Thermodynamics HW Solutions 649

Thermodynamics HW Solutions 649 - friction factor and the...

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Chapter 8 Internal Forced Convection 8-39 The average flow velocity in a pipe is given. The pressure drop and the pumping power are to be determined. Assumptions 1 The flow is steady and incompressible. 2 The entrance effects are negligible, and thus the flow is fully developed. 3 The pipe involves no components such as bends, valves, and connectors. 4 The piping section involves no work devices such as pumps and turbines. Properties The density and dynamic viscosity of water are given to be ρ = 999.7 kg/m 3 and μ = 1.307 × 10 -3 kg/m s, respectively. Analysis ( a ) First we need to determine the flow regime. The Reynolds number of the flow is 1836 s kg/m 10 307 . 1 m) 10 m/s)(2 2 . 1 )( kg/m 7 . 999 ( Re 3 - -3 3 = × × = = μ ρ D m V which is less than 2300. Therefore, the flow is laminar. Then the
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Unformatted text preview: friction factor and the pressure drop become kPa 188 V = = = = = = 2 2 3 2 kN/m 1 kPa 1 m/s kg 1000 kN 1 2 m/s) 2 . 1 )( kg/m 7 . 999 ( m 0.002 m 15 0349 . 2 0349 . 1836 64 Re 64 m D L f P f Water 1.2 m/s L = 15 m D = 0.2 cm ( b ) The volume flow rate and the pumping power requirements are W 0.71 V V = = = = = = = /s m kPa 1 W 1000 ) kPa 188 )( / m 10 77 . 3 ( / m 10 77 . 3 ] 4 / m) (0.002 m/s)[ 2 . 1 ( ) 4 / ( 3 3 6 pump 3 6 2 2 s P V W s D A V m c m & & & Therefore, power input in the amount of 0.71 W is needed to overcome the frictional losses in the flow due to viscosity. 8-11...
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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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