20 - 10/15/2010 1 Internal Flow Chapter 8 8.3,4 What...

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Unformatted text preview: 10/15/2010 1 Internal Flow Chapter 8 8.3,4 What statement is not true about flow inside cylinders? a)The free stream velocity is best used to determine the Reynolds number. b)When the flow is fully developed, the velocity profile does not change with distance along the tube. c)Transition to turbulent flow has a lower Re than for external flow. d)The hydrodynamic boundary layer becomes fully developed faster than the thermal boundary layer (i.e., closer to the entrance region) for fluids with a high Prandtl numbers. e)All statements are true. Fully Developed Conditions Assuming steady flow and constant properties, hydrodynamic conditions, including the velocity profile, are invariant in the fully developed region. The pressure drop may be determined from knowledge of the friction factor f, where, ( ) 2 / / 2 m dp dx D f u Laminar flow in a circular tube: 64 Re D f = Turbulent flow in a smooth circular tube: ( ) 2 0.7901n Re 1.64 D f = ( ) 2 / / 2 m u D dx dp...
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20 - 10/15/2010 1 Internal Flow Chapter 8 8.3,4 What...

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