过冷水滴凝固机理及凝固组织特征
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摘要
针对飞机过冷水滴结冰的精细化预测需求,基于相变热力学与相变动力学相关理论,采用示差扫描量热法(DSC)、结冰风洞试验及微结构测试相结合的方法,研究了过冷水滴凝固过程的热力学机理及凝固组织特征。基于示差扫描量热法,研究了冷却速率及形核条件对结晶凝固特性的影响规律;基于结冰风洞试验开展了不同温度条件下冰相的宏观形貌及微结构特征研究。结果表明,过冷条件及冷却速率是影响过冷水滴结晶速率及结晶完善程度的重要因素。降温速率越大,结晶速率常数增大、结晶速率相应提高。同时,结晶峰变宽,结晶初始温度向低温方向移动,过冷效应相对显著;反之亦然。过冷度及冷却速率对冰相的宏观及微观形貌均有着重要影响。过冷度越大则相同时间内冷却速率越大,晶体生长过程越不充分,晶体不规则程度相对较高,同时晶粒密度变大、尺度变小,冰相表观透明度相对降低;反之,过冷度越小,则晶粒密度变小、尺度变大,冰相表观透明度相对较高。异相形核条件对加速结晶过程有重要促进作用,晶种的存在可有效加速二次结晶的触发,使过冷效应显著减弱。相关研究可为飞机结冰速率、冰相物理特征及冰形宏观形貌的精细化预测提供参考。
To better meet the demand of refined prediction of the aircraft icing process,the freezing mechanisms and microstructure characteristics in solidification of supercooled water droplets are studied combining the theory of phase-change thermodynamics and kinetics with tests.Based on the Differential Scanning Calorimetry(DSC)test,the effects of cooling rate and nucleation conditions on the solidification characteristics are studied.Icing tunnel tests are carried out at different temperature conditions,and the macroscopic morphology and microstructure characteristics of ice are obtained.The results indicate that icing conditions and cooling rate have great influence on the crystallization behavior of supercooled water.The greater the cooling rate,the greater the crystallization rate.At the same time,the crystallization peak becomes wider,and the initial temperature of crystallization becomes lower,and vice versa.The subcooling and cooling rate have important influence on the macroscopic and microscopic morphology of ice.The greater the subcooling and cooling rate,the more irregular the grains,the larger density and the smaller the grains,and the ice phase looks more opaque.On the contrary,the smaller the subcooling,the lower density and the larger the grains,and the ice phase looks more transparent.Heterogeneous nucleation conditions play an important role in accelerating the crystallization process.The addition of crystal seeds can trigger the crystallization effectively,significantly reducing the supercooling effect.The results lay an important foundation for better understanding the mechanisms of aircraft icing,which has important value for predicting the icing process more accurately.
To better meet the demand of refined prediction of the aircraft icing process,the freezing mechanisms and microstructure characteristics in solidification of supercooled water droplets are studied combining the theory of phase-change thermodynamics and kinetics with tests.Based on the Differential Scanning Calorimetry(DSC)test,the effects of cooling rate and nucleation conditions on the solidification characteristics are studied.Icing tunnel tests are carried out at different temperature conditions,and the macroscopic morphology and microstructure characteristics of ice are obtained.The results indicate that icing conditions and cooling rate have great influence on the crystallization behavior of supercooled water.The greater the cooling rate,the greater the crystallization rate.At the same time,the crystallization peak becomes wider,and the initial temperature of crystallization becomes lower,and vice versa.The subcooling and cooling rate have important influence on the macroscopic and microscopic morphology of ice.The greater the subcooling and cooling rate,the more irregular the grains,the larger density and the smaller the grains,and the ice phase looks more opaque.On the contrary,the smaller the subcooling,the lower density and the larger the grains,and the ice phase looks more transparent.Heterogeneous nucleation conditions play an important role in accelerating the crystallization process.The addition of crystal seeds can trigger the crystallization effectively,significantly reducing the supercooling effect.The results lay an important foundation for better understanding the mechanisms of aircraft icing,which has important value for predicting the icing process more accurately.
引文
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[20]潘环,艾剑良.飞机结冰冰形预测的建模与仿真[J].系统仿真学报,2014,26(1):221-224.PAN H,AI J L.Modeling and simulation of aircraft ice shape prediction[J].Journal of System Simulation,2014,26(1):221-224(in Chinese).
[21]LI Y,WANG S,SUN C,et al.Icing distribution of rotating blade of horizontal axis wind turbine based on quasi-3Dnumerical simulation[J].Thermal Science,2018,22(S2):S681-S692.
[22]黄起森,刘礼,韦修勋,等.过冷Ni-P合金的凝固行为[J].物理学报,2012,61(16):367-374.HUANG Q S,LIU L,WEI X X,et al.Solidification behavior of undercooling Ni-P alloy[J].Acta Physica Sinica,2012,61(16):367-374(in Chinese).
[23]杜雁霞,李明,桂业伟,等.飞机结冰热力学行为研究综述[J].航空学报,2017,38(2):520706.DU Y X,LI M,GUI Y W,et al.Review of thermodynamic behaviors in aircraft icing process[J].Acta Aeronautica et Astronautica Sinica,2017,38(2):520706(in Chinese).
[24]李伟斌,易贤,杜雁霞,等.基于变分分割模型的结冰形测量方法[J].航空学报,2017,38(1):120167.LI W B,YI X,DU Y X,et al.A measurement approach for ice shape based on variational segmentation model[J].Acta Aeronautica et Astronautica Sinica,2017,38(1):120167(in Chinese).
[25]桂业伟,周志宏,李颖晖,等.关于飞机结冰的多重安全边界问题[J].航空学报,2017,38(2):520723.GUI Y W,ZHOU Z H,LI Y H,et al.Multiple safety boundaries protection on aircraft icing[J].Acta Aeronautica et Astronautica Sinica,2017,38(2):520723(in Chinese).
[2]National Transportation Safety Board.Aviation accident statistics[R].Washington,D.C.:National Transportation Safety Board,2008.
[3]ROISMAN I V.Fast forced liquid film spreading on a substrate:Flow,heat transfer and phase transition[J].Journal of Fluid Mechanics,2010,656:189-204.
[4]BLAKE J,THOMPSON D,RAPS D,et al.Simulating the freezing of supercooled water droplets impacting a cooled substrate[J].AIAA Journal,2015,53(7):1725-1739.
[5]徐祖耀.相变原理[M].北京:科学出版社,1988:123-124.XU Z Y.Principles of phase transformations[M].Beijing:Science Press,1988:123-124(in Chinese).
[6]SHIBKOV A A,GOLOVIN Y I,ZHELTOV M A,et al.Morphology diagram of non-equilibrium patterns of ice crystals growing in supercooled water[J].Physica A:Statistical Mechanics and Its Applications,2003,319:65-79.
[7]KING W D.Freezing rates of water droplets[J].Journal of the Atmospheric Sciences,1975,32(2):403-408.
[8]TABAKOVA S,FEUILLEBOIS F,RADEV S.Freezing of a suspended supercooled droplet with a heat transfer mixed condition on its outer surface[C]∥1st International Conference on Applications of Mathematics in Technical and Natural Sciences.New York:AIP Publishing,2009:240-247.
[9]GENNES P G D.Wetting:Static and dynamics[J].Review of Modern Physics,1985,57(3):827-863.
[10]CAMPOS A L,SILVA N T,MELO F C L,et al.Crystallization kinetics of orthorhombic mullite from diphasic gels[J].Journal of Non-Crystalline Solids,2002,304(1):19-24.
[11]IQBAL N,VAN DIJK N H,VERHOEVEN V W J,et al.Experimental study of ordering kinetics in aluminum alloys during solidification[J].Acta Materialia,2003,51(25):4497-4504.
[12]DAVIS S H.Theory of solidication[M].New York:Cambridge University Press,2001:26-27.
[13]LYNCH M,GILL W N,ANANTH R.The growth of ice dendrites under mixed convection conditions[J].Chemical Engineering Communications,1987,55:295-312.
[14]曲凯阳,江亿.均质形核结冰随机性及形核率的研究[J].物理学报,2000,49(11):2214-2219.QU K Y,JIANG Y.Studies on randomness and nucleation rate of supercooled water freezing from homogeneous nucleation[J].Acta Physica Sinica,2000,49(11):2214-2219(in Chinese).
[15]ELLEN N,JACCO M H,EDWIN W,et al.Aircraft icing in flight:Effects of impact of supercooled large droplets[C]∥29th Congress of the International Council of the Aeronautical Sciences,2004:1-17.
[16]LIU M,ZHAO Q,WANG Y,et al.Melting behaviors,isothermal and non-isothermal crystallization kinetics of nylon 1212[J].Polymer,2003,44(8):2537-2545.
[17]JEZIORNY A.Parameters characterizing the kinetics of the non-isothermal crystallization of poly(ethylene terephthalate)determined by DSC[J].Polymer,1978,19(10):1142-1144.
[18]PURI S,WADHAWAN V.Kinetics of phase transitions[M].Boca Raton,FL:CRC Press,2009:8-68.
[19]裘燮纲,韩凤华.飞机防冰系统[M].北京:航空专业教材编审室,1985.QIU X G,HAN F H.Aircraft anti-icing system[M].Beijing:Aviation Professional Textbook Editorial Office,1985(in Chinese).
[20]潘环,艾剑良.飞机结冰冰形预测的建模与仿真[J].系统仿真学报,2014,26(1):221-224.PAN H,AI J L.Modeling and simulation of aircraft ice shape prediction[J].Journal of System Simulation,2014,26(1):221-224(in Chinese).
[21]LI Y,WANG S,SUN C,et al.Icing distribution of rotating blade of horizontal axis wind turbine based on quasi-3Dnumerical simulation[J].Thermal Science,2018,22(S2):S681-S692.
[22]黄起森,刘礼,韦修勋,等.过冷Ni-P合金的凝固行为[J].物理学报,2012,61(16):367-374.HUANG Q S,LIU L,WEI X X,et al.Solidification behavior of undercooling Ni-P alloy[J].Acta Physica Sinica,2012,61(16):367-374(in Chinese).
[23]杜雁霞,李明,桂业伟,等.飞机结冰热力学行为研究综述[J].航空学报,2017,38(2):520706.DU Y X,LI M,GUI Y W,et al.Review of thermodynamic behaviors in aircraft icing process[J].Acta Aeronautica et Astronautica Sinica,2017,38(2):520706(in Chinese).
[24]李伟斌,易贤,杜雁霞,等.基于变分分割模型的结冰形测量方法[J].航空学报,2017,38(1):120167.LI W B,YI X,DU Y X,et al.A measurement approach for ice shape based on variational segmentation model[J].Acta Aeronautica et Astronautica Sinica,2017,38(1):120167(in Chinese).
[25]桂业伟,周志宏,李颖晖,等.关于飞机结冰的多重安全边界问题[J].航空学报,2017,38(2):520723.GUI Y W,ZHOU Z H,LI Y H,et al.Multiple safety boundaries protection on aircraft icing[J].Acta Aeronautica et Astronautica Sinica,2017,38(2):520723(in Chinese).