• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.29-36
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• 2003

Exhaust manifolds suffer from serious temperature variation during the thermal fatigue test. The spatial distribution of temperature changes at each moment. Because transient flow can not be simulated during the long period of temperature change, the simulation can not be performed by conjugate heat transfer analysis. In this study, a new procedure for transient thermal analysis is established by decoupling fluid-solid analysis. The procedure consists of (1) transient CFD calculation (2 cycles), (2) mapping heat transfer coefficient to the inner surface of solid mesh as a boundary condition of heat conduction analysis and (3) transient heat conduction analysis in the long period (30 min). The realistic temperature change can be predicted by this procedure.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.41-55
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• 2018

General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

• Journal of the Korean Institute of Gas
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• v.24 no.1
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• pp.49-55
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• 2020

Experimental investigations were conducted to understand the multi-staged combustion characteristics of a swirl-stabilized double cone premixed burner nozzle used for industrial gas turbines for power generation. Multi-staged combustion is implemented by injecting the fuel through the existing manifold of the side slots as well as through the apex of the cone with two fuel injection angles which are slanted or axial. NOx and CO emissions, and wall temperature distributions were measured for various fuel distributions and operating conditions. Results show that NOx emissions are decreased when the fuel distribution to the apex is 3% of the total amount of fuel, which is due to more uniform fuel distribution inside the nozzle, hence less hot spots at the flame. NOx emissions are rather increased when the fuel distribution to the apex is 8% of the total amount of fuel for axial fuel injection by occurrence of flash back in premixing zone of burner.

• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.314-319
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• 2011

In this study, the flow behavior of Newtonian and non-Newtonian coating liquids inside slot die has been scrutinized for the purpose of optimal internal die design in slot coating system from three-dimensional computations by CFD Fluent solver. A hybrid slot die could be optimally designed by changing the chamber or manifold structure to guarantee the uniform velocity distribution of coating liquids at die exit. Especially, for the non-Newtonian coating liquids, the length of coat-hanger for the uniform coating has been properly chosen, according to the degree of their shearthinning properties.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3553-3558
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• 2009

This study has been conducted to improve coolant flow pattern in the gasoline engine. Flow field has been calculated for the coolant passage mainly around the exhaust ports and valves. For the original model, a flow stagnant region has existed between exhaust valves of the second cylinder. To improve coolant flow characteristics, coolant passage area has been re-modeled and optimized. Furthermore, for the improved coolant core model, coolant passage under the exhaust manifold has been added to reduce exhaust-gas temperature. It was found that the flow through a gasket plays a critical role for the flow in the cylinder head and around exhaust valves. Finally, coolant flow around exhaust valves and in the cylinder head has been improved in terms of flow rate distribution.

• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.817-824
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• 2017

Residual stress is a critical element in determining the integrity of parts and the lifetime of welded structures. It is necessary to estimate the residual stress of a welding zone because residual stress is a major reason for the generation of primary water stress corrosion cracking in nuclear power plants. That is, it is necessary to estimate the distribution of the residual stress in welding of dissimilar metals under manifold welding conditions. In this study, a cascaded support vector regression (CSVR) model was presented to estimate the residual stress of a welding zone. The CSVR model was serially and consecutively structured in terms of SVR modules. Using numerical data obtained from finite element analysis by a subtractive clustering method, learning data that explained the characteristic behavior of the residual stress of a welding zone were selected to optimize the proposed model. The results suggest that the CSVR model yielded a better estimation performance when compared with a classic SVR model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.297-305
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• 1991

Recently, automotive air conditioning system manufacturers have been made a great efforts on the system compactness and high efficiency. This growing interest comes improvements in evaporator thermal performance, one of the most important factors affecting the performance of air conditioning system. In order to improve design of compact type evaporator, this study executes performs to develop a computer program for evaporator thermal performance prediction of automotive air conditioning system. The brief summaries of this study are as follows: 1) To predict the overall thermal performance of serpentine type evaporator, the new simulating method is developed. 2) The calculations are performed as functions of oil mass concentration and refrigerant two-phase distribution at inlet manifold of evaporator. 3) The validity of this simulating program is confirmed by comparing the predicted thermal performance results to experimental results of practical available evaporator. 4) Based on these results, suggestions are made to improve the thermal performance of evaporator.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.3
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• pp.83-89
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• 2011

Diesel engines can produce higher fuel efficiency and lower $CO_2$ emission, they are subject to ever more stringent emission regulation. However, there are two major emission concerns fo diesel engines like such as particulate matter (PM) and nitrogen oxides (NOx). Moreover, it is not easy to satisfy the regulations on the emission of NOx and PM, which are getting more strengthened. One of the solutions is to apply the new combustion concept using multistage injection such as HCCI and PCCI. The other solution is to apply after-treatment systems. For example, lean NOx trap catalyst, Urea-SCR and others have various advantages and disadvantages Especially, Urea-SCR system have advantages such as a high conversion efficiency and a wide operation conditions. Hence the key factor to implementation of Urea-SCR technology, good mixing of urea(Ammonia) and gas, reducing Ammonia slip. Urea mixer components are required to facilitate evaporation and mixing because the liquid state of urea poses significant barriers for evaporation, and the distance to mixer is the most critical that affect mixer performance. In this study, to find out the distance from injector to mixer and simulation factor, a laser diagnostics and high speed camera are used to analyze urea injector spray characteristics and to present a distribution of urea solution in transparent manifold In addition, Droplet Uniformity Index is calculated from the acquired images by using image processing method to clarify the distribution of spray.

• Journal of Distribution Science
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• v.12 no.12
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• pp.119-130
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• 2014

Purpose - Franchise industries are significant both socially and economically. However, with increasing interest, there are manifold problems. It is necessary to seek measures for mature operation constantly despite unprepared franchisors, negative perceptions of the media and society toward franchise, and rapid changes in business start-up trends and propensity to consume that make business start-ups difficult. The paper aims to explain the effects of relational commitment and performance on the franchisor's management characteristics and justice in the food service franchise system. Research design, data, and methodology - This is an exploratory survey examining franchising in Korea. Based on a literature synthesis, we extract five constructs: managerial characteristics, support, fairness, trust, and satisfaction. We hypothesize that these factors influence the trust, satisfaction, and performance of franchisees. To examine these hypotheses empirically, we conducted a survey on the database of the Franchising Council of Korea. The study employs data from May to September 2014. In total, 135 completed questionnaires were received, of which 128 were usable. The data was analyzed with SPSS/PC 22.0. First, to test unidimensionality and nomological validity of the measures of each construct, we employed a scale refinement procedure. The result of a reliability test with Cronbach's α and factor analysis warranted unidimensionality of the measures for each construct. In addition, nomological validity of the measures was warranted from the result of the correlation and regression analysis. By analyzing the data, we can confirm most hypotheses. Results - Frist, franchisor characteristics have a positive effect on trust and satisfaction. Second, franchisor fairness has an effect on trust and satisfaction. Third, franchisor support has an effect on satisfaction. Further, the franchisee trust has an effect on satisfaction. Fourth, the satisfaction of a franchisee with a franchisor affects the performance of a franchisee. Finally, there is a possibility that not only franchisee performance but also increasing the credibility and improving the image of the franchisor through communication between franchisor and franchisee can improve franchisees' performance and satisfaction by motivating the franchisee for sustainable growth. Franchisers should endeavor for franchisees to obtain stable revenue with continuous and practical support. They should recognize that they can expand their business by supporting their franchisees. Franchisors should not only instantly respond to franchisees' troubles with interactive communications but also raise the ability of supervisors for better support. Franchisors should share their visions and goals with their franchisees and provide systematic and continuous support based on trust and clear company management. Franchisees should understand franchisors' position as well as participate in establishing the basic franchise system. Contributions - The paper contributes to understanding franchising in Korea. It offers insights and assistance to franchisors hoping to start franchises. This paper explores measurement issues related to franchisee performance by estimating its determinant factors (managerial characteristics, support, fairness, trust, and satisfaction). This study provides franchisors and practitioners planning to extend their franchising business with some practical knowledge.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2008.04a
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• pp.199-205
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• 2008

In this study, a system to measure continuously the fuel concentration in a steady flow rig on the basis of Rayleigh scattering is presented. The system can be employed to measure both the temporal and the spatial distribution. Also, it is possible to calibrate the system for the measurement of accurate absolute concentration. Firstly, the system was tested at a calibration chamber for the determination of scattering cross section from propane, butane, acetylene, Freon-12 and Genetron 143a. After this, the system was adapted to a steady flow rig to measure the temporal and spatial fuel concentration. The rig is composed of cylinder head, intake manifold, injector, and transparent cylinder which can simulate internal combustion engine. To cope with the problem of Mie scattering interference, a software filter was developed, which is based on the rise time and the time constant of the photomultiplier-amplifier system. The results show that LRS can provide useful informations about concentration field and the software filter is very effective method to remove Mie interference.