In a shell-and-tube heat exchanger, what is the primary purpose of baffles installed in the shell?

1. A. To prevent the tube bundle from expanding and buckling under thermal stress.
2. B. To separate the two fluid streams and prevent them from mixing.
3. ✓ To direct the shell-side fluid back and forth across the bundle, raising velocity and turbulence.Correct
4. D. To reduce the log-mean temperature difference between the two fluid streams.