• Composites Research
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• v.13 no.4
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• pp.33-41
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• 2000

In this research, the mathematical modeling of the formation of SiC layer on the activated carbon was studied to improve the durability and the oxidation resistance of catalyst supports. SiC layer on the activated carbon was formed by permeating SiC from dichlorodimethylsilane(DDS) into pores and depositing while the porous structure was kept. The best conditions of manufacturing the support were found by studying the characteristics of SiC/C which was modelled under various deposition conditions. Changes of the amount of deposition, the pore diameter, the surface area with time were obtained by simulating convection, diffusion and reaction in an isothermal reactor at a steady state. The uniform deposition in the pores of samples was obtained at a lower concentration of the reactant and a lower pressure. Additionally, it was observed that the pore diameter and the surface area have points of inflection at certain times of deposition, because deposition occurred on the inside surface of the pore at first and then on the outside surface of the particle.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.25-31
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• 2021

Boundary conditions for thermal-hydraulic problems of soils play an essential role in the numerical accuracy. This study presents a boundary condition considering the thermo-hydraulic interaction between the ground and the atmosphere. Ground surface energy balance consists of solar radiation, ground radiation, wind convection, latent heat from water evaporation, and heat conduction to the ground. Equations for each heat flux are presented, and numerical analyses are performed in conjunction with the FEM program for the thermal-hydraulic phenomenon of unsaturated soils. Numerical results using the weather data at the Ulsan Meteorological Observatory are similar to the measured surface temperature. Latent heat caused by water evaporation during the daytime lowers the surface temperature of the bare soil, and a thermal equilibrium is reached at nighttime when the effect of the ground condition is significantly reduced. The temperature change of the surface ground is diminished at the deeper ground due to its thermal diffusion. Numerical analysis where the surface ground temperature is the primary concern requires considering the thermo-hydraulic interaction between the ground and the atmosphere.

• Journal of the Korean Geotechnical Society
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• v.26 no.2
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• pp.33-43
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• 2010

Geothermal energy is gaining wide attention as a highly efficient renewable energy and being increasingly used for heating/cooling systems of buildings. The standing column well (SCW) is especially efficient, cost-effective, and suitable for Korean geological and hydrological conditions. However, a numerical model that simulates the SCW has not yet been developed and applied in Korea. This paper describes the development of the SCW numerical model using a finite-volume analysis program. The model, through hydro-thermal coupled analyses, simulates heat transfer through advection, convection, and conduction. The accuracy of the model was verified through comparisons with field data measured at SCWs in the U.S. and Korea. Comparisons indicated that the SCW numerical model can closely predict the performance of a SCW. The numerical model was used to perform a comprehensive parametric study in the companion paper.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.181-188
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• 2012

The present study on nitrogen-diluted non-premixed counterflow flames with finite burner diameters experimentally investigates the important role of the outer edge flame in flame extinction. Flame stability diagrams mapping the flame extinction response of nitrogen-diluted non-premixed counterflow flames to varying global strain rates in terms of the burner diameter, burner gap, and velocity ratio are explored. There exists a critical nitrogen mole fraction beyond which the flame cannot be sustained, and also the curves of the critical nitrogen mole fraction versus the global strain rate have C-shapes in terms of burner diameter, burner gap, and velocity ratio. In flames with sufficiently high strain rates, the curves of the critical nitrogen mole fractions versus global strain rate collapse into one curve, and the flames can have the 1-D flame response of typical diffusion flames. Three flame extinction modes are identified: flame extinctions through the shrinkage of the outer edge flame with and without an oscillation of the outer edge flame prior to the extinction and flame extinction through a flame hole at the flame center. The measured flame surface temperature and a numerical evaluation of the fractional contribution of each term in the energy equation show that the radial conductive heat loss at the flame edge destabilizes the outer edge flame, and the conductive and convection heat addition to the outer edge from the trailing diffusion flame stabilizes the outer edge flame. The radial conductive heat loss at the flame edge is the dominant extinction mechanism acting through the shrinkage of the outer edge flame.

• Journal of the Korean GEO-environmental Society
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• v.13 no.5
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• pp.35-40
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• 2012

In this study, adsorption characteristics of expanded graphite (EG) were investigated by a series of batch adsorption tests using p-Xylene as a model volatile organic compounds (VOCs). After acid treatment, graphite were expanded at various temperature from $600^{\circ}C$ to $1000^{\circ}C$ for one minute. The optimal temperature was $800^{\circ}C$, where the expansion ratio reached 195 times of original volume. The BET specific surface area of EG was $92.4m^2/g$, which was only 1/10 of granular activated carbon (GAC), however the adsorption of p-Xylene by EG was almost completed within 5 minutes while that of GAC continued for 7 days because the majority of pores of EG was consisted with meso- and macro-pores. According to the Langmuir isotherm analysis, the maximum specific adsorption of p-Xylene onto EG was 24.0 mg/L with the adsorption constant of 7.94. In conclusion, the adsorption capacity of EG was much less than that of GAC due to the significantly lower specific surface area, but the first order kinetic constant was more than 500 times larger than GAC. Overall, EG might be effective where the fast adsorption is required.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.4
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• pp.145-152
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• 2023

The average Nusselt numbers in the source and crystal region for the variation of thermal Grashof number (Gr_t) in the range of 2.31 × 10⁴ ≤ Gr_t ≤ 4.68 × 10⁴ are obtained through numerical simulations. It is shown the average Nusselt number in the crystal region is more than twice as large as the average Nusselt number in the source region. The average Nusselt number in the source region shows an increasing tendency with increasing the thermal Grashof number, Gr_t, while the average Nusselt number in the crystal region shows a decreasing tendency with increasing thermal Grashof number, Gr_t. For the variation of the solutal Grashof number (Gr_s) in the ran ge of 3.28 × 10⁵ ≤ Gr_s ≤ 4.43 × 10⁵, the average Sherwood number in the source region and crystal region tends to decrease as the solutal Grashof number, Gr_s increases. The average Sherwood number in the crystal region is about four times greater than the average Sherwood number in the source region.

• Korean Journal of Ecology and Environment
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• v.37 no.4 s.109
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• pp.436-447
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• 2004

Wetland plants have evolved specialized adaptations to survive in the low-oxygen conditions associated with prolonged flooding. The development of internal gas space by means of aerenchyma is crucial for wetland plants to transport $O_2$ from the atmosphere into the roots and rhizome. The formation of tissue with high porosity depends on the species and environmental condition, which can control the depth of root penetration and the duration of root tolerance in the flooded sediments. The oxygen in the internal gas space of plants can be delivered from the atmosphere to the root and rhizome by both passive molecular diffusion and convective throughflow. The release of $O_2$ from the roots supplies oxygen demand for root respiration, microbial respiration, and chemical oxidation processes and stimulates aerobic decomposition of organic matter. Another essential mechanism of wetland plants is downward water movement across the root zone induced by water uptake. Natural and constructed wetlands sediments have low hydraulic conductivity due to the relatively fine particle sizes in the litter layer and, therefore, negligible water movement. Under such condition, the water uptake by wetland plants creates a water potential difference in the rhizosphere which acts as a driving force to draw water and dissolved solutes into the sediments. A large number of anatomical, morphological and physiological studies have been conducted to investigate the specialized adaptations of wetland plants that enable them to tolerate water saturated environment and to support their biochemical activities. Despite this, there is little knowledge regarding how the combined effects of wetland plants influence the biogeochemistry of wetland sediments. A further investigation of how the Presence of plants and their growth cycle affects the biogeochemistry of sediments will be of particular importance to understand the role of wetland in the ecological environment.

• Journal of the Korean Society of Safety
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• v.7 no.2
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• pp.63-70
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• 1992

The aim of this research is to obtain a basic quantitative understanding of the effect of a noncondensable gas on the absorption of water vapor by a $H_2O$ / LiBr combination with n-octanol as the surfactant. Nonflowing aqueous solutions of LiBr (40,45,50 mass％) were exposed to saturated water vapor following the addition of an n-octanol sufactant (0.01 and 0.6 mass％). A small amount of a noncondensable gas (air) was allowed into the absorber (0.03 volume％) and its effect was analyzed by measuring the amount of water vapor absorbed. This study will aid to predict the performance of heat pump and safety operating condition when the noncondensable gas is not allowed in the absorber The results indicate that, in the presence of small amounts of a noncondensable gas, vapor absorption enhancement ratios are less than half o( those obtained under the same experimental conditions when a noncondensable gas is not present (1). The presence of a noncondensable gas causes the partial vapor pressure of air to increase at the vapor / liquid interface, which results in an instability of vapor absorption rate nd. hence, in an inhibition of interfacial disturbance.

• Journal of Bio-Environment Control
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• v.32 no.2
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• pp.172-180
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• 2023

This study was carried out to determine the sprouting period of early and mid-season varieties, which includes 'Atlantic', 'Chubaek', and 'Superior', during the summer storage period in a semi-underground warehouse without cooling system. And also it was investigated the effect of chlorpropham [Propan-2-yl N-(3-chlorophenyl)carbamate, CIPC] treatment on the sprouting inhibition for the varieties. This study was conducted to figure out a sprout inhibitory effect when CIPC was applied to 1kg of the potato tubers at concentrations of 10 mg and 20 mg which are lower than the treatment concentrations of ca 30 mg prescribed by the positive list system (PLS). The internal temperature of the warehouse used in this experiment was lowered by 5℃ or more than the outside temperature. The difference between the lowest and highest temperature during the experiment throughout the day was 5℃. It showed the effect of reducing to 1/2 of the difference in outdoor temperature. As for the sprouting of potatoes, the extremely early variety 'Chubaek' sprouts appeared at the 6th week of storage of control and it was the fastest sprouting potato among the control groups of the varieties. Sprouting began to appear in the Superior at the 6th week of storage, while the 'Atlantic' sprouted at the 8th week of storage. The appearance of sprouts was suppressed in all treatment groups of 'Atlantic' and 'Superior' varieties in CIPC treatments. Sprouts were observed in all treatment groups of 'Chubaek' after the 7th week, but the elongations of the sprouts in tubers were completely inhibited until the 8th week of storage. 'Atlantic' and 'Superior' seemed to have a sprouting inhibitory effect even with a low CIPC concentration of 10 mg·kg^-1, with the exception of extremely early variety 'Chubaek' that breaks out of the dormancy quickly. Although weight loss occurred continuously during storage, it was minor loss of 0.7-1.6%. There was no consistent trend for changes of the loss in the varieties and CIPC treatments. Most common pathological disorder was the dry rot during the experiment, but only few were affected. The use of the tubers treated at 18℃ and 90% RH for 10 days and the rack of refrigeration system which lead to lack of convection seemed to have suppressed the spread of pathogens.