# Air at a temperature of 20 °C passes… solved problem

#### Air at a temperature of 20 °C passes through a heat exchanger at a velocity of 40 m/s where its temperature is raised to 820°C. It then enters a turbine with same velocity of 40 m/s and expands till the temperature falls to 620°C. On leaving the turbine, the air is taken at a velocity of 55 m/s to nozzle where it expands until the temperature has fallen to 510°C. If the air flow rate is 2.5 kJ/s, calculate : (i) Rate of heat transfer to the air in the heat exchanger ; (ii) The power output from the turbine assuming no heat loss ; (iii) The velocity at exit from the nozzle, assuming no heat loss. Take the enthalpy of air as h = cpt, where cp is the specific heat equal to 1.005 kJ/kg°C and t the temperature.

Air at a temperature of 20 °C passes through a heat exchanger at a velocity of 40 m/s where its temperature is raised to 820°C. It then enters a turbine with same velocity of 40 m/s and expands till the temperature falls to 620°C. On leaving the turbine, the air is taken at a velocity of 55 m/s to nozzle where it expands until the temperature has fallen to 510°C. If the air flow rate is 2.5 kJ/s, calculate :
(i) Rate of heat transfer to the air in the heat exchanger ;
(ii) The power output from the turbine assuming no heat loss ;
(iii) The velocity at exit from the nozzle, assuming no heat loss.
Take the enthalpy of air as h = cpt, where cp is the specific heat equal to 1.005 kJ/kg°C and t the temperature.  