Question 2.49: 2700 kJ/min at 800° C is supplied to an engine which rejects...

Principles of Mechanical Engineering

2700 kJ/min at 800° C is supplied to an engine which rejects at 125° C. If heat rejected is (a) 1000 kJ/min, (b) 800 kJ/min, and (c) 1200 kJ/min, specify the process.

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$\begin{aligned}&T_1=800+273=1073 \mathrm{~K} \\&T_2=125+273=398 \mathrm{~K}\end{aligned}$

(a) $\quad \oint \frac{\delta Q}{T}=\frac{Q_1}{T_1}-\frac{Q_2}{T_2}=\frac{2700}{1073}-\frac{1000}{398}=2.516-2.512 \approx 0$

The cycle is reversible.

(b) $\quad \oint \frac{\delta Q}{T}=\frac{2700}{1073}-\frac{800}{398}=2.516-2.010=0.506>0$

The cycle is impossible.

(c) $\quad \oint \frac{\delta Q}{T}=\frac{2700}{1073}-\frac{1200}{398}=2.516-3.015=-0.499<0$

The cycle is irreversible.

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