Solving Vibration Issues in Shell and Tube Heat Exchangers
Shell and tube heat exchangers are ubiquitous due to their reliability and adaptability. However, like all mechanical systems, they’re not without their challenges. One common issue experienced by designers and operators alike is vibration. Excessive vibration can lead to acoustic noise, mechanical wear, and even tube failure. Thankfully, there are several tried and true methods for addressing and mitigating these vibrations. Here are some of the best solutions for vibration issues in shell and tube heat exchangers.
Acoustic Vibration
The frequency of sound produced by the high-velocity gas or vapour flow can create acoustic (sound) vibration in a heat exchanger, which can range from a low-hum to a piercing scream like a jet engine!. By manipulating the flow patterns or modifying certain design elements (shell diameter), it’s possible to shift the frequency to a range that doesn’t resonate with the structural elements of the heat exchanger. For example, introducing `deresonating’ or `detuning’ baffles that run lengthwise along the shell, one can increase the acoustic frequency of the shell, and eliminate the potential for acoustic vibrations.
Lowering the Velocity on the Shell Side
One of the most direct ways to combat flow-induced vibrations is by reducing the velocity of the fluid on the shell side. When the fluid flows at a high speed over the tubes, it can induce vibrations. By checking that the design allows for optimal flow rates and not excessively high velocities, it’s possible to reduce the forces acting on the tubes, thereby decreasing the potential for vibration. This can be achieved with larger nozzles, increased baffle spans, and/or increased baffle cuts. Increasing the tubing pitch can help as well.
Try to Increase the Natural Frequency of the Tube
Every structure has a natural frequency at which it tends to vibrate if disturbed. If the flow-induced frequency matches this natural frequency, resonance occurs, amplifying the vibrations. By changing the material, geometry, or support conditions of the tubes, one can alter their natural frequency, so it doesn’t match with any frequencies the fluid flow might induce. This can be achieved by reducing the maximum unsupported tubing spans by reducing baffle spacing (more baffles), adding intermediate baffle supports, changing to no-tube-in-window (NTIW) baffle layouts, or adding specifically placed tube supports (aka FIVERS – Flow Induced Vibration Supports) in areas of high-velocity and/or larger tube-spans.
U-Bend Supports
Another area of concern for vibration in a shell & tube heat-exchanger is the U-bend area on U-tube (AEU, BEU, CEU, etc) type heat exchangers. Historically, the U-bend area was ignored for heat-transfer and vibration as shell-side process flow was minimal in this area due to nozzle locations. However, many process engineers and thermal designers are now making use of the U-bend area for “free” heat transfer, placing the shell inlet or outlet nozzle beyond the U-bend. On larger diameter exchangers, the unsupported span of the outer U-tubes can easily exceed the longest span in the rest of the bundle. Without careful consideration, these long U-bends can easily move and vibrate at low velocities.
U-bends can be supported via a full-support baffle (welded together from strips), or a grid mesh made of rods. Multiple supports may be required for longer outer U-tubes. The inner U-bends do not require support, and the exchanger designer should specify at which point support is required.
Contact Altex Industries for Support and Manufacturing for Shell and Tube Heat Exchangers
If you find yourself plagued by persistent vibration issues or are just in the design phase and want to avoid future complications, turning to experts is always a wise choice. Altex Industries specializes in shell and tube heat exchangers, bringing a wealth of experience and knowledge to the table. By partnering with us, you can leverage our expertise to design, modify, or troubleshoot your heat exchangers for optimal performance and longevity. Contact Altex Industries for support and manufacturing for shell and tube heat exchangers.
