Question

If a baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid

• A. Remains unchanged
• B. Increases
• C. Decreases
• D. Increases or decreases based on number of shell passes

Hint:

Increasing baffle spacing reduces shell side velocity, so shell side Reynolds number decreases.

Answer 1

The Correct Option is C

In a shell and tube heat exchanger, baffles are used on the shell side. Baffles support the tubes and direct the shell side fluid across the tube bundle. When baffle spacing is small, the flow area becomes smaller and the shell side velocity becomes higher. When baffle spacing is increased, the flow path becomes wider. As a result, shell side fluid velocity decreases. Reynolds number is given by: \[ Re=\frac{\rho vD}{\mu} \] where, \[ v=\text{fluid velocity} \] For the same fluid and characteristic dimension, Reynolds number is directly proportional to velocity: \[ Re\propto v \] So, if baffle spacing increases, shell side velocity decreases. Therefore, Reynolds number also decreases. Hence, the correct answer is: \[ \text{Decreases} \]