Question

Oxygen enters an insulated 14.2-cm-diameter pipe with a velocity of 60 m/s. At the pipe entrance, the oxygen is at 240 kPa and 20°C; and, at the exit, it is at 200 kPa and 18°C Calculate the rate at which entropy is generated in the pipe.

Answer 1

Answer:

Entropy generation==0.12 KW/K

Explanation:

$s_2-s_1=C_p\ln \frac{T_2}{T_1}-R\ln \frac{P_2}{P_1}$

$s_2-s_1=0.891\ln \frac{291}{293}-0.2598\ln \frac{200}{240}$

$s_2-s_1=0.0412\frac{KJ}{kg-K}$

Mass flow rate= $\rho\times\dfrac{\pi}{4}d^2V$

$\rho_1=\dfrac {P_1}{RT_1}$

$\rho_1=\dfrac {240}{0.2598\times 293}$

$\rho_1=3.51\frac{kg}{m^3}$

mass flow rate=$\rho_1A_1V_1$

So by putting the values

Mass flow rate=2.97 kg/s

So entropy generation=(2.97)(0.0412)

                                    =0.12 KW/K