Chapter 4 Transient Heat Conduction4-119A watermelon is placed into a lake to cool it. The heat transfer coefficient at the surface of the watermelon and the temperature of the outer surface of the watermelon are to be determined. Assumptions1The watermelon is a homogeneous spherical object. 2 Heat conduction in the watermelon is one-dimensional because of symmetry about the midpoint. 3The thermal properties of the watermelon are constant. 4The 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). PropertiesThe properties of the watermelon are given to be k = 0.618 W/m.°C, α= 0.15×10-6m2/s, ρ= 995 kg/m3and Cp= 4.18 kJ/kg.°C. AnalysisThe Fourier number is 252.0m)10.0(s/min60min)4060(4/s)m1015.0(2262=×+××=α=τ−ortWater melon Ti= 35°C
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