• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.709-715
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• 1999

To optimize a heating and cooling system, we need an exact solution lot radiant heat transfer in any form of room or building. This paper describes the solution method of view factor by the area weighted average and graphical method to calculate the radiant heat exchange or daylighting level in any form of room or building. This study shows that the area weighted average and graphical methods have many points of merits(calculation speed, correctness and calculation capability in an arbitrary form of room shapes etc.) compared with existing methods

• Journal of the Korea Organic Resources Recycling Association
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• v.17 no.4
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• pp.59-65
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• 2009

The antimicrobial activity-possessing materials were screened in the cell free supernatant (CFS) of fourteen lactic acid-fermenting strains isolated from pig's intestine. Each cell free supernatant of cultured strains was treated with various proteinases, heat, and/or alkali (NaOH). The antimicrobial activities were remained even after the enzyme and heat treatment but disappeared after neutralization with 1M NaOH, implying that the materials would be organic acids rather than proteins. Further purification of CFS through solid phase extraction using Sep-pak $C_{18}$ Cartridges and high performance anion exchange chromatography using Bio-LC system revealed that four organic acids, such as oxalic acid, citric acid, lactic acid, and acetic acid, were the main materials for the activity. Lactic acid was the highest amount in all organic acids, ranging from 54% to 77%. This strongly implies that the lactic acid would be the primary material for the antimicrobial activity in all tested strains.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.2
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• pp.134-141
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• 2010

Small PEM (Proton Exchange Membrane) fuel cell systems do not require humidification and have great commercialization possibilities. However, methods for controlling small PEM fuel cell stacks have not been clearly established. In this paper, a control method for small PEM fuel cell systems using a dual closed loop with a static feedforward structure is defined and realized using a DSP (Digital Signal Processor). The fundamental elements that need to be controlled in fuel cell systems include the supply of air and hydrogen, water management inside the stack, and heat management of the stack. For small PEM fuel cell stacks operated without a separate humidifier, fans are essential for air supply, heat management, and water management of the stack. A purge valve discharges surplus water from the stack. The proposed method controls the fan using double control loops to quicken transient response of the fan thereby improving the supply rate of air. Feedback control to compensate for the voltage change in fuel cell stack improves the response characteristics in fuel cell to load variations. The feasibility of proposed method was proved by the experiments with a 60W small PEM fuel cell system and operation of a notebook computer using this system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1889-1894
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• 2017

Global automobile manufacturers are developing electric vehicles (EVs) to eliminate the pollutant emissions from internal combustion vehicles and to minimize fossil fuel consumptions for the future generations. However, EVs have a disadvantage of shorter traveling distance than that of conventional vehicles. To answer this shortfall, more batteries are installed in the EV to satisfy the consumer expectation for the driving range. However, as the energy capacity of the battery mounted in the EV increases, the amount of heat generated by each cell also increases. Naturally, a better battery thermal management system (BTMS) is required to control the temperature of the cells efficiently because the appropriate thermal environment of the cells greatly affects the power output from the battery pack. Typically, the BTMS is divided into an active and a passive system depending on the energy usage of the thermal management system. Heat exchange materials usually include gas and liquid, semiconductor devices and phase change material (PCM). In this study, an application of PCM for a BTMS was investigated to maintain an optimal battery operating temperature range by utilizing characteristics of a PCM, which can accumulate large amounts of latent heat. The system was modeled using Dymola from Dassault Systems, a multi-physics simulation tool. In order to compare the relative performance, the BTMS with the PCM and without the PCM were modeled and the same battery charge/discharge scenarios were simulated. Number of analysis were conducted to compare the battery cooling performance between the model with the aluminum case and PCM and the model with the aluminum case only.

• Tribology and Lubricants
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• v.19 no.6
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• pp.335-341
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• 2003

Recently, the automotive industry is being developed rapidly. On this, a demand of high quality performance­test­machine is increased too. But it is progressive technology that must be combined hydraulic, mechanic and electronic technologies. To construct this system, the design of oil hydraulic circuit, interface skill between sensor and personal computer, data acquisition & display system and integrated control are very important skill. Moreover, reliable data is obtained with vacuum system and complex heat exchange system. Therefore, in this study, we designed a performance­test­machine by using above key technologies and we also made a integrated PC control system using personal computer which is more progressive and flexible method than PLC control.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.9
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• pp.631-636
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• 2008

Solar thermal systems are recently refocused by higher oil prices, but did not completely restore the people's confidence owing to the past bad systems. Several types of solar water heating systems were analyzed in characteristics and some proper systems were proposed under Korean climates and system scale. As a small system, natural circulation system should be installed only in a southern region of Korea, with a freeze protection valve instead of heating coil for freeze protection. In most area of Korea, the forced circulation type with a heat exchange coil inside a thermal storage tank or with a spiral-jacketed storage tank, proposed and verified by the authors, has a merit of stable performance and freeze protection.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.570-580
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• 2000

The performance simulation of refrigeration system for the automotive vehicles was peformed, in which the refrigerant was HFC-l34a as an alternative to CFC-12. The coefficient of performance of the system for HFC-l34a was lower than that for CFC-12 operated in the same operating and design conditions. The optimal design conditions were obtained as a function of optimum capacity ratios of condenser and evaporator.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.359-366
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• 2008

A two-dimensional thermal model of proton exchange membrane fuel cell with large active area is developed to investigate the performance of fuel cell with large active area over various thermal management conditions. The core sub-models of the two-dimensional thermal model are one-dimensional agglomerate structure electrochemical reaction model, one-dimensional water transport model, and a two-dimensional heat transfer model. Prior to carrying out the simulation, this study is contributed to set up the operating temperature of the fuel cell with large active area which is a maximum temperature inside the fuel cell considering durability of membrane electrolyte. The simulation results show that the operating temperature of the fuel cell and temperature distribution inside the fuel cell can affect significantly the total net power at extreme conditions. Results also show that the parasitic losses of balance of plant component should be precisely controlled to produce the maximum system power with minimum parasitic loss of thermal management system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.19-26
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• 2010

A PEMFC(proton exchange membrane fuel cell) is a good candidate for residential power generation to be coped with the shortage of fossil fuel and green house gas emission. The attractive benefit of the PEMFC is to produce electric power as well as hot water for home usage. The thermal management of PEMFC for RPG is to utilize the heat of PEMFC so that the PEMFC can be operated at its optimal efficiency. In this study, thermal management system of PEMFC stack is modeled to understand the dynamic response during load change. The thermal management system of PEMFC for RPGFC is composed of two cooling circuits, one for controling the fuel cell temperature and the other for heating up the water for home usage. The different operating strategy is applied for each cooling circuit considering the duty of those two circuits. Even though the capacity of PEMFC system (1kW) is enough to supply hot domestic water for residence, heat-up of reservior takes some hours. Therefore, in this study, time schedule of the simulation reflects the heat-up process. Dynamic responses and operating strategies of the PEMFC system are investigated during load changes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.892-897
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• 2020

Previous plastic heat exchangers are expensive because the mold must be newly manufactured depending on the air conditioning space. On the other hand, danpla is so thin that the heat exchange performance is excellent. Moreover, danpla can be used easily in ventilation systems in view of fabrication. This study proposes correlations for the cooling performance of an indirect evaporative cooling system. The experimental apparatus consisted of a heat exchanger, spray nozzle, fan, thermostat, pump, and measuring sensors for temperature, humidity, and airflow rate. The results showed that the effectiveness decreased gradually as the airflow rate increased. In addition, there was an optimal condition in terms of effectiveness. The performance prediction correlations were determined using the experimental data from various conditions. The proposed correlations showed performance accuracies within 4 % error.