Air is heated by being passed over some tubes through which steam flows steadily. Steam enters the heat exchanger at 200 kPa and 200 C at a rate of 8 kg/min, and leaves at 180 kPa and 100C. Air enters at 100 kPa and 25 C and leaves at 47 C. Determine the volume flow rate of air at the inlet?please try to use the numbers in the question and not just provide the equations,Thank you very much in advance!
Is there some information missing here, viz. the specific heat of steam and air? I assume that the steam does not condense in the exchanger. Specific heat of steam at the average pressure of 190 kPa (1.9 bar) is 2.1124 kJ/kgK. The rate of heat loss by the steam is therefore 8kg/min x 2.1124 kJ/kg x 100K = 1690 kJ/min. Specific heat of dry air at 1 atm is 1.005 kJ/kgK. Therefore 1690 kJ/min = mass flow rate of air x 1.005 kJ/kgK x 22 K mass flow rate = 1690 / (1.005 x 22) = 76.4 kg/min Density of air = 1.2 kg/m3, so volume flow rate of air at inlet = 76.4/1.2 = 64 m3/min.
