At the design phase a number of changes can be made to reduce vibration problems (Chenoweth, 1982; Chenoweth, 1977). Most require a compromise to satisfy all of the requirements and added cost is a likely result. When an exchanger already in service has a serious vibration problem, there are still some temporary fixes that can be made in the field.

A. Possible design changes to correct anticipated vibration problems

If a vibration analysis shows that vibration is probable, design elements can be reconsidered from die standpoint of vibration. Assuming that the process conditions cannot be changed, the following design changes should be considered.

Reduce the shell-side velocities. If the flow rate of the shell-side fluid is fixed, velocities can be reduced by increasing the tube pitch or using TEMA X-or J-shell styles. This is particularly attractive when the design is pressure drop-limiting, but it may result in a larger shell.

Increase the tube natural frequency. The most effective way to increase the tube natural frequency is to reduce the longest unsupported span length. Reducing the span length to 80% increases the natural frequency by more than 50%. Secondary effects can be produced by changing the tube material and increasing the tube wall thickness, but neither of these will greatly increase the natural frequency within normal industrially acceptable limits. The natural frequency can be increased by lacing or driving wedges between tubes to limit movement. This technique has been particularly effective in controlling vibration in the bend region of U-tube bundles.