疏水性对竖直冷表面上自然对流结霜特性的影响
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摘要
本文采用控制表面氧化法制备超疏水表面(153. 2°),并对自然对流条件下竖直放置的超疏水表面与裸铜表面进行可视化结霜实验,观察并对比实验初期有液核与无液核生成成霜时疏水性对结霜过程的影响,研究了疏水性对结霜的影响随冷表面温度(-50～-30℃)、空气相对湿度(30%～70%)的变化规律。结果表明,有液核成霜时,超疏水表面具有显著的抑霜效果;无液核成霜时,疏水表面不再具有抑霜效果,反而超疏水表面霜晶生长更为密实;疏水性对无液核成霜过程的影响随空气相对湿度的增大、冷表面温度的降低而减弱;从云物理学与核化理论角度分析了无液核生成时超疏水表面霜晶分布更密的原因,发现实验制备的超疏水表面上凹坑与CuO晶体颗粒为凝华核化提供了有利位置。
A series of visible frosting experiments on vertical superhydrophobic surfaces( 153. 2°) that were prepared by chemical etching and bare copper surfaces were conducted under natural convection conditions. The effect of hydrophobicity on the frosting process was investigated and compared under liquid nuclei and no-nuclei frost deposition mode. Furthermore,the effect of hydrophobicity on frost deposition was studied for cold surface temperatures(-50 to-30 ℃) and different air relative humidities( 30%-70%). The experimental results showed that there was no liquid nucleation at the beginning of the experiment when the cold surface temperature was lower than-30 ℃ at an ambient air temperature of 16 ℃ and a relative humidity between 30% and 70%. It was found that the frost crystals on the superhydrophobic surface were much denser compared than those on a copper surface under the no-nuclei frost deposition mode. This result was completely different from that of the liquid-nuclei frost deposition mode in which the frost formation on the superhydrophobic surface was suppressed significantly during the initial period of frost deposition. The frost crystal coverage of the cold surface was defined to characterize the density of the frost crystal distribution. It was revealed that as the relative humidity increased and the cold surface temperature decreased,the effects of hydrophobicity on frost deposition was mitigated,the frost crystal coverage difference between the superhydrophobic and plain copper surfaces was reduced,and the time during which the frost coverage difference lasted was shortened. The maximum frost coverage difference between the superhydrophobic and plain copper surfaces was greater than 15% and lasted for approximately35 min in the case of cold surface temperatures-30 ℃,with the ambient air temperature at 16 ℃ and the relative humidity at 30%. The hydrophobicity had little effect on the frost deposition once the cold surface temperature was reduced to a sufficiently low temperature. The phenomena observed were also analyzed according to the theory of cloud physics and nucleation. It was found that the concave pits and the CuO crystal particles on the superhydrophobic surface provided advantageous sites for desublimation nucleation.
A series of visible frosting experiments on vertical superhydrophobic surfaces( 153. 2°) that were prepared by chemical etching and bare copper surfaces were conducted under natural convection conditions. The effect of hydrophobicity on the frosting process was investigated and compared under liquid nuclei and no-nuclei frost deposition mode. Furthermore,the effect of hydrophobicity on frost deposition was studied for cold surface temperatures(-50 to-30 ℃) and different air relative humidities( 30%-70%). The experimental results showed that there was no liquid nucleation at the beginning of the experiment when the cold surface temperature was lower than-30 ℃ at an ambient air temperature of 16 ℃ and a relative humidity between 30% and 70%. It was found that the frost crystals on the superhydrophobic surface were much denser compared than those on a copper surface under the no-nuclei frost deposition mode. This result was completely different from that of the liquid-nuclei frost deposition mode in which the frost formation on the superhydrophobic surface was suppressed significantly during the initial period of frost deposition. The frost crystal coverage of the cold surface was defined to characterize the density of the frost crystal distribution. It was revealed that as the relative humidity increased and the cold surface temperature decreased,the effects of hydrophobicity on frost deposition was mitigated,the frost crystal coverage difference between the superhydrophobic and plain copper surfaces was reduced,and the time during which the frost coverage difference lasted was shortened. The maximum frost coverage difference between the superhydrophobic and plain copper surfaces was greater than 15% and lasted for approximately35 min in the case of cold surface temperatures-30 ℃,with the ambient air temperature at 16 ℃ and the relative humidity at 30%. The hydrophobicity had little effect on the frost deposition once the cold surface temperature was reduced to a sufficiently low temperature. The phenomena observed were also analyzed according to the theory of cloud physics and nucleation. It was found that the concave pits and the CuO crystal particles on the superhydrophobic surface provided advantageous sites for desublimation nucleation.
引文
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[3]刘中良,黄玲艳,勾昱君,等.结霜现象及抑霜技术的研究进展[J].制冷学报,2010,31(4):1-6.(LIU Zhongliang,HUANG Lingyan,GOU Yujun,et al. A review on frost formation and anti-frosting technology[J].Journal of Refrigeration,2010,31(4):1-6.)
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[6] HUANG Lingyan,LIU Zhongliang,LIU Yaomin,et al.Preparation and anti-frosting performance of super-hydrophobic surface based on copper foil[J]. International Journal of Thermal Sciences,2011,50(4):432-439.
[7]黄玲艳.表面特性对冷壁面结霜过程影响的研究[D].北京:北京工业大学,2011.(HUANG Lingyan. A study on the effects of cold surface characteristics on frost formation[D]. Beijing:Beijing University of Technology,2011.)
[8] HUANG Lingyan,LIU Zhongliang,LIU Yaomin,et al.Effect of contact angle on water droplet freezing process on a cold flat surface[J]. Experimental Thermal and Fluid Science,2012,40(7):74-80.
[9] LIU Y,KULACKI F A. An experimental study of defrost on treated surfaces:effect of frost slumping[J]. International Journal of Heat and Mass Transfer,2018,119:880-890.
[10] CHU Fuqiang,WU Xiaomin,ZHU Yi. Defrosting on horizontal hydrophobic surfaces and the shrink angle[J]. International Journal of Refrigeration,2016,71:1-7.
[11]徐文骥,宋金龙,孙晶,等.铝基体超疏水表面结冰结霜特性研究[J].制冷学报,2011,32(4):9-13.(XU Wenji,SONG Jinlong,SUN Jing,et al. Characteristics of ice and frost formation on superhydrophobic surfaces on aluminum substrates[J]. Journal of Refrigeration,2011,32(4):9-13.)
[12]李丽艳,刘中良,赵玲倩,等.结霜初期无液核形成时的抑霜研究[J].工程热物理学报,2019,40(1):198-203.(LI Liyan,LIU Zhongliang,Zhao Lingqian,et al.Study on anti-frosting performance of hydrophobic surface without the appearance of water nuceli at the initial stage of frost formation[J]. Journal of Engineering Thermophysics,2019,40(1):198-203.)
[13] WANG Zuojia,KWON D J,DEVRIES K L,et al. Frost formation and anti-icing performance of a hydrophobic coating on aluminum[J]. Experimental Thermal and Fluid Science,2015,60:132-137.
[14]汪峰,梁彩华,张友法,等.结霜初期超疏水表面凝结液滴的自跳跃脱落及其对结霜过程的影响[J].东南大学学报(自然科学版),2016,46(4):757-762.(WANG Feng,LIANG Caihua,ZHANG Youfa,et al.Jumping of condensation droplets on superhydrophobic surfaces at early frosting stage and its effects on frost formation[J]. Journal of Southeast University(Natural Science Edition),2016,46(4):757-762.)
[15]徐煦,曲凯阳.两类结霜过程的实验研究[J].制冷学报,2002,23(4):1-4.(XU Xu,QU Kaiyang. Experimental study on two types of the frost formation[J]. Journal of Refrigeration,2002,23(4):1-4.)
[16]王鹏飞,李子华.微观云物理学[M].北京:气象出版社,1989.(WANG Pengfei,LI Zihua. Microphysics of clouds[M]. Beijing:China Meteorological Press,1989.)
[17]钱柏太,沈自求.控制表面氧化法制备超疏水Cu O纳米花膜[J].无机材料学报,2006,21(3):748-752.(QIAN Botai,SHEN Ziqiu. Super-hydrophobic Cu O nanoflowers by controlled surface oxidation on copper[J]. Journal of Inorganic Materials,2006,21(3):748-752.)
[2] BAXTER V D,MOYERS J C. Field-measured cycling,frost and defrosting losses for a high efficiency air source heat pump[J]. ASHRAE Transactions,1985,91:2b.
[3]刘中良,黄玲艳,勾昱君,等.结霜现象及抑霜技术的研究进展[J].制冷学报,2010,31(4):1-6.(LIU Zhongliang,HUANG Lingyan,GOU Yujun,et al. A review on frost formation and anti-frosting technology[J].Journal of Refrigeration,2010,31(4):1-6.)
[4] BARTHLOTT W,NEINHUIS C. Purity of the scared lotus,or escape from contamination in biological surfaces[J].Planta,1997,202(1):1-8.
[5] LIU Zhongliang,GOU Yujun,WANG Jieteng,et al. Frost formation on a super-hydrophobic surface under natural convection conditions[J]. International Journal of Heat Transfer,2008,51(25/26):5975-5982.
[6] HUANG Lingyan,LIU Zhongliang,LIU Yaomin,et al.Preparation and anti-frosting performance of super-hydrophobic surface based on copper foil[J]. International Journal of Thermal Sciences,2011,50(4):432-439.
[7]黄玲艳.表面特性对冷壁面结霜过程影响的研究[D].北京:北京工业大学,2011.(HUANG Lingyan. A study on the effects of cold surface characteristics on frost formation[D]. Beijing:Beijing University of Technology,2011.)
[8] HUANG Lingyan,LIU Zhongliang,LIU Yaomin,et al.Effect of contact angle on water droplet freezing process on a cold flat surface[J]. Experimental Thermal and Fluid Science,2012,40(7):74-80.
[9] LIU Y,KULACKI F A. An experimental study of defrost on treated surfaces:effect of frost slumping[J]. International Journal of Heat and Mass Transfer,2018,119:880-890.
[10] CHU Fuqiang,WU Xiaomin,ZHU Yi. Defrosting on horizontal hydrophobic surfaces and the shrink angle[J]. International Journal of Refrigeration,2016,71:1-7.
[11]徐文骥,宋金龙,孙晶,等.铝基体超疏水表面结冰结霜特性研究[J].制冷学报,2011,32(4):9-13.(XU Wenji,SONG Jinlong,SUN Jing,et al. Characteristics of ice and frost formation on superhydrophobic surfaces on aluminum substrates[J]. Journal of Refrigeration,2011,32(4):9-13.)
[12]李丽艳,刘中良,赵玲倩,等.结霜初期无液核形成时的抑霜研究[J].工程热物理学报,2019,40(1):198-203.(LI Liyan,LIU Zhongliang,Zhao Lingqian,et al.Study on anti-frosting performance of hydrophobic surface without the appearance of water nuceli at the initial stage of frost formation[J]. Journal of Engineering Thermophysics,2019,40(1):198-203.)
[13] WANG Zuojia,KWON D J,DEVRIES K L,et al. Frost formation and anti-icing performance of a hydrophobic coating on aluminum[J]. Experimental Thermal and Fluid Science,2015,60:132-137.
[14]汪峰,梁彩华,张友法,等.结霜初期超疏水表面凝结液滴的自跳跃脱落及其对结霜过程的影响[J].东南大学学报(自然科学版),2016,46(4):757-762.(WANG Feng,LIANG Caihua,ZHANG Youfa,et al.Jumping of condensation droplets on superhydrophobic surfaces at early frosting stage and its effects on frost formation[J]. Journal of Southeast University(Natural Science Edition),2016,46(4):757-762.)
[15]徐煦,曲凯阳.两类结霜过程的实验研究[J].制冷学报,2002,23(4):1-4.(XU Xu,QU Kaiyang. Experimental study on two types of the frost formation[J]. Journal of Refrigeration,2002,23(4):1-4.)
[16]王鹏飞,李子华.微观云物理学[M].北京:气象出版社,1989.(WANG Pengfei,LI Zihua. Microphysics of clouds[M]. Beijing:China Meteorological Press,1989.)
[17]钱柏太,沈自求.控制表面氧化法制备超疏水Cu O纳米花膜[J].无机材料学报,2006,21(3):748-752.(QIAN Botai,SHEN Ziqiu. Super-hydrophobic Cu O nanoflowers by controlled surface oxidation on copper[J]. Journal of Inorganic Materials,2006,21(3):748-752.)
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