🔍 Key Concepts

• Water-tube vs fire-tube – in which type does water flow inside the tubes, and in which type do hot gases flow inside the tubes? Look at the small circular elements around the furnace in the illustration. • Natural vs forced circulation – natural circulation relies on density difference between hot and cold water; forced circulation uses a pump to move water through the tubes. • Flow path of gases vs flow path of water/steam – trace the arrows showing combustion gas movement and compare with the arrows on the water/steam side and any pump shown (labeled near the feedwater inlet).

💭 Think About

• From the illustration, decide whether the tubes surrounding the combustion chamber are carrying water/steam or hot gases. How can the arrow directions help you decide? • Look carefully for any pump in the water/steam circuit (not just the basic feedwater pump). Does the system rely only on heating and rising of water, or is there a dedicated circulation path being driven mechanically? • Ask yourself: would this compact, high-output heating boiler on a supply vessel more likely use many small tubes with high circulation rate, or a large shell with a few big gas passages?

✅ Before You Answer

• Identify whether the hot gas path (from burner to uptake) is mainly inside the large central chamber or inside the small tubes. This tells you fire-tube vs water-tube. • Check if there is a separate circulation loop from the boiler through an external component (like the steam separator at F) driven by a pump, indicating forced circulation. • Confirm whether the only driving force for water movement inside the tubes would be density differences (natural circulation) or whether a mechanical pump is clearly part of the main circulation path.