How does a shell-and-tube heat exchanger operate?

• A. Both fluids flow through the same shell space
• B. One fluid flows through tubes, another around tubes in shells, transferring heat across the tube walls
• C. Fluids mix in the shell to exchange heat
• D. Heat exchange occurs through direct contact between fluids

Answer: (B)

The main idea is transferring heat between two fluids without letting them mix, using a solid barrier. In a shell-and-tube heat exchanger, one fluid travels through a bundle of tubes, while the other fluid flows around those tubes inside a larger shell. Heat moves through the tube walls from the hotter fluid to the cooler one, providing the temperature change without any mixing of the fluids. This setup creates a large surface area for efficient heat transfer and keeps the streams separate.

That’s why this option fits best: it describes one fluid inside tubes and the other around the tubes in the shell, with heat crossing the tube walls. The other ideas would require mixing the fluids, sharing the same space, or relying on direct contact, which is not how shell-and-tube exchangers operate.