A boiler may have waste gases leaving the installation when artificial draught is used at 450 K . The natural draught chimney is of 50 m height. The hot gases within chimney are at temperature of 600 K and air requirement is 15 kg per kg of fuel burnt. The atmospheric air is at 27 C temperature and mean specific heat of hot gases is 1.0032 kJ/kg.K. The calorific value of fuel burnt is 32604 kJ/kg. Determine (a) the efficiency of chimney, (b) the extra heat carried away by flue gases per kg of fuel.