Question

Air at a temperature of 15c passes through a heat exchanger at a velocity of 30 m/s where its temperature is raised to 800c. It then enters a turbine with the same velocity of 30 m/s and expands until the temperature falls to 650c. On leaving the turbine the air is taken at a velocity of 60 m/s to a nozzle where it expands until the temperature has fallen to 500c. If the air flow rate is 2 kg/s, calculate i. The 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 k and t the temperature.

Answer 1

Air at a temperature of 15C passes through a heat exchanger at a velocity of 30 m/s where its temperature is raised to 800C . It then enters a turbine with the same velocity of 30 m/s and expands until the temperature falls to 650C. On leaving the turbine, the air is taken at a velocity of 60 m/s to a nozzle where it expands until the temperature has fallen to 500C. If the air flow rate is 2 kg/s, calculate
(a) the rate of heat transfer to the air in the heat exchanger.
(b) the power output from the turbine assuming no heat loss.
(c) the velocity at exit from the nozzle, assuming no heat loss.