Thermodynamics HW Solutions 270

Thermodynamics HW Solutions 270 - Chapter 3 Steady Heat...

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Chapter 3 Steady Heat Conduction 3-160E The surface temperature of a baked potato drops from 300 ° F to 200 ° F in 5 minutes in an environment at 70 ° F. The average heat transfer coefficient and the cooling time of the potato if it is wrapped completely in a towel are to be determined. Assumptions 1 Thermal properties of potato are constant, and can be taken to be the properties of water. 2 The thermal contact resistance at the interface is negligible. 3 The heat transfer coefficients for wrapped and unwrapped potatoes are the same. Properties The thermal conductivity of a thick towel is given to be k = 0.035 Btu/h ft °F. We take the properties of potato to be those of water at room temperature, ρ = 62.2 lbm/ft 3 and C p = 0.998 Btu/lbm ⋅° F. Analysis This is a transient heat conduction problem, and the rate of heat transfer will decrease as the potato cools down and the temperature difference between the potato and the surroundings decreases.
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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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