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单词 boundary layer
释义
boundary layer

Physics
  • The thin layer of fluid formed around a solid body or surface relative to which the fluid is flowing. Adhesion between the molecules of the fluid and that of the body or surface causes the molecules of the fluid closest to the solid to be stationary relative to it. The transfer of heat or mass between a solid and a fluid flowing over it is largely controlled by the nature of the boundary layer.


Mathematics
  • In fluid dynamics, a boundary layer is a thin layer of fluid close to a surface where the effects of viscosity are important. The Navier-Stokes equations can then be separately analysed in the boundary layer, where the thinness of the layer is to some extent negligible, and outside the boundary layer, where the effects of viscosity are negligible.


Astronomy
  • In a planetary atmosphere, the level of the atmosphere in direct contact with the planet’s surface, in which friction between the surface and the air plays a significant role in determining atmospheric movements. On Earth, the boundary layer lies at the base of the troposphere and varies in depth from a few hundred metres under stable conditions to 1–2 km when convection is strong.


Chemical Engineering
  • The region between a surface or wall and a point in a flowing fluid over it where the velocity is at a maximum. Within this region, the movement of the fluid flow is governed by frictional resistance. By convention the edge of this region is assumed to lie at a point in the flow that has a velocity equal to 99 per cent of the local mainstream velocity. Within the boundary layer, which is laminar in flow, the transfer of heat and mass across it occurs only by molecular diffusion.


Geology and Earth Sciences
  • 1. At the interface between a solid surface and a fluid, a thin fluid layer that is static because of friction between molecules of the fluid and the solid.

    2. See planetary boundary layer.


Geography
  • Any layer of the atmosphere significantly affected by the Earth’s surface. The laminar boundary layer is the few millimetres above the surface; the turbulent boundary layer denotes the conspicuously turbulent part of the atmosphere.

    http://www.esrl.noaa.gov/research/themes/pbl/ NOAA pages on surface and planetary boundary layer processes.


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