• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.9
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• pp.401-408
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• 2014

This paper proposes an optimum operation method for open type ground heat exchangers. A series of TRTs and artificial heating/cooling operations were carried out while monitoring temperature in the hole of SCW. The ground temperature naturally increases with depth, but a switch between the cooling/heating mode results in a change in the distribution of ground temperature. The effect of the mode change was evaluated by performing LMTD and COMSOL multiphysics analysis for a reduced model with the depth of 150 m. As a result, in the cooling mode, the upstream operation is more efficient than the downstream operation and reduces EWT by $2.26^{\circ}C$. On the other hand, in the heating mode, the downstream operation is advantageous over the upstream operation and increases EWT by $3.19^{\circ}C$. The merit of the optimum operation will be enhanced for the typical dimension of SCW with a depth of 400~500 m. In the future, an open type ground heat exchanger system adopting the optimum operation with variation in the ground temperature will be used in practice.

• Food Science and Preservation
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• v.10 no.1
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• pp.23-27
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• 2003

This study was conducted to develop the corrugated fiberboard box which is suitable to pre-cooling and low temperature distribution of chinese cabbage Consider from a cooling performance viewpoint, the folding type box with 5.4% vent hole ratio was most efficient for fast cooling and even temperature distribution in the packaging box. At the end of storage periods, the compressive strength of the folding type box was less than the bliss type box. However, the compressive strength of the folding type box after storage was higher than required safety compressive strength for long term storage. So the folding type box was considered to have no problems toy practical use. The shelf-life of the chinese cabbage packaged with the developed box was 6∼7 days which was 2∼3 days longer than usual packaging.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.3
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• pp.110-116
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• 2009

Research for climate control seats is being vigorously pursued because requests for passenger's thermal comfort are increasing. Recently, thermoelectric devices have been applied to automotive seats for both cooling and heating operations. The climate control seats using thermoelectric devices can rapidly control the air temperature passing through the devices and directly affect the thermal comfort of passengers. The performance characteristics of the climate control seats were analyzed by experiments for two different types of a leather covered seat and a mesh applied seat. Experimental results show that the cooling and heating performance for the mesh applied seat by using the discharge port of the shape of nozzle was improved significantly in comparison with that for the leather covered seat. The variation of temperature between the inlet air and the outlet air of the climate control seat for the enhanced mesh applied type was by $-3.5^{\circ}C$ at cooling mode, and was by $15.0^{\circ}C$ at heating mode, after about 30 minutes, respectively. Also, it is possible to provide rapid thermal comfort to passengers sitting on the seat in the vehicle cabin by using the proposed climate control seat.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.8 no.2
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• pp.36-47
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• 2012

Time-series variation of groundwater temperature in Mongolia shows that maximum temperature is occured from end of October to the first of February(winter time) and minimum temperature is observed from end of April to the first of May(summer time). Therefore ground temperature is s a good source for space heating in winter and cooling in summer. Groundwater temperatures monitored from 3 alluvial wells in Ulaabaatar at depth between 20 and 24 m are $(4.43{\pm}0.8)^{\circ}C$ with average of $4.21^{\circ}C$ but mean annual ground temperature(MAGT) at the depth of 100 m in Ulaanbaatar was about $3.5{\sim}6.0^{\circ}C$. Bore hole length required to extract 1 RT's heat energy from ground in heating time and to reject 1 RT's heat energy to ground in summer time are estimated about 130 m and 98 m respectively. But in case that thermally enhanced backfill and U tube pipe placement along the wall are used, the length can be reduced about 25%. Due to low MAGT of Ulaabaatar such as $6^{\circ}C$, the required length of GHX in summer cooling time is less than the one of winter heating time. Mongolia has enough available property, therefore the most cost effective option for supplying a heating energy in winter will be horizontal GHX which absorbs solar energy during summer time. It can supply 1 RT's ground heat energy by 570 m long horizontally installed GHX.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.771-779
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• 1989

Numerical analysis by SIMPLE algorithm has been performed to predict the characteristics of flow and heat transfer in channels between the printed circuit boards of an electronic cabinet. It is assumed that the electronic parts release uniform heat flux per unit axial length to the cooling air. The air flow between channels is assumed fully developed laminar, incompressible, and mixed convective. In this study, the electronic parts are mounted on both sides of the prinked circuit boards by two kinds of configuration such as the zig-zag and the symmetric one. The Rayleigh numbers ranging from 0 to 10$^{6}$ are considered to predict the characteristics of the main flow and the secondary flow occurred by natural convection, the temperature distribution in channel, the heat transfer rate from heated electronic parts and the increase of friction factor by natural convection. As the results of numerical calculation, several conclusions are drawn as follows. The influence of natural convection on the flow characteristics appears strong when the Rayleigh number is above 10$^{4}$. The main axial flow rate decreases by a half or more at the Rayleigh number of 10$^{6}$ . Although the friction factor increases as Rayleigh number increases, the increasing rate of heat transfer is higher than that of the friction factor. The cooling efficiency of the zig-zig-configuration is superior to that of the symmetric configuration at same Rayleigh number.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.943-951
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• 1999

The welded structure unnecessarily remains residual stress due to the very high heating of local region and lastly cooling. The residual stress sometimes causes fracture initiation of welded structures. In this paper, distribution and magnitude of tensile and compressive residual stresses in the TIG(Tungsten Inert Gas) welded aluminum alloy such as Al5083-H112 are measured by using the hole-drilling method. Furthermore, the effects of residual stresses in the TIG welded aluminum CCT(Center Crack Tension) and SEN(Single Edge Notched) Specimens on the fatigue crack propagation behavior are analyzed. The fatigue cracks initiated at residual stresses region are influnced by tensile and compressive residual stresses. However, the effects are found to be released fast for both cases according to the cyclic loads and extension of crack length.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.1
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• pp.62-66
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• 2011

In this study, the thermal performance of disk can be compared with disk and disk with holes through numerical analysis. The capacity of thermal emission on general disk becomes more than on disk with holes at the distribution of temperature at first and the magnitude of equivalent stress on general disk becomes less than on disk with holes at the distribution of stress. The capacity of thermal emission or the magnitude of thermal deformation on disk with holes becomes less than that on general disk 30 minutes later. The disk with holes is worn less and more durable than general disk. The performance of cooling and braking force at disk and pad can be improved by installing the disk with holes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2466-2473
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• 2002

In twin roll strip casting process, the design of casting roll is the most important equipment for producing strip. Analyses of heat transfer and deformation for the casting roll are carried out by using the finite element program, ANSYS. Both the elastic deformation and the elasto-plastic deformation under a thermal load are considered in the analysis. Optimization to minimize the volume of roll is performed under the various thermal loads such as the heat flux and the roll speed. Design variables are defined by diameters and positions of the cooling hole in the roll , Although the thermal load remarkably varies, the design variables and objective function are found to be consistent.

• Journal of Welding and Joining
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• v.21 no.1
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• pp.42-47
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• 2003

Stainless rolling stocks are usually fabricated by spot welding process without painting. Indentation on the surface of the car body after spot welding injures the beauty of the stainless rolling stocks. In this study, insulated electrode tips to reduce the indentation are developed and applied to the actual spot welding works. The developed tips are composed of head, neck, hole for cooling water, body and resistance material. They provide large surface contact area with the base materials during spot welding and enhance the current density by necking. Experimental results using the developed tips show that small indentation and sufficient tensile shear strength is produced due to large contact area and enhanced current density.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.1
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• pp.78-81
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• 2008

A hollow cathode which has extremely stable discharge characteristic has been developed. This is composed of the two separated lanthanum hexaboride(LaB6) of a disk type in the tube as the electron emitters. The way of design is of great advantage to extend the surface discharge area of the LaB6, which is also useful for optimal fixing of the LaB6. The hollow cathode is capable of producing 30 kW(100 V, 300 A) of power continuously. Because the generated plasma beam with the high temperature(above $3000^{\circ}C$) from the hollow cathode passes through the center hole of the two intermediate electrodes, it is designed with the high temperature material of the tungsten and the suitable structure of the water cooling. The combinations of the hollow cathode and the two intermediate electrodes are practically useful for the ion plating plasma beam source.