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Thermodynamics HW Solutions 537

# Thermodynamics HW Solutions 537 - 2 The edge effects are...

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Chapter 6 Fundamentals of Convection 6-50 A metallic airfoil is subjected to air flow. The average friction coefficient is to be determined. Assumptions 1 Steady operating conditions exist. 2 The edge effects are negligible. Properties The properties of air at 25 ° C and 1 atm are (Table A-15) ρ = 1.184 kg/m 3 , C p =1.007 kJ/kg-K, Pr = 0.7296 Analysis First, we determine the rate of heat transfer from W 2083 s) 60 2 ( C ) 150 160 ( C) J/kg kg)(500 50 ( ) ( 1 2 airfoil p, = × ° ° = Δ = t T T mC Q Then the average heat transfer coefficient is C W/m 335 . 1 C ) 25 155 )( m 2 (1 W 2083 ) ( ) ( 2 2 ° = ° = = ⎯→ = T T A Q h T T hA Q s s s s where the surface temperature of airfoil is taken as its average temperature, which is (150+160)/2=155 ° C. The average friction coefficient of the airfoil is determined from the modified Reynolds analogy to be 0.000227 = ° ° = ρ = C) J/kg m/s)(1007 8 )( kg/m 184 . 1 ( ) 7296 . 0 ( C) W/m (1.335 2 Pr 2 3 3 / 2 2 2/3 p f C h C V Air 25 ° C 8 m/s L =3 m 6-51 A metallic airfoil is subjected to air flow. The average friction coefficient is to be determined. Assumptions 1 Steady operating conditions exist.
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Unformatted text preview: 2 The edge effects are negligible. Properties The properties of air at 25 ° C and 1 atm are (Table A-15) ρ = 1.184 kg/m 3 , C p =1.007 kJ/kg-K, Pr = 0.7296 Analysis First, we determine the rate of heat transfer from W 2083 s) 60 2 ( C ) 150 160 ( C) J/kg kg)(500 50 ( ) ( 1 2 airfoil p, = × ° − ° ⋅ = Δ − = t T T mC Q & Then the average heat transfer coefficient is C W/m 335 . 1 C ) 25 155 )( m 2 (1 W 2083 ) ( ) ( 2 2 ° ⋅ = ° − = − = ⎯→ ⎯ − = ∞ ∞ T T A Q h T T hA Q s s s s & & Air 25 ° C 12 m/s L =3 m where the surface temperature of airfoil is taken as its average temperature, which is (150+160)/2=155 ° C. The average friction coefficient of the airfoil is determined from the modified Reynolds analogy to be 0.0001512 = ° ⋅ ° ⋅ = ρ = C) J/kg m/s)(1007 12 )( kg/m 184 . 1 ( ) 7296 . ( C) W/m (1.335 2 Pr 2 3 3 / 2 2 2/3 p f C h C V 6-26...
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