• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.25 no.1
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• pp.57-81
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• 1997

Numerical prediction of nocturnal thermal high in summer of the 1995 near Taegu city located in a basin has been carried out by a non-hydrostatic numerical model over complex terrain through one-way double nesting technique in the Z following coordinate system. Under the prevailing westerly winds, vertical turbulent fluxes of momentum and heat over mountains for daytime hours are quite strong with a large magnitude of more than $120W/\textrm{m}^2$, but a small one of $5W/\textrm{m}^2$ at the surface of the basin. Convective boundary layer (CBL) is developed with a thickness of about 600m over the ground in the lee side of Mt. Hyungje, and extends to the edge of inland at the interface of land sea in the east. Sensible heat flux near the surface of the top of the mountain is $50W/\textrm{m}^2$, but its flux in the basin is almost zero. Convergence of sensible heat flux occurs from the ground surface toward the atmosphere in the lower layer, causing the layer over the mountain to be warmed up, but no convergance of the flux over the basin results from the significant mixing of air within the CBL. As horizontal transport of sensible heat flux from the top of the mountain toward over the basin results in the continuous accumulation of heat with time, enhancing air temperature at the surface of the basin, especially Taegu city to be higher than $39.3^{\circ}C$. Since latent heat fluxes are $270W/\textrm{m}^2$ near the top of the mountain and $300W/\textrm{m}^2$ along the slope of the mountain and the basin, evaporation of water vapor from the surface of the basin is much higher than one from the mountain and then, horizontal transport of latent heat flux is from the basin toward the mountain, showing relative humidity of 65 to 75% over the mountain to be much greater than 50% to 55% in the basin. At night, sensible heat fluxes have negative values of $-120W/\textrm{m}^2$ along the slope near the top of the mountain and $-50W/\textrm{m}^2$ at the surface of the basin, which indicate gain of heat from the lower atmosphere. Nighttime radiative cooling produces a shallow nocturnal surface inversion layer with a thickness of about 100m, which is much lower than common surface inversion layer, and lifts extremely heated air masses for daytime hours, namely, a warm pool of $34^{\circ}C$ to be isolated over the ground surface in the basin. As heat transfer from the warm pool in the lower atmosphere toward the ground of the basin occurs, the air near the surface of the basin does not much cool down, resulting in the persistence of high temperature at night, called nocturnal thermal high or tropical night. High relative humidity of 75% is found at the surface of the basin under the moderate wind, while slightly low relative humidity of 60% is along the eastern slope of the high mountain, due to adiabatic heating by the srong downslope wind. Air temperature near the surface of the basin with high moisture in the evening does not get lower than that during the day and the high temperature produces nocturnal warming situation.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.283-290
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• 2008

In this paper, experiments with an air-breathing proton exchange membrane fuel cell (PEMFC) for mobile devices were carried out according to cathode conditions. These conditions are defined by the cathode flow field plate type (the channel type, the open type) and the cathode surface direction. Single-cell and 6-cell stack were used in the experiments. The experimental results showed that the open-type cathode flow field plate gave a better performance than the small channel type. In the experiments related to the direction of the slits on the cathode flow field plate, the horizontal slit cell was better than the vertical one. With respect to the cathode surface direction, when the cathode surface is placed in the direction normal to the ground, the PEMFC generated more stable power in the mass transport loss region. Since stable power in the mass transport region is closely related to the air supply, computational fluid dynamics (CFD) analysis for air-breathing PEMFC of different cathode surface directions was performed.

• Journal of ILASS-Korea
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• v.12 no.3
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• pp.160-165
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• 2007

In this study, the breakup characteristics of mono disperse droplets were studied with various fuels, ethanol, diesel fuel, biodiesel fuel extracted from soybean oil, and pure water. In order to investigate the droplet behavior in air cross-flow conditions, the experimental equipment was composed of a droplet generator with an air nozzle, and a high-magnification photo detecting system. Droplets produced by the droplet generator were injected into the air stream flowing normal to a direction of liquid drop jet. Digital images of the droplet behavior in air flow field were recorded by controlling the air flow rate. From the inspections, droplet breakup mechanism is primarily classified into the two kinds of stage, first breakup stage and second breakup stage. At the first breakup stage, droplet deformation rate seems to be affected by the force induced by the surface tension and the viscosity. On the other hand, at the second breakup stage, droplet is broken up mainly induced by the surface tension, so the breakup transition can be divided by the regular Weber number.

• Journal of Soil and Groundwater Environment
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• v.26 no.1
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• pp.1-7
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• 2021

Air-water interfacial area is of great importance for the analysis of contaminant mass transfer processes occurring in the soil systems. Capillary bundle model has been proposed to estimate the specific air-water interfacial areas in unsaturated soils. In this study, the measured air-water interfacial areas of a soil (loam) using the gaseous interfacial tracer technique were compared to those from capillary bundle model. The measured values converged to the specific solid surface area (7.6×104 ㎠/㎤) of the soil. However, the simulated air-water interfacial areas based on the capillary bundle model deviated significantly from those measured. The simulated values were substantially over-estimated at low end of the water content range, whereas the model under-estimated the air-water interfacial area for the most of the water content range. This under-estimation is considered to be caused by the nature of the capillary bundle model that replaces the soil pores with a bundle of glass capillaries and thus no surface roughness at the inner surface of the capillaries is taken into account for the estimation of the air-water interfacial area with the capillary bundle model. Subsequently, appropriate correction is necessary for the capillary bundle model to estimate the air-water interfacial area in soils. Since the soil-moisture release curve data is the basis of the capillary bundle model, the model can be of use due to its simplicity, while the gaseous tracer technique requires complicated experimental equipment followed by moment analysis of the breakthrough curves. The size distribution profile of the pores filled with gas estimated by the water retention curve was found to be similar to that of particle size at different size range. The shifted distribution of gas-filled pores toward smaller size side compared to the particle size distribution was also found.

• PNF and Movement
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• v.11 no.2
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• pp.95-102
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• 2013

Purpose : The purpose of this study was to investigate a plantar pressure distribution and the trajectory of the center of pressure on double limb support and single limb support according to level surface, air cushion, and aero step. Methods : 21 healthy adults participated in this study. The plantar pressure were assessed at three different surface conditions(on the level surface, air cushion, and aero step) on double limb support and single limb support. Testing orders were selected randomly. Results : Plantar pressure distribution show a significant difference contact area 1 and contact area 3 on double limb support and single limb support. The trajectory of the center of pressure show an significant difference anteroposterior(AP), mediolateral(ML), and total displacement on double limb support and single limb support. Conclusion : Through the use of soft surface as air cushion and aero step will be using the ankle strategy. This will be to strengthen the muscles around the ankle. Consequently, should help to improve stability and coordination.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.533-538
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• 2005

The number of domestic ice-rink is little by little increasing recently. Therefore, the demand for air-conditioning system to adjust adequately the indoor condition of ice-rink is constantly increasing. But, if air-conditioning system for ice-rink isn't designed properly, the problems such as fogging, ice surface condensation, structural deterioration, odors, generation of dew condensation on the surface of a wall occur. The solutions for these problems are to lower the relative humidify of indoor. The objectives of this paper is to apply of desiccant dehumidifier on ice-rink, solve these problems.

• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.182-188
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• 2009

The surface plasmon resonance ellipsometer (SPRE), using a multiple air injection system with an extraction of air system, has been proposed and developed to minimize measurement error of signals due to diffusion of reagent into running buffer. Since the diffusion of reagent into running buffer affects the refractive index of the running buffer by changing the concentration, characteristics of binding between various bio-molecules don't appear clearly in measurement results. The diffusion between running buffer and reagent can be blocked by using an air bubble injection system. An extraction of air system is used to remove the noise signal due to unnecessary air bubbles flowing in a channel. Reliability of measurement results has been improved by using the valve system.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.1
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• pp.37-49
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• 2004

Four different data reduction methods for the heat transfer coefficients from experimental data under dehumidifying conditions are compared. The four methods consist of two heat and mass transfer models and two fin efficiency models. Data are obtained from two heat exchanger samples having plain fins or wave fins. Comparison of the reduced heat transfer coefficients revealed that the single potential heat and mass transfer model yielded the humidity-independent heat transfer coefficients. Two fin efficiency models-enthalpy model and humidity model-yielded approximately the same fin efficiencies, and accordingly approximately the same heat transfer coefficients. The heat transfer coefficients under wet conditions were approximately the same as those of the dry conditions for the plain fin configuration. For the wave fin configuration, however, wet surface heat transfer coefficients were approximately 12% higher. The pressure drops of the wet surface were 10% to 45% larger than those of the dry surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.845-852
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• 2001

The phenomena of energy separation in vortex tubes was investigated experimentally to see the effects of the conductivity of a tube and convective heat transfer on the outer surface of a tube. The experiment was carried out with different conductivity (pyrex, stainless steel and copper) of a tube and three kinds of convective heat transfer modes (adiabatic condition, natural convection (air) and forced convection (water) on the outer surface of a tube. the results were obtained that hot exit fluid temperature was highly affected by a change of conductivity of a tube when the outer surface was cooled by the forced convection of water. However, the cold exit temperature was little affected by heat transfer modes on the outer surface in vortex tubes.

• Tribology and Lubricants
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• v.32 no.5
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• pp.160-165
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• 2016

AISI 4140 steel is widely used in various mechanical components owing to its superior mechanical properties. Surface hardening techniques are often used to further improve the properties, particularly for applications with moving components. The aim of this research is to understand the effect of heat treatment process on surface properties and tribological characteristics of AISI 4140 steel. In this work, we prepare two different AISI 4140 steel specimens- one cooled by air and one by oil- and determine surface properties such as surface topography and roughness using a confocal microscope. We also observe the cross-sections of the specimens using a scanning electron microscope to understand the difference in the material structure. In addition, we assess the hardness with respect to the distance from the surface using a micro-Vickers hardness tester. After characterizing the surfaces of the specimens, we investigate the wear characteristics of the specimens under hydrodynamic lubrication. The results show the presence of grooves on the surface of the oil-cooled specimens. It is likely that such grooves are formed during the cooling process using the oil. However, we observe no other significant differences in the surface properties of the specimens. The wear test results show the occurrence of severe wear on the oil-cooled specimens, which may be due to the groove formed on the surface. The results of this work may be helpful to improve surface properties using surface hardening techniques from a tribological perspective.