코일이 揷入된 水平圓管內의 强制對流 熱傳達 特性에 關한 硏究 = (A) Study on the Forced Convection Heat Transfer in Coil ribbed Horizontal Tubes

다국어 초록 (Multilingual Abstract)

The need for high performance thermal systems has stimulated research interest in methods to augment heat transfer. Single-phase heat transfer coefficients can be artificially increased by modifying the surface of the tube - roughened surface, extended surface, inlet vortex generator, swirl flow devices. These methods enhance convective heat transfer by introducing swirl into the bulk flow or periodic disruption of the boundary layer at the tube surface due to repeated changes in the surface geometry.
However, The increase in heat transfer is accompanied by the increase in the resistance to fluid flow. Many investigators have studied this problem in an attempt to develop accurate predictions of the behavior of a given roughness geometry and to define a geometry which gives the best heat transfer performance for the given flow friction.
This work presents experimental information for single phase turbulent forced convection in coil ribbed circular tubes. Both heat transfer and pressure drop enhancements were observed for a Reynolds numbers of 10,000~40,000. The dimensionless geometric parameters are pitch to height ratio(p/e), efficiency index(η) and the flow attack angle(α). Test section was electrically uniformly heated and the pressure drop accross the test section was obtained by a differential pressure sensor. Before initiating experiments with the coil ribbed circular tubes, the friction factor and heat transfer coefficient were determined for a smooth tube and compared with previous workers results. Experiments are performed for coil ribbed tubes which have different pitch to height ratios(5, 10, and 15). Both the Stanton number and friction factor have a maximun value when the pitch to height ratio of the rib is five. As Reynolds number is increased, the 'efficiency index', η≡ (St/St_(s))/(□/□_(s)) decreases. A performance comparison show that the coil ribbed circular tube with a 15 pitch to height ratio gives higher heat transfer for the same friction power then the others.

목차 (Table of Contents)

• 목차
• ABSTRACT = ⅰ
• LIST OF FIGURES = ⅲ
• NOMENCLATURE = ⅴ
• 제1장 서론 = 1
• 제2장 기존연구검토 = 3
• 제3장 본 연구와 관련된 기초 이론 = 6
• 3.1 열전달 시스템의 최적화 = 6
• 3.2 무차원수 = 6
• 3.3 관내 마찰계수 및 압력강하 = 7
• 3.4 열전달계수 = 9
• 3.5 거친 관과 매끈한 관에서의 성능 비교 = 13
• 제4장 실험 = 15
• 4.1 실험장치 = 15
• 4.2 시험부 = 20
• 4.3 시험부의 압력강하 측정 = 22
• 4.4 시험부의 온도측정 = 25
• 4.5 시험부의 재원 = 27
• 제5장 실험결과 및 고찰 = 29
• 5.1 매끈한 관에서의 열전달 특성 및 마찰손실계수 측정 = 29
• 5.2 코일이 삽입된 관에서의 열전달 특성 및 마찰손실계수 측정 = 35
• 5.3 매끈한 관과 코일이 삽입된 관에서의 열전달계수 및 마찰손실계수 비교 = 41
• 5.4 관내 형상에 따른 열전달 특성 비교 = 47
• 제6장 결론 = 55
• 향후연구과제 = 57
• 참고문헌 = 58
• 감사의글 = 62