Page 167 - Handbook of Energy Engineering Calculations

Hence, the tube-bundle vibration problem is unlikely to occur. However, the
vortex shedding and acoustic frequencies are close. If the air flow increases
slightly, the two frequencies will be close. By inserting a baffle in the tube
bundle (dividing the ductwork into two along the gas flow direction) we can
double the acoustic frequency as the width of the gas path is now halved.

This increases the difference between vortex shedding and acoustic
frequencies and prevents noise problems.
Noise problems arise when the acoustic and vortex shedding frequencies

are close—usually within 20 percent. Tube-bundle vibration problems arise
when the vortex shedding frequency and natural frequency of the bundle are
close—within 20 percent. Potential noise problems must also be considered
at various turndown conditions of the equipment.

Related Calculations. For a thorough analysis of a plant or its components,

evaluate the performance of heat-transfer equipment as a function of load.
Analyze at various loads the possible vibration problems that might occur. At
low loads in the above case, tube-bundle vibration is likely, while at high
loads acoustic vibration is likely without baffles. Hence, a wide range of

performance must be reviewed before finalizing any tube-bundle design, Fig.
20.
This procedure is the work of V. Ganapathy, Heat Transfer Specialist,
ABCO Industries, Inc.