What are the main differences between fire-tube and water-tube boilers?

Fire-tube boilers and water-tube boilers differ fundamentally in their design and the way they transfer heat. In fire-tube boilers, the combustion gases travel through tubes that are filled with water, transferring heat from the gases to the water surrounding the tubes. This design means that the heat is applied to the outside of the tubes, with the water heated by the thermal energy of the flue gases.

In contrast, water-tube boilers operate on a different principle: they contain water-filled tubes that are heated by hot gases flowing around them. This design allows for a larger surface area and more direct contact between the water and the heat source, enhancing heat transfer efficiency.

This distinction in the arrangement of water and combustion gases contributes to differences in thermal performance, size, and operational characteristics. Overall, the variation in how each type of boiler manages heat transfer highlights the fundamental operational differences between fire-tube and water-tube systems, making option B the correct choice.