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Thermodynamics HW Solutions 577

# Thermodynamics HW Solutions 577 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-48 An aircraft is cruising at 900 km/h. A heating system keeps the wings above freezing temperatures. The average convection heat transfer coefficient on the wing surface and the average rate of heat transfer per unit surface area are to be determined. Assumptions 1 Steady operating conditions exist. 2 Radiation effects are negligible. 3 Air is an ideal gas with constant properties. 4 The wing is approximated as a cylinder of elliptical cross section whose minor axis is 30 cm. Properties The properties of air at 1 atm and the film temperature of (T s + T )/2 = (0-55.4)/2 = -27.7 ° C are (Table A-15) 7422 . 0 Pr /s m 10 106 . 1 C W/m. 02152 . 0 2 5 - = × = ° = υ k 18.8 kPa V = 900 km/h T = -55.4 ° C Note that the atmospheric pressure will only affect the kinematic viscosity. The atmospheric pressure in atm unit is P == (. . 188 01855 kPa) 1 atm 101.325 kPa atm The kinematic viscosity at this atmospheric pressure is /s m 10 961 . 5 1855
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