• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.4
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• pp.1-5
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• 2015

In this work, a study was conducted to investigate the effect of diaphragm thickness on the regression rate of the hybrid rocket motor. To observe the flow pattern and the recirculation zone, visualizations of combustion chambers with different diaphragm thickness (5mm, 10mm) were performed. It was found that the case with 5 mm thickness had a larger recirculation zone and therefore, had a higher regression rate than the case with 10mm thickness due to the increased residence time and heat transfer toward the fuel surface. Finally, it was concluded that the thickness of diaphragm can be a critical parameter for the enhancement of the regression rate.

• Journal of the Korean Solar Energy Society
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• v.22 no.2
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• pp.11-17
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• 2002

This paper is concerned with the development of a new method for making, separating ice and storage floated ice by installing an evaporation plate at under-water within a storage tank. In a conventional harvest-type ice storage system, a tank saves ice by separating an ice from an installed evaporation plate, which is located above an ice storage tank as an ice storage system. Developed new harvest-type method shows good heat transfer efficiency than a convectional method. It is because the evaporation panel is directly contacted with water in a storage tank. Also, at a conventional system a circulating pump, a circulating water distributor and a piping are installed, however these components are not necessary in a new method. In this study ice storage systems are experimentally investigated to study the charge and discharge of thermal energy. The results show the applicable possibility and performance enhancement of a new type.

• Journal of Energy Engineering
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• v.9 no.3
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• pp.202-211
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• 2000

본 연구는 다양한 각도를 가지는 와이어코일을 사용하여 관내 단상 열전달 촉진 및 압력강하 특성 실험을 수행하였다. 작동유체는 순수 물과 에틸렌글리콜을 체적비율로 50% 혼합하여 사용하였으며, 시험부 관지름은 11mm와 13.88mm이고, 시험부 길이는 760mm를 사용하였다. 평활관과 와이어코일을 삽입한 열전달촉진관에 대한 관내 열전달계수와 마찰계수는 실험에서 측정한 온도, 유량, 압력강하 값을 기초로 구하였다. 와이어코일에 대한 거친표면해석을 수행하였으며, 그 결과를 거칠기 래이놀즈수에 대한 운동량전송 거칠기함수와 열전달 거칠기함수로 표현하였으며 이에 대한 상관식을 제시하였다. 이 상관식들은 거칠기 레이놀즈수, 코일 각도, 프란틀수의 함수로 표현하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.33-36
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• 2006

The effective thermal conductivities of $Mm\;(La_{0.6-0.8})\;Ni_{4.0}Co_{0.6}Mn_{0.2}Al_{0.2}$ (TL-492) with hydrogen and helium have been examined. Experiment results show that pressure has great influence on effective thermal conductivity in Low pressure range (below 0.5 MPa). And that influence decreases rapidly with increase of gas pressure. The reason is at low pressure, the mean free path of gas becomes greater than effective thickness of gas film which is important to the heat transfer mechanism in this research. And, carbon fibers have been used to try to enhance the poor thermal conductivity of TL-492. Three types of carbon fibers and three mass fractions have been examined and compared. Naturally, the highest effective thermal conductivity has been reached with carbon fiber which has highest thermal conductivity, and highest mass fraction. This method has acquired 4.33 times higher thermal conductivity than pure metal hydrides with quite low quantity of additives, only 0.99wt% of carbon fiber. This is a good result comparing to other method which can reach higher effect ive thermal conductivity but needs much higher mass fraction of additives too.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.12
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• pp.815-824
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• 2016

The fuel assembly for pressurized water reactor (PWR) consists of fuel rod bundle, spacer grid and bottom/top end fittings. The cooling water in high pressure and temperature is introduced in lower plenum of reactor core and directed to upper plenum through the subchannel which is formed between the fuel rods. The main thermal-hydraulic performance parameters for the PWR fuel are pressure drop and critical heat flux in normal operating condition, and quenching time in accident condition. The Korea Atomic Energy Research Institute (KAERI) has been developing an advanced PWR fuel, dual-cooled annular fuel and accident tolerant fuel for the enhancement of fuel performance and the localization. For the key thermal-hydraulic technology development of PWR fuel, the KAERI LWR fuel team has conducted the experiments for pressure drop, turbulent flow mixing and heat transfer, critical heat flux(CHF) and quenching. The computational fluid dynamics (CFD) analysis was also performed to predict flow and heat transfer in fuel assembly including the spent fuel assembly in dry cask for interim repository. In addition, the research cooperation with university and nuclear fuel company was also carried out to develop a basic thermal-hydraulic technology and the commercialization.

• Journal of Fisheries and Marine Sciences Education
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• v.5 no.1
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• pp.31-44
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• 1993

Through the early 1900's, the evolution of the surface condenser was closely tied to the development of steam engine and the turbine. As the chemical and petroleum industries evolved in the 1900's, the use of surface condensers in many different processes. Today, industry uses condensers in many shapes and sizes. The actual condensation process occurs on the outside surface of tubes. The nature of this surface geometry affects the condenser's heat transfer performance. The first condensers were built with plain tubes. As tube manufacturing techniques advanced, manufacturers started making tubes with integral fins. In the 1940's, fin densities were limited to about 600 to 700 fins per meter(fpm) because of manufacturing procedure. Today new manufacturing techniques allow production of tubes with fin densities ranging from 750 to 1600 fpm. The integral-fin tubes investigated in this paper are nominally 19 mm diameter. Eight tubes have been used with trapezodially shaped integral-fins having fin density from 748 to 1654 fpm and 10, 30 grooves. For comparison, tests are made using a plain tube having the same inside diameter and an outside diameter equal to that at the root of the fins for the finned tubes. Betty and Katz's theoretical modelis is used to predict the R-11 condensation coefficient on horizontal integral-fin tubes having 748, 1024 and 1299 fpm. Experiments are carried out using R-11 as working fluid. The refrigerant condensates at a saturation state of $30^{\circ}C$ on the outside tube surface cooled by coolant. The amount of noncondensable gases present in the test loop is reduced to a negligible value by repeated purging. For a given heat input to the boiler and given cooling water flow rate, all test data are taken at steady state. The observed heat transfer enhancement for the finned and grooved tubes significantly exceeded that to be expected on grounds of increased area. For the eight fin tubes and one plain tube tested, the best performance has been obtained with a tube having a fin density of 1299 fpm, and a fin bight of 1.2mm and 30 grooves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.339-345
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• 2016

In this study, we numerically investigate the thermal performance of an enhanced radial heat sink with a perforation and chimney structure. We estimate the thermal performance of the enhanced radial heat sink, and compared it with that of a conventional radial heat sink. The results show that the radial heat sink with perforation has a higher thermal performance when either of the diameter and the number of perforations is high. With regards to the radial heat sink with a chimney structure, we investigate primarily the effect of the fin number, and the spacing between the chimney and the base plate on the thermal performance. The results show that there are optimal values for the fin number and the spacing between chimney and base plate. In addition, the enhanced radial heat sinks have maximum thermal performance when facing upward ($0^{\circ}$), while it has worst performance when facing sideward ($90^{\circ}$). The perforation and chimney are shown to cause thermal performance enhancements of 17% and 20%, respectively, compared with a conventional radial heat sink. The proposed method is useful for starting business, and is useful in terms of venture and entrepreneurship.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.113-117
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• 2020

In this paper, We investigated the effect of heat treatment process using photo-thermal effect in order to improve mechanical properties of nanostructure on polymer films made by nanoimprint process with hybrid resin. Nanostructures which have a low refractive characteristic were fabricated by UV nanoimprint and after that heat treatment was performed using IPL (intense pulsed light) under process condition of 550 V voltage, pulse width 5 ms, frequency 0.5 Hz. The transmittance and mechanical property of fabricated nanostructure films were evaluated to observe changes in the pattern transfer rate and mechanical properties of nanostructures. The transmittance of the nanostructure was measured at 97.6% at 550 nm wavelength. Nanoindentation was performed to identify improved anti-scatch properties. Result was compared by the heat source. In case of post treatment with IPL, hardness was 0.51 GPa and in the case of hotplate was 0.27 GPa, resulting the increase of hardness of 1.8 times. Elastic modulus of IPL treated sample was 5.9GPa and Hotplate treated one was 4GPa, showing the 1.4 time increase.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.463-467
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• 2014

In this paper, the thermal behaviors of expanded graphite(EG)/erythritol composites with different contents of EG were studied. The surface and structure properties of the composites were determined by using scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD), respectively. The thermal properties were investigated by differential scanning calorimetry (DSC) and thermal conductivity (TC). As experimental results, the thermal conductivity of the composites increased with increasing the EG content. However, the latent heat was somewhat decreased in the presence of EG. We could concluded that EG was highly promising materials for improving the heat transfer enhancement and energy storage capacity of phase change materials (PCMs).

• Proceedings of the KOSOMBE Conference
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• v.1998 no.11
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• pp.74-75
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• 1998

The present study employs weak shock theory and bio-heat transfer function to predict the temperature rise due to nonlinear propagation of high amplitude ultrasound. The theory shows that, for the focused ultrasound which is assumed to have an gaussian beam profile and has the focal intensity of $1000W/cm^2$, the temperature rise of liver tissue exposed for 1 second to the energy lost during nonlinear propagation goes up to about $30^{\circ}C$. This indicate that it is necessary to consider the nonlinear propagation induced heating enhancement when setting exposure condition of high intensity focused ultrasound used for cancer thermotherapy.