臺灣博碩士論文加值系統

本文主要研究螺旋管熱傳系統之熱對流及熵增率分析。研究內容分為螺旋管內之強制對流與螺旋管外自然對流二部分，在強制對流部分，探討之範圍包括入口部分和完全發展部分。所分析的模組涵蓋雷諾數1000至7500、管壁熱通量為160 w/m2、320 w/m2和640 w/m2，曲率比 =0.07、0.11、0.15和0.2等情況。各項流場特性如二次流、溫度分佈、軸向速度、纽塞數和摩擦因子等皆於文中進行分析討論，尤其，螺旋管內之熵增率為重要之探討課題。根據熵增值最小化原理和熱力學第二定律，本文成功的求出在不同操作條件環境之最佳雷諾數與最佳螺旋管徑，在此最佳條件操作下，可使熱傳系統有最小的不可逆性和最佳可用能之利用。在螺旋管外自然對流部分，則探討不同的擺放位置對熱傳係數及熵增值的影響。

In the present paper, the laminar convection and entropy generation in a helical coil with constant wall heat flux are numerically investigated. Both of the entrance region and the fully developed region are included. The studied cases cover a Reynolds number range from 1000 to 7500, and wall heat flux of 160, 320 and 640 w/m and curvature ratio =0.07, 0.11, 0.15, 0.2. The development of the flow fields, including the secondary flow motion, distributions of temperature, Nusselt number and friction factor are given and discussed. In particular, the distributions of the entropy generation rate in the helical coil are especially highlighted. According to the minimum entropy generation principle and the thermodynamic second law, the analysis of the optimal Reynolds number and coiled tube size for the helical coil flow with constant wall heat flux is carried out. The optimal Re and coiled tube size should be chosen as the flow operating condition so that the thermal system could have the least irreversibility and the best exergy utilization. In addition, about the part of natural convection for helical coil, we’re going to study the effects of different angle of inclination positions on the coefficient of heat transfer and entropy generation.

目錄
中文摘要……………………………………………………………………………i
英文摘要……………………………………………………………………………ii
誌謝…………………………………………………………………………………iv
目錄…………………………………………………………………………………v
表目錄………………………………………………………………………………vii
圖目錄………………………………………………………………………………viii
第一章 緒論 ………………………………………………………………………1
1.1前言……………………………………………………………………..1
1.2文獻回顧…………………………………………………….………….1
1.3本文之目的與研究方法………………………………………………..2
1.4本文主要內容…………………………………………………………..3
第二章 理論分析 …………………………………………………………………4
2.1 統御方程式…………………………………………………………….4
2.2 熵增率計算…………………………………………………………….5
2.2.1熱力學第二定律………………………………………………...5
2.2.2熵的性質………………………………………………………...5
2.2.3熵增定理………………………………………………………...6
2.2.4熵的產生………………………………………………………...6
第三章 數值方法 …………………………………………………………………11
3.1 網格系統……………………………………………………………….11
3.2 差分方程式…………………………………………………………….11
3.3 SIMPLEC法則…………………………………………………………11
3.4鬆弛係數與收斂標準…………………………………………………..14
3.4.1 鬆弛係數………………………………………………………..14
3.4.2 收斂標準………………………………………………………..15
第四章 結果與討論 ………………………………………………………………16
4.1 螺旋管內強制對流及熵增分析……………………………………….16
4.1.1 基本參數設定……………………………………….………….16
4.1.2 計算準確度之驗證與格點獨立測試…………………………..17
4.1.3 不同雷諾數之螺旋管內強制對流分析.……………………….19
4.1.3.1 基本模組流場分析……………….………………………..20
4.1.3.2 紐賽數與摩擦因子分析……………………………….…..22
4.1.3.3 熵增值分析………………………………………………...22
4.1.3.4 最佳雷諾數分析……………………………………….…..25
4.1.4螺旋管徑對螺旋管內強制對流及熵增分析..……………….…25
4.1.4.1紐賽數與摩擦因子分析……………………….………...…26
4.1.4.2熵增值分析………………………………….…………...…26
4.1.4.3螺旋管徑對於 與 的效應分析……………………….28
4.1.4.4最佳螺旋管徑分析………………………………...….……30
4.2螺旋管外自然對流及熵增分析……………………………….……….30
4.2.1基本參數設定………………………………………………...31
4.2.2紐塞數及熵增發展分析……………………………………...31
第五章 結論 ………………………………………………………………………34
5.1 結論………………….…………………………………………………34
5.1.1 強制對流討論………………………………………………..34
5.1.2 自然對流討論………………………………………………..36
5.2 建議與未來研究方向….………………………………………………36
參考文獻……………………………………………………………………………76
符號說明……………………………………………………………………………78

參考文獻
[1] T. M. Liou, “Flow visualization and LDV measurement of fully developed laminar flow in helically coiled tubes”, Exp. Fluids, 13, 332-338 (1992).
[2] S. Liu, “Laminar flow and heat transfer in helical pipes with finite pitch”, Ph.D dissertation, University of Alberta, Edmonton, Canada (1992).
[3] S. Liu and J. H. Masliyah, “Axially-invariant laminar flow in helical pipes with a finite pitch”, J. Fluid Mech, 251, 315-353 (1993).
[4] S. A. Berger, L. Talbot, and L. S. Yao, “Flow in curved pipes”, Annual Review of fluid Mechanics, 15, 461-512 (1983).
[5] R. K. Shah and S. D. Joshi, Convective heat transfer in a curved duct, in: S. Kakac, R. K. Shah and W. Aung (Eds), Handbook of Single-Phase Convective Heat Transfer, Chap. 5, Wiley, New York (1987).
[6] R. Manlapaz and S. W. Churchill, “Fully developed laminar convection form a helical coil”, Chem. Eng. Commum, 9, 185-200 (1981).
[7] S. Liu and J. H. Masliyah, “Developing convective heat transfer in helical pipes with finite pitch”, Int. J. Heat and Fluid Flow, 15(1), 66-74 (1994).
[8] C. X. Lin, P. Zhang and M. A. Ebadian, “Laminar forced convection in the entrance region of helical pipes”, Int. J. Heat Mass Transfer, 40(14), 3293-3304 (1997).
[9] A. Narasimha, M. Sen, and H. C. Chang, “Heat transfer enhancement in coiled tubes by chaotic mixing”, Int. J. Heat Mass Transfer, 35(10), 2475-2489 (1992).
[10] Mohamed E. Ali, “Experimental investigation of natural convection from vertical helical coiled tubes. “, Int. J. Heat Mass Transfer, 17, 4, 665-671, (1994).
[11] Mohamed E. Ali, “Laminar natural convection from constant heat flux helical coiled tubes. “, Int. J. Heat Mass Transfer, 41, 14, 2175-2182, (1998).
[12] A. Bejan, Entropy Generation Minimization. CRC Press, Boca Raton, FL (1996).
[13] A. Bejan, Entropy Generation Through Heat and Fluid Flow. Wiley, New York (1982).
[14] P. K. Nag and K. Naresh, “Second law optimization of convection heat transfer through a duct with constant heat flux”, Int. J. Energy Research, 13, 537-543 (1989).
[15] A. Z. Sahin, “Irreversibilities in various duct geometries with constant wall heat flux and laminar flow”, Energy, 23(6), 465-473 (1998).
[16] A. Z. Sahin, “Thermodynamics of laminar viscous flow through a duct subjected to constant heat flux”, Energy, 21(12), 1179-1187 (1996).
[17] S. Z. Shuja, “Optimal fin geometry based on exergoeconomic analysis for a pin-fin array with application to electronics cooling”, Exergy, 2, 248-258 (2002).
[18] S.V. Partankar, Numerical Heat Transfer and Fluid Flow, Hemisphere, Washington, D. C. (1980).
[19] J. P. Van Doormaal and G. D. Raithby, “Enhancements of the SIMPLE method for Predicting Incompressible Fluids Flows”, Numerical Heat Transfer, 7, 147-163, 1984.
[20] J. H. Lienhard, A Heat Transfer Textbook, Prentice-Hall, Inc., Englewood Cliffs, N. J., p. 315 (1981)
[21] Larry R. Austin and J. D. Seader, “Entry region for steady viscous flow in coiled circular pipes”, AIChE. J. July, 820-822 (1974).