• Design & Manufacturing
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• 제16권2호
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• pp.33-38
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• 2022

Currently, Korea is an aging society, and it is expected to enter a super-aging society in about 4 years. Accordingly, many X-ray technologies are being developed. In X-rays, 99% of X-rays are converted into heat energy and 1% into light energy (X-rays). 99% of the thermal energy raises the temperature of the anode and its surroundings, and the cooling system is an important factor as overheating can affect the deterioration of X-ray quality and shortened lifespan. There is a method of forced air cooling using natural convection. Therefore, in this study, when X-rays were taken 5 times, Flow analysis was performed on heat removal according to temperature rise and cooling time for the heat generated at the anode of the X-ray tube (input power 60kW, 75kW, 90kW). Based on one-shot, the most rapid temperature rise section increased by more than 57% to 0.03 seconds, A constant temperature rises from 0.03 seconds to 0.1 seconds, It is judged that the temperature rises by about 8.2% or more at one time. After one-shot cooling, the cooling drops sharply from about 60% to 0.03 seconds, It is judged that the temperature has cooled by more than 86% compared to the temperature before shooting. One-shot is cooled by more than 86% with cooling time after 0.1 seconds, As the input power of the anode increases, the cooling temperature gradually increases. Since the tungsten of the anode target inside the X-ray tube may be damaged by thermal shock caused by a rapid temperature rise, an improvement method for removing thermal energy is required when using a high-input power supply.

• 설비공학논문집
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• 제22권11호
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• pp.812-819
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• 2010

Recently residential buildings are characterized with high-rise and high density. Under this circumstance, achieving comfortable and healthy indoor environment with minimized energy consumption becomes a very challenging engineering and societal issue. Along this the increased size and transparency of window as well as light surface caused by high stories lowers the heat shield efficiency of building. Since glass that constitutes building surface has low heat efficiency, it aggravates heat loss of all building considerably, thereby resulting in extreme heating load and cooling load in the country where temperature varies much in summer and winter. The research will check whether experiment can be effectively done by overcoming the limit of existing artificial solar laboratory constructed in the country and properly adjusting controlled variables with simplified function through construction of this experimental set.

• 설비공학논문집
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• 제21권7호
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• pp.380-385
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• 2009

This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening polybutylene double piping system with header. Experiments were conducted under the following conditions: initial pressure $0.1{\sim}0.5$ MFa, flow velocity $0.5{\sim}3.0$ m/s and water temperature $25^{\circ}C$.

• 한국정밀공학회지
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• 제18권5호
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• pp.57-64
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• 2001

The high speed in the wire-drawing process to meet the demands for the increased productivity has a great effect on the heat generated due to plastic deformation and friction between the wire and the drawing dies. During the high carbon steel wire drawing process, the temperature rise gives a great influence to the fracture of wire. In this paper, to control the temperature rise in the wire after the deformation through the drawing die, the calculation method of the wire temperature, which includes the temperature rise in the deformation zone as well as the temperature drop in the block considering the heat transfer among the wire, cooling water and surrounding air, is proposed. These calculated results of the wire temperature at the inlet and exit of the drawing die at each pass are compared with the measured wire temperatures and verified its efficiency. So, using the program to predict the wire temperature, the isothermal pass schedule program was developed. By applying this isothermal pass schedule program to the conventional process condition, a new isothermal pass schedule is redesigned through all passes. As a result, the possibility of wire fracture could be considerably reduced and the productivity of final product could be more increased than before.

• Nuclear Engineering and Technology
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• 제43권4호
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• pp.391-398
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• 2011

The U metal chips generated in developing nuclear fuel and a gamma radioisotope shield have been stored under immersion of water in KAERI. When the water of the storing vessels vaporizes or drains due to unexpected leaking, the U metal chips are able to open to air. A new oxidation treatment process was raised for a long time safe storage with concepts of drying under vacuum, evaporating the containing water and organic material with elevating temperature, and oxidizing the uranium metal chips at an appropriate high temperature under conditions of controlling the feeding rate of oxygen gas. In order to optimize the oxidation process the uranium metal chips were completely dried at higher temperature than $300^{\circ}C$ and tested for oxidation at various temperatures, which are $300^{\circ}C$, $400^{\circ}C$, and $500^{\circ}C$. When the oxidation temperature was $400^{\circ}C$, the oxidized sample for 7 hours showed a temperature rise of $60^{\circ}C$ in the self-ignition test. But the oxidized sample for 14 hours revealed a slight temperature rise of $7^{\circ}C$ representing a stable behavior in the self-ignition test. When the temperature was $500^{\circ}C$, the shorter oxidation for 7 hours appeared to be enough because the self-ignition test represented no temperature rise. By using several chemical analyses such as carbon content determination, X-ray deflection (XRD), Infrared spectra (IR) and Thermal gravimetric analysis (TGA) on the oxidation treated samples, the results of self-ignition test of new oxidation treatment process for U metal chip were interpreted and supported.

• 국제초고층학회논문집
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• 제1권2호
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• pp.107-116
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• 2012

The overarching objective of this study is to predict the convective heat transfer around a human body under forced strong airflow conditions assuming a strong wind blowing through high-rise buildings or an air shower system in an enclosed space. In this study, computational fluid dynamics (CFD) analyses of the flow field and temperature distributions around a human body were carried out to estimate the convective heat transfer coefficient for a whole human body assuming adult male geometry under forced convective airflow conditions between 15 m/s and 25 m/s. A total of 45 CFD analyses were analyzed with boundary conditions that included differences in the air velocity, wind direction and turbulence intensity. In the case of approach air velocity $U_{in}=25m/s$ and turbulent intensity TI = 10%, average convective heat transfer coefficient was estimated at approximately $100W/m^2/K$ for the whole body, and strong dependence on air velocity and turbulence intensity was confirmed. Finally, the formula for the mean convective heat transfer coefficient as a function of approaching average velocity and turbulence intensity was approximated by using the concept of equivalent steady wind speed ($U_{eq}$).

• Tribology and Lubricants
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• 제17권1호
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• pp.10-15
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• 2001

Generally, it is said that the heat generation of air bearing is negligible. But the air bearing using at the built-in spindle is different from the general air bearing itself because of the thermal effects from the spindle motor and high-speed conditions. In this paper, in order to analysis the characteristics of air bearing by the heat, We made easy -heating-bearing-system (EHBS) and hard-heating-bearing-system (HHBS) and could identify the changes between the two bearing systems from the experiments and simulation. When spindle system reached at thermal steady-state, the changes means that the stiffness of air bearing becomes change due to the clearance change between bearing and journal. It is shown that the temperature rise and thermal effects to cause the thormal expansions have to be considered when designing air spindle system.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.11-20
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• 1999

Acoustic pressure response and NO formation of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flame let in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such non-monotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. Acoustic pressure response in each regime is investigated based on the Rayleigh criterion. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted. Emission index of NO shows similar behaviors as to the peak-temperature variation with pressure.

• Journal of Mechanical Science and Technology
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• 제14권4호
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• pp.433-440
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• 2000

The influence of combustion air at temperatures on nitric oxide emission was studied. The nitric oxide emission generally increases with a rise in the temperature of the combustion air. However, if combustion products for dilution of fuel or combustion air are used before the combustion reaction, then the nitric oxide emission can be reduced even when highly preheated air for combustion air is used. Combustion in low oxygen concentrations flattens the firing mode, resulting in a uniform reaction, and, thus, low nitric oxide emission can be achieved.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2009년도 춘계 학술논문 발표대회 학계
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• pp.119-122
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• 2009

As architectures have recently become high-risers and mega-structured, stable high strength products have been ensured. Accordingly, use of precast concrete accouplement has been increased in order to facilitate air compression and rationalize construction. Since not only external heating but a1so internal temperature rise caused by the accumulation of cement hydration heat in manufacturing process, precast concrete members with large cross-section used for high-rise mega-structure's columns and beams may exhibit different temperature history compared to the precast concrete members for wall and sub-floor with relatively small cross-sections. Therefore, this study aims to elucidate the characteristics of temperature history of mass concrete members cast with high-strength concrete fur precast concrete application. In this study, large cross-sectional precast concrete mock-up, unit cement quantity, and temperature histories in manufacturing precast concrete member under different curing condition were inclusively investigated.