What creates flow in a Thermosyphon reboiler?

• A. Mixing heat and liquid.
• B. A pump drives the flow.
• C. External agitation from a motor.
• D. Gravity alone without heating.

Answer: (A)

Flow in a thermosyphon reboiler comes from natural circulation created by heating the liquid. When heat is applied, the liquid near the heat source boils and becomes less dense. This lighter liquid tends to rise, while cooler, denser liquid moves downward under gravity, establishing a continuous loop without any pump. That interplay of heating and liquid density drives the flow, which is why mixing heat and liquid is the correct description.

A pump isn’t used because there’s no external energy forcing the flow, external agitation isn’t part of how a thermosyphon operates, and gravity alone won’t sustain circulation without the density differences produced by heating.