STV-4 Flow-Induced Acoustic Vibration in Tube Bundles

J. M. Chenoweth
1988; revised 1994

Acoustic vibration is defined as a sound, usually of a characteristic pitch ranging from a low rumble to a piercing scream, caused by the shellside fluid flowing through the bundle. The frequency of pitch of the sound increases in steps as the shellside flow rate increases. The intensity of the sound can build by resonance to levels that are intolerable to the human ear. Intensities of 165 dB have been recorded in the vicinity of heat exchangers experiencing acoustic vibration.

Acoustic vibration is most commonly found in heat exchangers of large shell diameters, typically over 49 in. (1.25 m). It rarely matches the natural frequency of tubes; therefore, accompanying tube vibration or tube damage is seldom a problem. Acoustic vibration is most often observed when the shellside fluid is a gas or a vapor and is not observed when the shellside fluid is a liquid. However, acoustic vibration has been observed in shellside condensers where the two-phase, liquid/gas mixture liquid volume fraction did not exceed about 15 percent.

The prediction of the occurrence of acoustic vibration in shell-and-tube heat exchangers is not precise. It occurs when resonance develops once there is a near match of the acoustic frequency of the shell with a flow-induced exciting frequency produced by vortex shedding or turbulent buffeting. The prediction of these frequencies is controversial and subject to interpretation. To further complicate the situation, the prediction of the mode at which acoustic vibration first starts is uncertain. However, acoustic vibration can be prevented by conservative operation and design.

If acoustic vibration should develop, there are effective corrective measures to minimize or eliminate it. The most common measure is the installation of so-called "deresonating" or "detuning" baffles to increase the acoustic frequencies of the shell. These have little effect on the hydraulic or thermal performance of the exchanger other than reflected by a slight reduction in surface area for the tubes that must be removed for their installation.

A procedure for checking a shell-and-tube heat exchanger for possible acoustic vibration problems is outlined in this report. It involves checking for the most probable modes of acoustic vibration and suggesting possible design modifications to mitigate or eliminate acoustic vibration should it be predicted.