Marangoni效应对降膜流动影响的模拟研究
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摘要
采用计算流体力学的方法,提出了1个三维模型来研究竖直板上受热和受冷降膜的Marangoni效应对降膜流动的影响,得到了液膜表面温度、速度、涡量以及润湿面积比等参数随时间变化关系.模拟结果表明,液膜受冷其润湿面积增大,受热收缩.Marangoni效应在液膜的水平方向表现得更加明显,受热液膜径向修正Marangoni数为轴向修正Marangoni数的8倍.受热液膜表面波动加强,边缘处涡量增大,而液膜主体流向速度由于受到液膜收缩的影响也增大.
Marangoni effect induced by temperature gradient is introduced into a three-dimensional computational fluid dynamics(CFD)model to investigate the hydrodynamic characteristics of the heated or cooled falling liquid films flowing down along a vertical flat plate.The parameters of temperature,velocity,vorticity and wetting ratio are obtained.It is found that the wetting ratio of the falling film increases when it is cooled and decreases when heated.Marangoni effect on the transverse direction of the falling liquid film is the main influence factor,and the radial modified Marangoni number is 7 times larger than the axial modified Marangoni number.It shows that the surface of the falling film is more unstable and the vorticity at the edge of heated falling film increases.Moreover,the velocity of the main body also increases due to the shrinkage of film.
Marangoni effect induced by temperature gradient is introduced into a three-dimensional computational fluid dynamics(CFD)model to investigate the hydrodynamic characteristics of the heated or cooled falling liquid films flowing down along a vertical flat plate.The parameters of temperature,velocity,vorticity and wetting ratio are obtained.It is found that the wetting ratio of the falling film increases when it is cooled and decreases when heated.Marangoni effect on the transverse direction of the falling liquid film is the main influence factor,and the radial modified Marangoni number is 7 times larger than the axial modified Marangoni number.It shows that the surface of the falling film is more unstable and the vorticity at the edge of heated falling film increases.Moreover,the velocity of the main body also increases due to the shrinkage of film.
引文
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[4]Kabov O A,Chinnov F A.Heat transfer from a local heat source to subcooled liquid film[J].High Temperature,2001,3(5):703-713.
[5]Kapitza P L,Kapitza S P.Wave flow of thin layers of a viscous fluid[J].Zh Eksp Teor Fiz,1949,19(2):105-120.
[6]张锋,耿皎,赵贤广,等.红外热像法研究降膜流动[J].化工进展,2006,25(10):1188-1192.Zhang Feng,Geng Jiao,Zhao Xianguang,et al.Thermal imaging study of falling liquid films[J].Chemical Industry and Engineering Progress,2006,25(10):1188-1192(in Chinese).
[7]Zhang F,Zhang Z B,Geng J.Study on shrinkage characteristics of heated falling liquid films[J].AICh E Journal,2005,51(11):2899-2907.
[8]赵贤广,张志柄.受热降膜Marangoni效应临界状态表征[J].化工时刊,2010,24(12):1-6.Zhao Xianguang,Zhang Zhibing.Characteristic of the threshold of Marangoni effect on heated falling film[J].Chemical Industry Times,2010,24(12):1-6(in Chinese).
[9]Séamus M O S,Anthony J R.Numerical investigation of bobble-induced Marangoni convection[J].Interdisciplinary Transport Phenomena,2009,1161(1):304-320.
[10]Nicolaiewsky E M A,Fair J R.Liquid flow over textured surfaces.1.Contact angles[J].Ind Eng Chem Res,1999,38(1):284-291.
[11]Brackbill J U,Kothe D B,Zemach C.A continuum method for modeling surface tension[J].Journal of Computational Physics,1992,100(2):335-354.
[12]Cazabat A M,Heslot F,Troian S M,et al.Fingering instability of thin spreading films driven by temperature gradients[J].Nature,1990,346(628):824-826.
[13]Surface Tension of Water in Contact with Air[EB/OL].http://www.engineeringtoolbox.com/water-surfacetension-d_597.html,2011-10-27.
[14]Ehrard P,Davis S H.Non-isothermal spreading of liquid drops on horizontal plates[J].Journal of Fluid Mechanics,1991,229(8):365-388.
[15]Kabov O A,Chinnor E A.Heat transfer from a local heat source to subcooled liquid film[J].High Temperature,2001,39(5):703-713.