Question

Main function of baffles on the shell side of a heat exchanger is to

• A. Decrease the pressure drop
• B. Reduce the scale deposit
• C. Hold the tubes in position
• D. Create turbulence

Hint:

Baffles in a heat exchanger primarily provide mechanical support to hold tubes in place, while also enhancing heat transfer by directing flow and creating turbulence.

Answer 1

The Correct Option is C

Step 1: Understand the role of baffles in a heat exchanger. 
In a shell-and-tube heat exchanger, baffles are plates or structures placed on the shell side (outside the tubes) through which the shell-side fluid flows. Baffles serve multiple purposes, but their primary functions are:
To support the tubes mechanically, preventing sagging or vibration. To direct the shell-side fluid flow across the tubes, enhancing heat transfer by creating turbulence and increasing the heat transfer coefficient. 
Step 2: Analyze the functions of baffles. 
Mechanical support: Baffles hold the tubes in position, providing structural stability and preventing vibration or deformation, especially in long tube bundles.
Flow direction and turbulence: Baffles force the shell-side fluid to flow perpendicular to the tubes (cross-flow), which increases turbulence, disrupts the boundary layer, and enhances heat transfer. However, this is a secondary effect of their placement.
Pressure drop: Baffles increase the pressure drop on the shell side because they create a more tortuous flow path, contrary to decreasing it.
Scale deposit: While baffles may influence flow patterns that could affect fouling, their primary purpose is not to reduce scale deposits; proper design and maintenance (e.g., fluid velocity, cleaning) address scaling. 
Step 3: Evaluate the options. 
(1) Decrease the pressure drop: Incorrect, as baffles increase the pressure drop by creating a more complex flow path. Incorrect.
(2) Reduce the scale deposit: Incorrect, as baffles are not primarily designed to reduce scaling; their effect on fouling is incidental. Incorrect.
(3) Hold the tubes in position: Correct, as the primary mechanical function of baffles is to support and hold the tubes in place, preventing vibration and ensuring structural integrity. Correct.
(4) Create turbulence: Incorrect, as while baffles do create turbulence (enhancing heat transfer), this is a secondary effect; their main function is structural support. Incorrect. 
Step 4: Select the correct answer. 
The main function of baffles on the shell side of a heat exchanger is to hold the tubes in position, matching option (3).