• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1215_1216
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• 2009

Most transformer use insulating and cooling fluids derived from petroleum crude oil, but mineral oil is some possibility of environmental pollution and fire with explosion. vegetable oil fluids extracted from seed has superior biodegradation and fire-resistant properties including an exceptionally high fire point enhancing fire safety. In this study, it is aimed at the practicality of substituting natural ester dielectric fluid for mineral oil in liquid insulation system of transformers. As a rise in coil winding temperature has a direct influence on transformer life time, it is important to evaluate the temperature rise of coil winding in vegetable oil in comparison with mineral oil. Three transformers for the test are designed with 10KVA, 13.2KV, one phase unit. The temperature are directly measured in insulating oil of these transformers with the two sorts of natural ester and mineral oil dielectric fluid respectively. Temperature of vegetable oil transformers was similar to temperature of mineral oil transformer in the same design at 80% load and above.

• 한국정밀공학회지
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• 제20권7호
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• pp.26-35
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• 2003

This study explains the effects of lubricant and surface treatment on hot forging die life. The mechanical and thermal load, and thermal softening which is happened by the high temperature of die, in hot and warm forging, cause die wear, heat checking and plastic deformation, etc. This study is fur the effects of solid lubricants and surface treatment condition for hot forging die. Because cooling effect and low friction are essential to the long life of dies, optimal surface treatment and lubricant are very important to improve die life for hot forging process. The main factors, which affect die hardness and heat transfer, are surface treatments and lubricants, which are related to thermal diffusion coefficient and heat transfer coefficient, etc. For verifying these effects, experiments are performed for hot ring compression test and heat transfer coefficient in various conditions as like different initial billet temperatures and different loads. The effects of lubricant and surface treatment for hot forging die life are explained by their thermal characteristics. The new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• 열처리공학회지
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• 제29권4호
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• pp.181-189
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• 2016

The variation in microstructure and mechanical properties during heat treatment was examined in a series of 0.27% C-1.0% Si-1.5% Mn steels with chromium contents in the range of 0 to 1.0 wt%. It was found that chromium decreased the martensite packet size through the austenite grain refinement and increased tensile strength in the as-quenched steel, about 70 MPa per 1.0 wt%. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel showed tensile strength of 1700 MPa in the as-quenched steel. The 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel revealed a full martensitic structure after air cooling from $900^{\circ}C$ to room temperature, showing air hardening characteristics. Tempering at $150^{\circ}C$ slightly decreased the tensile strength and increased elongation, which is in a good agreement with impact toughness result.

• 방사성폐기물학회지
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• 제18권spc호
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• pp.1-19
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• 2020

Based on the current high-level radioactive waste management basic plan and the analysis results of spent nuclear fuel characteristics, such as dimensions and decay heat, an improved geological disposal concept for spent nuclear fuel from domestic nuclear power plants was proposed in this study. To this end, disposal container concepts for spent nuclear fuel from two types of reactors, pressurized water reactor (PWR) and Canada deuterium uranium (CANDU), considering the dimensions and interim storage method, were derived. In addition, considering the cooling time of the spent nuclear fuel at the time of disposal, according to the current basic plan-based scenarios, the amount of decay heat capacity for a disposal container was determined. Furthermore, improved disposal concepts for each disposal container were proposed, and analyses were conducted to determine whether the design requirements for the temperature limit were satisfied. Then, the disposal efficiencies of these disposal concepts were compared with those of the existing disposal concepts. The results indicated that the disposal area was reduced by approximately 20%, and the disposal density was increased by more than 20%.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.271-274
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• 1999

We are investigating epitaxially grown YBa$_2Cu_3O_x$(123) on MgO single crystal by partial melting process for high power application. After fabricating of BaCuO$_2$(011), Y$_2BaCuO_5$(211) powder, we made YBa$_2Cu_3O_x$(123) Paste with just mixing of (211), (011) and CuO(001) powders. Screen printing method was used to coat YBa$_2Cu_3O_x$(123) paste on MgO single crystal. To reduce the reaction in low temperature, rapid heating was conducted at partial melting temperature. The film was analysed with the difference of cooling-rate, thickness, reaction temperature by XRD, SEM, in-plane alignment, out-of-plane alignment, temperature-resistivity characteristics.

• 한국세라믹학회지
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• 제52권1호
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• pp.41-47
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• 2015

Celadon shards from Gangjin and Buan were analyzed for their color, chemistry and microstructures. They exhibited similar chromatic characteristics in a $CIEL^*a^*b^*$ analysis. All of the glazes assessed showed comparable compositional areas, while the bodies from Gangjin shards had higher $RO_2$ concentrations. A high degree of similarity was also noted in the microstructures of the glaze and bodies from both regions. Anorthite crystals appeared in the glaze layer, and phase separation behavior developed around these crystals. This may have been caused by the glaze chemistry and the sintering process given the lengthy heating and cooling time. A Raman analysis indicated higher isolated $SiO_4$ unit ($Q_0$) values for the Buan samples. This can stem from the higher firing temperature or the longer sintering process.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• 제22권1호
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• pp.24-32
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• 1994

A special upper-air observation including airsonde and pibal observations was performed to investigate the characteristics features of the vertical distribution of the meteorological elements over Taegu on a selected clear day of each season from October 1991 to August 1992. The diurnal and seasonal variations of the vertical profiles of air temperature and mixing ratio were obtained from airsonde observations and wind speed and direction from pibal observations. The results of these special upper-air observations are as follow : The diurnal variation of the vertical distribution of air temperature reveals the characteristic features associated with the atmospheric boundary layer. All case days, except for the summer season, show upper-level inversion layer which influenced by surface high, and surface inversion layer produced by radiative cooling. The diurnal variation of mixing ratio shows the maximum vale at 1500 LST in both the upper and low levels, and is larger on the lower level than the upper level. The mixing ratio of the lower level is larger than that of the upper level. On the average the mixing ratio decrease with the height, and is the wettest on the summer case day and the driest on the winter case day. The diurnal variation of the wind velocity and direction are variable in the lower level with time and height, while they are steady in the upper level. On the average, the wind direction is southerly or southeasterly for the summer case day, westerly or northwesterly for the spring and fall case days, and northerly or northwesterly for the winter case day.

• 한국환경과학회지
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• 제16권5호
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• pp.593-602
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• 2007

The frequency of tropical nights and tropical days in Busan during summer season (June-August) from 1995 to 2004 were investigated. When air temperature higher than $25^{\circ}C$ continuously maintains at night in summer, it is called the occurrence of tropical night. Tropical day is defined that maximum air temperature is higher than $30^{\circ}C$, In Jin-Gu and Daeyeon-dong shows a lot of frequency of tropical day and tropical night because there were located in downtown. Relatively, the areas where are located in seaside and riverside show very low frequency. This can be explained the cooling effects of sea and river. The main meteorological characteristics during tropical nights and tropical days is proved pattern of reverse tendency through wind rose. We analyzed heat index and discomfort index during tropical night and tropical day. This study is useful to understand the aspect of urban thermal environment but need some more observation to quantify.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1389-1394
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• 2003

$CO_2$ is a well-known green house gas, which is the major source of global warming. Many researchers have studied to reduce $CO_2$ emission in combustion processes. Among the method for reducing $CO_2$ emission, oxygen-enriched combustion has been proposed. But the adiabatic flame temperature is too high. So existing facilities must be changed, or the adiabatic flame temperature in the combustion zone should be reduced. The combustion characteristics, composition in the flame zone, temperature profile and emission gases were studied experimentally for the various oxygen-enriched mtios(OER) by addition of $CO_2$ under coustant $O_2$ flowrate. Results showed that the reaction zone was quenched, broadened, as addition of $CO_2$ was increased. Temperature has a large effect on the NOx emission. The emission of NOx in flue gas decreased due to the decreased temperature of reaction zone. It was also shown that the reaction was delayed by the cooling effect. As the addition of $CO_2$ was increased, the composition of CO in the flame zone increased due to the increase of reaction rate by increasing mixing effect of oxidant/fuel at OER=0, but the composition of CO decreased by quenching effect at OER=50 and 100%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1491-1498
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• 2003

Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. A high-speed digital video camera was used to simultaneously record images of the drop from below. The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The splat diameter was observed to increase with time just after the initial transient dies out due to the growth of the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the bubble corresponded to a sudden decrease in droplet heat transfer.