What does a spiral baffle do?

A spiral baffle is designed primarily to slow down the flow of flue gases. By creating a series of obstacles in the path of the gases, the baffle increases the residence time of the flue gases within the system. This extended interaction allows for more efficient heat exchange between the flue gases and the surrounding surfaces, optimizing performance in heating applications.

The design of the spiral baffle encourages the gases to travel a longer, more winding path, which enhances the heat transfer process, ensuring that more heat is extracted from the gases before they exit the system. This setup can lead to better efficiency and lower emissions, as it promotes complete combustion and better thermal management.

Consequently, while other options may relate to aspects of combustion systems, such as flue gas removal or temperature control, the primary function of a spiral baffle is specifically to moderate the speed of flue gases, making option C the most accurate choice in this context.