The thermal efficiency of the hypothetical cycle shown is

Concept:

The area under the curve on T-S diagram shows the heat interaction for a reversible process

The area enclosed by the cycle on the T-S diagram gives the work interaction for the cycle

In the cyclic process

W_net = Q_net = Q_In – Q_Out

Q_out = Heat rejection at the lowest temperature in the cycle

Q_out = T_min∆S

Where ∆S is the entropy change

Calculation:

Net work is equal to the area enclosed by the cycle, i.e. area of the triangle

\({W_{net}} = \frac{1}{2} \times 4 \times 400 = 800\;kJ\)

∴ Wnet = 800 kJ

Q_out = 300 × (5 - 1) = 1200 kJ

So, Q_In = 800 + 1200 = 2000 kJ

The efficiency of the cycle \({\eta _{cycle}} = \frac{{{W_{net}}}}{{{Q_{in}}}} = \frac{{800}}{{2000}} = 0.4\)