What is the effect of combustion gases in a watertube boiler?

In a watertube boiler, the design allows combustion gases to pass through the tubes that contain water. This configuration is critical for the efficient transfer of heat from the gases to the water, thereby generating steam. The heat from the combustion gases warms the tubes, and in turn, the water inside them absorbs this heat to produce steam. This process is essential for the operation of the boiler, as it directly impacts the efficiency and effectiveness of steam generation.

The other options do not accurately represent the function or behavior of combustion gases in a watertube boiler. For instance, combustion gases do not cool the water; rather, they are responsible for heating it. They are also not contained within the boiler in the same way that they might be in other types of boilers, such as firetube boilers. Additionally, combustion gases do not condense into liquid form within watertube boilers; instead, they remain as gases until they are vented out of the system after transferring their heat.