증기압축식 냉동장치에서 팽창장치인 단열모세관의 유동특성과 길이 선정에 관한 연구 :A study on flow characteristics and length selection of adiabatic capillary tube on expansion devices in vapor compression refrigeration system

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자료유형: 학위논문

저자정보: 임원택 (동명대학교, 동명대학교 대학원)

지도교수: 구학근

발행연도: 2020

저작권: 동명대학교 논문은 저작권에 의해 보호받습니다.

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2020

증기압축식 냉동장치에서 팽창장치인 단열모세관의 유동특성과 길이 선정에 관한 연구

임원택 기계시스템공학과 2020.01 학위논문

2019

자연냉매용 소형냉동장치에서의 단열모세관 길이 예측

임원택 한국기계기술학회지 2019.01 학술저널

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본 논문은 균질유동모델을 적용하여 단열모세관내 자연냉매의 유동특성을 이론적으로 조사하였다. 이 모델은 시뮬레이션 해석에 필요한 기본적인 연속, 에너지, 질량 운동량 방정식에 근거하고 있다. 또한 마찰인자와 점성계수 모델을 이용하여 유동특성을 파악하였고, 자연냉매의 열역학 및 열전달 물성치는 EES 물성치 코드를 이용하여 계산하였다. 자연냉매용 단열모세관내 질량유량, 압력강하, 응축온도, 증발온도, 과냉각도, 관내경 등은 증기압축식 냉동장치에서의 모세관 전체길이에 영향을 준다. 자연냉매용 팽창장치인 단열모세관의 길이 예측을 위해 규제대상 R134a를 사용하는 증기압축식 냉동장치에서 대체냉매인 자연냉매 등을 적용하여 비교?분석하고, 질량유량, 압력강하, 응축온도, 증발온도, 과냉각도, 관내경 등의 변화에 따른 단열모세관 길이 예측하여 시스템의 성능특성을 실험적으로 비교한 결과 다음과 같은 결론을 얻을 수 있었다.
1. 마찰계수상관식은 Churchill의 상관식이 우수한 성능을 보였다. Lin et al의 이상마찰승수 모델과 Cicchitti et al의 점성계수 모델이 Churchill의 마찰계수 모델과 함께 사용되어 실험값을 예측하였다. 각각의 상관식을 조합하여 계산한 값과 실험값을 비교해 보면 모세관의 길이를 잘 예측한 상관식 조합이 모세관의 유량예측에도 좋은 결과를 보여 주었다.
2. 모세관 관경이 1.0㎜인 증기압축식 냉동장치에서 응축온도가 증가할수록 모세관 입구압력과 모세관 출구압력 사이의 압력차가 증가하기 때문에 모세관 길이가 증가한다는 것을 알 수 있었고 응축온도가 일정한 경우, 모세관 입구압력과 모세관 출구압력 사이의 압력차가 일정하여 냉매유량이 감소할수록 모세관 길이는 증가한다는 것을 알 수 있다.
3. 모세관 관경이 1.0㎜인 증기압축식 냉동장치에서 증발온도가 증가할수록 압력차는 감소하게 되지만, 이에 반해 모세관 출구의 건도 감소로 인해 밀도차가 증가하게 되어, 압력차 감소와 밀도차 증가의 상쇄현상으로 인해 이상류 영역의 모세관 길이도 일정하게 된다는 것을 알 수 있다.
4. 모세관 관경이 1.0㎜인 증기압축식 냉동장치에서 과냉각도 변화에 따른 모세관 길이를 비교한 결과 과냉각도가 증가할수록 모세관 입구온도가 감소하여 모세관 입구압력과 모세관 출구압력 사이의 압력차가 증가하고 모세관 길이는증가한다는 것을 알 수 있다.
5. 자연냉매용 단열모세관내 유동특성에 영향을 미치는 응축온도, 증발온도, 과냉각도, 관내경 등의 인자들에 대해 확인할 수 있었고, 이들 각각의 변수들과 모세관 전체길이에 대한 상관관계를 아래와 같은 비례식으로 정리할 수 있다.
6. 모세관 길이가 1.0m일 때 단열모세관의 관내경 변화에 따른 자연냉매인 R1270과 R290의 COP는 전 실험범위에서 R134a에 비해 높게 나타났고, R1234yf와 R600a의 COP는 R134a보다는 낮게 나타났으나 자연냉매인 R1270과 R290는 성능계수 측면에서 충분히 R134a를 대체할 수 있을 것으로 판단된다.

In this study, the flow characteristics of natural refrigerants in an adiabatic capillary tube were theoretically investigated by applying the homogeneous flow model. The model is based on fundamental equations of mass, energy and momentum that are necessary for simulation analysis. In addition, the flow characteristics were identified using the model of friction factor and viscosity coefficient, and the thermodynamic and heat transport properties of the natural refrigerant were calculated using the EES(Engineering Equation Solver) code. Condensation temperature, evaporation temperature, subcooling degree, pipe diameter, superheat degree, mass flow, and pressure drop in adiabatic capillary for natural refrigerant affect the total length of capillary in the Vapor Compression Refrigeration System. In order to predict the length of adiabatic capillary which is a natural refrigerant expansion device, the natural refrigerant, which is an alternative refrigerant in a refrigeration device using a regulated R134a, was used for comparison and analysis. and condensing temperature and evaporating temperature. As a result of experimentally comparing the performance characteristics of the system by estimating the length of adiabatic capillary due to the change of condensing temperature, evaporating temperature, subcooling degree, inner diameter tube, superheating degree, mass flow and pressure drop, the following conclusions were obtained.
1. Friction factor correlation showed that Churchill''s correlation was excellent. Lin et al.''s. two-phase frictional multiplier model and Cicchitti et al.''s. Viscosity model were used in conjunction with Churchill''s coefficient of friction model to predict the experimental values. Comparing the experimental results with the values calculated by combining the correlations, the combination of well predicted capillary lengths also showed the good results for the flow rate prediction of the capillaries.
2. It was found that the capillary length increases because the pressure difference between the capillary inlet pressure and the capillary outlet pressure increases as the condensation temperature increases. It can be seen that the pressure difference between the pressure and the capillary outlet pressure is constant, so that the capillary length increases as the refrigerant flow rate decreases.
3. In the vapor compression refrigeration unit with a capillary tube diameter of 1.0 mm, the pressure difference decreases as the evaporation temperature increases, but the difference in density increases due to the decrease in dryness of the capillary outlet, which offsets the decrease in pressure difference and increase in density difference. As a result, it can be seen that the capillary length of the outflow region is also constant.
4. As a result of comparing the capillary length according to the change of subcooling degree in the small refrigerator with capillary tube diameter 1.0mm, the capillary inlet temperature decreases as the subcooling degree increases, making the pressure difference between capillary inlet pressure and capillary outlet pressure increase, and making the capillary length increase.
5. Factors such as condensation temperature, evaporation temperature, subcooling, degree and inner diameter tube which affect the flow characteristics in the insulating capillaries for natural refrigerants were identified. The correlations between these variables and the total capillary length can be summed up in the following proportional formula.
6. When the capillary length is 1.0m, the COP of natural refrigerant(R1270, R290) according to the capillary diameter change was higher than that of R134a in the entire experimental range, and it is considered that it can sufficiently replace R134a in terms of performance coefficient.

Ⅰ. 서론 ···············································································································1
1. 연구 목적 ·····································································································1
2. 연구의 방법 및 범위 ·················································································3
3. 논문 구성 ·····································································································6
Ⅱ. 이론해석 ······································································································8
1. 모세관내에서의 유동특성 ·········································································8
2. 모세관내에서의 유동 지배방정식 ·························································10
3. 유량예측 상관식 ·······················································································26
4. 냉동사이클 모델 ·······················································································31
Ⅲ. 실험장치 및 방법 ···················································································44
1. 실험장치 ·····································································································44
2. 실험방법 ·····································································································46
Ⅳ. 결과 및 고찰 ····························································································49
1. 유동특성 ·····································································································49
2. 냉동능력의 변화 ·······················································································93
3. 압축일량의 영향 ·······················································································94
4. 성능계수 ·····································································································95
Ⅴ. 결론 ·············································································································98
참고문헌 ········································································································100
Abstract ········································································································106

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