• Advances in Energy Research
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• 제8권1호
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• pp.21-39
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• 2022

In this study, the first law of thermodynamics was used to establish a one-dimensional (1-D) thermal model for parabolic trough receiver (PTR) taking into account the pressure drop and kinetic energy loss effects of the heat transfer fluid (HTF) flowing inside the absorber tube. The validation of the thermal model with data from the SEGS-LS2 solar collector-test showed a good agreement, which is consistent with the previously established models for the conventional straight and smooth (CSS) receiver where the effects of pressure drop and kinetic energy loss were neglected. Based on the developed model and code, a comparative study of the newly designed parabolic trough S-curved receiver versus the CSS receiver was conducted and solar unit's performances were analyzed. Without any supplementary devices, the S-curved receiver enhances the performance of the parabolic trough module, with a maximum of 0.16% compared to CSS receiver with the same sizes and mass flow rates. Thermal losses were reduced by 7% due to the decrease in the temperature of the outer surface of the receiver tube. In addition, it has been shown that from a mass flow rate of 9.5 kg/s the heat losses of the S-curved receiver remain unchanged despite the improvement in the heat transfer rate.

• Advances in Energy Research
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• 제5권3호
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• pp.227-237
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• 2017

The continuous increase of emission rates of green house gases and the effects on global warming added a new dimension to the problem of substituting the petroleum and its derivatives by environment friendly and sustainable energy sources for the world. Solar and wind energy appear at the top of the list of renewable of high potential, widely available, of dominated technology and well accepted. Brazil is one of the few countries in the world that receives number hours of sunshine exceeding 3,000 hours per year with a daily average of 4.5 to 6 kWh. However, this potential is largely unexplored and poorly tapped. The number of renewable systems implanted in Brazil has grown in recent years, but still insignificant when compared, for example, with Germany and Spain among others. This paper presents the results of an optical study on small concentration solar collector with evacuated tube enveloping the absorber and internal reflective surface fixed on the bottom part of the evacuated tube. The designed collector has a 2D geometrical concentration ratio between 2.455 and 4.91. The orientation of the solar collector, the ratio of the radius of the receiver to the radius of the absorber, the incidence angle for each period of the year, the collector inclination angle, the aperture angle of the reflective surface, concentration and optical efficiency were determined. The ray traces and flux distribution on the absorber of the evacuated tube solar collector were determined by using the program Ray Optics Simulation. The optical efficiency varies during the year according to the solar declination. For the periods were the solar declination is close to zero the efficiencies are maximum, and the variation during the day is around 25.88% and 99.9%. For the periods were the solar declination is maximum the efficiencies are minimum, and the variation during the day is around 23.78% and 91.79%.

• 태양에너지
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• 제20권3호
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• pp.61-73
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• 2000

Heat losses from receivers for a dish-type solar energy collecting system are numerically investigated. The analytical method for predicting conductive heat loss from a cavity receiver is used. The Stine and McDonald Model is used to estimate convective heat loss. Two kinds of techniques for the radiation analysis are used. The Net Radiation Method that is based on the radiation heat balance on the surface is used to calculate the radiation heat transfer rate from the inside surface of the cavity receiver to the environment. The Monte-Carlo Method that is the statistical approach is adopted to predict the radiation heat transfer rate from the reflector to the receiver. Based on the heat loss analysis, the performance of two different receivers for multifaceted parabolic solar collectors with several flat facets can be estimated, and the optimal facet size is obtained.

• Journal of Mechanical Science and Technology
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• 제17권8호
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• pp.1185-1195
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• 2003

Heat losses from the receivers of a dish-type solar energy collecting system at the Korea Institute of Energy Research (KIER) are numerically investigated. It is assumed that a number of flat square mirrors are arranged on the parabolic dish structure to serve as a reflector. Two different types of receivers, which have conical and dome shapes, are considered for the system, and several modes of heat losses from the receivers are thoroughly studied. Using the Stine and McDonald model convective heat loss from a receiver is estimated. The Net Radiation Method is used to calculate the radiation heat transfer rate by emission from the inside surface of the cavity receiver to the environment. The Monte-Carlo Method is used to predict the radiation heat transfer rate from the reflector to the receiver. Tracing the photons generated, the reflection loss from the receivers can be estimated. The radiative heat flux distribution produced by a multifaceted parabolic concentrator on the focal plane is estimated using the cone optics method. Also, the solar radiation spillage around the aperture is calculated. Based on the results of the analysis, the performances of two different receivers with multifaceted parabolic solar energy collectors are evaluated.

• 한국정보과학회논문지:정보통신
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• 제29권5호
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• pp.482-494
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• 2002

최근 등장한 메일 기반의 계좌이체 시스템은 송금인이 수금인의 계좌번호를 알 필요 없이 메일 주소만 알면 계좌 이체가 가능하도록 하여 사용자에게 많은 편의를 제공한다. 그러나 대부분의 메일기반 계좌이체 시스템은 SSL 기반으로 동작하고 있어 거래 사실에 대한 부인이 가능하고, 영수증 발급이 불가능하다는 문제점이 있다. 이에 따라 이 논문에서는 기밀성, 무결성, 사용자 인증, 부인 봉쇄 둥의 보안 서비스를 제공하고 인증서 기반으로 동작하는 국제 표준 메일 보안 메커니즘인 S/MIME을 적용한 메일 기반의 지불 메커니즘을 제안한다. 이 메커니즘에서는 'Check'라는 수표와 같은 역할을 하는 메시지를 통해 모든 계좌이체 정보가 송금인과 수금인 및 메일 결제 서버 사이에서 전달된다. 이 시스템은 기존의 시스템과 마찬가지로 수금인의 메일 주소만 알면 계좌이체가 가능한 편리성을 제공함과 동시에 S/MIME에 기반한 보안 서비스를 제공함으로서 기존 지불 시스템에서 가장 문제가 되는 송신 부인 문제를 해결하고 영수증 발급도 가능하다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 하계학술발표대회 논문집
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• pp.169-169
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• 2007

• 태양에너지
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• 제12권1호
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• pp.88-94
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• 1992

태양광 고온가스가열 장치를 위하여 후레넬렌즈면적 $0.5m^2$을 갖는 소형태양집열 및 추적시스템과 고급의 소형 밀폐형 유동층 태양광 수열기를 개발하였다. 개발된 태양광 수열기는 개방형 유동층의 단점인 SiC입자의 유출과 열사이폰효과를 개선하였다. 공기의 최대 도달온도는 1140K이며, 최대 열효율은 64%얻어졌다. 본 연구에서 개발한 태양광수열기는 기존의 평판이나 관형의 고체표면을 갖는 태양 집열기와 비교할 때 아주 고온에서 효율 좋게 작동된다.

• 한국전자파학회논문지
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• 제22권7호
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• pp.729-736
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• 2011

본 논문은 X-대역에서 바랙터 다이오드가 없는 전압 제어 발진기 구조를 제안하고, 마이크로웨이브 레이더 신호 감지용 수신기에 적용 가능성을 확인하였다. 부성 저항을 발생하는 능동 소자의 콜렉터-베이스 PN-접합으로 바랙터 다이오드를 대체하여, 단일 RF BJT 소자로 전압 제어 발진기를 구현하여 수신기에서 요구하는 튜닝 전압 1.0~7.0 V에서 11.20~11.75 GHz 주파수 가변 특성, 9.0~12.0 dBm 출력 전력 및 선형적인 주파수 튜닝 특성을 만족하였다.

• Journal of Positioning, Navigation, and Timing
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• 제4권4호
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• pp.173-180
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• 2015

In this study, an algorithm that detects a spoofing signal for a GPS L1 signal was proposed, and the performance was verified through RF spoofing signal simulation. The proposed algorithm determines the reception of a spoofing signal by detecting a correlation distortion of GPS L1 C/A code caused by the spoofing signal. To detect the correlation distortion, a detection criterion of a spoofing signal was derived from the relationship among the Early, Prompt, and Late tap correlation values of a receiver correlator; and a detection threshold was calculated from the false alarm probability of spoofing signal detection. In this study, an RF spoofing environment was built using the GSS 8000 simulator (Spirent). For the RF spoofing signal generated from the simulator, the RF spoofing environment was verified using the commercial receiver DL-V3 (Novatel Inc.). To verify the performance of the proposed algorithm, the RF signal was stored as IF band data using a USRP signal collector (NI) so that the data could be processed by a CNU software receiver (software defined radio). For the performance of the proposed algorithm, results were obtained using the correlation value of the software receiver, and the performance was verified through the detection of a spoofing signal and the detection time of a spoofing signal.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2198-2204
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• 2003

In order to make a match of the insufficient direct solar radiation, in this study, the target output is lowered to 9 kW smaller than 25 kW in former studies. It is also necessary to match the collector/receiver with engine/generator systems to accomplish the power level of a system. The simulation analyses of a dish solar power system with stirling engine are totally carried out to predict the system performance with the designed values. In addition, an influence of direct solar radiation on system performance and operation control is discussed in simulation. It is found that the diameter of concentrator could be made small to 8 m regardless of slope errors with 2.5 and 5.0 mrad radiation, and the operation range of mean pressure control. is wide even if the direct solar radiation is a quit low.