• 청정기술
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• 제26권2호
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• pp.137-144
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• 2020

저농도 암모니아의 재생 및 농축을 위하여 초음파 함침법으로 금속 첨착 활성탄을 제조하였다. 금속으로는 마그네슘과 구리를 선정하였고, 염화물(Cl^-)과 질산염(NO₃^-) 전구체를 사용하여 활성탄 표면에 첨착하였다. 흡착제의 물리 및 화학적 특성은 TGA, BET 그리고 NH₃-TPD를 통해 분석되었다. 암모니아 파과실험은 고정층 반응기를 사용하여 암모니아(1000 mg L^-1 NH₃, balanced N₂)를 100 mL min^-1으로 주입하였으며, 온도변동 흡착법(TSA)과 압력변동 흡착법(PSA, 0.3, 0.5, 0.7, 0.9 Mpa)에서 수행하였다. 암모니아의 흡착 및 탈착 성능은 NH₃-TPD와 TSA 및 PSA 공정에서 AC-Mg(Cl) > AC-Cu(Cl) > AC-Mg(N) > AC-Cu(N) > AC 순으로 나타났다. 그 중 MgCl₂를 사용한 AC-Mg(Cl)은 TSA에서 평균 흡착량 2.138 mmol g^-1을 나타내었다. 또한 PSA 0.9 Mpa에서 3.848 mmol g^-1로 가장 높은 초기 흡착량을 나타내었다. 활성탄 표면에 금속이 첨착되면 물리흡착뿐만 아니라 화학흡착이 수반되어 흡착 및 탈착 성능이 증가하는 것을 확인하였다. 또한 흡착제는 반복적인 공정에도 안정적인 흡착 및 탈착 성능을 나타내어 TSA와 PSA 공정에서의 적용 가능성을 확인하였다.

• 에너지공학
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• 제15권3호
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• pp.181-187
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• 2006

본 논문에서는 소방 비상용으로 이용되는 태양전지 발전시스템을 제안하고, 발전시스템의 효율을 증대시키기 위한 새로운 고효율의 전력변환장치(승압용 초퍼와 인버터)가 설계된다. 직류-직류(DC-DC) 승압용 초퍼와 직류-교류(DC-AC) 인버터는 사용된 제어스위치들의 스위칭 손실을 최소화하기 위해 공진회로를 이용한 새로운 소프트 스위칭 기법이 적용되고 시스템의 효율을 증대시킨다. 또한 본 논문에서는 태양전지(solar cell)의 최대전력 전송에 의한 태양전지의 효율적인 사용을 위한 태양전지 발전전력의 최대점 $P_{max}$을 손쉽게 추종하고 검출하는 새로운 제어기법과 제어회로에 대해 상세히 해석된다. 고효율의 전력변환 장치와 태양전지 최대전력 전송회로는 컴퓨터 시뮬레이션과 실험을 통하여 그 타당성이 입증된다.

• 한국수소및신에너지학회논문집
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• 제34권1호
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• pp.8-16
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• 2023

In this work, we report basic performance test results of a lab-scale three phase alternative current (AC) arc plasma torch system for plasma gas reforming applications. The suggested system primarily consists of three graphite electrodes inclined at 12.5° to the central axis, a 𝞥 150 mm cylindrical gas path and a three phase-60 Hz AC power supply. At air flow rate of 50 Lpm and arc currents of 100-175 A, test results revealed that plasma resistances were decreasing from 1.08 Ω to 0.53 Ω with the increase of plasma power from 9.3 kW to 13.8 kW, causing the decrease of power factor and increase of the line voltages. However, the injected air can be heated quickly up to the temperatures of >1,200℃ when injecting AC arc plasma powers of >10 kW.

• Carbon letters
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• 제4권3호
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• pp.121-125
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• 2003

The Pt-Ru/Carbon as an anode catalyst supported on the commercial activated carbon (AC) having high surface area and micropore was characterized for application of Direct Methanol Fuel Cell (DMFC). The Pt-Ru/AC anode catalyst used in this experiment showed the performance of $600\;mA/cm^2$ current density at 0.3 V. The borohydride reduction process using $NaBH_4$, denoted as a process A, showed much higher current and power densities than process B prepared by changing the reduction and washing process of process A. The particle sizes are strongly affected by the reduction process than the specific surface area of raw active carbon and the sizes are almost constant when the specific surface area of carbon are over than the $1200\;m^2/g$. Smaller particle size of catalyst and more narrow intercrystalite distance increased the performance of DMFC.

• 한국소음진동공학회논문집
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• 제20권4호
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• pp.397-404
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• 2010

The use of equivalent circuit models of piezoelectric energy harvesters is inevitable when power circuitry including rectifying and smoothing circuit elements is connected to them for evaluating DC electrical outputs. This is because it is difficult to incorporate the electro-mechanical coupling resulting from the additional circuitry into the conventional finite element analysis. Motivated by this observation, we propose a method to accurately extract the equivalent circuit parameters by using commercially available FEM software such as ANSYS which provides three-dimensional AC piezoelectric analysis. Then the equivalent circuit can be analyzed by circuit simulators such as $SimPowerSystems^{TM}$ of MATLAB. While the previous works have estimated the circuit parameters by experimental measurements or by analytical solutions developed only for limited geometries and boundary conditions, the proposed method has no such limitation because piezoelectric energy harvesters of any shapes and boundary conditions can be treated in FEM software. For the verification of the proposed method, multi-modal AC electrical power output by using a corresponding equivalent circuit is compared with that by ANSYS. The proposed method is then shown to be very useful in the subsequent evaluation of DC electrical output which is obtained by attaching a bridge diode and a storage capacitor to a piezoelectric energy harvester.

• ETRI Journal
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• 제31권6호
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• pp.688-694
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• 2009

In this paper, we present the results of a preliminary study on the piezoelectric energy harvesting performance of a Zr-doped $PbMg_{1/3}Nb_{2/3}O_3-PbTiO_3$ (PMN-PZT) single crystal beam. A novel piezoelectric beam cantilever structure is used to demonstrate the feasibility of generating AC voltage during a state of vibration. The energy-harvesting capability of a PMN-PZT beam is calculated and tested. The frequency response of the cantilever device shows that the first mode resonance frequency of the excitation model exists in the neighborhood of several hundreds of hertz, which is similar to the calculated value. These tests show that several significantly open AC voltages and sub-mW power are achieved. To test the possibility of a small scale power source for a ubiquitous sensor network service, energy conversion and the testing of storage experiment are also carried out.

• Journal of Electrochemical Science and Technology
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• 제1권2호
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• pp.97-101
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• 2010

In order to apply hybrid capacitor, $Li_2Mn_3O_7$ was synthesized by combustion method using $LiNO_3$, $Li(CH_3COO){\cdot}2H_2O$ and $Mn(CH_3COO){\cdot}4H_2O$. Spinel pattern was identified the samples calcined over $400^{\circ}C$ in XRD. Intensity of $Mn_2O_3$ peak increased as the calcination temperature increased. To decide n/p ratio and to investigate electrochemical properties, charge-discharge tests of Li/$Li_2Mn_3O_7$ and Li/AC half-cell were carried out. Applying to AC/$Li_2Mn_3O_7$ hybrid capacitor, it had high discharge capacitance of 32.8 F/cc at 100 mA/g.

• Journal of Power Electronics
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• 제19권2호
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• pp.529-539
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• 2019

The modular multilevel converter (MMC) has become a promising topology for high-voltage direct current (HVDC) transmission systems. To control a MMC system properly, the ac-side current, circulating current and submodule (SM) capacitor voltage are taken into consideration. This paper proposes a low-computation indirect model predictive control (IMPC) strategy that takes advantages of the conventional MPC and has no weighting factors. The cost function and duty cycle are introduced to minimize the tracking error of the ac-side current and to eliminate the circulating current. An optimized merge sort (OMS) algorithm is applied to keep the SM capacitor voltages balanced. The proposed IMPC strategy effectively reduces the controller complexity and computational burden. In this paper, a discrete-time mathematical model of a MMC system is developed and the duty ratio of switching state is designed. In addition, a simulation of an eleven-level MMC system based on MATLAB/Simulink and a five-level experimental setup are built to evaluate the feasibility and performance of the proposed low-computation IMPC strategy.

• 한국수소및신에너지학회논문집
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• 제33권3호
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• pp.226-231
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• 2022

Power converter are usually equipped for fuel cell power generation system to connect alternating current (AC) electric power grid. When converting direct current (DC) of fuel cell power source into AC, the power converter has a frequency ripple, which affects the fuel cell and the grid. Therefore, an equivalent circuit having dynamic characteristics of fuel cell power, for example, impedance, is useful for designing an inverter circuit. In this study, the current, voltage and impedance characteristics were calculated through fuel cell modeling and validated by comparing them with experiments. The equivalent circuit element values according to the current density were formulated into equations so that it could be applied to the circuit design. It is expected that the process of the equivalent circuit modeling will be applied to the actual inverter circuit design and simulated fuel cell power sources.

• 핵의학기술
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• 제17권1호
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• pp.25-29
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• 2013

SPECT/CT에서 140 kVp를 사용하는 CT 평균 에너지를 60 keV로 가정하고, CT 평균 에너지와 $^{201}Tl,\;^{99m}Tc,\;^{131}I$의 각기 다른 3가지 에너지를 서로 비교하여 감쇠 보정과 산란 보정의 정확도를 평가하고자 한다. Cylindrical phantom 에 $^{201}Tl$은 55.5 MBq (2 mCi), $^{99m}Tc$은 281.2 MBq (7.6 mCi), $^{131}I$은 96.2 MBq (2.66 mCi)를 주입하고 장비는 GE사의 Hawkeye 4 SPECT/CT를 사용하였다. 모든 SPECT는 frame 당 약 50 kcounts, CT는 140 kVp, 2.5 mA로 하여 영상을 얻었다. 영상은 OSEM (iteration: 2, subset: 10)으로 재구성하였고, 이때 감쇠 보정 적용 유무, 산란 보정 적용 유무를 서로 비교했다. 전체 phantom 영상의 uniformity를 모두 측정하고, center to peripheral ratio (CPR)를 구하여 평가하였다. $^{201}Tl$과 $^{99m}Tc$의 재구성 영상에 감쇠 보정만 적용한 경우 약 10-20% 정도 uniformity가 향상되지만, SC만 적용한 경우에는 약 2% 감소하였다. $^{131}I$의 uniformity는 감쇠 보정과 산란 보정을 모두 적용한 경우에 조금 향상되었다. 또한 CPR은 $^{201}Tl$과 $^{99m}Tc$에서 감쇠 보정만 적용한 경우에 1에 가까웠고, $^{131}I$의 영상에서는 감쇠 보정만 적용한 경우 1에 가깝지 않은 결과가 나타났다. SPECT/CT에서 140 kVp의 CT 평균 에너지를 60 keV이라고 가정했을 때, 대체적으로 에너지가 낮은 $^{201}Tl$과 $^{99m}Tc$은 감쇠 보정만 적용한 경우에 uniformity가 향상되었고, 에너지가 높은 $^{131}I$ 은 감쇠 보정과 산란 보정을 모두 적용한 경우에만 향상되었다.