• Title/Summary/Keyword: System efficiency

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Study on the Characteristics of Low-pressure Automotive Polymer Electrolyte Membrane Fuel Cell System Efficiency with Blower Configuration (블로워 구성 변경에 따른 상압형 자동차용 고분자전해질형 연료전지 시스템의 효율 특성 연구)

  • KIM, IL-JOONG;LEE, JUNG-JAE;KIM, HAN-SANG
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.2
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    • pp.181-189
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    • 2018
  • Polymer electrolyte membrane fuel cell (PEMFC) system receives great attention as a promising power device for automotive applications. For the wide commercialization, the efficiency and performance of automotive PEMFC system should be further improved in terms of total system (stack and balance of plant [BOP]). Air supply module, which is a major part of the BOP, greatly affects the efficiency of automotive PEMFC system. In this paper, a systematic study on the low-pressure automotive PEMFC system was made in an attempt to enhance the net system efficiency. This study mainly presents an investigation of the effect of blower configuration (1-blower and 2-blower) on the net system efficiency of automotive PEMFC system. For this purpose, the effect of operating pressure and cathode stoichiometry on the system efficiency was investigated with stack temperature under the fixed net system power condition. Results indicate that 1-blower system is better in system efficiency over 2-blower system under an air stoichiometry of 2. However, 2-blower system is better in system efficiency under an air stoichiometry of 3. The simulation results show that the optimum operating strategy needs to be established for various blower system configurations considering blower performance maps.

Investigation of System Efficiency of an Electro-hydrostatic Actuator with an External Gear Pump (소형 외접기어펌프를 사용하는 EHA의 시스템 효율 분석)

  • Kim, Jong-Hyeok;Hong, Yeh-Sun
    • Journal of Drive and Control
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    • v.16 no.2
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    • pp.15-21
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    • 2019
  • In this study, the maximum system efficiency of the electro-hydrostatic actuators was experimentally investigated, where small size external gear pumps with volumetric displacement under 1.3 cc/rev were combined with a 400W servomotor as the prime mover. Since the efficiency data of the servomotor, gear pumps and hydraulic cylinder were not provided by the suppliers, experimental apparatuses for their efficiency measurement were extra built up. When a gear pump with a volumetric displacement of 1.27cc/rev was used on an electro-hydrostatic actuator system, the maximum system efficiency was not higher than 70%. This was because the most effective operation ranges of the motor and pump did not coincide each other. In order to match their operation ranges as one of the most crucial design factors, a speed reduction mechanism can be used, such as a timing belt. It was shown in the study that the maximum system efficiency could be increased from 70% to 76% in that way.

Level Number Effect on Performance of a Novel Series Active Power Filter Based on Multilevel Inverter

  • Karaarslan, Korhan;Arifoglu, Birol;Beser, Ersoy;Camur, Sabri
    • Journal of Electrical Engineering and Technology
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    • v.13 no.2
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    • pp.711-721
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    • 2018
  • This paper presents a single-phase asymmetric half-bridge cascaded multilevel inverter based series active power filter (SAPF) for harmonic voltage compensation. The effect of level number on performance of the proposed SAPF is examined in terms of total harmonic distortion (THD) and system efficiency. Besides, the relationship between the level number and the number of switching device are compared with the other multilevel inverter topologies used in APF applications. The paper is also aimed to demonstrate the capability of the SAPF for compensating harmonic voltages alone, without using a passive power filter (PPF). To obtain the required output voltage, a new switching algorithm is developed. The proposed SAPF with levels of 7, 15 and 31 is used in both simulation and experimental studies and the harmonic voltages of the load connected to the point of common coupling (PCC) is compensated under two different loading conditions. Furthermore, very high system efficiency values such as 98.74% and 96.84% are measured in the experimental studies and all THD values are brought into compliance with the IEEE-519 Standard. As a result, by increasing the level number of the inverter, lower THD values can be obtained even under high harmonic distortion levels while system efficiency almost remains the same.

Design Performance Analysis of Micro Gas Turbine-Organic Rankine Cycle Combined System (마이크로 가스터빈과 유기매체 랜킨사이클을 결합한 복합시스템의 설계 성능해석)

  • Lee Joon Hee;Kim Tong Seop
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.6
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    • pp.536-543
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    • 2005
  • This study analyzes the design performance of a combined system of a recuperated cycle micro gas turbine (MGT) and a bottoming organic Rankine cycle (ORC) adopting refrigerant (R123) as a working fluid. In contrast to the steam bottoming Rankine cycle, the ORC optimizes the combined system efficiency at a higher evaporating pressure. The ORC recovers much greater MGT exhaust heat than the steam Rankine cycle (much lower stack temperature), resulting in a greater bottoming cycle power and thus a higher combined system efficiency. The optimum MGT pressure ratio of the combined system is very close to the optimum pressure ratio of the MGT itself. The ORC's power amounts to about $25\%$ of MGT power. For the MGT turbine inlet temperature of $950^{\circ}C$ or higher, the combined system efficiency, based on shaft power, can be higher than $45\%$.

Parametric Study of SOFC System Efficiency Under Operation Conditions of Butane Reformer (부탄 개질기 운전조건에 따른 SOFC 시스템 효율에 대한 연구)

  • Kim, Sun-Young;Baek, Seung-Whan;Bae, Gyu-Jong;Bae, Joong-Myeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.4
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    • pp.341-347
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    • 2010
  • In this study, the efficiency of a solid-oxide fuel cell (SOFC) system with a steam reformer or prereformer was analyzed under various conditions. The main components of the system are the reformer, SOFC, and water boiling heat recovery system. Endothermic and exothermic reactions occur in the reformer and SOFC, respectively. Hence, the thermal management of the SOFC system greatly influences the SOFC system efficiency. First, the efficiencies of SOFC systems with a steam reformer and a prereformer are compared. The system with the prereformer was more efficient than the one with steam reformer due to less heat loss. Second, the system efficiencies under various prereformer operating conditions were analyzed. The system efficiency was a function of the heat requirement of the system. The efficiency increased with an increase in the operating temperature of the prereformer, and the maximum system efficiency was observed at $450^{\circ}C$ for a S/C of 2.0.

Design and analysis of a free-piston stirling engine for space nuclear power reactor

  • Dai, Zhiwen;Wang, Chenglong;Zhang, Dalin;Tian, Wenxi;Qiu, Suizheng;Su, G.H.
    • Nuclear Engineering and Technology
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    • v.53 no.2
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    • pp.637-646
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    • 2021
  • The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell's thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

Improvement of Efficiency of Kalina Cycle and Performance Comparison (Kalina 사이클의 효율 향상 방안 및 성능 비교)

  • Yoon, Jung-In;Son, Chang-Hyo;Choi, Kwang-Hwan;Son, Chang-Min;Seol, Sung-Hoon;Lee, Ho-Saeng;Kim, Hyeon-Ju
    • Journal of the Korean Solar Energy Society
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    • v.35 no.5
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    • pp.11-19
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    • 2015
  • In this paper, EP-Kalina cycle applying liquid-vapor ejector and motive pump is newly proposed. In this EP-Kalina cycle, the liquid-vapor ejector is used to increase pressure difference between inlet and outlet of the turbine. Also the motive pump enhances the performance of liquid-vapor ejector, resulting in increase of system efficiency of OTEC cycles. The comparison cycles in this study are basic, Kalina, EKalina and EP-Kalina ones. The pump work, net power, APRe, APRc, TPP and system efficiency of each cycle are compared. In case of net power, EP-Kalina cycle is lowest among the cycles due to the application of the motive pump. But, the net power difference of cycles seems to be minor since the pump work of cycles is merely about 1kW, compared to turbine gross power of 20kW. The system efficiency of EP-Kalina cycle shows 3.22%, relatively 44% higher than that of basic OTEC cycle. Therefore, the system efficiency is increased by applying the liquid-vapor ejector and the motive pump. Additional performance analysis is necessary to optimize the proposed EP-Kalina cycle.

Study on the Efficiency of Multi-State κ-out-of-n System (다상태 κ-out-of-n 시스템의 효율에 관한 연구)

  • Kim, Jihyun;Nam, Hae Byur;Cha, Ji Hwan
    • The Korean Journal of Applied Statistics
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    • v.26 no.1
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    • pp.119-130
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    • 2013
  • A system with $n$ components which functions when at least ${\kappa}$ of the components function is called ${\kappa}$-out-of-$n$ system. Most studies on ${\kappa}$-out-of-$n$ system derive the system reliability based on the assumption that the system has just two states: functioning or failed. However, the system efficiency may depend on the number of functioning components. This paper considers a Multi-state ${\kappa}$-out-of-$n$ system and derives the total system efficiency. In addition, assuming that the system is repairable, the optimal repair policy to maximize the system efficiency is studied. The system efficiency considered in this paper can be regarded as a generalized measure of the mean time to the failure of the system.

Dynamic Analysis of PEM fuel cell system (PEM 연료전지시스템의 동특성 해석)

  • Kim Beomsoo;Jeon Soonil;Lim Wonsik;Park Yeong-il
    • 한국신재생에너지학회:학술대회논문집
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    • pp.353-356
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    • 2005
  • We developed a dynamic model of PEM fuel cell system which can analyze its transient response to dynamic load current. System components such as compressor, air cooler, humidifier, and stack were modeled based on their dynamic equations and performance maps by using Matlab Simulink platform. Through this simulation model, dynamic characteristics of fuel cell system including oxygen excess rat io, stack voltage, and system efficiency were shown. In addition to that, we briefly analyzed the humidity effect on cathode pressure and system efficiency, expecting that this model can be further used to optimize fuel cell system parameters just like operating pressure and temperature, humidity and oxygen excess ratio.

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A Study of Optimal Driving Method for Piezoelectric Device Applications (압전소자 응용분야의 최적효율 운전연구)

  • Kim, Yong-Wook;Kim, Dong-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.10
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    • pp.1540-1546
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    • 2017
  • In piezoelectric device applications, it is important to improve a system efficiency because of the low generated power. In this paper, an optimal driving method is proposed to improve a system efficiency for a piezoelectric energy harvesting system. The proposed method considers disappear energy in input capacitors and the converter efficiency according to the input voltage magnitude to minimize energy losses. Experimental results based on various energy generation cases verify that the proposed method significantly improves the system efficiency; the efficiency is approximately 9.97% higher than that of the conventional method.