Every design of a shell-and-tube heat exchanger should be reviewed to ensure that it is free from potential flow-induced vibration problems. Some items may require major changes in the design while others will be minor.

A. Vibration analysis primary check

A four-step primary check is suggested to minimize the probability of flow-induced vibration problems. The steps can be taken in any order and should be repeated for the inlet, central, and outlet regions. For a high probability of not having vibration, it must not be predicted for any of the following steps:

Step 1. Acoustic vibration. For a gas or vapor as the shell-side fluid, compare the vortex shedding frequency f_vs (Equation 443.2 with u = u_c and Figure 443.2) and turbulent buffeting frequency f_tb (Equation 443.3) with the acoustic frequency f_a (Equation 443.6). If cither is within 20% of f_a acoustic vibration is possible.

Step 2. Fluid clastic instability. For either gas or liquid as the shell-side fluid, compare the cross-flow velocity u_c with the critical velocity u_crit to initiate fluid clastic instability (Equation 443.4. Figure 443.4, and δ₀ = 0.03 for gases and vapors and = 0.10 for liquids and two-phase mixtures). Vibration and damage are probable when u_c is greater than u_crit.