Characteristics of Marangoni dynamic condensation modes for water-ethanol mixture vapors on horizontal surface

doi:10.11949/j.issn.0438-1157.20160031

Abstract

Abstract:

An experimental system was designed and built for condensation on a horizontal surface. Using the high-speed camera, the characteristics of Marangoni dynamic condensation modes for water-ethanol mixture vapors was investigated. The influence of initial vapor-to-surface temperature, ethanol vapor concentration and vapor velocity on the condensation modes was obtained. Using the method of edge detection to process the condensation pictures, the variation of maximum droplet radius, which was considered as an important parameter for quantitatively expressing Marangoni condensation modes, was obtained. The results showed that the condensation modes altered dramatically as condensation started. Then, the generation, merging and growing process of droplets could be observed until the condensation modes nearly kept constant. The order of magnitudes for the droplets growth time was about 10 s. On the beginning of condensation, when the initial vapor-to-surface temperature was high, filmwise and dropwise condensations were all on the surface. The number of droplets increased with the decrease of initial vapor-to-surface temperature. With the initial vapor-to-surface temperature kept decreasing, the surface would be covered by many small droplets. When the initial vapor-to-surface temperature decreased and ethanol vapor concentration increased, the droplets growth time would be longer, the droplets would grow slower. By contrast, the growth of droplets was slightly affected by vapor velocity. The maximum droplet radius increased during the condensation process and it would increase from 2 mm to more than 10 mm. At the same condensation time, the maximum droplet radius increased with the increase of initial vapor-to-surface temperature and decrease of ethanol vapor concentration.

Key words: codensation, surface, condensation modes, binary mixture, maximum droplet radius

摘要：

设计搭建了水平表面上凝结实验系统，利用高速摄像机对水-酒精混合蒸气Marangoni瞬态凝结过程的凝结形态进行观察记录，获得了初始过冷度、酒精蒸气浓度及蒸气流速对凝结形态的影响规律。采用图像边缘提取技术对凝结图像进行处理，统计得到了作为定量表征Marangoni凝结形态参数之一的最大液珠半径的变化规律。研究结果表明：凝结开始的一段时间内凝结形态变化剧烈，液珠经历形成、合并及逐渐长大的过程，最终凝结形态基本保持不变，液珠成长时间数量级约为10 s。在凝结的初始阶段，当过冷度较大时，膜状凝结与珠状凝结同时存在于凝结表面；随着过冷度降低，小液珠数目增多；过冷度继续降低，凝结面全部被大量小液珠所覆盖。随着初始过冷度降低、酒精蒸气浓度增高，凝结液珠成长时间增长，液珠的生长速度变慢。蒸气流速对液珠的成长过程影响相对不明显。随着凝结进行，最大液珠半径从2 mm增大到10 mm的数量级；同一凝结时刻，随着初始过冷度增加、酒精蒸气浓度降低，最大液珠半径逐渐增大。

关键词: 凝结, 表面, 凝结形态, 二元混合物, 最大液珠半径

CLC Number:

TK124

CHEN Nana, WANG Jinshi, LI Yong, XIA Kai, YAN Junjie. Characteristics of Marangoni dynamic condensation modes for water-ethanol mixture vapors on horizontal surface[J]. CIESC Journal, 2016, 67(9): 3574-3582.

陈娜娜, 王进仕, 李勇, 夏凯, 严俊杰. 水平表面水-酒精混合蒸气Marangoni瞬态凝结过程的凝结液形态[J]. 化工学报, 2016, 67(9): 3574-3582.

References 24

[1]	杨世铭, 陶文铨. 传热学[M]. 北京:高等教育出版社, 1998. YANG S M, TAO W Q. Heat Transfer Theory[M]. Beijing:Higher Eduction Press, 1998.
[2]	施明恒, 甘永平. 沸腾和凝结[M]. 北京:高等教育出版社, 1995. SHI M H, GAN Y P. Boiling and Condensation[M]. Beijing:Higher Eduction Press, 1995.
[3]	IRKOVICH V V, MISSEN R W. Non-filmwise condensation of binary vapors of miscible liquids[J]. The Canadian Journal of Chemical Engineering, 1961, 39(2):86-87.
[4]	HIJIKATA K, FUKASAKU Y, NAKABEPPU O. Theoretical and experimental studies on the pseudo-dropwise condensation of a binary vapor mixture[J]. Journal of Heat Transfer, Transactions of ASME, 1996, 118(1):140-147.
[5]	FUJⅡ T, KOYAMA S, NDIWALANA N M, et al. Experimental study of gravity controlled condensation of binary vapor mixtures on a smooth horizontal tube[C]//Proceedings of the 9th International Heat Transfer Conference, Washington, DC:1990, 3:109-114.
[6]	FUJⅡ T, KOYAMA S, NISHIDA S. Expressions of physical properties concerning condensation of ethanol-water-air mixture:reports of Research Institute of Industrial Science[R]. Kyushu University, 1983:63-76.
[7]	FUJⅡ T, KOYAMA S, SHIMIZU Y. Gravity controlled condensation of an ethanol and water mixture on a horizontal tube[J]. Trans. Jpn. Soc. Mech. Eng. (Series B), 1989, 55(509):210-215.
[8]	FUJⅡ T, OSA N, KOYAMA S. Free convection condensation of binary vapor mixtures on a smooth horizontal tube:condensing mode and heat transfer coefficient of condensate[C]//Proceedings of US Eng. Found. Conference, 1993:171-182.
[9]	UTAKA Y, WANG S X. Characteristic curves and the promotion effect of ethanol addition on steam condensation heat transfer[J]. International Journal of Heat and Mass Transfer, 2004, 47(21):4507-4516.
[10]	YAN J J, YANG Y S, HU S H, et al. Effects of vapor pressure/velocity and concentration on condensation heat transfer for steam-ethanol vapor mixture[J]. Heat and Mass Transfer, 2007, 44(1):51-60.
[11]	胡申华, 严俊杰, 王进仕. Marangoni凝结形态的影响因素[J]. 化工学报, 2011, 62(11):3053-3059. HU S H, YAN J J, WANG J S. Affecting factors of Marangoni condensation mode[J]. CIESC Journal, 2011, 62(11):3053-3059.
[12]	YAN J J, WANG J S, YANG Y S, et al. Research on Marangoni condensation modes for water-ethanol mixture vapors[J]. Microgravity Science and Technology, 2009, 21(1):77-85.
[13]	MA X H, LAN Z, XU W, et al. Effect of surface free energy difference on steam-ethanol mixture condensation heat transfer[J]. International Journal of Heat and Mass Transfer, 2012, 55(4):531-537.
[14]	兰忠, 马学虎, 李晓楠, 等. 表面自由能差对乙醇-水混合蒸气冷凝传热特征的影响[J]. 高校化学工程学报, 2009, 23(3):369-374. LAN Z, MA X H, LI X N, et al. The effect of surface free energy difference on ethanol-steam mixture condensation[J]. Journal of Chemical Engineering of Chinese Universities, 2009, 23(3):369-374.
[15]	JIANG R, MA X H, LAN Z, et al. Visualization study of condensation of ethanol-water mixture in trapezoidal microchannels[J]. International Journal of Heat and Mass Transfer, 2015, 90:339-349.
[16]	姜睿, 马学虎, 兰忠, 等. 梯形微通道内乙醇水混合蒸气冷凝流型可视化实验[J]. 化工学报, 2015, 66(11):4320-4326. JIANG R, MA X H, LAN Z, et al. Visualization study of flow patterns of ethanol-water mixture condensation in microchannels[J]. CIESC Journal, 2015, 66(11):4320-4326.
[17]	UTAKA Y, KENMOTSU T, YOKOYAMA S. A study on Marangoni condensation (measurement and observation for water and ethanol vapor mixture)[J]. Heat Transfer, 1998, 6:397-402.
[18]	UTAKA Y, NISHIKAWA T. Unsteady measurement of condensate film thickness for solutal Marangoni condensation[C]//Proceedings of the 12th International Heat Transfer Conference, Grenoble, France, 2002:893-897.
[19]	UTAKA Y, NISHIKAWA T. An investigation of liquid film thickness during solutal Marangoni condensation using a laser absorption method:absorption property and examination of measuring method[J]. Heat Transfer-Asian Research, 2003, 32(8):700-711.
[20]	UTAKA Y, NISHIKAWA T. Measurement of condensate film thickness for solutal Marangoni condensation applying laser extinction method[J]. Journal of Enhanced Heat Transfer, 2003, 10(2):119-129.
[21]	胡申华, 严俊杰, 王进仕. Marangoni凝结液珠脱离半径分析[J].中国电机工程学报, 2011, 31(32):88-93. HU S H, YAN J J, WANG J S. Droplet departure radii for Marangoni condensation[J]. Proceeding of the CSEE, 2011, 31(32):88-93.
[22]	李杨. 竖直管外水-酒精混合蒸气Marangoni凝结换热特性研究[D]. 西安:西安交通大学, 2008. LI Y. Heat transfer characteristics of Marangoni condensation of ethanol-water on vertical tubes[D]. Xi'an:Xi'an Jiaotong University, 2008.
[23]	WATANABE N, ARITOMI M, MACHIDA A. Time-series characteristics and geometric structures of drop-size distribution density in dropwise condensation[J]. International Journal of Heat & Mass Transfer, 2014, 76(6):467-483.
[24]	陈娜娜, 李勇, 王进仕, 等.基于环形光源的凝结液珠边缘提取方法研究[C]//中国工程热物理年会会议论文集. 西安, 陕西:2015. CHEN N N, LI Y, WANG J S, et al. The study of edge detection for condensation droplet based on circle light[C]//Proceedings of Chinese Conference on Engineering Thermophysics. Xi'an, Shaanxi:2015.