What is the main difference between a fire-tube boiler and a water-tube boiler?

The main difference highlighted in the correct answer is based on the flow of heat and water in the two types of boilers. In a fire-tube boiler, the configuration involves hot gases produced from combustion passing through tubes that are surrounded by water. This results in the transfer of heat from the gases to the water, which then generates steam. The design allows for effective heat exchange due to the surface area provided by the tubes, ensuring that the water is heated efficiently.

This differentiates it significantly from a water-tube boiler, where the water flows through tubes that are heated by combustion gases surrounding them. In this scenario, steam is produced within the tubes as heat transfers to the water. The distinction between the flow paths is crucial as it affects the design, application, and performance characteristics of each boiler type.

While electric heating elements are not applicable specifically to fire-tube boilers, and water-tube boilers typically operate with higher efficiencies compared to fire-tube boilers, the core difference remains in the flow of hot gases and water, which the correct answer clearly identifies. Understanding this fundamental aspect of boiler design is essential for managing and operating steam systems effectively.