• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1300-1307
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• 1995

The effect of thermal stratification on the turbulent dispersion from a fine cylindrical heat source was experimentally examined in a wind tunnel with and without a strong temperature gradient. A 0.5 mm dia. nichrome wire was used as a line heat source. Turbulent intensities, r.m.s. value of temperature and convective heat fluxes were measured by using a hot-wire and cold-wire combination probe. The results show that the peack value and the spread of the vertical turbulent intensity for the stratified case are far lower than those in the neutral case, which indicates that the stable temperature gradient suppresses the vertical velocity component. All of the third order moments including heat fluxes measured in the stable condition have very small values than those of the neutral case. This nature suggests that the decrease of scalar fluctuations in the stably stratified flow is mainly due to the suppression ofthe turbulent diffusion processes by the stable stratification. A simple gradient model with a composite timescale which has a simple weighted algebraic mean between dynamic and thermal time scale yields reasonably good numerical values in comparison with the experimental data.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.5
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• pp.551-561
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• 2008

In order to clarify the impact of anti-heat insulation pavement on the thermal structure of atmospheric boundary layer, field experiments and numerical simulations were carried out. Field experiment with various pavements were also conducted for 24 hours from 09LST 19 June 2007. And numerical experiment mainly focused on the impact of albedo variation, which is strongly associated with thermal characteristics of insulated pavement materials, on the temporal variation of planterly boundary layer. Numerical model used in this study is one dimension model with Planterly Boundary Layer developed by Oregon State University (OSUPBL). Because anti-heat insulation pavement material shows higher albedo value, not only maximum surface temperature but also maximum surface air temperature on anti-heat insulation pavement is lower than that on asphalt. The maximum value of surface temperature only reach on $49.5^{\circ}C$. As results of numerical simulations, surface sensible heat flux and the height of mixing layer are also influenced by the values of albedo. Therefore the characteristics of urban surface material and its impact on atmosphere should be clarified before the urban planning including improvement of urban heat environment and air quality.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.1
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• pp.10-15
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• 2011

Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440(H) and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440(H) and SNCM439 with 150 mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440(H) showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440(H) was relatively small. Heat treated mechanical properties of the alloys with 25 mm diameter were more uniform value than those with 150 mm diameter.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.11 no.4
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• pp.22-27
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• 2015

Quality characteristics of Shiitake mushroom using two types of dryers, energy-efficient heat pump hot-air dryer and electric heater hot-air dryer were compared. Energy consumed during drying by heat pump hot-air dryer and electric heater hot-air dryer were 22.8 kWh and 28.9 kWh, respectively. Total polyphenol content of heat pump hot-air dryer and electric heater hot-air dryer after drying were $290.55{\pm}10.56ppm$ and $192.99{\pm}6.53ppm$, respectively. No differences were observed between dryers in reconstitution rate and browning ratio after drying. Also, there were no differences between dryers in color value and ${\Delta}E$ value after drying. Shiitake mushroom drying at $45^{\circ}C$ by heat pump hot-air dryer was proved to be more efficient in energy consumption than by electric heater hot-air dryer.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.191-196
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• 2007

This paper presents the measuring technique for local heat transfer coefficients using a copper sensor in a rod bundle with mixing vanes. A copper sensor consists of a cartridge heater and four pieces of thermocouple. The Heater is located at the center of the copper sensor and thermocouples measure the surface temperature of the copper sensor. Unheated copper sensor and heated copper sensor are able to measure the local heat transfer coefficient at the position where the heated copper sensor is installed. However the entire region of a rod bundle is actually not heated, the decay of local heat transfer coefficients measured represents overestimated value rather than an actual value. The calibration curve for local heat transfer coefficients is presented using the correction factor calculated by CFD.

• Journal of the Korean Solar Energy Society
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• v.37 no.5
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• pp.65-75
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• 2017

In this study, the change of heat loss due to the degree of deterioration of the XPS insulation in KEPCO's office buildings is analyzed. The acceleration aging test of the XPS insulation was carried out according to the test method A of KS M ISO 11561: 2009. The performance of the insulation was analyzed by applying it to the three - dimensional steady state heat transfer analysis program. The acceleration aging test of the XPS insulation, show that the thermal resistance performance decreased by 1.44% at the A regional headquarters, 0.85% at the B regional headquarters, 6.41% at the C branch office, 7.76% at the D regional headquarters, 8.51% at the E branch office, and by 8.54% at the F branch office respectively. Using simulation, we determined that the thermal resistance value of E branch office decreased by 8.04%, while its heat loss increased by 8.52%. At A regional headquarters, the thermal resistance decreased by 1.38%, and the heat loss increased by 1.51%. At D regional headquarters, these value are 6.82% and 7.17%, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.551-561
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• 1998

This paper was studied to understand the characteristics of heat transfer coefficients and surface temperature distributions around a circular combustion chamber within the heat-intercept duct of kerosene fan heater. The experiment was carried out in the heat-intercept duct of kerosene fan heater attached to the blow-down-type subsonic wind tunnel with a test section of 240 mm * 240 mm * 1200 mm. The purpose of this paper was to obtain the basic data related with normal combustion for new design from conventional kerosene fan heater, and to investigate the effect of surface temperature, local and mean heat transfer coefficients versus flow-rate of convection axial fan according to the variations of heat release conditions from kerosene fan heater during normal combustion. Consequently it was found that (i) the revolution of convection axial fan during combustion had a smaller value than that of non-combustion because of the thermal resistance due to the high temperature in the heat-intercept duct, (ii) the pressure ratio P$_{2}$/P$_{1}$ had a comparatively constant value of 0.844 according to the revolution increase of turbo fan and the heating performance of kerosene fan heater had a range of 1,494 ~ 3,852 kcal/hr, (iii) the local heat transfer coefficient around a circular combustion chamber had a comparatively larger scale in the range of 315 deg. < .theta. < 45 deg. than that in the range of 90 deg. < .theta. < 270 deg. as a result of heat transfer difference between front and back of a circular combustion chamber, and (iv) the mean heat transfer coefficient around a circular combustion chamber increased linearly like a H$_{m}$=95.196Q+104.019 in condition of high heat release according to the increase of flow-rate of axial fan.n.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.1
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• pp.9-15
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• 1998

Hourly meteorological data from a marine buoy ($34^{\circ}49'00"N$, $125^{\circ}46'00"E$) operated by the Korean Meteorological Agency were obtained from July, 1996 to February, 1997. From the data air-sea heat fluxes and marine meteorological characteristics around the area are estimated. The maximum outflux of sensible heat from the sea surface occurred in January (monthly mean value, 12.6 $Wm^{-2}$ and the maximum influx to the sea occurred in July (monthly mean value, 5.5 $Wm^{-2}$). This means that the sea is heated in summer while it loses its heat in winter, and that there is inequality between the absolute values of the two seasons. The outflux of the maximum latent heat occurred in November (monthly mean value, 86.5 $Wm^{-2}$) and reach a value of 300 $Wm^{-2}$, and the maximum influx occurred in July (monthly mean value, 4.6 $Wm^{-2}$). Big difference is shown in their absolute values when the wind becomes strong. The outgoing latent heat flux reaches its maximum in autumn, and it maintains the high value through the whole winter. According to the wave data analysis, the significant wave heights are larger in winter than in summer. The periods of the significant waves are 4~6 sec. In winter, waves propagated from north and northeast are dominant because of the winter monsoon, while in summer waves from south, southwest, and west are relatively frequent.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.50-59
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• 2000

An experimental study has been carried out in order to investigate the heat storage characteristics for a latent heat storage tank with horizontal shell and tube type. The heat exchanger consisted of horizontal cylindrical capsules with a staggered tube bank layout. Based on the obtained data, the effects of flow rate and inlet fluid temperature on the melting time and heat storage rates were examined. It is found that the melting time decreased with increase of the flow rate and the inlet temperature. Results also show that at the initial stage of heat transfer the heat storage rate represents the maximum value and rapidly decreases.

• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.1063-1072
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• 2003

Direct immersion cooling has been considered as one of the promising methods to cool high power density chips. A fluorocarbon liquid such as FC-72, which is chemically and electrically compatible with microelectronic components, is known to be a proper coolant for direct immersion cooling. However, boiling in this dielectric fluid is characterized by its small value of the critical heat flux. In this experimental study, we tried to enhance the critical heat flux by increasing the nucleate boiling area in the heat spreader (Conductive Immersion Cooling Module). Heat nux of 2 MW/㎡ was successfully removed at the heat source temperature below 78$^{\circ}C$ in FC-72. Some modified boiling curves at high heat flux were obtained from these modules. Also, the concept of conduction path length is very important in enhancing the critical heat flux by increasing the heat spreader surface area where nucleate boiling occurs.