不同压力下竖直深冷表面结霜现象实验研究
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摘要
文章建立了一个结霜可视化实验装置,对在不同气压条件下的低温竖直表面的结霜现象进行实验研究,掌握了低温环境下的结霜过程和霜层微观形貌特征,实验过程中冷表面的温度控制在-180℃。实验结果表明:常压低温结霜工况下,霜晶呈羽毛状,初始晶核趋向于在冷板的边缘形成,之后平行于冷板表面向下生长,并且在初始霜晶形成后的一段时间内,霜层平行于冷板表面向下的生长速度明显大于垂直于冷板表面的生长速度,向下生长的速度达到0.3 mm/min;真空低温结霜工况下,霜层以颗粒状固体存在,生长速度缓慢,在冷表面上分布均匀,并在霜层生长过程中发现开裂现象。此实验装置提供的清晰结霜图像可为后续展开真空条件下的结霜机理研究提供参考。
In order to study the frost growth morphology, a visualization platform is set up. By using the platform, a series of experiments are carried out to study the frost deposited on a vertical flat copper plate in the atmospheric pressure and in vacuum, respectively. The plate is cooled by the liquid nitrogen and controlled at a temperature of-180 ℃. It is shown that under the atmospheric pressure and cryogenic temperature conditions, the initial nucleation tends to take place on the edge of the cold plate, then the frost grow downward along the plate surface with a growth rate of about 0.3 mm per minute. The growth rate in parallel to the cold plate direction is significantly greater than that in the perpendicular direction; under vacuum and cryogenic temperature conditions,the frost is in the form of solid particles and grows very slowly, to reach a uniform distribution on the plate.Cracks are found in the frosting process. The clear frosting images provided by the platform are expected to be used for investigating the frosting mechanism in the future.
In order to study the frost growth morphology, a visualization platform is set up. By using the platform, a series of experiments are carried out to study the frost deposited on a vertical flat copper plate in the atmospheric pressure and in vacuum, respectively. The plate is cooled by the liquid nitrogen and controlled at a temperature of-180 ℃. It is shown that under the atmospheric pressure and cryogenic temperature conditions, the initial nucleation tends to take place on the edge of the cold plate, then the frost grow downward along the plate surface with a growth rate of about 0.3 mm per minute. The growth rate in parallel to the cold plate direction is significantly greater than that in the perpendicular direction; under vacuum and cryogenic temperature conditions,the frost is in the form of solid particles and grows very slowly, to reach a uniform distribution on the plate.Cracks are found in the frosting process. The clear frosting images provided by the platform are expected to be used for investigating the frosting mechanism in the future.
引文
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[2]HAYASHI Y,AOKI A,ADACHI S,et al.Study of frost properties correlating with frost formation types[J].Journal of Heat Transfer,1977,99(2):239-245
[3]吴晓敏,王维城.冷表面结霜初始形态的理论分析[J].工程热物理学报,2003,24(2):286-288WU X M,WANG W C.Theoretical analysis of initial behavior of frost formed on a cold surface[J].Journal of Engineering Thermophysics,2003,24(2):286-288
[4]吴晓敏,单小丰,王维城,等.冷表面结霜的微细观可视化研究[J].清华大学学报(自然科学版),2003,43(10):1437-1440WU X M,SHAN X F,WANG W C.Meso-scale visualobservation of frost formation on cold surfaces[J].Journalof Tsinghua University:Science and Technology,2003,43(10):1437-1440
[5]李栋,陈振乾,王鑫,等.冷表面霜晶演化的微观可视化观测[J].东南大学学报(自然科学版),2017,47(1):79-84LI D,CHEN Z Q,WANG X,et al.Visualization observation of frost crystal evolution on cold surface[J].Journal of Southeast University:Natural Science Edition,2017,47(1):79-84
[6]李瑞霞,吴晓敏,王维城.铝表面结霜现象实验研究[J].热科学与技术,2005,4(4):0315-0318LI R X,WU X M,WANG W C.Experimental study of frost phenomena on aluminum plate[J].Journal of Thermal Science and Technology,2005,4(4):0315-0318
[7]LI L Y,LIU Z L,LI Y X,et al.Frost deposition on a horizontal cryogenic surface in free convection[J].International Journal of Heat and Mass Transfer,2017,113:166-175
[8]姚淑婷,陈叔平,任金平,等.深冷工况下结霜传热分析[J].低温工程,2013(6):15-20YAO S T,CHEN S P,REN J P,et al.Heat transfer analysis of frosting under cryogenic condition[J].Cryogenics,2013(6):15-20
[9]安彭军,谢福寿,陈叔平,等.自然对流深冷结霜工况下湿空气流动状态实验分析[J].低温工程,2012(4):30-33AN P J,XIE F S,CHEN S P,et al.Experimental analysis of flow state for natural convection moist air under cryogenic frosting condition[J].Cryogenics,2012(4):30-33
[10]MOELLER T M,SMITH L M,COLLINS F G,et al.Measurement of the accumulation of water ice on optical components in cryogenic vacuum environments[J].Optical Engineering,2012,51(11):115601(1-8)