Visualization Study of Condensation on Copper Surface
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摘要: 通过建立蒸气冷凝过程的可视化实验装置,在地面重力条件下对蒸气在铜表面的冷凝情况进行实验.采用高速摄像仪对蒸气在铜表面上发生的冷凝过程进行观测,并对比分析了H2O,R141b以及FC-72蒸气的冷凝情况.研究发现水蒸气在冷凝过程中一些大液滴在合并周围小液滴后会发生回弹现象,从而清理掉周边区域的小液滴.随着冷凝的进行,被清理掉小液滴的区域又会重新生成小液滴.这种回弹现象相当于延长了滴状冷凝的时间,从而起到强化冷凝换热效果.R141b及FC-72在光滑铜表面上均未发生滴状冷凝.在加大过冷度后,冷凝器内残留的空气还会在冷凝液膜上冷凝成小水滴,产生滴膜共存现象.水蒸气在铜表面冷凝过程中,滴状冷凝转换成膜状冷凝后热流量降低约20%,因此需要对铜表面进行改性处理,降低其表面能,从而强化冷凝换热.Abstract: In this paper, the visualization experiment device for vapor condensation is established, and vapor condensation on the copper surface is studied by use of the device. Firstly, vapor condensation on the copper surface is observed by using high-speed camera. The condensations of H2O, R141b and FC-72 are analyzed. The observation results show that a rebound phenomenon emerge after small droplets are merged by the nearby large droplets, thus the small droplets around large droplets are cleaned out. As the condensation has progressed, small droplets are regenerated in the region where they are merged. The rebound phenomenon is equivalent to prolong the dropwise condensation time, and accordingly enhance the effect of condensation heat transfer. Dropwise condensation does not occur as R141b and FC-72 condenses on the smooth surface of copper. After increasing the degree of subcooling, the residual air in the condenser condenses into small droplets on the condensation film, and coexistence phenomenon of droplet and liquid film emerge. In the process of water vapor condensing on the copper surface, heat flux decreases about 20% when dropwise condensation turns into film condensation. Therefore, the copper surface should be modified to reduce its surface energy, so as to enhance the condensation heat transfer.
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Key words:
- Normal gravity /
- Condensation /
- Visualization
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[1] YANG Shiming, TAO Wenshuan. Heat Transfer[M]. Beijing: Higher Education Press, 1998:21-31, 209, 211(杨世铭,陶文栓. 传热学. 北京: 高等教育出版社, 1998, 21-31, 209, 211) [2] BURNSIDE B M, HADI H A. Digital computer simulation of dropwise condensation from equilibrium droplet to detectable size[J]. Int. J. Heat Mass Trans., 1999, 42(16):3137-3146 [3] WU Y T, YANG G X, YUAN X G. Drop Distributions and numerical simulation of dropwise condensation heat transfer[J]. Int. J. Heat Mass Trans., 2001, 44(23):4455-4464 [4] WAN Kai, MIN Jingchun. The random distribution characteristics of droplets in dropwise condensation[C]//Proceeding of Heat and Mass Transfer, Chinese Society of Engineering Thermophysics. Beijing: Chinese Society of Engineering Thermophysics, 2003:341-344(万凯,闵敬春. 滴状冷凝中液滴的随机分布特性. 中国工程热物理学会传质传热学学术会议论文集. 北京: 中国工程热物理学会, 2003:341-344) [5] YU L, WASDEN F, DUKLER A E, et al.Non-linear evolution of waves on falling films at high Reynolds num-bers[J].Phys. Fluids , 1995, 7(8):1886-1902 [6] BRAUNER N, MARON D M, ZIJL W.Interfacial collocation equations of thin liquid film: stability analysis[J]. Chem.Eng.Sci., 1987, 42(8):2025-2035 [7] MARSCHALL E, LEE C Y.Stability of condensate flow down a vertical wall[J].Int.J.Heat Mass Trans., 1973, 16:44-48 [8] CHEN Z Q, HERMANSON J C, SHEAR M A, PEDERSEN P C. Ultrasonic monitoring of interfacial motion and growth of condensing and non-condensing liquid film[J]. Flow Meas. Instrum., 2005, 16:353-364 [9] HERMANSON J C, PEDERSEN P C, ALLEN J S, et al. Stability and heat transfer characteristics of condensing films[C]//Sixth Microgravity Fluid Physics and Transport Phenomena Conference. Washington: NASA, 2002 [10] WAYNER J P C. Nucleation, growth and surface movement of a condensing sessile droplet[J]. Colloid. Surf.: A Physicochem. Eng. Asp., 2002, 206(1):157-165
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