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	Visual and theoretical analyses of the early stage of frost formation on cold surfaces
	Wu, Xiaomin ; Dai, Wantian ; Shan, Xiaofeng ; Wang, Weicheng ; Tang, Liming
	2010-05-10 ; 2010-05-10
会议名称	JOURNAL OF ENHANCED HEAT TRANSFER ; 13th International Heat Transfer Conference ; Sydney, AUSTRALIA ; Web of Science
关键词	frost formation hydrophobic surface supercooled droplets nucleation rate GROWTH PLATE FLOW AIR Thermodynamics Engineering, Mechanical
中文摘要	Meso-scale visual observations were conducted to investigate the process of frost formation on both bare and hydrophobic coated copper surfaces, which had contact angles of 560 and 110 degrees. The experiments were carried out for -20-0 degrees C surface temperatures, 19-22 degrees C ambient air temperatures, and 15-85% relative humidities. The tests showed that the frost formation on cold surfaces was not a simple process of transition from steam directly to frost, but actually followed five steps: the formation of condensate droplets, droplet growth including coalescence of the supercooled droplets, freezing of the droplets, formation of initial frost crystals on the frozen droplets, and growth of frost crystals accompanied by collapse of some of the crystals. Compared to the bare copper surface, the hydrophobic surface had a sparser distribution of condensate droplets but larger droplet sizes, delayed droplet freezing and frost formation, and a smaller frost height, all of which support the observation that the hydrophobic surface retards frost formation and growth. The frosting phenomenon was also analyzed theoretically. The initial vapor condensation before frosting was explained based on the free energies for nucleation. For condensation of steam on cold surfaces below 0 degrees C, the Gibbs free energy barrier for water nuclei is smaller than that for ice nuclei, so condensate droplets appear before frost on cold surfaces. Further, since the hydrophobic surface has a higher Gibbs free energy barrier for nucleation than the bare surface, the droplets form more readily on the bare surface.
会议录出版者	BEGELL HOUSE INC ; REDDING ; 50 CROSS HIGHWAY, REDDING, CT 06896 USA
语种	英语 ; 英语
内容类型	会议论文
源URL	[http://hdl.handle.net/123456789/19682]
专题	清华大学
推荐引用方式 GB/T 7714	Wu, Xiaomin,Dai, Wantian,Shan, Xiaofeng,et al. Visual and theoretical analyses of the early stage of frost formation on cold surfaces[C]. 见:JOURNAL OF ENHANCED HEAT TRANSFER, 13th International Heat Transfer Conference, Sydney, AUSTRALIA, Web of Science.

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