臺灣博碩士論文加值系統

中文摘要：
本文中以實驗的方式研究一般情況下與外加電場下之結霜現象。在一般情況下，實驗結果顯示環境溫度對霜的發展過程有顯著而重要的影響。當環境溫度高於零度時，結霜的初期水氣以微小的水滴凝結於鰭片表面，在成長過程中伴隨著水滴之間相互的凝聚現象。當環境溫度低於零度時，水氣接觸鰭片表面立即結霜，成長過程則是霜與霜之間的相互擠壓現象。當相互凝聚之小水滴成長到直徑約80 mm時不再彼此合併，不久之後霜長成冰狀的六角型結構，霜層也顯的平滑並且半透明。當環境溫度低於零度時，因為成長過程缺少水滴相互凝聚的現象，霜的結構顯的多變且成不規則之形狀，霜層也較為粗糙。
在電場環境下，霜的結晶受到電極的吸引顯現出細長而脆弱的結構，霜層則相應呈現白色的雪花狀。而此脆弱的結構在霜長到一定長度時因無法承受自身的重量而斷裂並且落下。除此之外，實驗顯示電極的極性也影響到霜的成長。在供給負電時，霜長得較長，成長後接著斷裂的頻率也較高。負電場下的影響比起供給正電時來的活躍。此現象可能是因為在供應負電時dielectric force 與electrostrictive force作用於同一方向，而在供應正電時dielectric force與electrostrictive force作用於相反的方向。

Abstract：
Frost formation above and below the sub-freezing temperature in the presence and the absence of EHD is studied experimentally. In the present study, the mechanism of frost formation is investigated to exhibit a striking dependence on the environmental temperature. For the ambient temperature above the sub-freezing point, the water vapor deposits on the surface in the form of condensate and the ice columns develop with mutual coalescence; otherwise, the frost appears immediately as the moisture attaches to the cold surface and the ice columns develop with mutual squeezing at the early stage of frost formation. The number of droplets increases with the relative humidity but the size of the droplet decreases with it. A hexagonal structure is observed as the droplets grow over a critical size (d > 80 mm). However, for the ambient temperatures below the sub-freezing temperature, the hexagonal structure is not seen because of the lack of droplet coalescence, and the frost structure is comparatively uneven. In the presence of EHD, the ice column is pulled up towards the electrode and has a skinny and fragile structure. The weak structure can be easily broken up and fall down due to the influence of gravity. The electric polarity also affects the frost formation. For a negative polarity, the frost grows more quickly and the break-off frequency of the ice column is higher. It is likely that this phenomenon is related to the same direction of the dielectric force and the electrostrictive force at a negative polarity whereas the opposite direction of the dielectric force and the electrostrictive force at a positive polarity.

CONTENTS：
Chapter 1 Introduction 7
Chapter 2 Literature Review 9
2.1 Frost Accumulation on Plates： 9
2.2 Frost formation with EHD application ： 11
Chapter 3 Experimental Setup 17
3.1 Experimental Setup： 17
3.2 Experimental procedure： 18
Chapter 4 Results and Discussion 29
Chapter 5 Conclusion 43
5.1 Conclusion： 43
5.2 Challenges Encountered： 44
Chapter 6 References 47
Chapter 7 Photographs 50

Chapter 6 References
1. E. U. Okoroafor, M. Newborough, 2000, “Minimizing frost growth on cold surfaces exposed to humid air means of crosslinked hydrophilic polymeric coatings, ”Applied Thermal Engineering, Vol. 20, pp. 737-758.
2. X. M. Wu, Ralph L. Webb, 2001, “Investigation of the possibility of frost release from a cold surface, ”Experimental Thermal and Fluid Science, Vol. 24, pp. 151-156.
3. M. Molki, M. M. Ohadi, M. Bloshteyn, 2000, “Frost Reduction Under Intermittent Electric Field, “Proceedings of NHTC’00 34th National Heat Transfer Conference, Pittsburgh, Pennsylvania, August 20-22.
4. J. S. Marshall, and K. L. S. Gunn, 1957, “A First Experiment on Snow-Crystal Growth,” in Artificial Simulation of Rain (Eds. H. Weickmann and W. Smith), Pergamon Press, New York, pp. 340-345.
5. M. M. Ohadi, N. Sharaf, D. A. nelson, 1991, “Electrohydrodynamic Enhancement of Heat Transfer in a Shell and Tube Heat Exchanger, “ Experimental Heat Transfer, Vol. 4, pp. 19-39.
6. J. T. Bartlett, A. P. Van Den Heuval, B. J. Mason, 1963, “The Growth of Ice Crystals in an Electric Field, “ Zeitschrift Fur Angewandte Mathematik Und Physik, Vol. 14, pp. 599-610.
7. V. J. Schaefer, 1953, “Project Cirrus, “ Final Report, General Electric Research Laboratory, Schenectady, New York, pp. 250.
8. J. Maybank, N. N. Barthakur, 1967, “Growth and Destruction of Ice Filaments in an Electric Field, “ Nature, Vol. 216, pp. 50-52.
9. T. Munakata, A. Yabe, I. Tanasawa, 1993, “Effect of Electric Fields on Frosting Phenomenon, “ The 6th International Symposium on Transport Phenomena in Thermal Engineering, pp. 381-386.
10. A. Yabe, Y. Mori, K. Hijikata, 1978, “EHD study of the Corona Wind between Wire and plate Electrode, “ AIAA Journal, Vol. 16, NO. 4, pp. 340-345.
11. K. G. Libbrecht, V. M. Tanusheva, 1999, “Cloud Chambers and Crystal Growth: Effects of Electrically Enhanced Diffusion on Dendrite Formation from Neutral Molecules, “ Physical Review E, Vol. 59, No. 3, pp. 3253-3261.
12. A. Z. Sahin, 2000, “Effective Thermal Conductivity of Frost During the Crystal Growth Period, “ Int. J. Heat Mass Transfer, Vol. 43, pp. 539-553.
13. Y. X. Tao, R. W. Besant, Y. mao, 1993, “Characteristics of Frost Growth on a Flat Plate During The Early Growth Period, “ ASHRAE Transactions, Vol. 99, pp. 746-753.
14. S. Mishra, A. Gidwani, M. M. Ohadi, and S. Dessiation, 1997, ”An Overview of Basic Models on Frost Formation Phenomenon and Recent Progress on the Use of an Applied Electric Field in Suppressing or Promoting Frost, ” Heat Transfer, AICHE Symposium Series, American Institute of Chemical Engineers, Vol. 93, pp. 197-210.
15. H. W. Schneider, 1978 ”Equation of the growth rate of frost forming on cooled surface, ” Int. J. Heat Mass Transfer, Vol. 21, pp. 1019-1024.
16. D. L. O’Neal, and D. R. Tree, 1985, “A review of frost formation in simple geometries,” ASHRAE Trans, Vol. 91, pp.267-281.
17. N. Yamakawa, N. Takahashi, and S. Ohtani, 1972, “Forced convection heat and mass transfer under frost conditions”, Heat Transfer — Japanese Research, Vol. 1, No. 2, pp. 1-10.
18. R. Ostin, and S. Anderson, 1991, “Frost growth parameters in a forced air stream,” Int. J. Heat Mass Transfer, Vol.34, No.4/5, pp.1009-1017.
19. Y. Mao, R. W. Besant, and K. S. J. Rezkallah, 1992, “Measurement and Correlations of Frost Properties with Air Flow over a Flat Plate,” ASHRAE Transaction, Vol. 98, (2), pp. 65-78.
20. B. W. Jones, and J. D. Parker, 1975, “Frost Formation with Varying Environmental Parameters,” J. Heat Transfer, Vol. 97, pp. 255-259.
21. Y. Hayashi, A. Aoki, S. Adachi, and K. Hori, 1977, “Study of Frost Properties Correlating with Frost Formation Types,” J. Heat Transfer, Vol. 99, pp. 239-245.
22. C. H. Cheng, and C. C. Shiu, “Frost Formation and Frost Crystal Growth on a Cold Plate in Atmospheric Air Flow,” Proceedings of the 18th National conference of the CSME, Taipei, Taiwan, R. O. C., 7-8 December 2001.
23. M. M. Padki, S.A. Sherif, and R. M. Nelson, 1989, “A Simple Method for Modeling the Frost Formation Phenomenon in Different Geometries,” ASHRAE Transaction, Vol. 95, pp. 1127-1137.
24. S. Sherif, S. P. Raju, M. M. Padki, and A. B. Chen, 1993, “A semi-empirical transient method for modeling frost formation on a flat plate,” Int. J. Refrig, Vol. 16, pp. 321-326.
25. M. C. Zaghdoudi, M. Lallemand, 1999 “Analysis of the polarity influence on nucleate pool boiling under a DC electric field”, ASME J. of Heat Transfer, Vol. 121, pp. 856-864.
26. S. R. Fan, Frost Accumulation on Fins in a Low-Temperature Air Flow, M. S. Thesis, National Tsing-Hwa University, Hsinchu, Taiwan, 2002.