• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3313-3321
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• 1996

A fundamental study in cooling and solidification process focused on ice storage was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation in the cooling and freezing processes with supercooling in a space between double cylinders. When water was cooled under the freezing point by a cooling wall in a cavity, solidification was not started at once, but a subcooled region was formed near the wall. Especially, when the cooling rate was low, subcooled region extended to a wide area. However, after a few minutes, supercooling is released by some triggers. Dendritic ice is suddenly formed within a subcooled region, and a dense ice layer begins to be developed from the cooling wall. Due to the difficulties, most previous studies on solidification process with numerical methods had not treated the supercooling phenomena, i.e. the case considering only the growth of dense ice. In this study, natural convection and ice formation considering existence of supercooling and dendritic ice were analyzed numerically with using finite difference method and boundary fixing method. The results of numerical analysis were well compared with the experimental results.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.520-523
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• 2003

In this paper, heatsink design for high power converter is presented. There are many ways of designing heatsink, but air cooling is by far the most used and much more practical than any of the other methods. In this paper, the practical methods of cooling which include the method to reduce a noise and a vibration due to a fan and the method to design a gap resistance and a contact resistance due to mounting force between thyristor and heatsink is proposed. Finally, simulation and experimental results are described to verify validity of the proposed method.

• Journal of Biomedical Engineering Research
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• v.24 no.5
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• pp.375-380
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• 2003

In this study. we have intended to control the properties of surface reaction zone generated between pure titanium and oxide investment moulds. Commercially pure titanium was centrifugally casted and silica$.$alumina based phosphate bonded investment was used as the mould material. The effect of cooling methods after casting on the surface reaction zone and mechanical properties of casts were investigated. The resulting casts showed the multilayered surface reaction zone regardless of cooling method. Especially. water cooling method produced the titanium casts with thinner surface reaction zone. weaker strength. and higher elongation properties compared to air cooling. It can thus be known that the resulting casts had satisfactory mechanical properties as dental materials. From these results, the cooling rate dependence of interfacial and mechanical properties can be attributed to the diffusion of oxygen from casting environment, which control the reaction of titanium and mould.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1018-1027
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• 2003

This study treats the analysis of the performance and the design of plume abatement wet/dry cooling tower with dry type heat exchanger using a numerical method. A two-dimensional analysis is performed using the finite volume method for mechanical draft counterflow and crossflow tower. For a coupling problem between water and air system, a turbulent two phase flow is considered. Effectiveness-NTU method is used for modeling of the dry type heat exchanger. The parameter change simulations of the outer wall shape, the relative flowrate of air, and attachment of an air mixer are performed to examine the effect on plume abatement. It is found that if the relative air flowrate ratio and the adequate air mixer type are chosen well in addition to the ratio of water to air flowrate, the loss of the cooling capacity and the additional cost are reduced and the plume is abated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.23-26
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• 2003

This paper explains the die cooling method for improving tool life in the hot forging process. In continuous forming operation such as hot forging process, performed at high speeds, temperature increases of several hundred degrees may be involved. Die hardness was reduced due to thermal softening. Factor of die fracture are wear and plastic deformation of die due to hardness reduction by high temperature. Because die service life was reduced due to this phenomenon during hot forging, quantified data for optimal die cooling method is required. The new developed techniques for predicting tool life applied to estimate the production quantity for a spindle component and these techniques can be applied to improve the tool life in hot forging process

• Journal of Powder Materials
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• v.22 no.1
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• pp.10-14
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• 2015

In recent years, industrial demands for superior mechanical properties of powder metallurgy steel components with low cost are rapidly growing. Sinter hardening that combines sintering and heat treatment in continuous one step is cost-effective. The cooling rate during the sinter hardening process dominates material microstructures, which finally determine the mechanical properties of the parts. This research establishes a numerical model of the relation between various cooling rates and microstructures in a sinter hardenable material. The evolution of a martensitic phase in the treated microstructure during end quench tests using various cooling media of water, oil, and air is predicted from the cooling rate, which is influenced by cooling conditions, using the finite element method simulations. The effects of the cooling condition on the microstructure of the sinter hardening material are found. The obtained limiting size of the sinter hardening part is helpful to design complicate shaped components.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.79-87
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• 2013

The improvement of cooling efficiency for the cabinet of automatic controller is the most efficient method of it's application. Therefore, this study has been analyzed and investigated the improvement of cooling efficiency and reduction of energy for the cabinet of automatic controller, respectively. So this study was conducted to enhancement of cooling efficiency for the cabinet of automatic controller by making a structure which produces difference of air pressures in the entrance tube of external air. And the structure has capacity of the pyrogen source (PTC elements) to make temperature range from $145^{\circ}C$ to $155^{\circ}C$. Consequently, temperatures of the upper, the lower in the interior of the cabinet of automatic controller and the exhaust part were revealed $28.57^{\circ}C$, $23.38^{\circ}C$and $36.14^{\circ}C$(average temperature of the exhaust part in case of existing method : $45^{\circ}C$) in target test of this study, respectively. It was found that the cabinet of the automatic controller has better cooling ability than the cabinet of automatic controller by using an existing method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.189-205
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• 1996

The twin-roll type strip continuous casting process(or direct rolling process) of steel materials is characterized by two rotating water cooled rolls receiving a steady supply of molten metal which solidifies onto the rolls. A solidification analysis of molten metal considering phase transformation and thermofluid is performed using finite diffefence method with curvilinear coordinate to reduce computing time and molten region analysis with arbitrary shape. An enthalpy-specific heat method is used to determine the temperatures inthe roll and the steel. The temperature distribution of cooling roll is calculated using two dimensional finite element method, because of complex roll shape due to cooling hole in rolls and improvemnt accuracy of calculation result. The energy equaiton of cooling roll is solved simultanuously with the conservation equaiton of molten metal in order to consider heat transfer through the cooling roll. The calculated roll temperature is compared to experimental results and the heat transfer coefficient between cooling roll surface and rolling material(steel) is also determined from comparison of measured roll temperature and calculated temperature.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.10a
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• pp.323-326
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• 2008

This paper presents a cooling system using thermoelectron for improving the output of BIPV module. The temperature characteristic in regard to improving the output of BIPV system has rarely teen studied up to now but some researchers only presented the method using a ventilator. The cooling system efficiency of BIPV module applied to a ventilator mainly depends on the weather such as wind, insolation etc. Because the cooling system of BIPV module using a ventilator is so sensitive, that is being set off by wind speed at all time but is unable to operate in the NOCT(Nominal Operating Cell Temperature) which is able to make the maximum output. The paper presents the cooling system using thermoelectron so as to solve such problems. The temperature control of thermoelectron can be controlled independently in the outside environment because that is performed by micro-controller. The temperature control of thermoelectron, also, can be operated around NOCT through algorithm of the temperature control. Therefore, outputs of the whole system increase and the efficiency rises. The paper demonstrates the validity of proposed method by comparing the data obtained through a experiment of the cooling method of BIPV using a ventilator and proposed thermoelectron.

• Journal of Korea Foundry Society
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• v.29 no.3
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• pp.144-149
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• 2009

In this study, we investigated optimum condition of cooling plate method to obtain semi-solid AM100A Mg alloy with fine and globular morphology. AM100A Mg alloy were hot extruded at $380^{\circ}C$ extrusion temperature under extrusion ratio of 25 : 1 and ram speed of 2.4 mm/sec. Vickers hardness test, optical microscopy, scanning electron microscopy, and image analyzer were performed to identify the optimum conditions of cooling plate method. Optimum conditions of cooling plate method to fabricate semi-solid AM100A Mg alloy with fine and globular microstructures were achieved at a pouring temperature of $602^{\circ}C$ and the angle of cooling plate of 60 degree.