A potato can be approximated as a cylinder of dimeter 4 cm a

A potato can be approximated as a cylinder of dimeter 4 cm and length 10 cm. This potato is initially at a uniform temperature of 20 oC and is dropped into boiling water at 100 oC. Taking the properties of the potato to be = 1100 kg/m3 and c = 3.32 kJ/(kg· oC), please determine:

How much heat is transferred to the potato by the time the average temperature of the potato rises to 40 oC.

The amount of entropy generation associated with this heat transfer process. Assume that the water is maintained as boiling during this process.

Solution

a) Heat transfered =   mass of potato * Cp * Temperature rise

                            = 1100 * pi * 0.02^2 * 0.1 * 3.32 * 40   = 18.357 kJ

b) Entropy generated   =   Q * (1 / (273 + 40) - 1 / (273 + 100) )

                                  = 18.357 * ( 1 /313 - 1 / 373 )    = 9.43 J/K