Effects of convection and solid wall on the diffusion in microscale convection flows

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	Effects of convection and solid wall on the diffusion in microscale convection flows
	Zhang J(张俊); Fan J(樊菁); Fei F(费飞); Fan J(樊菁)
刊名	Physics of Fluids
	2010-12-21
通讯作者邮箱	jfan@imech.ac.cn
卷号	22 期号:12 页码:122005
ISSN号	1070-6631
通讯作者	樊菁
合作状况	其它
中文摘要	The diffusive transport properties in microscale convection flows are studied by using the direct simulation Monte Carlo method. The effective diffusion coefficient D is computed from the mean square displacements of simulated molecules based on the Einstein diffusion equation D = x2 t /2t. Two typical convection flows, namely, thermal creep convection and Rayleigh– Bénard convection, are investigated. The thermal creep convection in our simulation is in the noncontinuum regime, with the characteristic scale of the vortex varying from 1 to 100 molecular mean free paths. The diffusion is shown to be enhanced only when the vortex scale exceeds a certain critical value, while the diffusion is reduced when the vortex scale is less than the critical value. The reason for phenomenon of diffusion reduction in the noncontinuum regime is that the reduction effect due to solid wall is dominant while the enhancement effect due to convection is negligible. A molecule will lose its memory of macroscopic velocity when it collides with the walls, and thus molecules are hard to diffuse away if they are confined between very close walls. The Rayleigh– Bénard convection in our simulation is in the continuum regime, with the characteristic length of 1000 molecular mean free paths. Under such condition, the effect of solid wall on diffusion is negligible. The diffusion enhancement due to convection is shown to scale as the square root of the Péclet number in the steady convection regime, which is in agreement with previous theoretical and experimental results. In the oscillation convection regime, the diffusion is more strongly enhanced because the molecules can easily advect from one roll to its neighbor due to an oscillation mechanism. © 2010 American Institute of Physics. doi:10.1063/1.3528310
学科主题	流体力学
类目[WOS]	Mechanics ; Physics, Fluids & Plasmas
研究领域[WOS]	Mechanics ; Physics
关键词[WOS]	RAYLEIGH-BENARD CONVECTION ; MOLECULAR-DYNAMICS ; THERMAL CREEP ; RAREFIED-GAS ; PASSIVE TRANSPORT ; HYDRODYNAMICS ; ATTRACTORS ; SIMULATION ; SYSTEM
收录类别	SCI
原文出处	http://dx.doi.org/10.1063/1.3528310
语种	英语
WOS记录号	WOS:000285770200010
公开日期	2010-12-24
内容类型	期刊论文
源URL	[http://dspace.imech.ac.cn/handle/311007/43261]
专题	力学研究所_高温气体动力学国家重点实验室
通讯作者	Fan J(樊菁)
推荐引用方式 GB/T 7714	Zhang J,Fan J,Fei F,et al. Effects of convection and solid wall on the diffusion in microscale convection flows[J]. Physics of Fluids,2010,22(12):122005.
APA	Zhang J,Fan J,Fei F,&樊菁.(2010).Effects of convection and solid wall on the diffusion in microscale convection flows.Physics of Fluids,22(12),122005.
MLA	Zhang J,et al."Effects of convection and solid wall on the diffusion in microscale convection flows".Physics of Fluids 22.12(2010):122005.