Thermodynamics HW Solutions 326

Thermodynamics HW - Chapter 4 Transient Heat Conduction 4-50 A person puts apples into the freezer to cool them quickly The center and surface

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Chapter 4 Transient Heat Conduction 4-50 A person puts apples into the freezer to cool them quickly. The center and surface temperatures of the apples, and the amount of heat transfer from each apple in 1 h are to be determined. Assumptions 1 The apples are spherical in shape with a diameter of 9 cm. 2 Heat conduction in the apples is one-dimensional because of symmetry about the midpoint. 3 The thermal properties of the apples 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 apples are given to be k = 0.418 W/m. ° C, ρ = 840 kg/m 3 , C p = 3.81 kJ/kg. ° C, and α = 1.3 × 10 -7 m 2 /s. Analysis The Biot number is Apple T i = 20 ° C Air T = -15 ° C 861 . 0 ) C
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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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