• Journal of the Korean Society for Precision Engineering
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• v.20 no.8
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• pp.54-61
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• 2003

The first stage rotating blade of industrial gas turbine is one of the components that is normally run in exposed state at the highest temperature of the combustion gas stream. For this reason superior materials and advanced cooling technology are required to allow higher heat resisting characteristics of the component. The 1st stage blade of a selected commercial gas turbine blade made of directionally solidified Ni-based superalloy has a row of cooling holes on its trailing edge. In most cases, minor cracks have been found at some of the root cooling holes after one cycle operation (24,000 hrs) or even shorter operation time because of the high temperature gradient and the frequently alternating thermal stress. In the repair process, unfortunately, it is usually very difficult to get rid of the damage due to the fact that cracks are initiated at the root cooling hole and propagated deep into the hole. In this study, the feasibility of removing the sidewall cracks in the hole by utilizing EDM drilling has been investigated. Also the criteria of surface integrity for EDM drilling were established to achieve high quality repair as well as machining accuracy.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.370-375
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• 2007

The cooling load in winter season is significant in many commercial buildings and hotels because of the usage of office equipments and high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this numerical study, a 4-room simultaneous heating and cooling heat pump system was modeled and its performance was calculated at each operating mode. Also, performance analysis was compared with experimental results.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.141-144
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• 2015

The superconducting fault current limiter (SFCL) is an electric power device that limits the fault current immediately in a power grid. Korea Electric Power Corporation (KEPCO) has been developing a 154 kV, 2 kA SFCL since 2011 to protect power grids from increasing fault current and improve the stability and quality of electric power. This SFCL adopts 2G YBCO wires and operates at 71 K and 5 bars. In this paper, a cooling system for the 154 kV SFCL and its cooling test results are reported. This cooling system uses a Stirling-type cooler to make sub-cooled liquid nitrogen ($LN_2$), which cools the superconductor modules of the SFCL. The $LN_2$ is circulated between the cooler and the cryostat that contains superconductor modules. The $LN_2$ also plays the role of a high voltage insulator between the modules and the cryostat, so the pressure was maintained at 5 bars for high insulation performance. After installation in a test site, the cooling characteristics of the system were tested. In this operation test, some important data were measured such as temperature distribution in $LN_2$, pressure change, performance of the heat exchanger, and cooling capacity of the total system. Consequently, the results indicate that the cooling system operates well as designed.

• Progress in Superconductivity and Cryogenics
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• v.20 no.2
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• pp.34-39
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• 2018

A cryogenic cooling system is designed for a 154 kV/ 2 kA three-phase hybrid type superconducting fault current limiter (SFCL). The superconducting modules of the SFCL have the operating condition of 71 K at 500 kPa. The total heat load of the SFCL including the cooling system is estimated at 9.6 kW. The cooling system of the closed loop is configured to meet the operating condition, depending on cooling methods of forced flow cooling and re-liquefaction cooling. The cooling system is composed of three cryostats with superconducting modules, cryocoolers, liquid nitrogen circulation pumps, a subcooler and a pressure builder. The basic cooling concept is to circulate liquid nitrogen between three SFCL cryostats and the cryocooler, while maintaining the operating pressure. The design criterion for the cooling system is based on the operation results of the cooling system for a 154 kV/2 kA single-phase hybrid SFCL. The specifications of system components including the piping system are determined according to the design criterion.

• Journal of the Korean Society of Industry Convergence
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• v.20 no.4
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• pp.325-332
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• 2017

The engine cooling system is a device that maintains the temperature in the engine room at an appropriate level by driving a cooling fan when the temperature in the engine room generated during the vehicle operation occurs over a certain temperature. In recent years, the vehicle cooling system has changed to an electronic system. Therefore, in this paper, we design and develop a hall sensor based electronic engine cooling system. In this paper, a hall sensor module and an actuator module for engine cooling control system are designed. In order to verify the performance of the designed module, the magnetic field control was verified through the simulation of the diameter and the head of the coil.

• Journal of Korea Foundry Society
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• v.2 no.1
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• pp.12-18
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• 1982

The present investigation was made to abtain a fine distribution of Pb Particles in AL - Pb binary alloys , which have a broad miscibility gap and large specific difference, by means of rapid Cooling of the molten alloys. Al-2.4% Pb, Al-5.5wt% Pb and Al-8.0wt % Pb alloy were used. The rapid cooling operation was performed by free falling of homogeneous liquid Al-Ph alloys into the water-cooled copper mold, and thermal analysis was made. Microstructures were observed, and variations of size and number of Pb particles were analysicle analyzer. By the result of examination with the varing cooling rates 100 to $210^{\circ}C/sec$ fine distributions of Pb particles were obtained with high cooling rate. Under same cooling condition, the best rapid cooling effect was recognized in Al-5.5wt% Pb alloy.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.22-29
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• 2008

In order to improve the efficiency of a main transformer in a tilting train, the optimal operation of a cooling system is necessary. For the development of optimal control algorithms of a cooling system, mathematical models of a main transformer cooling system were developed. These include dynamic models of a main transformer, an oil pump, an oil cooler, a blower, and a pipe. Control algorithms for a blower and an oil pump were selected in order to identify the effectiveness of dynamic models. A simulation program was developed by using the developed dynamic models and the selected control algorithms. Simulation results showed good predictions of dynamic behaviors of a main transformer cooling system. Therefore, dynamic models, which were developed in this study, may be effectively used to develop control algorithms of a main transformer cooling system.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.1
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• pp.15-19
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• 2014

As the space of the wind power generator stator end is limited, it is difficult for us to place the inner evaporative cooling system in it. We use the non-overlapping concentrated windings scheme to solve the placing and cooling problem. The characteristic of a 5MW direct-driven permanent magnet generator with non-overlapping concentrated windings were analyzed under no-load, rating-load and short-circuit by (Finite Element Method) FEM for verification of design. We studied the connection methods of the stator windings and designed the end connection member. The heat dissipation of the stator end was simulated by FEM, the result showed that the end cooling could satisfy the wind generator operation needs. These results show that the direct-driven permanent magnet wind power generators with non-overlapping concentrated windings and inner evaporative cooling system can solve the cooling problem of wind power generator, and obtain good performance at the same time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1049-1058
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• 2001

The performance and design analysis for a NWD cooling tower using a combined wet and dry type fill are numerically investigated and compared with the experimental results. The Stoecker's method is applied to the wet section and LMTD or NTU-Effectiveness method to the wet and dry sections. The efficiency ratio of the NWD cooling tower to a wet type crossflow cooling tower is 59.34%. The predicted result shows a good agreement with the experimental data within 1.4% error. Plume abatement is far better with a NWD cooling tower than a counterflow cooling tower. It costs less than a conventional wet/dry tower because the finned exchanger is eliminated. This method also leaves out complexity in structure and Intricacy in operation.

• 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.