MATH 3A03 Lecture Notes - Lecture 7: Boundary Layer Thickness, Nusselt Number, Laminar Flow
12 Oct 2016
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Document Summary
In external convection, boundary layers will always form freely since there is no adjacent surface to restrict boundary layer development there is always fluid outside the boundary layer where the velocity and temperature are constant. Examples: flow over flat plate (inclined or parallel), around cylinders/spheres/turbine blades, banks of tubes, etc. Goal of this chapter: to derive h for external convection geometries. Pr c p k: dimensionless value based only on fluid properties (i. e. independent of flow conditions or geometry, normally found in tables. Re geometry of the object over (or through) which the fluid passes: the characteristic length l is the length of a plate (x) or diameter (d) of a sphere, cylinder or duct (boundary layer development) Nu hl k: relates the relative importance of convection versus conductive heat transfer from the vantage point of the fluid (i. e. k = kfluid, or: relative contribution of advective heat transfer versus conductive heat transfer in determining h.
