壁面效应对纳米尺度气体流动的影响规律研究
|
摘要
采用分子动力学方法研究了过渡区纳米通道内的壁面力场对气体剪切流动的影响规律.在纳米尺度下,壁面力场对流场的主导作用更加显著,流动物理量对于壁面条件和系统温度的变化也更加敏感.壁面原子的运动采用Einstein模型模拟,结果表明随着壁面刚度的增加,气体在近壁面区域的速度峰值减小,气体分子与壁面的动量适应性变差.壁面粗糙度通过金字塔形模型来研究,发现无论是主流区域还是近壁区域,壁面粗糙度对流动的影响都非常明显.当粗糙单元高度增大时,气体分子在壁面处的聚集现象明显,与壁面完全动量适应.本文还研究了系统温度对纳米通道流动的影响,结果表明温度的影响是全局性的,温度的升高导致整个通道内流速降低,近壁区域气体密度减小,气-固动量适应性变差.
A three-dimensional non-equilibrium molecular dynamics method is adopted to investigate the influence of wall force field on the nanoscale gas flow in the transition regime. For the gas flow under nanoscale condition,the dominant effect of the wall force field on the flow field is more obvious, and the flow physical quantity is more sensitive to the change of the wall condition and system temperature. The motion of the wall atoms is governed by the Einstein theory, with using an elastic coefficient k to model the surface stiffness. The results indicate that the surface stiffness has little effect on the physical quantity distribution of the bulk flow region,but a certain influence on that of the near wall region. Increasing the value of the stiffness changes the velocity peak of the gas in the near-wall region and the tangential momentum adaptation coefficient(TMAC) towards lower values, thus demoting the momentum adaptability of the gas molecules to the surface. The wall roughness is simulated by a typical pyramidal model. It is found that the influence of wall roughness on the flow is very obvious, whether it is in the bulk flow region or in the near wall region. For the former case, the increase of roughness leads gas velocity and shear stress to increase, with density and normal stress remaining constant.The linear distribution of physical quantities is also affected to some extent. While for the latter case, as the roughness increases, the velocity of the fluid increases rapidly and approaches to the wall velocity. The peak of density increases, and the adsorption of gas molecules at the surface is obvious. The TMAC approaches to 1,suggesting that the gas and the surface achieve a complete momentum adaptation. Besides, the influence of system temperature on the gas flow in the nanochannel is also studied. The system temperature is controlled by the Nose-Hoover thermostat, making the flow field maintained at the target temperature through the damping coefficient. The results show that the effect of temperature is global in the whole flow region. The increase of temperature causes the flow velocity of the whole flow field to decrease, while the normal stress and shear stress to increase. A higher temperature leads to more frequent collisions between gas molecules, thus increasing the effective viscosity of the gas. At the same time, the degree of gas molecule adsorption in the near-wall region is reduced, contributing to a smaller TMAC value, and consequently a weaker gas-surface interaction.
A three-dimensional non-equilibrium molecular dynamics method is adopted to investigate the influence of wall force field on the nanoscale gas flow in the transition regime. For the gas flow under nanoscale condition,the dominant effect of the wall force field on the flow field is more obvious, and the flow physical quantity is more sensitive to the change of the wall condition and system temperature. The motion of the wall atoms is governed by the Einstein theory, with using an elastic coefficient k to model the surface stiffness. The results indicate that the surface stiffness has little effect on the physical quantity distribution of the bulk flow region,but a certain influence on that of the near wall region. Increasing the value of the stiffness changes the velocity peak of the gas in the near-wall region and the tangential momentum adaptation coefficient(TMAC) towards lower values, thus demoting the momentum adaptability of the gas molecules to the surface. The wall roughness is simulated by a typical pyramidal model. It is found that the influence of wall roughness on the flow is very obvious, whether it is in the bulk flow region or in the near wall region. For the former case, the increase of roughness leads gas velocity and shear stress to increase, with density and normal stress remaining constant.The linear distribution of physical quantities is also affected to some extent. While for the latter case, as the roughness increases, the velocity of the fluid increases rapidly and approaches to the wall velocity. The peak of density increases, and the adsorption of gas molecules at the surface is obvious. The TMAC approaches to 1,suggesting that the gas and the surface achieve a complete momentum adaptation. Besides, the influence of system temperature on the gas flow in the nanochannel is also studied. The system temperature is controlled by the Nose-Hoover thermostat, making the flow field maintained at the target temperature through the damping coefficient. The results show that the effect of temperature is global in the whole flow region. The increase of temperature causes the flow velocity of the whole flow field to decrease, while the normal stress and shear stress to increase. A higher temperature leads to more frequent collisions between gas molecules, thus increasing the effective viscosity of the gas. At the same time, the degree of gas molecule adsorption in the near-wall region is reduced, contributing to a smaller TMAC value, and consequently a weaker gas-surface interaction.
引文
[1] Verbridge S S, Craighead H G, Parpia J M 2008 Appl. Phys.Lett. 92 013112
[2] Cao B Y, Sun J, Chen M, Guo Z Y 2009 Int. J. Mol. Sci. 104638
[3] Boettcher U, Li H, Callafon R A, Talke F E 2011 IEEE Trans. Magn. 47 1823
[4] Song H Q, Yu M X, Zhu W Y, Zhang Y, Jiang S X 2013Chin. Phys. Lett. 30 014701
[5] Zhang W, Meng G, Wei X 2012 Microfluid. Nanofluid. 13 845
[6] Maxwell J C 1879 Phil. Trans. R. Soc. Lond. 170 231
[7] Sharipov F, Kalempa D 2004 Phys. Fluids 16 3779
[8] Zhang Z Q, Zhang H W, Ye H F 2009 Appl. Phys. Lett. 95154101
[9] Zhang H W, Zhang Z Q, Zheng Y G, Ye H F 2010 Phys. Rev.E 81 066303
[10] Bird G A 1994 Molecular Gas Dynamics and the Direct Simulation of Gas Flows(Oxford:Oxford University Press)pp199-206
[11] Fan J, Shen C 2001 J. Comput. Phys. 167 393
[12] Rapaport D C 2004 The Art of Molecular Dynamics Simulation(New York:Cambridge University Press)pp4, 5
[13] Cao B Y, Chen M, Guo Z Y 2006 Acta Phys. Sin. 55 5305(in Chinese)[曹炳阳,陈民,过增元2006物理学报55 5305]
[14] Cao B Y 2007 Mol. Phys. 105 1403
[15] Priezjev N V 2011 J. Chem. Phys. 135 204704
[16] Sun J, Li Z X 2008 Mol. Phys. 106 2325
[17] Spijker P, Markvoort A J, Nedea S V, Hilbers P A 2010 Phys.Rev. E81 011203
[18] Xie H, Liu C 2011 Mod. Phys. Lett.B 25 773
[19] Kamali R, Kharazmi A 2011 Int. J. Therm. Sci. 50 226
[20] Barisik M, Beskok A 2011 Microfluid. Nanofluid. 11 611
[21] Barisik M, Beskok A 2012 Microfluid. Nanofluid. 13 789
[22] Noorian H, Toghraie D, Azimian A R 2014 Heat Mass Transfer 50 105
[23] Bao F B, Huang Y L, Qiu L M, Lin J Z 2015 Mol. Phys. 113561
[24] Bao F B, Huang Y L, Zhang Y H, Lin J Z 2015 Microfluid.Nanofluid. 18 1075
[25] To Q D, Leonard C, Lauriat G 2015 Phys. Rev. E 91 023015
[26] Liakopoulos A, Sofos F, Karakasidis T E 2016 Microfluid.Nanofluid. 20 24
[27] Lim W W, Suaning G J, McKenzie D R 2016 Phys. Fluids 28097101
[28] Wang S, Xu J L, Zhang L Y 2017 Acta Phys. Sin. 66 204704(in Chinese)[王胜,徐进良,张龙艳2017物理学报66 204704]
[29] Zhang R, Xie W J, Chang Q, Li H 2018 Acta Phys. Sin. 67084701(in Chinese)[张冉,谢文佳,常青,李桦2018物理学报67 084701]
[30] Hook J R, Hall H E 1991 Solid State Physics(Chichester:Wiley)pp96-106
[31] Priezjev N V 2007 J. Chem. Phys. 127 144708
[32] Asproulis N, Drikakis D 2010 Phys. Rev. E 81 061503
[33] Asproulis N 2011 Phys. Rev. E 84 031504
[34] Wu L, Bogy D B 2002 J. Tribol.-T. ASME 124 562
[35] Cao B Y, Chen M, Guo Z Y 2005 Appl. Phys. Lett. 86 091905
[36] Cieplak M, Koplik J, Banavar J R 2001 Phys. Rev. Lett. 86803
[37] Zhang R, Chang Q, Li H 2018 Acta Phys. Sin. 67 223401(in Chinese)[张冉,常青,李桦2018物理学报67 223401]
[38] Evans D J, Hoover W G 1986 Annu. Rev. Fluid Mech. 18 243
[39] Fukui S, Shimada H, Yamane K, Matsuoka H 2005Microsyst. Technol. 11 805
[40] Bahukudumbi P, Park J H, Beskok A 2003 Microscale Thermophy. Eng. 7 291
[2] Cao B Y, Sun J, Chen M, Guo Z Y 2009 Int. J. Mol. Sci. 104638
[3] Boettcher U, Li H, Callafon R A, Talke F E 2011 IEEE Trans. Magn. 47 1823
[4] Song H Q, Yu M X, Zhu W Y, Zhang Y, Jiang S X 2013Chin. Phys. Lett. 30 014701
[5] Zhang W, Meng G, Wei X 2012 Microfluid. Nanofluid. 13 845
[6] Maxwell J C 1879 Phil. Trans. R. Soc. Lond. 170 231
[7] Sharipov F, Kalempa D 2004 Phys. Fluids 16 3779
[8] Zhang Z Q, Zhang H W, Ye H F 2009 Appl. Phys. Lett. 95154101
[9] Zhang H W, Zhang Z Q, Zheng Y G, Ye H F 2010 Phys. Rev.E 81 066303
[10] Bird G A 1994 Molecular Gas Dynamics and the Direct Simulation of Gas Flows(Oxford:Oxford University Press)pp199-206
[11] Fan J, Shen C 2001 J. Comput. Phys. 167 393
[12] Rapaport D C 2004 The Art of Molecular Dynamics Simulation(New York:Cambridge University Press)pp4, 5
[13] Cao B Y, Chen M, Guo Z Y 2006 Acta Phys. Sin. 55 5305(in Chinese)[曹炳阳,陈民,过增元2006物理学报55 5305]
[14] Cao B Y 2007 Mol. Phys. 105 1403
[15] Priezjev N V 2011 J. Chem. Phys. 135 204704
[16] Sun J, Li Z X 2008 Mol. Phys. 106 2325
[17] Spijker P, Markvoort A J, Nedea S V, Hilbers P A 2010 Phys.Rev. E81 011203
[18] Xie H, Liu C 2011 Mod. Phys. Lett.B 25 773
[19] Kamali R, Kharazmi A 2011 Int. J. Therm. Sci. 50 226
[20] Barisik M, Beskok A 2011 Microfluid. Nanofluid. 11 611
[21] Barisik M, Beskok A 2012 Microfluid. Nanofluid. 13 789
[22] Noorian H, Toghraie D, Azimian A R 2014 Heat Mass Transfer 50 105
[23] Bao F B, Huang Y L, Qiu L M, Lin J Z 2015 Mol. Phys. 113561
[24] Bao F B, Huang Y L, Zhang Y H, Lin J Z 2015 Microfluid.Nanofluid. 18 1075
[25] To Q D, Leonard C, Lauriat G 2015 Phys. Rev. E 91 023015
[26] Liakopoulos A, Sofos F, Karakasidis T E 2016 Microfluid.Nanofluid. 20 24
[27] Lim W W, Suaning G J, McKenzie D R 2016 Phys. Fluids 28097101
[28] Wang S, Xu J L, Zhang L Y 2017 Acta Phys. Sin. 66 204704(in Chinese)[王胜,徐进良,张龙艳2017物理学报66 204704]
[29] Zhang R, Xie W J, Chang Q, Li H 2018 Acta Phys. Sin. 67084701(in Chinese)[张冉,谢文佳,常青,李桦2018物理学报67 084701]
[30] Hook J R, Hall H E 1991 Solid State Physics(Chichester:Wiley)pp96-106
[31] Priezjev N V 2007 J. Chem. Phys. 127 144708
[32] Asproulis N, Drikakis D 2010 Phys. Rev. E 81 061503
[33] Asproulis N 2011 Phys. Rev. E 84 031504
[34] Wu L, Bogy D B 2002 J. Tribol.-T. ASME 124 562
[35] Cao B Y, Chen M, Guo Z Y 2005 Appl. Phys. Lett. 86 091905
[36] Cieplak M, Koplik J, Banavar J R 2001 Phys. Rev. Lett. 86803
[37] Zhang R, Chang Q, Li H 2018 Acta Phys. Sin. 67 223401(in Chinese)[张冉,常青,李桦2018物理学报67 223401]
[38] Evans D J, Hoover W G 1986 Annu. Rev. Fluid Mech. 18 243
[39] Fukui S, Shimada H, Yamane K, Matsuoka H 2005Microsyst. Technol. 11 805
[40] Bahukudumbi P, Park J H, Beskok A 2003 Microscale Thermophy. Eng. 7 291