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Problem 19-1 - Example 19-1 A roughly spherical potato of...

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Example 19-1 A roughly spherical potato of diameter 3” is placed in an oven at 350 ° F. If the potato is initially at 50 ° F, how long will it take for it to reach 300 ° F? Assume: Btu 0.29 hr ft R k = 2 Btu 2.5 hr ft R h = 3 lbm 52 ft ρ = 3 4 3 sph V r π = Btu 0.825 lbm °F p c = 2 4 sph A r π = Solution: Using the lumped system approximation ( ) ln p f i f mc T t T t h A T T = − 3 4 3 m V r ρ ρ π = = ( ) 3 2 4 ( ) 3 ln 4 p f i f r c T t T t T T h r ρ π π = −
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