Thermodynamics HW Solutions 562

Thermodynamics HW Solutions 562 - x cr where the Reynolds...

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Chapter 7 External Forced Convection 7-32 Air is flowing over a long flat plate with a specified velocity. The distance from the leading edge of the plate where the flow becomes turbulent, and the thickness of the boundary layer at that location are to be determined. Assumptions 1 The flow is steady and incompressible. 2 The critical Reynolds number is Re cr = 5 × 10 5 . 3 Air is an ideal gas. 4 The surface of the plate is smooth. Properties The density and kinematic viscosity of air at 1 atm and 25 ° C are ρ = 1.184 kg/m 3 and ν = 1.562×10 –5 m 2 /s (Table A-15). Analysis The critical Reynolds number is given to be Re cr = 5 × 10 5 . The distance from the leading edge of the plate where the flow becomes turbulent is the distance
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Unformatted text preview: x cr where the Reynolds number becomes equal to the critical Reynolds number, m 76 0.9 m/s 8 ) 10 5 )( /s m 10 562 . 1 ( Re Re 5 2 5 = = = = V V cr cr cr cr x x The thickness of the boundary layer at that location is obtained by substituting this value of x into the laminar boundary layer thickness relation, cm 0.69 m 006903 . ) 10 (5 m) 976 . ( 5 Re 5 Re 5 2 / 1 5 2 / 1 2 / 1 = = = = = cr cr cr x x x x V x cr Discussion When the flow becomes turbulent, the boundary layer thickness starts to increase, and the value of its thickness can be determined from the boundary layer thickness relation for turbulent flow. 7-24...
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This note was uploaded on 01/22/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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