두 개의 다른 증발온도를 가지는 이단압축 이산화탄소 사이클의 해석적 연구

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HCFC, which is widely used as a cooling agent in air conditioning systems is subject to international regulation regarding environmental pollution, global warming and ozone depletion. Among the alternatives, environment-friendly carbon dioxide generates a lot of interest because of its good compatibility with used materials and media and high production capacity. However, the refrigerant has many other thermodynamic characteristics compared with the existing subcritical cycle, which are cooling in supercritical region and high pressure operation of the system. Therefore, supercritical carbon dioxide system must improve the system performance, safety and reliability in order to compete with the existing subcritical system or replace previous used HVAC systems.
Generally, performance capacity of a heat pump using carbon dioxide is lower than that of subcritical refrigeration system because of large irreversibility during compression and gas cooling. Moreover, system reliability is rather low because of strong performance variation for variable outdoor temperature. For using in commercial refrigeration systems, system performance reliability must be improved. For CO2 heat pump the use of two-stage compression cycle offers the best means to this end. In earlier studies, performance research of the CO2 cycle has been mainly performed for a single-stage compression cycle using analytical methods. Only few studies have considered CO2 systems with two-stage compression cycle. Therefore, it is very important to analyze performance characteristics of the two-stage CO2 compression cycle with differential temperature evaporators and find out optimal operating pressure and mass distribution.
In this study, the performance characteristics of a two-stage CO2 system with two-different evaporator temperature have been analyzed according to outdoor air temperature, outdoor air velocity, and 2nd-stage EEV opening in order to increase the better understanding of the thermodynamic characteristics of the CO2 cycle. Through the verification of evaporator model with frost growth, the frost growth with time shows a similar trends under same frost surface temperature condition. Beside, the variation of cooling capacity of the present model has the similar one of other studies. As a result of simulation on performance of two-stage compression cycle, the cooling COP decreases by 22.9%, 16.1%, 18.9%, and 19.4% for 0%, -10%, -20%, and -30% of non-frost cooling capacity, respectively, when outdoor temperature increases. When the air velocity increases, the cooling COP improves by 9%, 9.2%, 7%, and 7.1% for 0%, -10%, -20%, and -30% of non-frost cooling capacity. Besides, the system has the maximum cooling COP for –10%, -20% of non-frost cooling capacity when the 2nd-stage EEV opening is 56%. Maximum cooling COP for –30% of non-frost cooling capacity has 1.003 when the 2nd-stage EEV opening is 52%.
Alternative Title
Analysis Study of a Two-stage Compression CO2 Cycle with Two Different Temperature Evaporators
Alternative Author(s)
Shin, Eunsung
조선대학교 기계공학과 대학원 신재생에너지실험실
일반대학원 기계공학과
Awarded Date
Table Of Contents
Contents ⅰ
List of figures ⅲ
List of tables ⅴ
Nomenclature ⅵ

제 1 장 서 론 1
제 1 절 연구 배경 1
제 2 절 국내·외 연구 동향 4
제 3 절 본 연구의 목적 7

제 2 장 두 개의 다른 증발온도를 가지는 이단압축 이산화탄소 사이클 모델링 09
제 1 절 압축기(compressor) 모델링 12
제 2 절 가스쿨러(gascooler) 모델링 14
1. 냉매측 열전달상관식 19
2. 공기측 열전달상관식 21
제 3 절 증발기(evaporator) 모델링 22
1. 고온측 증발기 상관식 25
2. 저온측 증발기 상관식 37
제 4 절 EEV(electronic expansion valve) 모델링 38
제 5 절 플래시(flash) 및 믹서(mixer) 탱크 모델링 39
제 3 장 해석 방법 및 조건 40
제 1 절 사이클 해석 방법 40
제 2 절 서리성장에 따른 증발기 성능해석 조건 42
제 3 절 두 개의 다른 증발온도를 가지는 이단압축 이산화탄소 사이클 성능해석 조건 43

제 4 장 결과 및 고찰 45
제 1 절 서리성장에 따른 증발기 성능예측 모델 검증 45
1. Xia and Jacobi(2010)에 대한 증발기 검증 45
2. Moallem 등(2012)에 대한 증발기 검증 50
제 2 절 두 개의 다른 증발온도를 가지는 이단압축 이산화탄소 사이클 성능에 대한 고찰 54
1. 서리성장에 따른 사이클 성능특성 54
2. 실외온도 변화에 따른 사이클 성능특성 60
3. 실외 공기의 풍속 변화에 따른 사이클 성능특성 67
4. 고단측 EEV 개도 변화에 따른 사이클 성능특성 73

제 5 장 결 론 79

조선대학교 대학원
신은성. (2012). 두 개의 다른 증발온도를 가지는 이단압축 이산화탄소 사이클의 해석적 연구.
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