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SOME FLOW AND THERMAL PHENOMENA AT MICRO/NANO SCALE

DOI: 10.1615/AnnualRevHeatTransfer.v14.150
pages 225-253

Zeng-Yuan Guo
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Haidian District, Beijing 100084, China

Abstract

In order to have deep insight on flow and thermal phenomena at micro/nano scale it is necessary to classify the physical mechanisms of the size effect on the flow and heat transfer into two groups a) the relative importance of factors varies which influence the flow and heat transfer as the characteristic length decreases, even if the continuum assumption is still valid; b) the continuum assumption breaks down as the characteristic length of the flow becomes comparable to the mean free path of the molecules. For the first group, the departure of most flow and thermal phenomena at microscale from conventional ones is because factors related to surface effects have more impact to the flow and heat transfer at small scales. Among these are: the surface friction induced flow compressibility, the surface roughness, the axial heat conduction in the wall, channel surface geometry, surface electrostatic charges, and measurement errors. For the second group, the incontinuity of fluid medium near the wall is the origin of the size effect on the flow and heat transfer. Molecular dynamics simulations show that velocity slips between of the gas flow in the nano channel are determined by fluid property, the Knudsen number, and by the surface roughness as well. In addition, molecular dynamics study indicates that bubble nucleation starts from the nanoscale low-density region in liquid, and only the fluid repulsive nanoparticle with a size close to the critical radius can enhance the bubble nucleation remarkably.

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