• Journal of Power System Engineering
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• v.18 no.3
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• pp.87-92
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• 2014

This study is aimed at investigating the thermal behavior of immersion-cooled high power LED lighting engines. 3D CFD models have been generated for the numerical analysis. Five cases in terms of the configuration of LED chips have been explored for various passive cooling conditions of the lighting engine, i.e., the natural air convection with a lens, the natural air convection without a lens, the deionized water-immersion cooling condition with a lens. The numerical study reveals that the deionized water-immersion cooled lighting engine has nearly twice better thermal performance than the natural air convection cooled lighting engine containing a lens. The investigation has also demonstrated that the four chips configuration has the better thermal performance than the single chip configuration.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.10
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• pp.394-401
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• 2016

The configuration of an extruded-type cooling structure was optimized for the light-emitting diode (LED) streetlights that have recently replaced convectional metal halide streetlights for energy saving. Natural convection and radiative heat transfer over the cooling structure were simulated using a numerical model with experimental verification. An improved cooling structure type was suggested to overcome the previous performance degeneration, as confirmed by analyzing the thermal flow around the existing cooling structure. A parameter study of the cooling structure geometries was also conducted and, based on the numerical results, the configuration was optimized to reduce the weight of the cooling structure. Consequently, the mass of the cooling structure was reduced by 60%, while the thermal performance was improved by 10%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.266-275
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• 1995

A numerical investigation on the conduction-natural convection-surface radiation conjugate heat transfer in the enclosure having substrate and chips has been performed. A 2-dimensional simulation model is developed by considering heat transfer by conduction, convection and radiation. The solutions to the equation of radiative transfer are obtained by the discrete ordinates method using S-4 quadrature. The effects of Rayleigh number and the substrate-fluid thermal conductivity ratio on the cooling of chip are analyzed. The result shows that radiation is the dominant heat transfer mode in the enclosure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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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.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.86-93
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• 2014

Increased demand of power-transformer's capacity inevitably results in an excessive temperature rise of transformer components, which in turn requires improved radiator design. In this paper, numerical simulation of the cooling performance of an ONAN-type (Oil Natural Air Natural) radiator surrounded by air was performed by using CFX. The natural convection of the air was treated with the full-model. The present parametric study considers variation of important variables that are expected to affect the cooling performance. We changed the pattern and cross-sectional area of flow passages, the fin interval, the flow rate of oil and shape of flow passages. Results show that the area of flow passage, the fin interval, the flow rate of oil and shape of flow passages considerably affect the cooling performance whereas the pattern of flow passages is not so much influential. We also found that for the case of the fin interval smaller than the basic design, the temperature drop decreases while a larger interval gives almost unchanged temperature drop, indicating that the basic design is optimal. Further, as the flow rate of oil increases, the temperature drop slowly decreases as expected. On the other hand, when the shape of flow passages are changed, temperature drop is increased, indicating that the cooling performance is enhanced thereupon.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.2
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• pp.299-305
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• 2008

This present study has dealt with the natural convection of water in a rectangular vessel which has cooling point at the center of itself with numerically. The finite difference method (FDM) is presented for the two-dimensional computer simulation of water controlled by natural convection and heat conduction. According to this study, It is cleared that the overturn of density is clearly existed at the temperature of $4[^{\circ}C]$ and that was compared with experimental result. Also the change of natural convection is known from the streamlines and isotherms. Most of all. It is cleared that the overturn of natural convection is changed with time caused by the fact that the temperature and density relationship of water.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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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.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.10
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• pp.20-26
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• 2019

This study was conducted on cooling systems in which, for the first time at home and abroad, cold water panels are embedded in the walls of small buildings for radiant cooling by heat absorption with cold water. In summer, cold water is circulated through cold water (chiller) circulation tubes embedded in three walls (two side walls and one rear wall) of a building to implement radiant cooling by the coldness of the water. From the results of this study, the experimental and theoretical natural convection heat transfer coefficients were relatively well-matched over the entire experimental range, thereby verifying the reliability of the experimental results. The surface temperature reduction rate of the walls in which cold water panels are embedded was large whereas that of the walls where no cold water panels are embedded was very small.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.324-329
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• 2008

The liquid cooling effect of a natural convection type radiator by using the PCM has been investigated experimentally. The radiator size is $423{\times}295{\times}83$ mm and PCM container size is $398{\times}270{\times}26$ mm. The objective is elapsed time higher than maximum time to reach for maximum operating temperature of a general liquid cooling radiator. This study, in order to study on the effects of the phase-change phenomenon, carried out the various mass flow rate, input electric power, ambient and melting point of three type PCM. For the above experimental parameter, the melting time was performed about 180/250/560 min at input power 150 W and ambient $30^{\circ}C$ from using the three type PCM(PCM_S1/S2/S3) respectively. Furthermore, the effects of the thermal dissipation was decreased higher input power than lower input power at heating block and melting time of PCM. However, the effects of mass flow rate did not nearly affect of the thermal performance especially.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.1
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• pp.138-143
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• 2018

In general, the operating temperature of electronic equipment is closely related to product life and reliability, and it is recognized that effectively cooling the parts is an important problem. In this paper, an experimental study on the cooling characteristic according to the pin array of the heat sink is conducted. The experiment on the heat sink was based on the natural convection and temperature distribution changes. The experimental results indicate that the pin array of the heat sink has an effect on the thermoelectric module's cooling characteristic.