What defines a fire tube boiler?

A fire tube boiler is defined by the arrangement of water and combustion gases. In these systems, the combustion gases flow through tubes which are surrounded by water. This is a crucial aspect of fire tube boilers because it allows the heat from the gases to transfer to the water, producing steam or hot water for various applications.

This choice highlights that the primary function of a fire tube boiler involves the flow of combustion gases within the tubes, while the surrounding water absorbs the heat, leading to an efficient heat exchange process. This specific configuration allows fire tube boilers to operate effectively, supporting a range of heating and power generation needs.

The other choices focus on elements that do not accurately describe a fire tube boiler's design. For example, mentioning water inside the tubes and combustion gases outside misrepresents the crucial heat exchange process inherent to fire tube boilers. Similarly, references to pressure vessels or radiant tube designs relate to other types of boiler systems and their functions, diverging from the defining characteristics of fire tube boilers.