What creates flow through a Thermosyphon reboiler?

• A. Natural circulation
• B. Forced circulation by a pump
• C. By gravity alone
• D. Electrical heating element

Answer: (A)

Flow in a thermosyphon reboiler is produced by natural circulation driven by density differences created when the liquid is heated. Heating causes boiling in the loop, making the hot liquid and vapor less dense so they rise in the hot leg. The cooler, denser liquid then falls and returns by gravity to the bottom of the loop, drawing more liquid into the heated section and keeping the circulation going without a pump. A pump would be needed for forced circulation, and while the heat source provides the energy, the movement of liquid itself comes from buoyancy due to the density change rather than an external pumping action.