Number of Tubes in Heat Exchanger (Depends on)

The number of tubes in an exchanger depends on the

•  Fluid flow rates
•  Available pressure drop.

The number of tubes is selected such that the

•  Tube side velocity for water and similar liquids ranges from 0.9 to 2.4 m/s (3 to 8 ft/sec)

•  Shell-side velocity from 0.6 to 1.5 m/s (2 to 5 ft/sec).

 The lower velocity limit corresponds to limiting the fouling, and the upper velocity limit corresponds to limiting the rate of erosion. 

When sand and silt are present, the velocity is kept high enough to prevent settling.