# A hot-wire anemometer is used to determine the boundary layer velocity profile in the air flow over a scale model of an automobile. The hot-wire is held in a traversing mechanism that moves the wire in a direction normal to

A hot-wire anemometer is used to determine the boundary layer velocity profile in the air flow over a scale model of an automobile. The hot-wire is held in a traversing mechanism that moves the wire in a direction normal to the surface of the model. The hot-wire is operated at constant temperature. The boundary layer thickness is to be defined as the distance from the model urface at which the velocity is 90% of the free stream. If the probe current is low when the hot-wire is held in the free stream velocity, U∞, What current will indicate the edge of the boundary layer? Neglect radiation heat transfer from the hot-wire and conduction from the ends of the wire.
GIVEN
Thin, electrically-heated constant-temperature wire in air flow near an automobile model
Boundary layer thickness ° point when velocity (Uy) = 90% free stream velocity Vo
Probe current at U∞ = Io
ASSUMPTIONS
Conduction from the ends of the hot-wire is negligible
Reynolds number is small

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## Principles of heat transfer

ISBN: 978-0495667704

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Authors: Frank Kreith, Raj M. Manglik, Mark S. Bohn

Posted Date: November 24, 2011 13:14:41