How does a fire-tube boiler differ from a water-tube boiler?

In a fire-tube boiler, the fundamental design involves hot combustion gases flowing through tubes that are surrounded by water. This allows for efficient heat transfer, as the hot gases heat the water outside the tubes. The design is advantageous for applications that require a moderate amount of steam or hot water, making it suitable for various heating and industrial processes.

This characteristic of hot gases traveling through the tubes that are enclosed in a water-filled shell is the defining feature of fire-tube boilers. It contrasts with water-tube boilers, where water flows through tubes that are exposed to the heat from flames and hot gases. This difference in arrangement affects the operating pressures, efficiencies, and applications of each type of boiler, with water-tube boilers generally being more suitable for high-pressure applications.

The other options highlight differences in configurations and sizes, but the key distinguishing feature is indeed the path of the hot gases and water interaction, solidifying the importance of option A in understanding the fundamental operation of fire-tube boilers.