An exhaust pipe of 75 mm outside diameter is cool by surrounding it by an annular space containing water. The exhaust ga

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An exhaust pipe of 75 mm outside diameter is cool by surrounding
it by an annular space containing water. The exhaust gas enters the
exhaust pipe at 350°C and the water enters from the mains at 10°C.
The heat transfer coefficients for the gases and water are 0.3 and
1.5 kW / m2 K, respectively and the pipe thickness may be taken to
be negligible. The gases are cool to 100 °C and the mean specific
heat capacity at constant pressure is 1.13 kJ/ kg K. The gas flow
rate is 200kg/hr and the water flow rate is 1400 kg/ h. The
specific heat capacity of water is 4.19 kJ/kg K. State three (3)
assumptions. Calculate:
(i) The required pipe length for parallel-flow;
(ii) The required pipe length for counter-flow.