Which boiler type typically has water flowing through tubes that are heated externally?

A water tube boiler is designed with water flowing through tubes that are heated externally by combustion gases. This construction allows for high-pressure steam generation and efficient heat transfer. In a water tube boiler, the water circulates within the tubes, which are exposed to the hot gases produced from burning fuel. As the gases pass around these tubes, they transfer heat to the water, causing it to transition into steam.

This design is particularly advantageous for high-capacity and high-pressure steam applications due to its ability to operate under greater pressures compared to firetube boilers, where the hot gases flow through the tubes and heat the water in a larger shell surrounding the tubes. The water tube boiler's structure promotes rapid heat transfer and allows for quick adjustments to load demand, making it a popular choice in industrial and power generation settings.