• Journal of Power System Engineering
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• v.20 no.5
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• pp.37-45
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• 2016

Exhaust gas recirculation has the advantage of being low-cost and easy to control of NOx emission. Therefore, it is most generally used to reduce NOx emission according to strengthen regulation. In the case of a non-road engine, such as the agricultural engine, since it mainly operate a middle or high-load state, NOx emission is decreased in accordance with the mapping range of the EGR rate, but results in an increase in the particulate matter which is caused to deposit and fouling problem of the EGR system. This problem has become an important issue for maintaining the performance of the engine, as well as emission performance. This study had examined the effects of cooler aging on the performance of heat transfer efficiency and NOx emission in non-road diesel engine. As a result of the EGR cooler aging during 200 hours engine operation, the cooling performance decreased about 25% compared with that of fresh cooler and the NOx emission increased about 14.6% on NRSC(non-road steady cycle) and 20% on NRTC(non-road transient cycle) compared with that of fresh cooler respectively.

• Nuclear Engineering and Technology
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• v.47 no.5
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• pp.567-578
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• 2015

In a nuclear reactor containment, wall condensation forms with noncondensable gases and their accumulation near the condensate film leads to a significant reduction in heat transfer. In the framework of nuclear reactor safety, the film condensation in the presence of noncondensable gases is of high relevance with regards to safety concerns as it is closely associated with peak pressure predictions for containment integrity and the performance of components installed for containment cooling in accident conditions. In the present study, CUPID code, which has been developed by KAERI for the analysis of transient two-phase flows in nuclear reactor components, is improved for simulating film condensation in the presence of noncondensable gases. In order to evaluate the condensate heat transfer accurately in a large system using the two-fluid model, a mass diffusion model, a liquid film model, and a wall film condensation model were implemented into CUPID. For the condensation simulation, a wall function approach with a heat/mass transfer analogy was applied in order to save computational time without considerable refinement for the boundary layer. This paper presents the implemented wall film condensation model, and then introduces the simulation result using the improved CUPID for a conceptual condensation problem in a large system.

• Journal of the Korean Solar Energy Society
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• v.23 no.4
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• pp.37-43
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• 2003

The aim of this research is to study the feasibility of the solar(hot fluid) driven $NH_3/H_2O$ absorption chiller, made by re-manufacturing of Gas fired $NH_3/H_2O$ absorption chiller. This experimental study is performed with the temperature of the inlet hot fluid of generator. In order to determine the inlet temperature of the generator, which gives maximum COP, the experimental data are obtained with various hot fluid supply temperature in range of $130\sim170^{\circ}C$. Remodeled chiller is operated with periodical cooling effect, which due to mixture subcooled pool boiling, then the COP is evaluated in average. The maximum COP$(\sim0.36)$ is at $160^{\circ}C$. The temperature is stable operation temperature range of typical vacuum collector. It offers a feasibility of solar driven $NH_3/H_2O$ absorption chiller.

• Journal of Welding and Joining
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• v.10 no.2
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• pp.51-62
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• 1992

A torch was designed and fabricated in order to develope the technology of "locally drying underwater welding" by water curtain method. The condition for the formation of the possible local cavity, the mechanical properties and the thermal cycle of welds were investigated in the developed welding equipment compared with in-air welding. The possibility of highly reliable and practical underwater welding was found. The proper local cavity was formed above the water flowrate of 30l/min and CO$_{2}$ gas flowrate of 100l/min. The bead width and penetration depth were increased with increasing welding current. The hardness of weldments is about 160Hv in air welding, but about 210Hv in underwater welding. The elongation and the impact value of underwater weldments are 15% and 6Kg/cm$^{2}$ respectively, which are only half as much as the values of in-air welding. The cooling time in the temperature range from 800.deg.C to 500.deg.C affecting the structure and the hardness of weldments is about 22sec. in air welding while about 10sec. in underwater welding.r welding.

• The KSFM Journal of Fluid Machinery
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• v.20 no.1
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• pp.21-28
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• 2017

Optimization process of pre-swirl nozzle geometry was conducted to improve the discharge coefficient of pre-swirl system by using CFD. The optimization of pre-swirl nozzle shape covered the converging angle and the location of the converging nozzle. Optimization process included Optimal Latin Hyper-cube Design method to get the experimental points and the Kriging method to create the response surface which gives candidate points. The process was finished when the difference between the predicted value and CFD value of candidate point was less than 0.1 %. This paper compared the Reference model, Initial model which is the first model of optimization and Optimized model to study flow characteristics. Finally, the discharge coefficient of Optimized model is improved about 17 % to the Reference model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.3
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• pp.119-126
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• 2017

Recently, ground source heat pump systems are being used in buildings for cooling and heating to reduce greenhouse gas and save energy. However, ground source heat pump systems mainly use the vertical closed-loop geothermal system design rather than the open-loop geothermal system design. This is due to a lack of knowledge and few research feasibility studies. In this research, a dynamic thermal analysis numerical simulation based on a standard house model was conducted for an open-loop geothermal system. Based on heating load analysis results, the life cycle costs of a standard house using an open two-well geothermal system were analyzed and compared with a vertical closed-loop geothermal system, and a diesel boiler. As a result, it was found that using an open two-well geothermal system shows economic return on investment after three years.

• Journal of the Korean Ceramic Society
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• v.54 no.6
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• pp.492-498
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• 2017

A thermal barrier coating (TBC) with self-healing property for cracks was proposed to improve reliability during gas turbine operation, including structural design. Effect of healing agent on crack propagation behavior in TBCs with and without buffer layer was investigated through furnace cyclic test (FCT). Molybdenum disilicide ($MoSi_2$) was used as the healing agent; it was encapsulated using a mixture of tetraethyl orthosilicate and sodium methoxide. Buffer layers with composition ratios of 90 : 10 and 80 : 20 wt%, using yttria stabilized zirconia and $MoSi_2$, respectively, were prepared by air plasma spray process. After generating artificial cracks in TBC samples by using Vickers indentation, FCTs were conducted at $1100^{\circ}C$ for a dwell time of 40 min., followed by natural air cooling for 20 min. at room temperature. The cracks were healed in the buffer layer with the healing agent of $MoSi_2$, and it was found that the thermal reliability of TBC can be enhanced by introducing the buffer layer with healing agent in the top coat.

• Journal of Hydrogen and New Energy
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• v.29 no.5
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• pp.442-449
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• 2018

Research on High temperature polymer electrolyte fuel cell (HT-PEMFC) has actively been conducted all over the world. Since the HT-PEMFC can be operated at a high temperature of $120-180^{\circ}C$ using phosphoric acid-doped polybenzimidazole (PBI) electrolyte membrane, it has considerable advantages over conventional PEMFC in terms of operating conditions and system efficiency. However, If the thermal distribution is not uniform in the stack unit, degradation due to local reaction and deterioration of lifetime are difficult to prevent. The thin plate separator reduces the volume of the fuel cell stack and improves heat transfer, consequently, enhancing the cooling effect. In this paper, a large area flow field of thin plate separator for HT-PEMFC is designed and sub-stack is fabricated. We have studied stack performance evaluation under various operating conditions and it has been verified that the proposed design can achieve acceptable stack performance at a wide operating range.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.8
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• pp.354-360
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• 2002

The partial discharge detecting method using the ultrasonic technique has been investigated to monitor the insulation ageing of a transformer. However, the result of the studies on the ultrasonic technique for detecting of partial discharge in the operating transformer is not enough yet to utilize. This paper presents the analysis of the ultrasonic signals due to the partial discharge in a model transformer and the corona in air at a shielded high voltage room. In addition, the ultrasonic signals due to the vibration from the core, operation of the cooling pump, the fan and the OLTC at the 345㎸ power transformer, were analyzed and corona noise from overhead transmission line in 345㎸ substation were measured to remove the electrical and mechanical noises from the transformer. Furthermore, ultrasonic signal due to the partial discharge in the 154㎸ power transformer with in $C_2$$H_2$ gas warning condition was measured. The inside of the transformer was examined with care. which confirms the existence of the partial discharge source.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.764-767
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• 2010

The high enthalpy plasma research center in Chonbuk national university is under construction for MW class plasma wind tunnel. Four types of plasma equipment will be installed in the research center. The equipments are 1set of 0.4 MW class enhanced Huels type plasma equipment, 1 set of 2.4 MW class enhanced Huels type plasma equipment, 1 set of 60 kW RF plasma equipment and 1 set of 200 kW RF plasma equipment. And electrical, water and gas utilities to assistant plasma equipments are under construction. The research center consists of experiment building, research building, power supply building, air supply building, cooling tower foundation.