• 해양환경안전학회지
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• 제26권7호
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• pp.915-921
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• 2020

연소실 내 공조현상으로 인해 발생되는 열음향 불안정성은 안정적인 연소시스템을 구현하기 위해 해결해야 하는 고질적인 문제로 제기되어 왔다. 열음향 불안정성은 크게 1차 2차 열음향 불안정성으로 나뉘며, 본 연구에서는 열음향 불안정성 중 2차 열음향 불안정성의 천이에 관해 열손실이 미치는 영향에 대한 실험적 연구를 진행하였다. 2차 열음향 불안정성을 발생시키기 위해 한쪽 끝이 열린 1/4 파장 공명기를 채택하여 수직으로 설치하였고, 공명기 내부에는 예혼합 가스를 주입하였다. 또한 공명기 상단으로 발생하는 열손실 효과를 비교하기 위해 추가적으로 외부 동축류 관을 설치하였다. 연료 농후조건의 예혼합 가스만을 채택하여 주입하였기 때문에 동축관에 주입되는 기체에 따라 공명기 상부에 추가적인 확산화염이 형성될 수 있다. 그 결과 확산화염이 발생되었을 경우 공명기 상단으로의 열손실이 감소하며 2차 열음향 불안정성이 발현되었으며, 확산화염이 억제되어 공명기 상단으로의 열손실이 증가하였을 경우 2차 열음향 불안정성의 발현이 억제되는 결과를 도출하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제3권1호
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• pp.64-68
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• 2001

An experimental study on the Joule-Thomson cryocooler with the mixed refrigerant (MR) is described in this paper, J-T refrigeration experiment was performed with a single stage regular air-conditioning compressor The mixed refrigerant in the experiment was composed of 75% mol fraction of $N_2$. 30% moi fraction of CH$_4$. 30% moi fraction of $C_2$H$_{6}$. 10% mot fraction of $C_3$H$_{8}$ and 15% mot fraction of iso-C$_4$H$_{10}$. Oil mist in the MR stream could be eliminated completely by the glass microfiber filter. Since a single stage compressor that had been designed thor R22 is not appropriate for high Pressure ratio of the mixed refrigerant especially during the transient period. two modifications were incorporated to regular J-T refrigeration cycle. First. a Portion of the MR was by-passed at the inlet of the heat exchanger and transferred directly to 7he suction of the compressor in the modified system. Second, a buffer volume was Prepared to change the mass flow rate of refrigerant. The pressure ratio in J-T expansion device was relieved at the beginning of the operation due to the by-Pass scheme. but it gradually decreased during the transient Process as some of the MR component condensed at low temperature. The buffer volume at the suction side was used to increase the MR gas density in the system after the transient cool-down period. Form the experiment with the modified system, the refrigerator could reach the lowest temperature of -152$^{\circ}C$ without cooling load. and about -15$0^{\circ}C$ with 5 W of cooling load . . . .

• 한국기계가공학회지
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• 제5권2호
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• pp.49-55
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• 2006

In the consideration of the problem occurred by certain return bender brazing welding works that depend only on handworks, the automatization of the whole production line is impossible due to the high dependency of skillful workers. In addition, it is difficult to establish a standardization due to the various heat exchanger model and irregular amount of orders, and the fault reduction is also impossible due to the severe difference in brazing conditions. It is necessary to develop a method, which quantitively analyzes the problem existed in this manual brazing welding of return benders and technically solves that problem, and to lead the improvement of the productivity and cost reduction in order to increase the business competitive power. Then, this will contribute the technical development of automatic welding for Korea's heat exchanger businesses. Thus, this study develops an automatic technology, which automatically controls the flame strength using digital control methods, for various models and produces a sample model. It is possible to increase the productivity and produce uniformed and qualified products by solving the problem existed in manual processes using the developed automatic return bender brazing system. In addition, the brazing condition can be automatically controlled according to the model and line speed, and such an economical operation can reduce the production cost. The developed system is expected to future applications not only heat exchangers in the field of refrigeration and air conditioning, but also other various industrial fields that apply heat exchangers, such as car and boiler industries.

• International Journal of Internet, Broadcasting and Communication
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• 제12권2호
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• pp.1-7
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• 2020

The secure access the lighting, Heating, ventilation, and air conditioning (HVAC), fire safety, and security control boxes of building facilities is the primary objective of future smart buildings. This paper proposes an authorized user access to the electrical, lighting, fire safety, and security control boxes in the smart building, by using color grid coded optical camera communication (OCC) with face recognition Technologies. The existing CCTV subsystem can be used as the face recognition security subsystem for the proposed approach. At the same time a smart device attached camera can used as an OCC receiver of color grid code for user access authentication data sent by the control boxes to proceed authorization. This proposed approach allows increasing an authorization control reliability and highly secured authentication on accessing building facility infrastructure. The result of color grid code sequence received by the unauthorized person and his face identification allows getting good results in security and gaining effectiveness of accessing building facility infrastructure. The proposed concept uses the encoded user access authentication information through control box monitor and the smart device application which detect and decode the color grid coded informations combinations and then send user through the smart building network to building management system for authentication verification in combination with the facial features that gives a high protection level. The proposed concept is implemented on testbed model and experiment results verified for the secured user authentication in real-time.

• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.138-145
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• 2012

Because of the climate changes and the development of building technologies, the cooling loads have been increased. Among the various renewable energies, geothermal energy is known as very useful and stable energy for heating and cooling of building. This study proposes a road snow-melting system of which heat is supplied from GSHP(Ground source heat pump) in viewpoint of the initial investment and annual running performance, which is also operating as a main facility of heating and cooling for common spaces. The results of this study is as followings. From the site measurement, it is found out that the road surface temperature above the geothermal heating pipe rose up to $5^{\circ}C$, which is the design temperature of road snow-melting, after 2 hours' operation and average COP(Coefficient of performance) was estimated as 3.5. The reliability of CFD has confirmed, because the temperature difference between results of CFD analysis and site measurement is only ${\pm}0.4^{\circ}C$ and the trend of temperature variation is quite similar. CFD analysis on the effect of pavement materials clearly show that more than 2 hours is needed for snow-melting, if the road is paved by ascon or concrete. But the road paved by brick is not reached to $5^{\circ}C$ at all. To evaluate the feasibility of snow-melting system operated by a geothermal circulation which has not GSHP, the surface temperature of concrete-paved road rise up to $0^{\circ}C$ after 2 hour and 40 minutes, and it does never increase to $5^{\circ}C$. And the roads paved by ascon and brick is maintained as below $0^{\circ}C$ after 12 hours geothermal circulation.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.136-141
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• 2009

The platform screen door(PSD) is installed in the station of the Seoul Metro 9th line for passengers' safety and comfortable environment of the station. The track way exhaust system(TES) is also operated with PSD to exhaust heat released from train. TES can also be used for the purpose of the heat and smoke control in an emergency case of the carriage fire. When the fire is occurred, operation of TES is switched to the smoke exhaust mode form its normal ventilation mode. In the present study, a subway station of Seoul Metro 9th line is modeled, and a 3-D CFD simulation is performed to investigate effectiveness of designed TES in case of fire. A scenario that a train under fire is arriving the station is simulated for several possible operation modes of the TES using moving mesh technique. As a result, temperature and CO concentration distribution in the station is obtained for each operation modes of TES. The effectiveness of TES operation in case of fire is also discussed.

• 한국소음진동공학회논문집
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• 제16권9호
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• pp.897-903
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• 2006

The reduction of the vehicle interior noise has been the main interest of noise and vibration harshness (NVH) engineers. The driver's perception on the vehicle noise is affected largely by psychoacoustic characteristic of the noise as well as the SPL. In particular, the heating, ventilation and air conditioning (HVAC) system sound among the vehicle interior noise has been reflected sensitively in psychoacoustics view point. Even though the HVAC noise is not louder than overall noise level, it clearly affects subjective perception to drivers in the way of making to be nervous or annoyed. Therefore, these days a vehicle engineer takes aim at developing sound quality as well as reduction of noise. In this paper, we acquired noises in the HVAC from many vehicles. Through the objective and subjective sound quality (SQ) evaluation with acquiring noises recorded by the vehicle HVAC system, the simple and multiple regression models were obtained for the subjective evaluation 'Pleasant' using the semantic differential method (SDM). The regression procedure also allows you to produce diagnostic statistics to evaluate the regression estimates including appropriation and accuracy. Furthermore, the neural network (NN) model were obtained using three inputs(loudness, sharpness and roughness) of the SQ metrics and one output(subjective 'Pleasant'). Because human's perception is very complex and hard to estimate their pattern, we used NN model. The estimated models were compared with correlations between output indexes of SQ and hearing test results for verification data 'Pleasant'. As a result of application of the SQ indexes, the NN model was shown with the largest correlation of SQ indexes and we found possibilities to predict the SQ metrics.

• Architectural research
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• 제17권3호
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• pp.109-115
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• 2015

The dynamic pricing of electricity, where the electricity rate increases in a time zone with a high demand for electricity is typically applied to a building whose power reception capacity is greater than a certain size. This includes the time of use(TOU) electricity pricing in Korea which can induce the effect of reducing the power demand of a building. Meanwhile, a VRF (Variable Refrigerant Flow) system that uses electricity is regarded as one of the typical heating and cooling systems along with central air conditioning (central HVAC) for its easy operation and application to the building. Thus, to reduce power energy and operating costs of a building in which the TOU and VRF systems are applied simultaneously, we suggested a control for changing the indoor temperature setting within the thermal comfort range or limiting the rotational speed of an inverter compressor. In this study, to describe the features of the above-mentioned control and verify its effects, we evaluated the results obtained from the analysis of its operation data. Through the actual measurements in winter operations for 73 days since mid- December 2014, we confirmed a reduction of 10.9% in power energy consumption and 12.2% in operating costs by the new control. Also, a reduction of 13.3% in power energy consumption was identified through a regression analysis.

• 한국건설관리학회논문집
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• 제6권2호
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• pp.129-138
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• 2005

본 연구는 LCC 기법을 이용한 냉 $\cdot$ 난방 공조설비 시스템에 대하여 사업 실행전 LCC와 사업 실행후 LCC를 예측, 성과측정 및 경제성 평가를 목적으로 진행되었다. 이를 위해 신기술 냉 $\cdot$난방 공조설비 시스템의 Life Cycle동안의 비용자료를 실적자료와 견적자료, 인터뷰등의 방법으로 조사 $\cdot$ 분석하였다. 또한 분석기간 15년 동안의 사업 실행전 $\cdot$ 후의 LCC를 예측하여 성과측정 및 경제성 평가를 실시하였다. 이와 같은 과정을 통해 수행된 본 연구의 결과는 다음과 같다: 1)일체형 개별냉 $\cdot$난방공조설비의 설치로 인해 할인비용시 $21.6\%$의 경제성이 있는 것으로 분석되었다. 3)성과측정은 투자대비 회수배율로서 할인비용시 회수배율은 신축의 경우 4.8배, 리모델링의 경우 14.4배의 경제성이 있는 것으로 분석되었다.

• 한국산학기술학회논문지
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• 제10권9호
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• pp.2195-2201
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• 2009

본 논문은 R290, R600a, R1270과 같은 탄화수소계 냉매를 사용하는 냉동사이클의 효율에 대한 흡입관 열교환기의 영향을 고려하였다. 이러한 흡입관 열교환기는 냉동시스템의 성능을 향상시킬 수도 있지만, 성능을 저하시킬 수도 있다. 본 논문에서는 흡입관 열교환기를 가진 냉동사이클의 성능 특성을 파악하기 위해서 정상상태의 수학적 모델을 사용하였다. 그리고 탄화수소계 냉매유량, 흡입관 열교환기의 내관 직경, 길이, 유용도 등과 같은 운전조건의 영향을 분석하였다. 연구결과는 흡입관 열교환기의 내관 직경, 길이, 유용도, 탄화수소계 냉매의 질량유량은 냉동사이클의 상대냉동능력지수, 냉동능력, 압축일량에 영향을 미치는 것을 알 수 있었다. 따라서 이러한 영향을 상세히 파악하여, 흡입관 열교환기를 설치한 탄화수소계 냉매용 증기압축식 냉동사이클을 설계할 필요가 있다.