Thermodynamics HW Solutions 330

Thermodynamics HW Solutions 330 - Chapter 4 Transient Heat...

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Chapter 4 Transient Heat Conduction 4-53 A hot baked potato is taken out of the oven and wrapped so that no heat is lost from it. The time the potato is baked in the oven and the final equilibrium temperature of the potato after it is wrapped are to be determined. Assumptions 1 The potato is spherical in shape with a diameter of 8 cm. 2 Heat conduction in the potato is one-dimensional because of symmetry about the midpoint. 3 The thermal properties of the potato are constant. 4 The heat transfer coefficient is constant and uniform over the entire surface. 5 The Fourier number is τ > 0.2 so that the one-term approximate solutions (or the transient temperature charts) are applicable (this assumption will be verified). Properties The properties of the potato are given to be k = 0.6 W/m. ° C, ρ = 1100 kg/m 3 , C p = 3.9 kJ/kg. ° C, and α = 1.4 × 10 -7 m 2 /s. Oven T = 170 ° C Potato T 0 = 70 ° C Analysis ( a ) The Biot number is Bi hr k o == ° ° = () ( . ) (. ) . 25 0 04 06 167 W/m . C m W/m. C 2 The constants λ 1 and A 1 corresponding to this Biot number are, from Table 4-1, 11 18777 14113 .. and A Then the Fourier number and the time period become
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This note was uploaded on 01/19/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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