• 대한기계학회논문집
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• 제19권11호
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• pp.3072-3083
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• 1995

The numerical simulation on the three-dimensional natural convection heat transfer in the enclosure with heat generating chip is performed, and the effects of convective heat loss and vents are also examined. The effects of the Rayleigh number and outer Nusselt number (Nu$_{0}$) on the maximum chip temperature and the fractions of heat loss from the hot surfaces are investigated. The results show that conduction through the substrate is dominant in heat dissipation. With the increase of Rayleigh number, heat dissipation through the chip surfaces increases and heat loss through the substrate decreases. Maximum dimensionless temperature with vents is found to decrease about 40% compared to the one without vents at Nu$_{0}$=0.l. It is also shown that effects of size and location of the vents are negligible.ble.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.867-868
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• 2011

LOx/케로신 로켓엔진 연소시 연소실로 전달되는 열전달과 그에 따른 벽온도 변화를 비정상 해석하였다. 막냉각이 없는 경우와 연료 막냉각이 있는 경우를 계산하였으며, 연소실 내측의 대류, 복사는 로켓엔진에 대한 경험식을 이용하였고, 벽 내부의 전도는 2차원 축대칭의 형태로 수치해석 하였다. 본 해석을 통하여 막냉각 냉각효과에 의한 벽면 온도의 시간에 따른 변화, 최대온도 지점의 변화등을 분석하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.643-646
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• 2017

탄화수소계열의 연료를 사용하는 액체로켓엔진에서 높은 열유속으로 인해 연소실 벽면이 구조적으로 손상 및 변형되는 것을 방지하기 위하여 연소실 벽면의 냉각은 필수적이다. 여러 가지 방법 중 연료를 냉각제로 사용 후 연소과정에 투입시키는 재생냉각 방식은 엔진 성능을 높여준다. 본 연구는 구리 단면적, 채널 내 유속, 채널에 가해지는 전류를 변화시켜 냉각제로 사용하는 케로신의 열전달 특성에 대해 알아보았다. 채널의 구리 단면적이 작을수록, 케로신의 유속이 빠를수록 대류 열전달이 빠르게 일어남을 알 수 있었다.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.478-483
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• 2017

본 논문에서는 소형 전자기기와 같은 발열부 온도 제어를 위해 압전 소자와 열전 소자를 이용하여 국소부 냉각 성능을 실험적으로 조사해 보았다. 실험은 열전 소자를 이용하여 실험 영역내에 냉각부를 형성하고, 압전 소자에 80Hz와 110Hz 의 인가주파수를 각각 적용하여, 압전 소자를 작동시켰을 때와 작동시키지 않았을 때 열전 소자에 의해 형성된 시험부의 냉각 영역에서 온도 분포를 측정하였다. 또한, 냉각 영역의 온도측정 결과를 토대로 압전 소자를 적용하였을 때와 적용하지 않았을 때 냉각 영역의 성능 계수를 계산하고, 가시화 장치를 구성한 후 시험부내에 냉각 영역의 열유동 현상도 확인해 보았다. 실험결과, 온도분포 측정 실험 결과와 성능 계수 계산 결과로 부터 압전 소자를 작동하지 않은 경우보다 압전 소자를 작동한 경우에서 냉각 성능이 개선되는 것을 확인할 수 있었다.. 또한, 가시화 결과를 토대로 열전 소자에 의해 형성된 냉각 영역에 압전 소자를 작동시켰을 경우에 냉각 영역의 국소부에 압전 소자에 의한 상하 진동의 강제 대류 현상이 발생하면서 냉각영역 전체에 고르게 분포하는 유동을 형성하고 냉각 성능이 개선되는 원인을 확인할 수 있었다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.1-14
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• 1997

Natural convection cooling of discrete heaters located in a two-dimensional vertical open top cavity is investigated experimentally. The five discrete heaters with same heat generation are located on the wall of the cavity. The heaters are arranged in two configurations; flush-mounted on a vertical wall and protruding from the wall about 4.5 mm. The materials used for the vertical walls are copper and epoxy-resin, and air is used as the cooling fluid. The temperature and flow fields in the cavity were visualized by means of Mach-Zehnder interferometer and smoke-method. Also, local temperature measurements are made along the vertical wall. Results are obtained for cavity aspect ratios of 4.6, 7.5 and 9.5 and modified Rayleigh numbers ranging from 10$^{3}$ to 10$^{6}$ . Results indicate that the cooling efficiency for the copper wall is superior to that of the epoxy-resin. For the epoxy-resin wall, the protrusion of the heaters plays a role in decreasing the heat transfer performance. The location of maximum temperature is significantly influenced by the wall materials and heater configurations. Correlations relating the Nusselt number to the modified Rayleigh number are proposed.

• 한국압력기기공학회 논문집
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• 제12권1호
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• pp.78-84
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• 2016

The FHX (Forced-draft sodium-to-air Heat Exchanger) employed in the ADHRS (active decay heat removal system) is a shell-and-tube type counter-current flow heat exchanger with M-shape finned-tube arrangement. Liquid sodium flows inside the heat transfer tubes and atmospheric air flows over the finned tubes. The unit is placed in the upper region of the reactor building and has function of dumping the system heat load into the final heat sink, i.e., the atmosphere. Heat is transmitted from the primary cold sodium pool into the ADHRS sodium loop via DHX (decay heat exchanger), and a direct heat exchange occurs between the tube-side sodium and the shell-side air through the FHX tube wall. This paper describes the DHRS and the structural design of the FHX.

• 대한기계학회논문집B
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• 제33권12호
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• pp.947-951
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• 2009

LED has the merits of high reliability, semi-permanent life, rapid-response and its small size for use as light source of head lamp. But the dependence of its performance and life on temperature affect on its practical use. Which dependence makes problem when the LED is heated up to a higher temperature level by self-generation of heat, due to "highly integration" to get enough quantity of light. To solve this problem, effective cooling system is needed that consider conduction, convection and radiation. This study points out the limits of natural convection cooling system and propose of forced convection with heat sink. Also, it describes a correlation between heat sink area and fluid velocity using numerical analysis to optimize the cooling system.

• 한국소음진동공학회논문집
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• 제16권10호
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• pp.1057-1066
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• 2006

Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.

• 한국기계가공학회지
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• 제17권6호
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• pp.117-123
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• 2018

Automotive headlamps have been continuously developed as one of the most important devices for securing the driver's view, and the LED lamps are getting popular in recent years. However, in case of the LED lamps, because the heat generated by the LED lamps are too high, it shorten the product life and lower the LED efficiency. Therefore, this study was investigated the cooling characteristics of the LED lamp heat sink for automobile by forced convection for LED heat generation control. In order to analyze the cooling characteristics of the heat sink, the temperature distribution results were investigated through the experiment and computational analysis under the increase of the air flow velocity, and the convective heat transfer coefficient was obtained. Also, convective heat transfer coefficient was calculated by the theoretical formula under the same condition and compared with experimental and computational results. From the result of this study, as the air flow velocity around the heat sink fins increased, the convective heat transfer coefficient significantly increased, confirming the improvement in the cooling effect.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2356-2366
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• 1996

High-power electronic chips have been advanced to such an extent that the heat dissipation capability of a system design has become one of the primary limiting factors. Therefore, thermal design must be considered in the early stage of the electronic system development. In present paper, the results of an experimental study on the forced convection cooling are presented to evaluate cooling performance of an electronic cabinet which in generally used for telecommunication system. Temperatures and thermal resistances are applied to compare the heat transfer characteristics for various locations of a fan unit as well as various configuration of non-uniform powering modules. As a result, the optimal configuration of a fan unit and powering configuration is suggested for the effective thermal design of telecommunication system.