Temperature of saturation steam = 200 + 273 = 473 K

Initial temperature of gases = 1000 + 273 = 1273 K

Final temperature of gases = 500 + 273 = 773 K

For gases : c_{pg} = 1 kJ/kg K

Latent heat of steam of 200°C

saturation temperature, h_{fg} = 1940.7 kJ/kg

Atmospheric temperature = 20 + 273 = 293 K

Heat lost by gases = Heat gained by 1 kg saturated water when it is converted to steam at 200°C.

m_{g}c_{pg} (1273 – 773) = 1940.7

[where m_{g} = mass of gases, c_{pg} = specific heat of gas at constant pressure]

m_{g} = \(\cfrac{1940.7}{(1273-773)}\) = 3.88 kg

Change of entropy of m_{g} kg of gas,

Change of entropy of water (per kg) when it is converted into steam,

Net change in entropy due to heat transfer

= – 1.935 + 4.103 = 2.168 kJ/K.

Increase in unavailable energy due to heat transfer

= 293 × 2.168, i.e., cross hatched area

= 635.22 kJ per kg of steam formed.