• KIEAE Journal
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• v.15 no.2
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• pp.117-122
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• 2015

Purpose: Generally, 30% of the total energy consumption in office building is used for artificial indoor lightings, and almost 75-85% of electric power in fluorescent and Light-Emitting Diode (LED) lightings can be dissipated as a form of heat into indoor environment. The heat generated by indoor lightings can cause the increase of cooling load in office buildings. Thus, it its important to consider indoor lightings as a heat and light source, simultaneously. Method: In this study, we installed two kinds of indoor lightings including fluorescent and LED lightings and measured surface temperature of both indoor lightings. In addition, we obtained ambient temperature of indoor space and finally calculated total heat dissipated from plenum area and surface of lightings. Result: Total indoor heat gain was 87.17Wh and 201.36Wh in cases of six 40W-LED lightings and 64W-fluorescent lightings, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.2
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• pp.219-225
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• 2011

Silicone resin is recently used as encapsulant for high-power LED module due to its excellent thermal and optical properties. In the present investigation, finite element analysis of cure process was attempted to examine residual stress evolution behavior during silicone resin cure process which is composed of chemical curing and post-cooling. To model chemical curing of silicone, a cure kinetics equation was evaluated based on the measurement by differential scanning calorimeter. The evolutions of elastic modulus and chemical shrinkage during cure process were assumed as a function of the degree of cure to examine their effect on residual stress evolution. Finite element predictions showed how residual stress in cured silicone resin can be affected by elastic modulus and chemical shrinkage behavior. Finite element analysis is supposed to be utilized to select appropriate silicone resin or to design optimum cure process which brings about a minimum residual stress in encapsulant silicone resin.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.317-332
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• 1998

The adiabatic nuclear demagnetization cooling technique has reduced the lowest accessible temperature to the regime of microkelvin, and consequently led to a large expansion in microkelvin physics such as solid and liquid $^{3}He$, superconductivity of noble metals, spin glass transition, and nuclear magnetism. Our ability to reach temperature in microkelvin regime has greatly facilitated by the developments of dilution refrigerator and superconductivity magnet. It is appropriate to divide nuclear demagnetization cooling into two categories; those in which only the nuclear spin system is cooled down and those in which the lattice and conduction electrons in the refrigerant or the specimen are also cooled by the cooling power of nuclear spin system. The former cooling technique has utilized to investigate the nuclear magnetism at temperature in nanokelvin regime. The latter is widely used in studying the phenomena occurring in microkelvin regime. In this review paper, we will discuss the basic principles of nuclear demagnetization cooling and its applications. This work is supported by the Basic Science Research Institute Program under contract number BSRI-97-2404.

• Journal of Energy Engineering
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• v.28 no.4
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• pp.35-41
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• 2019

In order to overcome these disadvantages, the halogen light source, which was previously used as a vehicle fog light, has increased power consumption and a short lifetime, and thus, an automobile light source is gradually being replaced with an LED. However, when the vehicle LED fog light is turned on, there is a disadvantage in reducing the life of the fog lamp due to the high heat generated from the LED. The heat generated by the LED inside the fog lamp is mainly emitted by the heatsink, but most of the remaining heat is released to the outside through convection. When cooling efficiency decreases due to convection, thermal energy generates heat to lenses, reflectors, and bezels, which are the main parts of lamps, or generates high temperatures in LED, thereby shortening the life of LED fog lights. In this study, we tried to improve the heat dissipation performance by convection in addition to the heat dissipation method by heat sink, and to determine the installation location of vents that can discharge the internal air or intake the external air of LED fog lamp for vehicle. Thermal fluid analysis was performed to ensure that the optimal data were reflected in the design. The average velocity of air increased in the order of Case3 and Case2 compared to Case1, which is the existing prototype, and the increase rate of Case3 was relatively higher than that of other cases. This is because the vents installed above and below the fog lamps induce the convective phenomena generated according to the temperature difference, and the heat is efficiently discharged with the increase of the air speed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.7
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• pp.3146-3151
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• 2012

For using them as a optical source of inspections equipment for LCD panel, the design ofexcellent backlight system, brightness uniformity and high power and good protection against heat is essential.In this paper, backlight system which is built in the 45 inch side emitting LCD backlight by LED arraystructure and driving circuit were designed and developed. After that, their performances were measured. Itshowed the luminance from 3,000 to 25,000[$cd/m^2$], the mean value x:0.3144, y:0.3076 of x-y chromaticity,dimming range of 27~515[$cd/m^2$], free flicker noise in the 80kHz and black level of 0.7~0.1[$cd/m^2$], thermaltest of cooling system in 20,000[$cd/m^2$] over values.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.2
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• pp.67-73
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• 2017

Transformation behavior and hardness change were studied in five kinds of self-control steels; standard, high V, modified Ni, W, and high C-Ni steels. In the cooling rates of $10-100^{\circ}C/min$, the primary ferrite and bainite were formed, and the amount of the former increased with decreasing cooling rate. The bainite transformation temperature, Bs, was measured as 570, 560, 590, 575, and $565^{\circ}C$ in experimental steels, respectively, which was similar to the calculated temperature. The self-control, that is, the consistency in hardness, was observed, in which the hardness increased with the decrease in Bs. In the case of hot compression testing, the lower temperature deformation led to the enhancement in hardness.

• Journal of Hydrogen and New Energy
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• v.34 no.6
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• pp.741-747
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• 2023

In this study, the heat transfer characteristics were numerically analyzed to investigate the possibility of utilizing cooling water using liquid nitrogen. From the study, as the mass flow rate of the hot fluid increased, the heat transfer rate increased by 8.9-81.7%. And lowering the inlet temperature of the hot fluid resulted in increase in the heat transfer rate by 33.8-71.5%. As for the filling level of liquid nitrogen, as higher filling level led to a decrease in the outlet temperature and an increase in the overall heat transfer coefficient.

• Horticultural Science & Technology
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• v.33 no.2
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• pp.233-241
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• 2015

Kimchi cabbage 'Choon Gwang' cultivar that was grown in highlands in Gangneung was subjected to predrying, room cooling, and forced air cooling, and then packed with/without 0.02 mm HDPE film to investigate the effect of postharvest treatment on quality characteristics during 8 weeks storage at $2^{\circ}C$ (RH $90{\pm}5%$). Weight loss in forced air cooling and room cooling was lower than 3-4% with 0.02 mm HDPE film liner treatment during storage. However, it was only below 10% in room cooling without liner treatment and forced air cooling without liner treatment led to the highest weight loss, above 15%. Conversely, the control had lower weight loss than the others. SSC was $2-4^{\circ}brix$ for all treatments and there was no difference between postharvest treatments and liner treatments. Color index and firmness both showed no differences with/without 0.02 mm HDPE film and postharvest treatments. In sensory evaluation, forced air cooling with liner treatment was effective, with the highest score, especially in appearance and crispness. After 6 weeks, control kimchi cabbage without liner treatment was damaged seriously in appearance and the internal color had changed to brown. Room cooling and predrying with liner treatment changed the start of internal browning to after 8 weeks storage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1730-1738
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• 2001

This paper presents an overview of testing and analyzing field performance of a centrifugal chiller which has a rated capacity of 200 RT(703 kW). Field data of a chiller installed in the cleanroom research building of KIST has been collected far performance analysis. The operating data included start-up, shut-down, and quasi-static state where cooling capacity and compressor power consumption varied cyclically. It was found that the steady-state thermodynamic model could be applied to relate the cooling capacity and COP under quasi-static conditions. The results led to finding the required cooling load pattern and a possible energy saving method. This study provides a method of evaluating performance of a large capacity centrifugal chiller in which field test is necessary.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.235-240
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• 2010

Transpiration cooling is the most effective cooling technique for liquid rocket and air-breathing engines operating in aggressive environments with higher pressures and temperatures. Combustor liners and turbine vanes are cooled by the coolant(air or fuel) passing through their porous walls and also the exit coolant acting as an insulating film. However, its practical implementation has been hampered by the limitations of available porous materials. The search for more practical methods of increasing the internal heat transfer within the walls has led to the development of multi-laminate porous structures, such as Lamilloy$^{(R)}$ and Transply$^{(R)}$. This paper reviews recent research activities of transpiration cooling for the propulsions of liquid rocket, gas turbine, and scramjet.