Which type of boiler is characterized by circulating water inside tubes?

A water-tube boiler is characterized by circulating water inside tubes. In this type of boiler, water is contained in tubes that are heated by the combustion gases surrounding them. The design allows for effective heat transfer and high efficiency, as the heat is directly transferred to the water flowing through the tubes.

Water-tube boilers are particularly advantageous in applications where high pressure and rapidly changing steam demands are common. They can accommodate higher pressures than many other boiler types and have a rapid start-up time, making them suitable for power generation and industrial applications.

In contrast, fire-tube boilers contain the combustion gases within tubes that are submerged in water, relying on the heat transferred from the gases to heat the surrounding water, which is a different principle than that used in water-tube boilers. Electric boilers generate steam through electrical resistance rather than through combustion, and condensing boilers recover heat from exhaust gases; neither of these types involves circulating water inside tubes in the same manner as water-tube boilers do.