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A numerical model is developed using the coupled level set and volume of fluid method including heat transfer and contact resistance to simulate air entrapment during a droplet impacting on a wetted surface. The dynamic characteristics of the phase interface are analysed. The mechanisms of deformation of the phase interface and formation of entrapped air are explored. The effects of impacting velocity and thickness of liquid film on characteristics of entrapped air are studied. The mechanism of heat transfer is also obtained in this article. The obtained results are as follows. The pressure difference between liquid and gas before the droplet impacting is the main factor determining the deformation of phases interface and the formation of air entrapment. The larger the impacting velocity, the larger the pressure inside the compressed air film is. When the droplet contacts the liquid film, the velocities of the droplet and liquid film increase to their maximum values, and at the impacting axis, they are approximately the same, nearly half the impacting velocity. The velocity distributions of phase interface of the droplet and liquid film are nearly the same in the area of impacting center. The impacting velocity has important effects on the dimensionless arc from bottom to breaking point and the dimensionless diameter of the air. The dimensionless arc and dimensionless diameter decrease with increasing impacting velocity. The dimensionless deforming heights of the droplet and liquid film are closely related to Stokes number: the larger the Stokes number, the larger the dimensionless deforming heights are, and they can be expressed as a power function with Stokes number. The initial thickness of liquid film also affects dimensionless deforming heights of the droplet and liquid film and dimensionless diameter of the entrapped air: the larger the dimensionless thickness of the liquid film, the larger the dimensionless deforming heights are, and the dimensionless diameter decreases with increasing dimensionless thickness of the liquid film. At the very initial stage of the impact, the entrapped air is important for surface heat flux distribution. The entrapped air presents contraction, breakup and detachment. The surface heat flux distribution changes closely with evolution of the entrapped air and tends to be uniform. The effect of the entrapped air on the surface heat flux distribution decreases gradually.
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Keywords:
- droplet impact /
- air entrapment /
- heat transfer
[1] Moreira A L N, Moita A S, Panao M R 2010 Prog. Energ. Combust. 36 554
[2] Guo J H, Dai S Q, Dai Q 2010 Acta Phys. Sin. 59 2601 (in Chinese) [郭加宏, 戴世强, 代钦 2010 59 2601]
[3] Liang G T, Guo Y L, Shen S Q 2013 Acta Phys. Sin. 62 184703 (in Chinese) [梁刚涛, 郭亚丽, 沈胜强 2013 62 184703]
[4] Lee S H, Hur N, Kang S 2011 J. Mech. Sci. Technol. 25 2567
[5] Liang G T, Shen S Q, Yang Y 2012 J. Therm. Sci. Tech. 11 8 (in Chinese) [梁刚涛, 沈胜强, 杨勇 2012 热科学与技术 11 8]
[6] Liang G T, Guo Y L, Shen S Q 2013 Acta Phys. Sin. 62 024705 (in Chinese) [梁刚涛, 郭亚丽, 沈胜强 2013 62 024705]
[7] Tran T, de Hlne M, Chao S, Lohse D 2013 J. Fluid Mech. 726 R31
[8] Hendrix M H W 2013 M. S. Dissertation (Enschede: University of Twente)
[9] Hicks P D, Purvis R 2011 Phys. Fluids 23 062104
[10] Chen S, Guo L 2014 Chem. Eng. Sci. 109 1
[11] Liang G, Guo Y, Shen S, Yang Y 2014 Theor. Comput. Fluid Dyn. 28 159
[12] Thoroddsen S T, Etoh T G, Takehara K 2005 J. Fluid Mech. 545 203
[13] Song Y C, Ning Z, Sun C H, Yan K, Fu J 2014 J. Mech. Eng. 50 153 (in Chinese) [宋云超, 宁智, 孙春华, 阎凯, 付娟 2014 机械工程学报 50 153]
[14] Thoroddsen S T, Etoh T G, Takehara K 2003 J. Fluid Mech. 478 125
[15] Li D S, Qiu X Q, Yu L, Xu J, Duan X L, Zheng Z W 2014 Ind. Heating 43 1 (in Chinese) [李大树, 仇性启, 于磊, 许京, 段小龙, 郑志伟 2014 工业加热 43 1]
[16] Mehdi N V, Mostaghimi J, Chandra S 2002 Phys. Fluids 15 173
[17] Brackbill J U, Kothe D B 1992 J. Comput. Phys. 100 335
[18] Ubbink O, Issa R I 1999 J. Comput. Phys. 153 26
[19] Lee J S, Weon B M, Je J H, Kamel F 2012 Phys. Rev. Lett. 109 204501
[20] Liu Y, Tan P, Xu L 2013 J. Fluid Mech. 716 R9
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[1] Moreira A L N, Moita A S, Panao M R 2010 Prog. Energ. Combust. 36 554
[2] Guo J H, Dai S Q, Dai Q 2010 Acta Phys. Sin. 59 2601 (in Chinese) [郭加宏, 戴世强, 代钦 2010 59 2601]
[3] Liang G T, Guo Y L, Shen S Q 2013 Acta Phys. Sin. 62 184703 (in Chinese) [梁刚涛, 郭亚丽, 沈胜强 2013 62 184703]
[4] Lee S H, Hur N, Kang S 2011 J. Mech. Sci. Technol. 25 2567
[5] Liang G T, Shen S Q, Yang Y 2012 J. Therm. Sci. Tech. 11 8 (in Chinese) [梁刚涛, 沈胜强, 杨勇 2012 热科学与技术 11 8]
[6] Liang G T, Guo Y L, Shen S Q 2013 Acta Phys. Sin. 62 024705 (in Chinese) [梁刚涛, 郭亚丽, 沈胜强 2013 62 024705]
[7] Tran T, de Hlne M, Chao S, Lohse D 2013 J. Fluid Mech. 726 R31
[8] Hendrix M H W 2013 M. S. Dissertation (Enschede: University of Twente)
[9] Hicks P D, Purvis R 2011 Phys. Fluids 23 062104
[10] Chen S, Guo L 2014 Chem. Eng. Sci. 109 1
[11] Liang G, Guo Y, Shen S, Yang Y 2014 Theor. Comput. Fluid Dyn. 28 159
[12] Thoroddsen S T, Etoh T G, Takehara K 2005 J. Fluid Mech. 545 203
[13] Song Y C, Ning Z, Sun C H, Yan K, Fu J 2014 J. Mech. Eng. 50 153 (in Chinese) [宋云超, 宁智, 孙春华, 阎凯, 付娟 2014 机械工程学报 50 153]
[14] Thoroddsen S T, Etoh T G, Takehara K 2003 J. Fluid Mech. 478 125
[15] Li D S, Qiu X Q, Yu L, Xu J, Duan X L, Zheng Z W 2014 Ind. Heating 43 1 (in Chinese) [李大树, 仇性启, 于磊, 许京, 段小龙, 郑志伟 2014 工业加热 43 1]
[16] Mehdi N V, Mostaghimi J, Chandra S 2002 Phys. Fluids 15 173
[17] Brackbill J U, Kothe D B 1992 J. Comput. Phys. 100 335
[18] Ubbink O, Issa R I 1999 J. Comput. Phys. 153 26
[19] Lee J S, Weon B M, Je J H, Kamel F 2012 Phys. Rev. Lett. 109 204501
[20] Liu Y, Tan P, Xu L 2013 J. Fluid Mech. 716 R9
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