1996

Many investigations have been made to determine the pressure drop and heat transfer characteristics for single phase flow in tape generated swirl flow. But few studies have been carried out to investigate the heat transfer in two component, two phase swirl flow with non-boiling. An experimental study has been conducted to determine the effects of tape twist ratios on two phase convective heat transfer coefficients, pressure drop, and void fraction distribution in a non-boiling, air-water, two phase flow. The flow conditions were both swirl and non swirl flows. The internal diameter of the test section is 42.5mm. The tape twist ratios of pitch to diameter ratio varied from 4.0 to 10.6. The heating conditions were isothermal and nonisothermal. The flow patterns identified with experiments were bubbly, bubbly-slug, slug, and slug-annular flow in up-flow. This study has concluded that no significant difference in void fraction distribution were observed both isothermal and nonisothermal conditions, the pressure drop for two phase flow with twisted tape swirler increase as the tape twist ratio decrease, and that values of two phase heat transfer coefficient increase when the tape twist ratio decreases.

• Atmosphere
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• v.25 no.4
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• pp.611-622
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• 2015

Heavy rainfall ($>30mm\;hr^{-1}$) over the Korean Peninsula is examined in order to understand thermo-dynamic characteristics of the atmosphere, using radiosonde observational data from seven upper-air observation stations during the last 17 years (1997~2013). A total of 82 heavy rainfall cases during the summer season (June-August) were selected for this study. The average values of thermo-dynamic indices of heavy rainfall events are Total Precipitable Water (TPW) = 60 mm, Convective Available Potential Energy (CAPE) = $850J\;kg^{-1}$, Convective Inhibition (CIN) = $15J\;kg^{-1}$, Storm Relative Helicity (SRH) = $160m^2s^{-2}$, and 0~3 km bulk wind shear = $5s^{-1}$. About 34% of the cases were associated with a Changma front; this pattern is more significant than other synoptic pressure patterns such as troughs (22%), migratory cyclones (15%), edges of high-pressure (12%), typhoons (11%), and low-pressure originating from Changma fronts (6%). The spatial distribution of thermo-dynamic conditions (CAPE and SRH) is similar to the range of thunderstorms over the United States, but extreme conditions (supercell thunderstorms and tornadoes) did not appear in the Korean Peninsula. Synoptic conditions, vertical buoyancy (CAPE, CIN), and wind parameters (SRH, shear) are shown to discriminate among the environments of the three types. The first type occurred with high CAPE and low wind shear by the edge of the high pressure pattern, but Second type is related to Changma front and typhoon, exhibiting low CAPE and high wind shear. The last type exhibited characteristics intermediate between the first and second types, such as moderate CAPE and wind shear near the migratory cyclone and trough.

• Atmosphere
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• v.17 no.1
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• pp.69-86
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• 2007

The characteristics of the dual-Doppler wind retrieval method based on a three dimensional variational (3DVAR) conception were investigated from the following four points of view; the sensitivity of the number of iteration, the effect of the weak constraint term, the effect of the smoothness term, and the sensitivity of the error mixing ratio of the radial velocities. In the experiment, the radial velocities relative to the Gosan and Jindo radar sites of the Korea Meteorological Administration (KMA) were calculated from the forecasting of the WRF (Weather Research and Forecast; Skamarock, 2004) model at 1330 UTC 30 June 2006, which is the one and half hour forecast from the initial time, 1200 UTC on that day. The results showed that the retrieval performance of the horizontal wind field was robust, but that of the vertical wind was sensitive to the external conditions, such as iteration number and the on/off of the weak constraint term. The sensitivity of error mixing ratio was so large that even the horizontal wind retrieval efficiency was reduced a lot. But the sensitivity of the smooth term was not so large. When we applied this method to the real mesoscale convective system (MCS) between the Gosan and Jindo radar pair at 1430 UTC 30 June 2006, the wind structure of the convective cells in the MCS was consistently retrieved relative to the reflectivity factor structure. By comparing the vertical wind structure of this case with that of 10 minutes after, 1440 UTC 30 June 2006, we got the physical consistency of our method.

• Fire Science and Engineering
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• v.30 no.6
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• pp.78-83
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• 2016

The characteristics of flame spread under similar atmospheric conditions to those inside the first stage of launch vehicles were investigated to provide fundamental knowledge to prevent fires and explosions of vehicles during launching operations. To this end, the rate of flame spread on the solid fuel was measured at elevated oxygen concentrations and reduced atmospheric pressures. A 0.18 mm diameter optical fiber was used as a solid fuel. The experimental results indicated that elevated oxygen concentrations can increase the rate of flame spread while increasing the atmospheric pressures to 1 atm can lead to decreases in the rate of flame spread. The increases in the rate of flame spread with pressure is due mainly to reductions in the convective heat loss that are clarified through an analysis of the pressure dependence on the convective heat transfer coefficient.

• Atmosphere
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• v.26 no.2
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• pp.321-336
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• 2016

Damages caused by torrential rain occur every year in Korea and summer time convection can cause strong thunderstorms to develop which bring dangerous weather such as torrential rain, gusts, and flash flooding. On 6 August 2013 a sudden torrential rain concentrated over the inland of Southern Korean Peninsula occurred. This was an event characterized as a mesoscale multicellular convection. The purpose of this study is to analyze the conditions of the multicellular convection and the synoptic and mesoscale nature of the system development. To this end, dynamical and thermodynamic analyses of surface and upper-level weather charts, satellite images, soundings, reanalysis data and WRF model simulations are performed. At the beginning stage there was a cool, dry air intrusion in the upper-level of the Korean Peninsula, and a warm humid air flow from the southwest in the lower-level creating atmospheric instability. This produced a single cell cumulonimbus cloud in the vicinity of Baengnyeongdo, and due to baroclinic instability, shear and cyclonic vorticity the cloud further developed into a multicellular convection. The cloud system moved southeast towards Seoul metropolitan area accompanied by lightning, heavy precipitation and strong wind gusts. In addition, atmospheric instability due to daytime insolation caused new convective cells to develop in the upstream part of the Sobaek Mountain which merged with existing multicellular convection creating a larger system. This case was unusual because the system was affected little by the upper-level jet stream which is typical in Korea. The development and propagation of the multicellular convection showed strong mesoscale characteristics and was not governed by large synoptic-scale dynamics. In particular, the system moved southeast crossing the Peninsula diagonally from northwest to southeast and did not follow the upper-level westerly pattern. The analysis result shows that the movement of the system can be determined by the vertical wind shear.