• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.641-647
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• 2002

Objectives of this paper are to investigate the effect of roughness of micro-hatching tubes on the absorption performance and to develop on experimental correlation of Nusselt as a function of the roughness. Three different micro-scale hatched tubes and a bare tube were tested in the present experiment. $H_{2}O/LiBr$ solution is used as working fluid. It was found that absorption performance of micro-scale hatched tubes were improved upto 2 times with an error band of ${\pm}25%$ compared with the bare tube. An experimental correlation of Nusselt was developed as a function of the roughness.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.11a
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• pp.211-216
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• 1999

One of the problems in a refrigerator operation is the frost formation on a cold surface of the evaporator. The frost layer is formed by the sublimation of water vapor when the surface temperature is below the freezing point. This frost layer is usually porous and formed on the cold surface of the evaporator. The frost layer on the surface of a evaporator will make side effect such as thermal resistance. However, these important factors have not been used in determining the defrosting period. In this report, a prediction taking into account the change of the fin efficiency due to the growth of the frost layer.

• Journal of Power System Engineering
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• v.9 no.3
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• pp.66-70
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• 2005

Structural components for aerospace, electronics and automobile industry are the main applications for magnesium alloys due to their lightweight and high specific strength. The adoption of magnesium alloys in sheet forming processes is still limited, due to their low formability at room temperature caused by the hexagonal crystal structure. In this paper, the authors aim to improve the formability of AZ31 magnesium alloy. For this, experiment and finite element analysis on used warm deep drawing process with a local heating and cooling technique were done. Both die and blank holder were heated at various warm temperature while the punch was kept at room temperature by cooling water.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.385-388
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• 2005

The use of magnesium alloys meets the need of reducing weight of componests(especially in automotive and aerospace industry) keeping unmodified their mechanical properties. The adoption of magnesium alloys in sheet forming processes is still limited, due to their low formability at room temperature caused by the hexagonal crystal structure. In this study, the authors aim to understand the process condition which can lead to a successful improvement in the formability of a magnesium alloy(AZ31). Experiment and simulations of deep drawing were doned at various warm temperature for the blank and tool(holde and die)while the punch was kept at room temperature by cooling wale. in order to confirm that the deep drawing performance of magnesium alloy can be considerably enhanced with using the local heating and cooling technique.

• International journal of advanced smart convergence
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• v.9 no.4
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• pp.203-208
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• 2020

In this paper, we propose the design and implementation of a desktop LED stand and smart app that automatically adjusts color temperature and illuminance for optimal brightness and eye health by improving the structural problem of the LED stand. It is a tabletop LED stand that supports optimal brightness through color temperature control and heat transfer through infrared LED to relieve eye strain through blood circulation and muscle movement. The LED stand works with the smartphone to automatically adjust the optimal brightness and color temperature for the user's environment. In addition, the brightness of the infrared LED is adjusted to a living frequency of 4Hz to relax the eye muscles and reduce eye strain. This study implemented an effective measured data-based system of previous studies through the color temperature and illumination of LED lighting, and near-infrared rays, and presented meaningful results by conducting an experiment to prove the effect through subjects.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.25-28
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• 2010

A cooldown time is one of the major factors in many cryocooler applications, especially for the design of conduction-cooled superconducting apparatus. The estimation of cooldown seeks the elapsed time to cool thermal object by a cryocooler during initial cooldown process. This procedure includes the dimension of cold mass, heat transfer analysis for cryogenic load and available refrigerating capacity of a cryocooler. This method is applied to the specific cooling system for a 3 Tesla superconducting magnet cooled by a two-stage GM cryocooler. The result is compared with that of experiment, showing that the results of proposed method have a good agreement with experiments during initial cooling of superconducting magnet.

• Clean Technology
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• v.28 no.1
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• pp.18-23
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• 2022

Using air as an insulator due to its low heat transfer coefficient has been studied and has been widely commercialized to save energy in the field of thermal insulation technology. In this study, we analyzed the heat insulating effect of hollow silica nanoparticles mixed in non-uniform size, and the maximum heat insulating efficiency of these particles given the limited number of particles that can be mixed with a medium such as paint. The hollow silica nanoparticles were synthesized via a sol-gel process using a polystyrene template in order to produce an air layer inside of the particles. After synthesis, the particles were analyzed for their insulation effect according to the size of the air layer by adding 5 wt % of the particles to paint and investigating the thermal insulation performance by a heat transfer experiment. When mixing the particles with white paint, the insulation efficiency was 15% or higher. Furthermore, the large particles, which had a large internal air layer, showed a 5% higher insulation performance than the small particles. By observing the difference in the insulation effect according to the internal air layer size of hollow silica nanoparticles, this research suggests that when using hollow particles as a paint additive, the particle size needs to be considered in order to maximize the air layer in the paint.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.915-924
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• 2014

In an aero gas-turbine engine, a surface air-oil heat exchanger (SAOHE) is used to cool the oil system for the gearboxes and electric generators. The SAOHE is installed inside the fan casing of the engine in order to dissipate the heat from the oil system into the bypass duct stream. The purpose of this study was to develop an effective numerical method for designing an SAOHE for an aero gas-turbine engine. A two-dimensional model using a porous medium was developed to evaluate the aero-thermal performance of the fins of the heat exchanger, and a one-dimensional flow and thermal network program was developed to save time and cost in the evaluation of the heat exchanger performance. Using this network program, the pressure drop and heat transfer performance of the heat exchanger were predicted, and the results were compared with two-dimensional computational fluid dynamics results and experiment data for validation.

• International Journal of Highway Engineering
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• v.18 no.3
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• pp.59-65
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• 2016

PURPOSES : This paper aims to develop a road pavement de-icing system using carbon sheet to replace the older snow de-icing method. Carbon sheet is a light and high-strength metal. Hence, various bodies of research for its applications in many industries have progressed. METHODS : The experiment was conducted in a laboratory. The carbon sheet supplied voltage through a power supply system, and produced heat transfers to the concrete surface. Various factors, such as pavement material, carbon sheet width, penetration depth, and freezing-thawing resistance, were considered in the conducted experiments to confirm the heating transfer efficiency of the carbon sheet. RESULTS : The carbon sheet used was a conductor. Therefore, it produced heat if voltage was supplied. The exposed carbon sheet on the atmosphere did not affect the carbon sheet width when it provided constant voltage. However, the sheet showed different heating behaviors by width change when the carbon sheet penetrated into the concrete. Moreover, the freezing-thawing resistance was decreased by the carbon sheet with increasing width. CONCLUSIONS : The experiments confirmed the possibility of developing a road snow melting system using a carbon sheet. The antiicing system using the carbon sheet to replace the traditional anti-icing system has disadvantages of environmental pollution risk and electric leakage. The pavement also improved its toughness resistance. The utilization value will be very high in the future if carbon sheet heat loss can be minimized and durability is improved.

• Journal of Welding and Joining
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• v.28 no.4
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• pp.26-32
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• 2010

The purpose of this study is to evaluate the residual stresses at the multi-pass FCA weldment using the finite element analysis (FEA). In order to do it, an H-type specimen was selected as a test specimen. The variable used was in-plane restraint intensity. The temperature distribution at the multi-pass FCA butt weldment was evaluated in accordance with the relevant guidance recommended by the KWJS. The effective conductivity for the weld metal corresponding to each welding pass was introduced to control the maximum temperature below the vaporization temperature of weld metal. The heat flux caused by welding arc was assumed to be applied to the weld metal corresponding to welding pass. With heat transfer analysis results, the distribution of transverse residual stresses was evaluated using the thermo-mechanical analysis and compared with the measured results by XRD and uniaxial strain gage. In thermo-mechanical analysis, the plastic strain resetting at the temperature above melting temperature of $1450^{\circ}C$ was considered and the weld metal and base metal was assumed to be bilinear kinematics hardening continuum. According to the comparison between FEA and experiment, transverse residual stresses at the multi-pass FCA butt weldment obtained by FEA had a good agreement with the measured results, regardless of in-plane rigidity. Based on the results, it was concluded that thermo-mechanical FE analysis based on temperature distribution calculated in accordance with the KWJS’s guidance could be used as a tool to predict the distribution of residual stress of the multi-pass FCA butt weldment.