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Q7. A combustion air heater has 100 tubes each of 2.5 m long in a single pass counter flow arrangement. Exhaust gas from the combustion process enters at 400℃ and heats 0.3334 kg/s of air from 25℃ to 170℃. The combustion air to fuel ratio is 20: 1 and the overall heat transfer coefficient is 6.391 W/m²K.

(a) Calculate EACH of the following:

(i) The outlet temperature of the exhaust gas; (5)

(ii) The log means temperature difference for the heater; (5)

(iii) The mean diameter of the heater tubes. (4)

(b) Sketch the heater temperature distribution (profile) diagram. (2)

Note: for air c_p=1.005  kJ⁄(kg K)

for exhaust gas c_p=1.15  kJ⁄(kg K).