• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.339-344
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• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• Journal of Energy Engineering
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• v.13 no.2
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• pp.118-127
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• 2004

The purpose of this study is experimentally to analyze that intake port swirl, injection system and turbocharger have an effect on the engine performance and the emission characteristics in a V8 type turbocharged intercooler D.I. diesel engine of the displacement 16.7ι, and to suggest the improvement of engine performance. Generally to enhance engine power, TCI diesel engine is put to practically use turbo-charged intercoler in order to increase boost efficiency which is cooled boost air. As results of considering the factors of the intake port of swirl ratio 2.25, compression ratio 17.5, re-entrant 8.5$^{\circ}$ combustion bowl, nozzle hole diameter ${\Phi}$0.33*3+${\Phi}$0.35*2, nozzle protrusion 3.18mm, injection timing BTDC 12$^{\circ}$CA and turbo charger (compressor 0.6A/R+46Trim, turbine 1.0A/R+57Trim) is the best in the full range of operating in the engine performance and the exhaust characteristics of NO$\_$x/ concentration. Therefore their factors are appropriated as intake system, injection and turbocharger system.

• Journal of Biosystems Engineering
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• v.34 no.6
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• pp.470-475
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• 2009

This study was performed to present the diagnosis basis of cooling performance deficiency according to air quantity included in refrigerant of air-conditioner by detecting the temperatures and pressures of refrigerant pipeline. The car air-conditioner of SONATA III (Hyundai motor Co., Korea) was tested by maximum cooling condition at 1500 rpm of engine speed in the room with controlled air condition at $33\sim35^{\circ}C$ and 55~57% RH. Measured variables were temperature differences between inlet and outlet pipe surface of the compressor (Tcom), condenser (Tcon), receive dryer (Trec) and evaporator (Teva), and high pressure (HP) and low pressure (LP) in the refrigerant pipeline, and temperature difference (Tcoo) between inlet and outlet air of the cooling vent of evaporator. Control variables were the refrigerant charging weight and the vacuum degree in the refrigerant pipeline before charging refrigerant. From the test, it was represented that the measuring values of (Tcom), LP and (Tcoo) were enabled to make the diagnosis of cooling performance deficiency according to quantity included in refrigerant of air-conditioner. The ranges of Tcom, LP and Tcoo to make the diagnosis of cooling performance deficiency were respectively less than $55^{\circ}C$, more than 166.7 kPa-g(1.7 kgf/$cm^2$) and less than $13.7^{\circ}C$. In the case of using only external sensors and the condition under the normal performances of air conditioner, it was considered that the ranges of LP and Tcoo to make the diagnosis of cooling performance deficiency were respectively more than 166.7 Pa and less than $12^{\circ}C$.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.2
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• pp.10-15
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• 2014

For hypersonic aircraft, increase of flight speeds causes heat loads that are from aerodynamic heat and engine heat. The heat loads could lead structural change of aircraft's component and malfunctioning. Endothermic fuels are liquid hydrocarbon fuels which are able to absorb the heat loads by undergoing endothermic reactions, such as thermal and catalytic cracking. In this study, methylcyclohexane was selected as a model endothermic fuel and experiments on endothermic properties were implemented. To improve heat of endothermic reaction, we applied zeolites and confirmed that HZSM-5 was the best catalyst for the catalytic performance. The objective is to investigate catalytic effects for heat sink improvement. The catalyst could be applied to system that use kerosene fuel as endothermic fuel.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.83-93
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• 2017

A numerical analysis is made of the fluid flow and heat transfer characteristics in the corrugated structure that traps the spent air in the corrugations between impinging jets to reduce crossflow effects on downstream jets in the array. All computations are performed by considering three-dimensional, steady state, and incompressible flow by using the ANSYS-CFX 15.0 code. Averaged jet Reynolds number is 10,000. The oblique angles of impingement jets on the spanwise section are $70^{\circ}$, $80^{\circ}$, $90^{\circ}$, and the oblique angles of impingement jets on the streamwise section are $70^{\circ}$, $90^{\circ}$, $110^{\circ}$. The investigation focuses on the oblique angle influence of impinging jet array on the fluid flow and heat transfer characteristics of a corrugated structure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.425-429
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• 2011

In the unlikely of nuclear reactor meltdown, the leaked core melt or corium must be contained in a device called core-catcher so that the corium can be cooled and stabilized. The ex-vessel behavior of corium involves complex physical and chemical mechanisms of flow propagation, heat transfer, and reactions with sacrificial substrates. In this study, the detailed characteristics of corium flow and heat transfer were investigated by using a commercial CFD code for VULCANO VE-U7 test reported in the literature. The volume-of-fluid (VOF) model was used to predict the interfacial surface formation of corium and the surrounding air, and the discrete ordinate model was adopted to calculate radiation between corium and the surroundings. It was found that cooling via radiation through the top surface of corium had a dominant effect on the temperature and viscosity profiles at the front of the corium flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.593-601
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• 2011

An analysis program to simulate the operation of a polymer electrolyte membrane fuel cell (PEMFC) system was set up, and system operation with variations in the working conditions of various components (especially the thermal management system) was simulated. The entire system included a PEMFC stack and balance-of-plant components such as an air-supply unit, a fuel-supply unit, and a heat-management unit (cooling system). Thermodynamic models of all components were made to evaluate the design performance of the entire system, and then off-design models were set up to simulate the operation of the entire system under arbitrary working conditions. A parametric study was carried out to examine the effects of varying the operating conditions (especially the ambient conditions and the operating conditions of the cooling system) on the operation and performance of the entire system.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.243-244
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• 2007

본 연구에서는 성형용 코어 가공에서 초경합금(WC, Co 0.5%)의 초정밀 가공특성을 파악하기 위하여 다이아몬드 휠의 메시, 주축 회전속도, 터빈 회전속도, 이송속도 및 연삭깊이에 따른 표면거칠기를 측정하여 최적연삭조건을 규명하였다. 규명된 최적연삭가공조건을 활용하여 페러렐 연삭법으로 초정밀 연삭가공을 수행하였다. 연삭가공은 초정밀가공기(ASP01, Nachi-Fujikoshi Co., Japan)를 사용하였다. 최종 정삭가공을 수행한 비구면 성형용 코어의 형상측정결과 형상정도(PV; ${\varphi}$ 3.0mm) 0.15${\mu}m$(비구면), 0.10${\mu}m$(평면)으로 3M급 이상의 고화질 카메라폰에 채용되고 있는 비구면 Glass렌즈 양산용 성형용 코어 규격에 만족한 결과로서 본 연구에 수행된 초정밀 가공조건 및 측정방법이 매우 유효함을 알 수 있었다. 형상정도(PV) 및 표면조도(Ra) 측정은 초정밀 자유곡면 측정기(UA3P, Panasonic Co., Japan)와 3차원 표면조도 측정기(NewView5000, Zygo Co., USA)를 각각 사용하였다. 초정밀 가공된 성형용 코어면에 이온증착법을 활용하여 DLC 코팅을 수행하였다. 코팅 전후의 성형용코어를 활용하여 Glass소재(K-BK7, Sumita Co., Japan)를 최적의 성형조건(성형온도, 압력, 냉각속도)으로 성형하였다. DLC 코팅과 성형은 DLC 코팅기(NC400, Nanotech Co., Japan)와 Glass렌즈 성형기(Nano Press-S, Sumitomo Co., Japan)을 각각 사용하였다. Fig. 1은 초정밀 연삭가공, DLC 코팅막 구조, 코팅된 성형용 코어, 그리고, 성형된 비구면Glass렌즈를 각각 나타낸다.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.1 no.2
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• pp.136-143
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• 1991

Inorganic mercury in urine and airborne was determined by cold vapor atomic absorption spectrophotometry. Detailed sampling methods and analylical results are as follows : 1. 100~200ml of urine for each person was taken in 250 ml borosilicate bottle and $K_2S_2O_8$ (0.1g/100ml urine) was added to prevent bacterial contamination. About 1001 air of workingplace was absorbed in l0ml of absorbing solution. Urine samples and absorbing solution tubes were stored at $4^{\circ}C$. Dillution solution to prepare standard solution used deionized water (D.W) for urine and absorbing solution (A.S) for air. 2. 1n this procedure deteclion limit was 1ng/ml and mercury contents of blank reagent solution was 1~2ng/ml. 3. Calibration range was $0.02{\sim}0.1{\mu}g/ml$ and in this range r.s.d for each calibration curve in D.W and A.S and ${\pm}7.9%$ and ${\pm}3.7%$, respectively. 4. Repeatability (n=5 times, conc. $0.05{\mu}g/ml$) was ${\pm}5.8%$, in D.W. and ${\pm}4.4%$ in A.S, respectively. 5. Recovery for urine adding spiked concentration ($0.05{\mu}g/ml$) was about 90%. 6. Analytical result of samples was $1{\sim}139{\mu}g/l$ in urine and ${\sim}0.127mg/m^3$ in airborne.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.811-819
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• 2012

An air-cooled condenser is a device that is used for converting steam into condensate by using ambient air. The air-cooled condenser is prone to suffer from a serious explosion when the condensate inside the tubes of a heat exchanger is frozen; in particular, tubes can break during winter. This is primarily due to the structural problem of the tube outlet of an existing conventional air-cooled condenser system, which causes the backflow of residual steam and noncondensable gases. To solve the backflow problem in such condensers, such a system was simulated and a new system was designed and evaluated in this study. The experimental results using the simulated condenser showed the occurrence of freezing because of the backflow inside the tube. On the other hand, no backflow and freezing occurred in the advanced new condenser, and efficient heat exchange occurred.