Chapter 7 External Forced Convection7-94A fan is blowing air over the entire body of a person. The average temperature of the outer surface of the person is to be determined. Assumptions1Steady operating conditions exist. 2Air is an ideal gas with constant properties. 3 The pressure of air is 1 atm. 4The average human body can be treated as a 30-cm-diameter cylinder with an exposed surface area of 1.7 m2. PropertiesWe assume the film temperature to be 35°C. The properties of air at 1 atm and this temperature are (Table A-15) D= 0.3 mPerson, Ts90 W ε= 0.9 V∞= 5 m/s T∞= 32°C 7268.0Pr/sm10655.1CW/m.02625.025-=×=°=υkAnalysisThe Reynolds number is 42510063.9/sm10655.1m)m/s)(0.3(5Re×=×=υ=−∞DVThe proper relation for Nusselt number corresponding to this Reynolds number is ()6.203000,28210063.917268.0/4.01)7268.0()10063.9(62.03.0000,282Re1Pr/4.01PrRe62.03.05/48/544/13/23/15.045/48/54/13/23/15.0=⎥⎥⎦⎤⎢⎢⎣⎡⎟⎟⎠⎞⎜⎜⎝⎛×++×+=
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