Part 1 - Flow Induced Vibration in Shell and Tube Heat Exchangers

Now that we have the understanding of Critical Flow Velocity in a Shell and Tube Heat Exchanger, we are going deeper into the calculation part.

Remember that if the velocity reaches the calculated Vc (Critical Flow Velocity), vibration will be generated with an unacceptable amplitude.

This is the formula;

Lower Natural Frequency of Vibration equates to susceptibility to Flow Induced Vibration

Lets understand, first and foremost, the failure region in a Shell and Tube Heat Exchanger. Remember, lower natural frequency, the easier to fail due to flow induced vibration.

If you need to recall the main components of a Shell and Tube Heat Exchanger, click here.

Right.

U-Tubes at U-bends - Outer row have a lower natural frequency of vibration, therefore it is more susceptible to FIV than the inner rows.

Tubesheet region - unsupported span is longer than in baffle region as per picture below and this results in lower natural frequency. Adding to it is the location of impingement plate at the inlet nozzle (high local velocity area) makes this area a primary concern for FIV.

The higher the span, the lower the natural frequency, the easier for the tube to vibrate.

High local velocity that can reach Vc and causing high vibration.

Nozzle entrance and exit area - Restricted entrance cause by impingement plates, larger outer diameter limits, and small nozzle diameter creates high local velocity which in turn could cause vibration.

Any obstruction - tie-rods, sealing strips, impingement plates can cause high localised velocity, initiate vibration and may cause failure of the tube due to FIV.

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