Chapter 9 Natural Convection 9-43E The average surface temperature of a human head is to be determined when it is not covered. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. 4 The head can be approximated as a 12-in.-diameter sphere. Properties The solution of this problem requires a trial-and-error approach since the determination of the Rayleigh number and thus the Nusselt number depends on the surface temperature which is unknown. We start the solution process by “guessing” the surface temperature to be 120 ° F for the evaluation of the properties and h . We will check the accuracy of this guess later and repeat the calculations if necessary. The properties of air at 1 atm and the anticipated film temperature of ( T s + T ∞ )/2 = (120+77)/2 = 98.5 ° F are (Table A-15E) 1-2 3 R 001791 .0 R
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.