Question

A heat engine is supplied with 278 k3/s of heat at a constant fixed temperature of 283°C and the best rejection takes place at 5°C The following results were reported (i) 208 klis are rejected, (ii) 139 klis are rejected, and (ii) 70 kJ/s are rejected Classify which of the results report a reversible cycle or irreversible cycle or impossible results

Answer 1

1.

$\Sigma\frac QT=\frac{278}{556}-\frac{208}{278}=-0.248<0,$ cycle is irreversible.

2.

$\Sigma\frac QT=\frac{278}{556}-\frac{139}{278}=0,$ cycle is reversible.

3.

$\Sigma\frac QT=\frac{278}{556}-\frac{70}{278}=0.248>0,$ this cycle is impossible by second law of thermodynamics, i.e. Clausius inequality.