• Journal of Power Electronics
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• 제11권2호
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.561-565
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• 2009

초음속 충동형 터빈의 성능에 관해 시험적 방법으로 고찰하였다. 초음속 충동형 터빈은 고온, 고압의 연소가스로 구동되나, 연구원 내의 시험장치 한계 및 위험성으로 인해 고압의 공기를 이용하여 상사점에 대한 성능 시험을 수행하여 실매질 시험시의 터빈 성능을 예측하였다. 실제 연소가스로 구동되는 노즐 면적을 가지는 본품용 터빈 시험기를 공기로 구동시킬 경우 상사 조건을 정확히 맞추기는 어렵다. 그러므로 두 가지 상사 조건 시험을 통해 실제 설계점은 두 가지 상사점 사이에 존재하며 이 설계점은 공기의 물성치에 맞게 계산된 노즐 면적을 가지는 시험용 터빈 시험기를 통해 예측된 상사점과 비슷한 구간에 있음을 나타내었다.

• 대한간호학회지
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• 제5권2호
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• pp.38-50
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• 1975

This study was conducted to find the shortest optimum time for taking oral temperature and axillary temperature, which does not affect reliability of body temperature. For this purpose, first, the time at which all the samples are reaching maximum temperature is identified Second, the mean maximum temperature is compared with the mean temperature of each consecutive measurement by T-test to find the time at which no significant changes in temperature occurs along time sequence. Third, optimum temperatures are set at points of -0.2℉, -0.4℉, -0.6℉, -0.8℉, -1.0℉, -1.2℉, -1.4℉, from maximum temperature. A point of time at which 90% of samples reach at optimum temperature is identified and defined as optimum time. The study sample, a total of 164 cases were divided into two groups according to their measured body temperature. The group with body temperature below 37 $^{\circ}C$(A group) and above 37$^{\circ}$1'C (B group) were compared on the time required to reach maximum temperature and optimum temperature. The results are as follow. 1. The time required for total sample to reach maximum temperature was 13 minutes in both groups by oral method, 15 minutes in A group and 13 minutes in B group by axillary method. Time required for 90 % of cases reach maximum temperature by oral method was 10 minutes in both group. By axillary method, 12 minutes in A group. (Ref: table 2) 2. Statistical analysis by means of T-test, the time which does not show a significant change by oral method were 12 minutes in A group and 11 minutes in B group, and by axillary method 14 minutes in A group and 11 minutes in B group. (Ref: table 5, 6.) 3. Where optimum temperature was defined as maximum temperature minus 0.2 ℉, optimum time was found 8 minutes in both groups by oral method, and 11 minutes in A group and 9 minutes in B group by axillary method 4. Where optimum temperature was defined as maximum temperature minus 0.4 ℉, optimum time was found 7 minutes in A group and 6 minutes in B group by oral method, and 9 minutes in A group and 7 minutes in B group by axillary method 5. Where optimum temperature was defined as maximum temperature minus 0.8 ℉, optimum time was found 6 minutes in A group and 6 minutes in B group by axillary method (Ref: table 7, 8, 9, 10) 6. The commonly practiced temperature taking time, 3 minutes in oral method and 5 minutes in axillary method can be accepted as pertinent when physiological variation of body temperature at the mean level of -1, 2 ℉ is accepted. 7. The difference in time required to resister maximum temperature was compared between the group with body temperature below 37$^{\circ}C$ and above 37$^{\circ}$1'C, and found no significant difference in oral mettled and 1 - 4 minute difference in axillary method with shorter time requirement in feverish group.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.35-39
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• 2003

A numerical study is carried out to investigate combustion phenomena in a model SCRamjet engine, which has been experimentally studied at the Australian National University using a T3 free-piston shock tunnel. The Mach number is 3.8, the static pressure 110kPa and the static temperature 1100K in the main air flow. The fuel is hydrogen, which is injected in the cavity. Equivalence ratio is set to either 0.25 or 0.5 to access its effect on the fuel-air mixing combustion phenomena. The results show that the cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs near the point of fuel injection. The flame is anchored by the cavity and generates the precombustion shock on the step. For a high equivalence ratio, the recirculation zones are bigger and the flame is present throughout the combustor.

• Structural Engineering and Mechanics
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• 제22권3호
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• pp.331-349
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• 2006

The stresses and deflections in a laminated rectangular plate under thermal vibration are determined by using the moving least squares differential quadrature (MLSDQ) method based on the first order shear deformation theory. The weighting coefficients used in MLSDQ approximation are obtained through a fast computation of the MLS shape functions and their partial derivatives. By using this method, the governing differential equations are transformed into sets of linear homogeneous algebraic equations in terms of the displacement components at each discrete point. Boundary conditions are implemented through discrete grid points by constraining displacements, bending moments and rotations of the plate. Solving this set of algebraic equations yields the displacement components. Then substituting these displacements into the constitutive equation, we obtain the stresses. The approximate solutions for stress and deflection of laminated plate with cross layer under thermal load are obtained. Numerical results show that the MLSDQ method provides rapidly convergent and accurate solutions for calculating the stresses and deflections in a multi-layered plate of cross ply laminate subjected to thermal vibration of sinusoidal temperature including shear deformation with a few grid points.

• 한국환경과학회지
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• 제4권2호
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• pp.169-180
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• 1995

This Daper presents effective simulation of the dispersion of thermal discharge which can be relesed at Boryong power plant. Applied numerical models are finite difference method for hydrodynamic analysis and Masch-model comprised of conditions for ambient current velocity. Application of these models is done in Cheonsu Bay Summing up the results of this study are as follows; 1. It is found that the result for measurements of temperature appears high at southwardly Songdo on flood. The reason is that tidal currents which flowed north direction were accompanied with southwardly dispersed thermal discharge. A minute Particle of thermal Plume has a tendency to dispels inward Deacheon Bay. 2. According to the results of numerical experiment, maximum distance for thermal discharge dispersion appeared 10.8 km at lower part and 8.6 km at upper part with power plant outlet as starting point. 3. Comparative the numerical simulation and Airbone Multispectral Scanner indicated that thermal discharge should be verified separative phenomena. The simulated results were compared with field data set showing good agreement. It is concluded that these model can be simulated well.

• 한국분말재료학회지
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• 제14권5호
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• pp.327-332
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• 2007

In a view point of environment, the advanced electric contact material without environmental load element such as cadmium has to be developed. Extensive studies have been carried out on $Ag-SnO_2$ electric contact material as a substitute of Ag-CdO contact materials. In the present study, powder metallurgy including compaction and sintering is introduced to solve the incomplete oxidation problems in manufacturing process of $Ag-SnO_2$ electrical contact material. The $Ag-SnO_2$ contact material, fabricated in this study, was actually set in an electric switchgear of which working voltage is 462V and current is between 25 and 40A, for the purpose of testing its performance. As a result, it exceeded the existing Ag-CdO contact materials in terminal-temperature ascent and main contact resistance.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.189-192
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• 2003

Inductivity Superconducting Fault Current Limiter is the Magnet that uses high temperature Superconductivity Coil. It is an important work that it controls Electric Power Converter of Inductivity SFCL. So, we wish to design the point part FPGA by One-Chip. Design of that can divide as following. One part that generate clock that offer to thyristor. One part that set 60Hz voltage to input Clock and do count. One part that change the value that require in CPU to the integer. And finally. there is part that send output (the fixed Clock) to the thyristor.

• 한국태양에너지학회 논문집
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• 제31권5호
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• pp.41-46
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• 2011

In the present work, a new freeze protection method has been proposed for a natural circulation system of solar water heater. Though electrothermal wire is popularly used for the purpose, there are freezing troubles by wire cut-off and excessive electric power consumption. In the experimental device, hot water in a storage tank was circulated by a small pump and used to heat the outdoor pipes if the cold water pipe surface temperature falls lower than a set point. As a result, It was observed that there was no hot water waste while the solar water heating system operated without freeze and burst.

• 설비공학논문집
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• 제9권4호
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• pp.527-535
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• 1997

Vapor-liquid equilibrium apparatus is designed and set up. The vapor-liquid equilibrium data of the binary system HFC32/134a are measured in the range between 258.15 and 283.15K at compositions of 0.2, 0.4, 0.6 and 0.8 mole fraction of HFC32. Twenty-two equilibrium data are obtained. Based upon the present data, the binary interaction parameter for Carnahan-Starling-De Santis equation of state is calculated. Temperature range of data is extended to 313.04K using the data in the open literatures. Interaction parameters are determined at nine isotherms.