착상조건에서 핀관 열교환기의 성능 해석 = Study on the Performance Analysis of Fin-tube Heat Exchangers under Frosting Conditions

다국어 초록 (Multilingual Abstract)

Experimentation and computer modeling were carried out to investigate the performance characteristics of fin-tube heat exchangers under frost conditions. As humid air passes over an evaporator coil that is below the freezing point, water condenses onto the evaporator coil surface. Moisture molecules migrate to the frosted surface and the void portion of frost layer leads to frost growth and densification of frost layer. Frost layer acts as an insulation layer between the fins and the air. In addition, the frost blocks airflow path, causing an increase in pressure drop and a decrease in airflow rate. Numerous experimental and theoretical investigations on frosting have been performed and reported, but most researches on frost formation have been focused on simple geometries such as flat plates and round tubes. Due to complex geometry of fin-tube heat exchangers and diversity of operating variables, a further study is required to design optimum heat exchanger, achieving both uniform frost distribution and delay of frost formation.
In this study, the correlations of heat transfer coefficient and friction factors for various geometries, such as the continuous and discrete flat plate finned tubes, were developed as a function of operating conditions and geometric parameters of fin-tube heat exchangers. An analytical model under frost conditions was developed using the correlations from experimental results. Computer simulations with the variation of operating conditions and geometry of fin-tube heat exchangers were performed to find out the optimal design parameters of fin-tube heat exchangers.
The developed analytical model predicted the decreasing rate of heat exchanger performance within 10% compared to the experimental results. The decreasing rate of air flow rate ratio and heat transfer rate ratio become higher at high inlet air temperatures, and relatively high humidity. Despite the same trend of frost growth rate, each driving fan had different tendency of air flow rate ratio due to its characteristic curve. R600a as an alternative refrigerant of R134a for commercial refrigeration system showed the same performance at a smaller flow rate compared to the existing system. There was a great difference in the frosting performance whether there was pipe heater or not. Smaller tube diameter had a small decreasing rate of air flow rate ratio.

Keywords : Frosting, Fin-tube heat exchanger, Heat transfer coefficient, Friction factor.

목차 (Table of Contents)

• Contents
• Abstract
• List of Tables
• List of Figures
• Nomenclauture
• 제 1 장 서 론
• 1.1 연구배경
• 1.2 연구동향
• 1.3 연구목적 및 연구내용
• 제 2 장 실험장치 및 방법
• 2.1 실험장치의 구성
• 2.2 시험부
• 2.3 실험조건
• 2.4 실험방법
• 2.4.1 온도측정
• 2.4.2 풍량측정
• 2.4.3 서리두께측정
• 2.4.4 노점측정
• 2.4.5 상대습도 조절
• 2.5 실험 관계식
• 제 3 장 착상조건에서 열전달 및 압력강하 상관식 개발
• 3.1 상관식의 데이터베이스(Database)
• 3.2 착상조건에서 공기측 압력강하 상관식
• 3.3 착상조건에서 공기측 열전달 상관식
• 3.4 상관식의 검증
• 3.4.1 일체형핀의 공기측 열전달 및 압력강하 상관식
• 3.4.2 독립핀의 공기측 열전달 및 압력강하 상관식
• 3.4.3 열교환기 형상 변화에 따른 착상 성능 비교
• 제 4 장 핀관 열교환기의 착상 성능해석 모델링
• 4.1 서리성장 모델링
• 4.2 핀관 열교환기 열량계산
• 4.2.1 직교류 배열(Cross-flow arrangment)에서 관의 열전달
• 4.2.2 핀관 열교환기에서의 총괄 열전달계수
• 4.3 핀관 열교환기의 실험상관식
• 4.3.1 공기측 상관식
• 4.3.2 냉매측 상관식
• 4.4 착상조건에서 열교환기 성능해석 프로그램
• 4.4.1 관순법
• 4.4.2 프로그램 계산순서
• 제 5 장 결과 및 토의
• 5.1 시뮬레이션 검증
• 5.2 해석을 이용한 운전변수에 따른 착상 성능 고찰
• 5.2.1 입구온도의 영향
• 5.2.2 상대습도의 영향
• 5.2.3 풍량의 영향
• 5.2.4 냉매 종류의 영향
• 5.3 해석을 이용한 열교환기 형상 변화에 따른 착상 성능 고찰
• 5.3.1 제상코일의 영향
• 5.3.2 냉매관경의 영향
• 제 6 장 결 론
• 6.1 실험 상관식의 개발
• 6.2 해석을 이용한 핀관 열교환기의 착상 성능 고찰
• 6.2.1 운전변수 변화에 따른 고찰
• 6.2.2 열교환기 형상 변화에 따른 고찰
• 참고문헌