Thermodynamics HW Solutions 321

Thermodynamics HW Solutions 321 - Chapter 4 Transient Heat...

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Chapter 4 Transient Heat Conduction 4-45 An egg is dropped into boiling water. The cooking time of the egg is to be determined. Assumptions 1 The egg is spherical in shape with a radius of r 0 = 2.75 cm. 2 Heat conduction in the egg is one-dimensional because of symmetry about the midpoint. 3 The thermal properties of the egg 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 thermal conductivity and diffusivity of the eggs can be approximated by those of water at room temperature to be k = 0.607 W/m. ° C, α = kC p / ρ = 0.146 × 10 -6 m 2 /s (Table A-9). Analysis The Biot number is Water 100 ° C Egg T i = 8 ° C 2 . 36 ) C W/m. 607 . 0 ( ) m 0275
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