소형냉동장치에서 단열모세관의 유동특성과 압력강하에 관한 연구 = A Study on Flow Characteristics and PressureDrop of Adiabatic Capillary Tube in SmallRefrigeration System

국문 초록 (Abstract)

본 논문은 균질유동모델을 적용하여 단열모세관내 대체냉매의 유동특
성을 이론적으로 조사하였다. 이 모델은 시뮬레이션 해석에 필요한 기본
적인 질량, 에너지, 운동량 방정식에 근거하고 있다. 또한 마찰인자와 점
성계수 모델을 이용하여 유동특성을 파악하였고, 대체냉매의 열역학 및
열전달 물성치는 시뮬레이션 프로그램을 이용하여 계산하였다. 대체냉매
용 단열모세관내 질량유량, 압력강하, 응축온도, 증발온도, 과냉각도, 관내
경 등은 소형냉동장치에서의 모세관 전체길이에 영향을 준다. 단열모세관
의 길이 예측을 위해 규제대상 R-134a를 사용하는 소형냉동장치에서 대체
냉매를 적용하여 비교・분석하고, 응축온도, 증발온도, 과냉각도, 관내경, 압
력강하, 냉매유량 등의 변화에 따른 단열모세관 길이 예측을 위한 소형냉동
시스템의 유동특성과 압력강하를 비교한 결과 다음과 같은 결론을 얻을
수 있었다.
1. 마찰계수상관식은 Churchill의 상관식이 우수한 성능을 보였다. Lin 등
의 이상마찰승수 모델과 Cicchitti 등의 점성계수 모델이 Churchill의 마찰
계수 모델과 함께 사용되어 실험값을 예측하였다. 각각의 상관식을 조합하
여 계산한 값과 실험값을 비교해 보면 모세관의 길이를 잘 예측한 상관식
조합이 모세관의 유량예측에도 좋은 결과를 보여 주었다.
2. 소형냉동장치에서 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. 소형냉동장치에서 증발온도가 증가할수록 압력차는 감소하게 되지만, 이에
반해 모세관 출구의 건도 감소로 인해 밀도차가 증가하게 되어, 압력차 감소와
밀도차 증가의 상쇄현상으로 인해 이상류영역의 모세관 길이도 일정하나, 과냉
각도가 증가할수록 모세관 입구온도가 감소하여 모세관 입구압력과 모세관 출
구압력 사이의 압력차가 증가하고 모세관 길이는 증가한다는 것을 알 수 있다.
4. 관내경이 클수록 모세관 길이는 증가하고 모세관내의 압력강하가 감소하
며, R-290은 평균 20∼22% 감소하고, R-1234yf는 40%이하로 감소하나
R-1270은 R-134a보다 평균 17∼19% 증가한다는 것을 각각 알 수 있었다.
5. 대체냉매용 단열모세관내 유동특성에 영향을 미치는 응축온도, 증발온
도, 과냉각도, 관내경 등의 인자들에 대해 확인할 수 있었고, 이들 각각의
변수들과 모세관 전체길이에 대한 상관관계를 아래와 같은 비례식으로 정
리할 수 있다.

다국어 초록 (Multilingual Abstract)

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 alternative refrigerant affect
the total length of capillary in the Vapor Compression Refrigeration
System. In order to predict the length of adiabatic capillary which is
the alternative refrigerant expansion device, the alternative refrigerant,
which is an alternative refrigerant in a refrigeration device using a
regulated R-134a, 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's two-phase frictional multiplier model and Cicchitti'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 a small refrigeration system, 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. However, it can be seen that as the
subcooling degree increases, the pressure difference between the
capillary inlet pressure and the capillary outlet pressure increases, and
the capillary length increases.
4. The larger the inner diameter, the longer the capillary length and the lower the pressure drop in the capillary, R290 decreased by
20-22% on average, R1234yf decreased by less than 40%, but R1270
increased by 17-19% on average compared to R-134a, respectively.
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.

목차 (Table of Contents)

• Ⅰ. 서론 ··············································································································· 1
• 1. 연구의 목적 ································································································· 1
• 2. 연구의 방법 및 범위 ················································································· 3
• 3. 논문의 구성 ································································································· 5
• Ⅱ. 이론해석 ······································································································ 7
• 1. 단열모세관 내 유동특성 ··········································································· 7
• 2. 단열모세관 내 유동 지배방정식 ····························································· 9
• 3. 유량예측 상관식 ······················································································· 23
• 4. 냉동사이클의 구성 ··················································································· 27
• Ⅲ. 결과 및 고찰 ···························································································· 41
• 1. 압력강하 ····································································································· 41
• 2. 유동특성 ····································································································· 43
• Ⅳ. 결론 ············································································································· 63
• 참고문헌 ·········································································································· 65
• Abstract ·········································································································· 70