Functions and application scenarios of baffles

Baffles are one of the core components of shell and tube heat exchangers. Their design directly affects the flow characteristics of the shell-side fluid, heat transfer efficiency and equipment stability. This article deeply analyzes the role of baffles from three aspects: basic functions, engineering value and innovative design.

1. From fluid control to structural support

①Forced turbulence and heat transfer enhancement

•     Flow path reconstruction: The baffles periodically change the flow direction of the shell-side fluid (horizontally or longitudinally), break the laminar boundary layer, convert laminar flow into turbulent flow, and significantly improve the shell-side convective heat transfer coefficient. Experiments show that the reasonable arrangement of baffles can increase the shell-side heat transfer efficiency by 30%~50%.
•     Flow velocity distribution optimization: Eliminate the "short circuit" phenomenon of shell-side fluid (the fluid flows directly along the gap between the shell and the tube bundle), force the fluid to flow evenly through all heat exchange tube surfaces, and avoid local heat transfer blind areas.

②Mechanical support and vibration suppression

•     Tube bundle positioning: The openings of the baffles are closely matched with the heat exchange tubes, fixing the tube bundle spacing to prevent the tube bundle from being displaced due to fluid impact or gravity.
•     Anti-vibration design: Under high pressure or high flow rate conditions, the baffles reduce the risk of fluid induced vibration (FIV) by increasing the stiffness of the tube bundle. For example, a chemical plant reduced the baffle spacing from 300 mm to 200 mm, reducing the tube bundle amplitude from 1.2 mm to 0.3 mm and avoiding fatigue fracture.

③Balance of pressure drop and energy consumption

•     Dense baffles (small spacing): Enhance turbulence but significantly increase pressure drop (e.g., if the spacing is reduced by 50%, the pressure drop will increase by about 200%);
•     Sparse baffles (large spacing): Reduce pump power consumption, but may sacrifice heat transfer efficiency.

 2. Tips for baffle design

①Baffle Type Selection

Segmented baffle

②Geometric parameter optimization

•     Cut rate (Cut%): The ratio of the notch height of the arcuate baffle to the shell diameter, usually 20%~35%. Too low a cut rate can easily lead to a dead zone in the flow, while too high a cut rate can weaken the turbulence effect.
•     Baffle Pitch: The recommended value is 0.2~1 times the shell diameter. Too small a cut rate can lead to a sharp increase in pressure drop, while too large a cut rate can reduce the support effect.
•     Helix Angle: The helix angle (30°~45°) of the helical baffle determines the fluid rotation intensity, and CFD simulation is required to balance the pressure drop and heat transfer.

③Special working condition selection

•     Anti-fouling design: For media prone to scaling (such as cooling water), large cut-out ratio or spiral baffles are used to reduce the deposition of dirt in the retention area.
•     Low-temperature brittle crack prevention: In LNG heat exchangers, austenitic stainless steel (such as 304L) is used for baffles to avoid low-temperature brittle failure.

3.Failure Cases and Design Lessons

Baffle design is not that simple. There are many cases that tell us what we must pay attention to when designing. And the later work also needs special attention.

①Vibration fracture accident

•     A refinery had excessive baffle spacing (400 mm), which resulted in excessive vibration of the tube bundle and 12 heat exchange tubes breaking within three months. After improvement, a 250 mm spacing + double-bow layout was adopted, and the equipment has been running stably for more than five years.

②Scaling and clogging problem

•     In seawater coolers, the heat transfer efficiency of traditional bow-shaped baffles decreased by 40% within half a year due to the accumulation of dirt in the retention area. After switching to spiral baffles, the dirt growth rate decreased by 60% and the cleaning cycle was extended to 2 years.

Baffles have evolved from simple "guide vanes" to carriers of synergistic effects of heat transfer, mechanics and fluid dynamics.Engineers need to balance heat transfer, pressure drop, vibration and cost from a global perspective to unleash the maximum potential of heat exchangers.If you have any questions or needs, you can click this paragraph to contact our engineers.