• Applied Chemistry for Engineering
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• 제10권8호
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• pp.1186-1191
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• 1999

By using a liquid-mix precursor, we prepared the hollow glass spheres(HGS) as an additive of polymer compound which are used in the field of modifier, promoter, filler, and reinforcement. Liquid-mix precursor is a mixture of 40% sodium silicate aqueous solution, boric acid as a insolubilizing agent, and urea as a blowing agent. To obtain the precursor particles which are fed into a gas flame furnae, the above liquid-mix precursor was dried in oven and crushed with ball mill. We assumed the size of precursor particles ($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$), temperature of furnace($800{\sim}1200^{\circ}C$), and amount of urea(0~30 g) as the parameters affecting on the properties of HGS. As a result mean particle size of HGS increases with increasing the temperature of furnace and the amount of urea and with decreasing the size of precursor particles. Also, we found that incresing the amount of urea is related to a decrease of the crush strength of HGS.

• Carbon letters
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• 제15권4호
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• pp.247-254
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• 2014

In this work, thermal treatment accompanied with different acid treatments was applied to a commercial coal tar pitch (CTP) to obtain a spinnable precursor pitch for carbon fiber. In the case of thermal treatment only, a relatively high reaction temperature of between $380^{\circ}C$ and $400^{\circ}C$ was required to obtain a softening point (SP) range of $220^{\circ}C-260^{\circ}C$ and many meso-phase particles were created during the application of high reaction temperature. When nitric acid or sulfuric acid treatment was conducted before the thermal treatment, the precursor pitch with a proper SP range could be obtained at reaction temperatures of $280^{\circ}C-300^{\circ}C$, which were about $100^{\circ}C$ lower than those for the case of thermal treatment only. With the acid treatments, the yield and SP of the precursor pitch increased dramatically and the formation of meso-phase was suppressed due to the lower reaction temperatures. Since the precursor pitches with acid and thermal treatment were not spinnable due to the inhomogeneity of properties such as molecular weight distribution and viscosity, the CTP was mixed with ethanol before the consecutive nitric acid and thermal treatments. The precursor pitches with ethanol, nitric acid, and thermal treatments were easily spinnable, and their spinning and carbon fiber properties were compared to those of air blowing and thermal treated CTP.

• The Journal of the Korea institute of electronic communication sciences
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• 제14권3호
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• pp.559-572
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• 2019

In the southeast sea of Korea, the cold water is concentrated in every summer, showing in abnormal oceanic conditions. Cold water occurred in the southeast sea is dominantly influenced by wind, which occurs when the south wind is continuously blowing for 3 to 7 days more. In this study, water temperature, wind speed and direction data of KMA, KHOA and KHNP, Chlorophyll-a of COMS/GOCI, GHRSST Level 4 SST of NASA, and red tide alert data of the National Institute of Fisheries Science were used to analyze the correlation between occurrence and change of the cold water and the red tide of Cochlodinium polykrikoides. The upwelling cold water mass showed a characteristic of moving northward along the current and occurrence a high concentration of chlorophyll along the water mass. Also, when the warm current were strong, the characteristic of red tide showed a northward moving.

• Journal of Bio-Environment Control
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• 제13권3호
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• pp.162-166
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• 2004

Air temperature variation along the length of the air duct in an air-heated plastic greenhouse was large, 13 ～ 15$^{\circ}C$ between the front and the rear side of a greenhouse. To reduce this temperature variation, a new PE-film air duct having a small duct inside a large duct (double duct) was developed. This double duct was consisted of an inner duct with air outlets at a 0.15 m interval and an outer duct with air outlets at a 2.5 m interval. Diameters of the air outlet holes were 7, 15, and 35 cm from the front to the end of the inner duct film, while identical 10 cm holes were used on the outer duct film. As a result, air temperature was $46^{\circ}C$ at the beginning side and $47^{\circ}C$ at the ending side, while the conventional single duct had $53^{\circ}C$ at the beginning point and $38^{\circ}C$ at the ending point with a variation of $15^{\circ}C$. Height of a cucumber crop grown in a greenhouse with the new double air duct system was 65.5 cm, 14% increase as compared to that in a greenhouse with a conventional air duct system. Total fruit yield per l0a greenhouse in a greenhouse with the new double air duct system was 4,616 kg, which was 17% greater than that in a greenhouse with a conventional air duct system. Amount of heating oil consumption during March 3 to April 24, 2002 was 3,233 L per l0a greenhouse with the new double air duct system, which was 13% less than that with a conventional air duct system.

• KOREAN JOURNAL OF CROP SCIENCE
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• 제35권6호
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• pp.504-511
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• 1990

Weather data acquisition and potential evapotranspiration (PET) calculation procedure were investigated to support the agricultural development efforts in the mid-altitude mountainous region of Cheju Island. Automated weather stations (AWS) were installed at two points representing the east and the west of the study area. A personal computer was employed to collect the near-real time weather data from AWS through the public telephone line. Hourly data were available for solar radiation, air and soil temperature, relative humidity, wind speed and direction, and precipitation. Based on the data for the month of June 1989, daily climatic features were comparatively analyzed for the two areas and the Penman equation was used to calculate PET. Air temperature was higher by 1 to 2 degree C in the east due mainly to the higher solar radiation and partly to the Fohn effect caused by the daytime southwesterly blowing over Mt. Halla. Diurnal march of soil temperature lagged by 4 hours behind that of air temperature and the diurnal range for 10cm subsurface soil was 3 degree C. Wind was consistently stronger and a marked sea-land breeze circulation was detected in the west. Calculated PET values were higher in the east by 6% than in the west. Overall values from the east and the west of the mid-altitude mountainous region were higher by 30% than those of the coastal region, which were estimated from the Class A Pan evaporation measured by the Korea Meteorological Service Offices.

• Polymer(Korea)
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• 제39권2호
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• pp.210-218
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• 2015

The reaction behavior of rigid polyurethane foams were studied on the effects of gelling catalysts of amine type, such as; dimethylcyclohexyl amine (DMCHA) and of potassium type, such as; potassium octoate (PO). Rigid polyurethane foams were provided with polymeric 4,4'-diphenylmethane diisocyanate, polyester polyol, silicone surfactant, blowing agent and a few gelling catalysts. As the contents of catalyst, DMCHA increased from 0 to 2.0 g, the reaction time decreased from ca. 330 to ca. 35 sec and due to the exothermic reaction, the maximum temperature increased from ca. 217 to ca. $234^{\circ}C$, respectively. As the contents of PO increased from 0 to 2.5 g, the reaction time decreased from ca. 79 to ca. 38 sec and the maximum temperature increased from ca. 182 to ca. $271^{\circ}C$, respectively. The kinetic parameters were calculated and the conversions were based on the temperature rising method of adiabatic process. As the content of DMCHA increased, the rate constant $k_0$ increased. But in the case of PO catalyst, $k_0$ did hardly depend upon its amount, and showed us similar reaction rate constants.

• Polymer(Korea)
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• 제35권5호
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• pp.467-471
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• 2011

PET bottle is manufactured by blow molding the preform, which is molded by injection molding. The neck part of the preform of PET bottle for juice or grain-based beverage is crystallized before blowing to improve heat resistance at the entrance of the bottle. However, residual stress, developed during injection molding of preform, prevents the crystallization. In order to release the residual stress in the preform, the preform is annealed after the injection molding. If the residual stress is reduced by optimizing the injection molding conditions of preform the annealing time would be shortened. In this study, the optimum conditions for minimizing the residual stress and increasing dimensional accuracy of the injection molded preform are suggested through CAE analysis. In order to optimize the molding conditions, minimizing residual stress and shrinkage, computer simulations have been carried out with help of design of experiment scheduling. Injection temperature, initial packing pressure and filling time were selected for control parameters. Residual stress was affected by injection temperature and filling time. Shrinkage was affected by injection temperature. It was found that maximum residual stress, distribution of residual stress and shrinkage were decreased by 22%, 40% and 25%, respectively at an optimum molding condition compared with the results of previous molding condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제39권3호
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• pp.271-278
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• 2015

The convective heat transfer of a crossflow fin-tube heat exchanger was studied numerically. In order to investigate the dependence of the heat transfer performance on the fan position, several cases with different blowing and suction types were selected for the fan position. A staggered tube arrangement was used for the heat exchanger, and the temperatures of the tube wall and air were $50^{\circ}C$ and $30^{\circ}C$, respectively. The three-dimensional flow structures were examined based on the results. In addition, the convective heat transfer coefficient and mean temperature difference between the inlet and outlet of the heat exchanger were analyzed for the various fan positions, and the heat transfer performance was investigated

• Transactions of the Korean Society of Mechanical Engineers B
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• 제39권1호
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• pp.37-43
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• 2015

Evaporative cooling is a very effective way for exhaust heat recovery that uses both latent heat and sensible heat. This study investigated the performance of a heat recovery system using evaporative cooling. The experimental apparatus comprised a plastic heat exchanger, a water spray nozzle, an air blowing fan, a water circulation pump, and measuring sensors for the temperature, humidity, and flow rate. The effectiveness of the sensible heat recovery without evaporation was measured and compared with that of the total heat recovery with evaporation. The effectiveness of the sensible and total heat recoveries decreased as the air flow rate increased, and a much higher effectiveness was obtained with the counterflow arrangement in both cases. For total heat recovery, the effectiveness increased with the water flow rate, and the parallel flow arrangement was found to be more sensitive to the water flow rate than the counterflow arrangement.

• Korean Journal of Materials Research
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• 제26권4호
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• pp.173-181
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• 2016

In order to use coal tar pitch (CTP) as a raw material for carbon fibers, it should have suitable properties such as a narrow range of softening point, suitable viscosity and uniform optical properties. In this study, raw CTP was modified by heat treatment with three types of polymer additives (PS, PET, and PVC) to make a spinnable pitch for carbon fibers. The yield, softening point, C/H ratio, insoluble yield, and meso-phase content of various modified CTPs with polymer additives were analyzed by changing the type of polymer additive and the heat treatment temperature. The purpose of this study was to compare the properties of CTPs modified by polymer addition with those of a commercial CTP. After the pitch spinning, the obtained green fibers were stabilized and carbonized. The properties of the respective fibers were analyzed to compare their uniformity, diameter change, and mechanical properties. Among three polymer additives, PS220 and PET261 pitches were found to be spinnable, but the carbon fibers from PET261 showed mechanical properties comparable with those of a commercial CTP produced by an air-blowing method (OCI284). The CTPs modified with polymer additive had higher ${\beta}$-resin fractions than the CTP with only thermal treatment indicating a beneficial effect of carbon fiber application.