Water at a rate of 45,500 kg/h is heated from 80 to 150 ? C in a heat exchanger having two shell passes and eight tube passes with a total surface area of 925 m2 . Hot exhaust gases having approximately the same thermophysical properties as air enter at 350 ? C and exit at 175 ? C.

A) Determine the overall heat transfer coefficient.

he exchanger must heat 2 kg/s of water from 300 to 350 K, using 1.25 kg/s of combustion gases entering at 700 K.

B)

1. Using the overall heat transfer coefficient determined in the example, find the required heat exchanger volume, assuming single-pass operation.

2. What is the number of tube rows NL in the longitudinal (gas-flow) direction?

3. If the velocity of water flowing through the tubes is 100 mm/s, what is the number of tube rows NT in the transverse direction?

4. What is the required tube length?