• 한국수소및신에너지학회논문집
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• 제33권4호
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• pp.419-429
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• 2022

Effects of operating variables on temperature profile and performance of 3 MWth chemical looping combustion system were estimated by mass and energy balance analysis based on configuration and dimension of the system determined by design tool. Air reactor gas velocity, fuel reactor gas velocity, solid circulation rate, and solid input percentage to fluidized bed heat exchanger were considered as representative operating variables. Overall heat output and oxygen concentration in the exhaust gas from the air reactor increased but temperature difference decreased as air reactor gas velocity increased. Overall heat output, required solid circulation rate, and temperature difference increased as fuel reactor gas velocity increased. However, overall heat output and temperature difference decreased as solid circulation rate increased. Temperature difference decreased as solid circulation rate through the fluidized bed heat exchanger increased. Effect of each variables on temperature profile and performance can be determined and these results will be helpful to determine operating range of each variable.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.278-281
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• 2009

소형 정찰 UAV의 새로운 동력원으로 적용하고자 하는 연료전지 시스템의 경량화를 위한 연구로 알루미늄 분리판의 성능을 측정하였다. 흑연 분리판과의 성능 비교를 통해 알루미늄 분리판이 흑연 분리판에 비해 무게 대비 높은 성능을 보이는 것을 확인하였다. 작동온도에 따른 성능 변화를 확인하기 위해 40 / 50 / $60^{\circ}C$의 작동온도에서 알루미늄 단위 전지의 성능을 측정한 결과 건조한 반응기체의 경우 일반적인 작동온도 보다 비교적 낮은 $40^{\circ}C$에서 가장 좋은 성능을 보이는 것을 확인하였다.

• 동력기계공학회지
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• 제16권5호
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• pp.55-62
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• 2012

Centrifugal compressors are widely used and each operating condition is different. However, it cannot be manufactured according to the every operating condition. In the this study, performance of compressor was evaluated with various rotational speeds of impeller and various stagger angles of diffuser in order to apply a typical model widely. A centrifugal compressor was designed and manufactured based on the design point. On this machines, an experiment was conducted and the performance was predicted at off-design point. The performance prediction was validated with the experimental result and the numerical result. Although the isentropic efficiency on the prediction was slightly lower than that on the experimental result due to the heat loss in the experiment, the pressure ratio was predicted well and also the predicted results were matched well with the numerical results. When the rotational speed of the impeller and the stagger angle of the diffuser were changed together, the compressor can be worked in the high efficiency region and avoided operating in the stall region.

• 설비공학논문집
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• 제23권7호
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• pp.505-512
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• 2011

Recently, many researchers have analyzed the performance of the transcritical $CO_2$ refrigeration cycle in order to identify opportunities to improve the system energy efficiency. The reduction of the expansion process losses is one of the key issues to improve the efficiency of the transcritical $CO_2$ refrigeration cycle. In this study, the analytical study on the performance characteristics of $CO_2$ cycle with an ejector carried out with a variation of outdoor temperature, gascooler inlet air velocity, evaporator inlet air velocity, and evaporator inlet air temperature. As a result, the system performance could be improved over 85% by using an ejector for various operating condition because of the reduction of compressor work. Moreover, the cooling capacity increased about 18% for variable outdoor condition. Therefore, the high performance of an ejector system could be maintained for wide operating conditions and system reliability could be improved compared to that of a basic system.

• 한국정보통신학회논문지
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• 제7권8호
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• pp.1726-1731
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• 2003

인터넷을 통해서 침입하는 해커나 침입자로부터 기관의 내부 정보시스템을 보호하기 위하여 침입 차단 시스템(firewall)의 사용이 보편화되고 있다. 하지만 사용자 입장에서는 침입 차단 시스템의 성능을 확인 할 수 없을 뿐 아니라, 동작 모드(브리지 모드(Bridge Mode), 게이트웨이 모드(Gateway Mode))에 따른 성능 차이를 알 수 없다. 이러한 문제를 해결하기 위하여 본 논문에서는 침입 차단 시스템의 운영체제(Windows 2000, Linux, FreeBSD) 환경에 따른 성능을 분석하였다. 끝으로 FreeBSD 커널 기반의 침입 차단 시스템을 서로 다른 동작 모드에서 성능을 비교하고 침입 차단 정책 수가 성능에 미치는 영향에 대하여 분석하였다.

• 설비공학논문집
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• 제17권6호
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• pp.552-559
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• 2005

This paper describes an experimental study on the inertance pulse tube refrigerator using a small compressor. The purpose of this experimental study is to identify the performance of the inertance pulse tube refrigerator for various operating conditions and to obtain the optimum configuration. The dead volume effect is verified by two experimental apparatuses with different dead volumes between the compressor and the aftercooler. The refrigerator of the smaller dead volume shows better performance. The influence of operating frequency and charging pressure on the performance of the refrigerator is experimentally investigated. Reducing the regenerator mesh size improves the performance of the refrigerator. Finally, the inertance pulse tube refrigerator has maximum cooling capacity at the specific combination of the pulse tube length and the inertance tube length. The loss analysis is used to analyze and predict the optimum condition of the pulse tube refrigerator.

• 한국수소및신에너지학회논문집
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• 제33권4호
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• pp.363-371
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• 2022

In this study, the operation characteristics of the internal reforming type molten carbonate fuel cell (MCFC) were studied using computational fluid dynamics (CFD) analysis according to the steam to carbon ratio (S/C ratio), operating temperature, and gas utilization. From the simulation results, the distribution of gas composition due to the electrochemical reaction and the reforming reaction was predicted. The internal reforming type showed a lower temperature difference than the external reforming type MCFC. As the operating temperature decreased, less hydrogen was produced and the performance of the fuel cell also decreased. As the gas utilization rate decreased, more gas was injected into the same reaction area, and thus the performance of the fuel cell increased.

• 한국콘텐츠학회논문지
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• 제14권1호
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• pp.318-325
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• 2014

본 연구는 국세청에서 공시한 2012년도 공공의료원의 손익계산서 분석을 통해 이익 측면에서의 공공의료원의 경영 분석에 대해 살펴보고자 한 것이다. 국세청에 공시된 2012년 공공의료원의 재무제표 총 38건의 손익계산서 중 중복된 자료를 제외하고 매출액, 매출원가, 판매비와 관리비의 구분 표기가 가능한 자료를 추출하여 최종 22건의 자료를 이용하였다. 분석에는 의료이익, 공헌이익, 매출액 추세를 이용하였다. 공공의료원의 의료이익을 분석한 결과 22개 공공의료원의 평균 의료이익은 손실로 -4,678.9백만 원이었고, 평균공헌이익은 12,572.5백만 원, 매출이 증가한 의료원의 평균 매출 증가액은 1,299.1백만 원이었다. 결과적으로 공공의료원의 의료이익은 손실이나 공헌이익이 발생하고 있고, 아울러 약 2/3의 의료원에서 매출액 증가 추이를 보이는 바 개별 의료원 차원만을 고려한 경영 의사결정 시에는 신중한 접근이 필요하며, 공공의료원이 전국에 지역별 거점 기관의 성격으로 개설되어 있는 국가 공공의료망의 일부라는 측면에서 전사적 차원, 즉 국가적 차원에서의 경영분석과 판단이 이루어져야 함을 제안한다.

• Journal of Biosystems Engineering
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• 제39권2호
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• pp.69-75
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• 2014

Purpose: This paper is aimed at analyzing the heating performance of the vertical closed loop type Geothermal Heat Pump System (GHPS) distributing the farm site and providing basic data of the GHPS. Method: Seedling greenhouse heating was made from October 2012 to May 2013. The seedling greenhouse was divided into 4 sectors (A, B, C and D zone, total $3,300m^2$) with different temperatures. It was heated from 5PM to 8AM, and during the night the greenhouse was covered by non-woven fabric thermal curtains along the upper 2m of the greenhouse for temperature maintenance. In order to analyze the heating performance of the GHPS, power consumption and operating time of the GHPS, inlet and outlet water temperature of the condenser, temperatures of each zone of the greenhouse, and ambient temperature were measured. Results: When operating only one heat pump unit, heat generated in the condenser decreased as the experiment progressed and power consumption increased correspondingly. However, the heating coefficient of performance decreased from 3.3 to 2.0 rapidly. Also, when operating two heat pump units, heat generated in the condenser decreased and power consumption increased. Heating coefficient of performance decreased from 4.5 to 3.7 rapidly. When the set temperature of the greenhouse was $13.7{\sim}20.1^{\circ}C$ and minimum ambient temperature was $-20.8{\sim}4.8^{\circ}C$, the annually accumulated heat and power consumption were 520,623 kW, 142,304 kW, respectively. Conclusion: When the set temperature of the greenhouse was $13.7{\sim}20.1^{\circ}C$ and the minimum ambient temperature was $20.8{\sim}4.8^{\circ}C$, the annually accumulated heat and power consumption were 520,623 kW, 142,304 kW, respectively. When operating only one heat pump unit, the heating COP was 2.0~3.3, and when operating 2 heat pump units, it was 3.7~4.5. If several heat pumps are installed in one GHPS, it is suggested that all heat pumps be operated except in special cases. Because the scale of the water pumps are set to the scale of when all heat pump units are operating, if even one unit is not operating, the power consumption will increase. That becomes the cause of COP decrease.

• ETRI Journal
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• 제42권4호
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• pp.505-517
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• 2020

The increasing size and complexity of deep neural networks (DNNs) necessitate the development of efficient high-performance accelerators. An efficient memory structure and operating scheme provide an intuitive solution for high-performance accelerators along with dataflow control. Furthermore, the processing of various neural networks (NNs) requires a flexible memory architecture, programmable control scheme, and automated optimizations. We first propose an efficient architecture with flexibility while operating at a high frequency despite the large memory and PE-array sizes. We then improve the efficiency and usability of our architecture by automating the optimization algorithm. The experimental results show that the architecture increases the data reuse; a diagonal write path improves the performance by 1.44× on average across a wide range of NNs. The automated optimizations significantly enhance the performance from 3.8× to 14.79× and further provide usability. Therefore, automating the optimization as well as designing an efficient architecture is critical to realizing high-performance DNN accelerators.