熱交換器隨著工業的進步商業的發展，一直是一個相當重要的設備。在工業生產中，是一種為了實現物料之間熱量傳遞的設備，作為通用工藝設備，有著廣泛的應用，統稱為熱交換器。
本論文利用COMSOL 模擬軟體，利用連續方程式、動量方程式、動能方程式、紊流模式和適當之邊界條件，研究探討螺旋和U型雙重管熱交換器之流體熱傳特性。
T7螺旋雙重管熱交換器管端工作流體R134A冷媒的熱交換方式，熱效率變化0.002，熱效率變化0.001己達到收斂，為螺旋雙重管熱交換器最佳構型熱傳效率。T1~T8螺旋雙重管熱交換器在構型(圈數)相同時，殼端工作流體設置R134A冷媒比管端工作流體設置R134A冷媒之熱傅效率高，所以高溫流體R134A冷媒適合在外側(殼側)，將內側(管側)冷流體包覆的情況，熱傳效率較高。
S7 U型雙重管熱交換器殼端工作流體R134A冷媒的熱交換方式，熱效率變化0.0011，為螺旋雙重管熱交換器最佳構型熱傳效率。S1~S8螺旋雙重管熱交換器在構型(組數)相同時，殼端工作流體設置R134A冷媒比管端工作流體設置R134A冷媒之熱傅效率高，所以高溫流體R134A冷媒適合在外側(殼側)，將內側(管側)冷流體包覆的情況，熱傳效率較高。
U型雙重管熱交換器有較佳的熱傳效率，以同樣熱傳總面積823.74平方公分，6組(S6)和6圈(T6) 雙重管熱交換器比較，U型雙重管熱交換器有增加0.002的熱傳效率，S6 U型雙重管熱交換器熱傳效率0.9927和T7螺旋雙重管熱交換器熱傳效率0.9920略大0.0007，但熱傳總面積少137.29平方公分，相對使用材料比較省，所以S6 U型雙重管熱交換器為研究最佳雙重管熱交換器構型。

Heat exchangers have always been important devices for advancements and developments in industrial and commercial activities. In industrial production, heat exchangers have a wide scope of applications and are a type of universal technological equipment designed to achieve heat transfer between materials.
In this study, COMSOL simulation software was employed and continuity equations, momentum equations, kinetic equations, turbulent models, and appropriate boundary conditions were adopted to investigate the heat transfer characteristics of fluids in helical-coil and U-shaped double tube heat exchangers.
In the T7 helical-coil double tube heat exchanger with R134A refrigerant at the tube end, convergence was not attained as the change in thermal efficiency was 0.002; however, in the T7 helical-coil double tube heat exchanger with R134A refrigerant at the shell end, convergence was attained as the change in thermal efficiency was 0.001. This configuration had the best heat transfer efficiency for helical-coil double tube heat exchangers. When the T1 to T8 helical-coil double tube heat exchangers had an equal number of turns, the working fluid R134A had a higher heat transfer efficiency when it was placed at the shell end than when it was placed at the tube end. Therefore, it is suitable for high-temperature R134A refrigerant to flow through the exterior (shell-side) which covers the cooling fluid flowing through the interior (tube-side), so as to achieve a higher heat transfer efficiency.
In the S7 U-shaped double tube heat exchanger with R134A refrigerant at the shell end, convergence was attained as the change in thermal efficiency was 0.0011. This configuration had the best heat transfer efficiency for U-shaped double tube heat exchangers. For an equal number of segments in the S1 to S8 U-shaped double tube heat exchangers, the working fluid R134A had a higher heat transfer efficiency when it was placed at the shell end than when it was placed at the tube end. Therefore, it is suitable for high-temperature R134A refrigerant to be flowed through the exterior (shell-side) which covers the cooling fluid flowing through the interior (tube-side), so as to achieve a higher heat transfer efficiency.
The U-shaped double tube heat exchangers had better heat transfer efficiencies. At equal heat transfer areas of 823.74 cm2 and at equal numbers of turns/segments (six), the S6 U-shaped double tube heat exchanger enhanced its heat transfer efficiency by 0.002. In other words, it achieved a heat transfer efficiency of 0.9927, which was slightly greater (by 0.0007) than the T7 helical-coil double tube exchanger’s heat transfer efficiency, which was 0.9920. However, the S6 exchanger’s total heat-transfer area was 137.29 cm2 less and the material cost was comparably lower; hence, the S6 U-shaped double tube heat exchanger was the optimal type of heat exchanger in this study.

摘要 I
ABSTRACT III
Acknowledgements VI
Table of Contents VII
List of Tables X
List of Figures XI
Symbols XII
Greek symbols XIV
Chapter 1 Introduction 1
1.1 Foreword 1
1.2 Research background 3
1.3 Research motivations and objectives 4
1.4 Thesis framework 6
Chapter 2 Basic principles, historical development, literature review, and types of heat exchangers 8
2.1 Basic principles 8
2.2 Historical development of heat exchangers 10
2.3 Literature review regarding spiral heat exchangers 14
2.4 Types of heat exchangers 19
2.4.1 Classification of heat exchangers 20
2.4.2 Regenerative Heat Exchangers 21
2.4.3 mixer-heat exchanger 23
2.4.4 Differential wall heat exchanger 24
Chapter 3 Physical models and numerical methods 37
3.1 Physical models and basic assumptions 37
3.2 Governing equations 49
3.3 Numerical simulation procedure 52
3.3.1 Pre-processing 53
3.3.2 Solution process 54
3.3.3 Post-processing 55
3.4 Boundary conditions specification 56
3.4.1 Helical-coil double tube heat exchanger 56
3.4.1.1 R134 refrigerant at tube-side, cooling water at shell-side 56
3.4.1.2 R134 refrigerant at shell-side, cooling water at tube-side 57
3.4.2 U-shaped double tube heat exchanger 58
3.4.2.1 R134 refrigerant at tube-side, cooling water at shell-side 58
3.4.2.2 R134 refrigerant at shell-side, cooling water at tube-side 59
3.5 Mesh generation 60
Chapter 4 Results and discussion 71
4.1 Flow field thermal distribution of helical-coil double tube heat exchanger 71
4.1.1 Analysis of heat transfer efficiency of R134 refrigerant at tube-side, cooling water at shell-side 72
4.1.2 Analysis of heat transfer efficiency of R134 refrigerant at shell-side, cooling water at tube-side 82
4.2 Flow field thermal distribution of U-shaped double tube heat exchanger 93
4.2.1 Analysis of heat transfer efficiency of R134 refrigerant at tube-side, cooling water at shell-side 94
4.2.2 Analysis of heat transfer efficiency of R134 refrigerant at shell-side, cooling water at tube-side 103
Chapter 5 Conclusion and recommendations 115
References 118

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