An ordinary egg can be approximated as a 5.5-cm diameter sphere. The egg is initially at a uniform temperature of 8°C and is dropped into boiling water at 97°C. Taking the properties of the egg to be r 1020 kg/m3 and cp 3.32kJ/kg · °C, determine (a) how much heat is transferred to the egg by the time the average temperature of the egg rises to70°C and (b) the amount of entropy generation associated with this heat transfer process.

Respuesta :

Answer:

a) [tex]Q_{in} = 13.742\,kW[/tex], b) [tex]\Delta S = 370.15\,\frac{kJ}{K}[/tex]

Explanation:

a) The heat transfered to the egg is computed by the First Law of Thermodynamics:

[tex]Q_{in} +U_{sys,1} - U_{sys,2} = 0[/tex]

[tex]Q_{in} = U_{sys,2} - U_{sys,1}[/tex]

[tex]Q_{in} = \rho_{egg}\cdot \left(\frac{4\pi}{3}\cdot r^{3}\right)\cdot c \cdot (T_{2}-T_{1})[/tex]

[tex]Q_{in} = \left(1020\,\frac{kg}{m^{3}}\right)\cdot \left(\frac{4\pi}{3}\right)\cdot (0.025\,m)^{3}\cdot \left(3.32\,\frac{kJ}{kg\cdot ^{\textdegree}C} \right)\cdot (70\,^{\textdegree}C - 8\,^{\textdegree}C)[/tex]

[tex]Q_{in} = 13.742\,kW[/tex]

b) The amount of entropy generation is determined by the Second Law of Thermodynamics:

[tex]\Delta S = \frac{Q_{in}}{T_{in}}[/tex]

[tex]\Delta S = \frac{13.742\,kJ}{370.15\,K}[/tex]

[tex]\Delta S = 370.15\,\frac{kJ}{K}[/tex]