• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.191-196
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• 2010

Hybrid heat pumps, which combine the vapor compression and absorption heat pump cycle, can efficiently produce hot water of $80^{\circ}-90^{\circ}C$ from the low temperature of ${\sim}50^{\circ}C$. In this study, the performance of a two-stage hybrid heat pump (HHP) was compared with a single-stage hybrid heat pump using EES (Engineering Equation Solver). For the same operating conditions, the two-stage HHP showed a slightly higher COP (Coefficient Of Performance) and more stable operating conditions than the single-stage HHP. Moreover, the maximum working fluid temperature of the two-stage HHP was found to be lower than that of the single-stage HHP by about 40 K, which makes the working conditions of the lubricating oil safer. The COPs of both systems decreased with increasing UA-values. However, the heat output of the HHP was increased at the same time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.139-145
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• 2002

이륙중량 4000kg, 10-12인승급 다목적 헬리콥터에 적용가능한 엔진 개량 개발을 목표로 기존 헬리콥터 엔진을 개량대상으로 선정하고 이러한 다목적 헬기의 요구조건에 부합하기 위해 기존 엔진의 요소부품을 재설계하였다. 첫 단계로 최소변경으로 720 hp에서 840 hp로 출력을 증강시키기 위하여 2단 축류압축기의 기존 입구 유도익을 제거하고 익현의 길이를 증가하여 유량 및 압축비를 증가시킴으로써 출력 증강을 얻도록 재설계를 수행하였다. 이러한 2단 축류압축기의 성능을 검증하기 위하여 두 번째 단 단독시험 및 전체 2단에 대한 성능시험이 수행되었으며 첫 번째 단의 성능은 이 결과로부터 도출되었다. 성능시험결과 전체 2단 압축기는 유량 3.088 kg/s에서 압력비 2.14, 단열효율 88%의 성능을 갖는 것으로 나타났으며 압축기 출구의 압력 및 온도 분포를 레이크를 이용하여 측정하였다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.4
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• pp.301-306
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• 2011

The paper presents an analysis of the heating cycle and discusses a desalination cycle that uses lowtemperature seawater. The basic heating cycle model is the heat pump cycle, and seawater desalination is usually performed by the indirect freezing desalination method. The low temperature of the seawater (below $5^{\circ}C$) acts as the heat source of the evaporator. R-134a, R-1234yf, R-600a are used as working fluids. In the 2-stage compression cycle, the compressor's work decreased by about 15.6% from that in the 1-stage compression cycle. Further, the COP in the 2-stage cycle was 17.6% higher than that in the 1-stage cycle. In the indirect desalination cycle, the energy per unit fresh water productivity in the 2-stage cycle was 19.8% lower than that in the 1-stage cycle.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.42-47
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• 2012

In this paper, alternative natural refrigerant R290(Propane), R600(Butane), R717(Ammonia), R1270(Propylene) for freon refrigerant R22 were used working fluids for 2-stage compression and 1-stage expansion refrigeration system. The operating parameters considered in this study included evaporation temperature, condensation temperature, subcooling degree, superheating degree, mass flow rate ratio of inter-cooler. The main results were summarized as follows : The COP of 2-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling degree and mass flow rate ration of inter-cooler, but decreases with the increasing evaporating temperature, condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of 2-stage compression and 1-stage expansion refrigeration system using natural refrigerants have an effect on COP of this system. The COP of natural refrigerants was higher than the COP of freon R22 in this study, so points to be considered are the security, the attached facilities for natural refrigerants than COP.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.3327-3335
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• 2014

In this study, comparison works have been performed for single-stage and multi-stage refrigeration cycle using propane as a refrigerant in order to cool down the natural gas stream. A comparative analysis has been performed for a single, two, three and four stage refrigeration cycle using propane as a refrigerant for cooling the natural gas stream. For the simulation, natural gas feedstock properties supplied by KOGAS were utilized and Peng-Robinson equation of state model was used. As the number of compression stages increase, the condenser heat duty is decreased. The refrigeration heat duty for a four-stage refrigeration cycle is decreased by 20.36% compared to that for a single-stage refrigeration cycle. Moreover, the total refrigerant circulation rate for a four-stage refrigeration system is was reduced by 14.53% compared to the single stage refrigeration cycle. The total compression power for a four-stage compression was reduced by 41.61% compared to the single stage compression.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.625-631
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• 2014

In order to obtain a low evaporation temperature ranging from $-30^{\circ}C{\sim}-50^{\circ}C$, a cascade refrigeration system and two-stage compression one-stage expansion refrigeration system is required. However, the research results of performance comparison of these refrigeration system are very scarce. This paper were compared the performance characteristics of R744-R404A cascade refrigeration system and R404A two-stage compression refrigeration system. The COP of R404A two-stage compression refrigeration system is about 36~57% greater than that of R744-R404A cascade refrigeration system in the range of evaporation temperature of $-30^{\circ}C{\sim}-50^{\circ}C$. But R404A two-stage compression refrigeration system is unstable because COP is significantly changed when evaporating temperature and compressor efficiency decreased. In particular, when compressor efficiency decreased, COP is significantly decreased. In this case, not efficient for long-term use. Whereas R744-R404A cascade refrigeration system using natural refrigerants. Therefore, it is environmentally friendly. And this system is high-efficiency refrigeration system. The reason it can be configured by selecting the suitable refrigerant at high-temperature side and low-temperature side. From the above results, select the appropriate low temperature refrigeration system by considering the environmental and performance aspects.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.106.1-106.1
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• 2005

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2022.11a
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• pp.116-118
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• 2022

MPEG-VCM(Video Coding for Machine)은 입력된 이미지/비디오의 특징(feature)를 압축하는 Track 1 과 입력 이미지/비디오를 직접 압축하는 Track 2 로 나뉘어 표준화가 진행 중이다. 본 논문은 Track 1 의 비전임무 네트워크로 사용하는 Detectron2 의 FPN(Feature Pyramid Network)에서 추출한 멀티-스케일 특징을 효율적으로 압축하는 MSFC 기반의 압축 모델의 개선 기법을 제시한다. 제안기법은 해상도를 줄여서 단일-스케일 압축맵을 압축하는 기존의 압축 모델에서 저해상도 특징맵을 고해상도 특징맵에 바텀-업(Bottom-Up) 구조로 합성하여 단일-스케일 특징맵을 구성하는 바텀-업 MSFF 를 가지는 압축 모델을 제시한다. 제안방법은 기존의 모델 보다 BPP-mAP 성능에서 1 ~ 2.7%의 개선된 BD-rate 성능을 보이며 VCM 의 이미지 앵커(image anchor) 대비 최대 -85.94%의 BD-rate 성능향상을 보인다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.341-344
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• 2009

본 연구에서는 허브 대 팁의 비가 큰 원심형 압축기의 성능시험을 수행하였으며, 이를 수치해석 결과와 비교하였다. 압력비의 경우 작동 회전수에서 성능시험과 수치해석의 결과의 경향이 일치하는 것을 확인하였다. 성능시험에서 임펠러의 성능은 매우 높게 나타났으나, 1단 및 2단 디퓨져에서 손실이 발생하여 전체적인 압력비 및 효율이 떨어지는 것을 확인하였다. 수치해석을 통해 내부 유동장을 확인한 결과 1단 디퓨져 및 2단 디스월러에서 격렬한 2차 유동으로 인한 유로차폐효과가 주 손실원인임을 확인하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.8
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• pp.3106-3111
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• 2010

In this study, a comparative study was performed between one- and two-stage refrigeration system to cool the natural gas temperature down to $-40^{\circ}C$ using propane as a chilling medium. As a thermodynamic model, Peng-Robinson equation of state equation was applied and PRO/II with PROVISION release 8.3 at Invensys company was utilized for the simulation of the refrigeration system. Through this study, optimization work showed that two-stage refrigeration system was proven to save about 33.5% refrigeration power consumption compared to the one-stage refrigeration cycle.