🔍 Key Concepts

• Identify where circulation begins and ends between the steam drum and the lower drum in a D-type boiler • Difference between downcomer tubes (protected from direct furnace heat) and riser/upcomer tubes (exposed to flame and hot gases) • How the location of item E on the illustration relates to water/steam flow direction in the natural circulation loop

💭 Think About

• Look at item E’s position relative to the furnace and the lower water drum: is it on the hot-gas side or shielded in a cooler, outer area? • Ask yourself: would the fluid in these tubes be mostly water flowing down or a water–steam mixture rising? What does that imply for their name? • Compare item E with the clearly heated tube banks in the furnace: does E look like part of the heated wall/riser bank, or like separate tubes carrying water to those heated sections?

✅ Before You Answer

• Verify whether item E connects from the steam drum down to the lower drum without being directly in the main flame path • Check if E is grouped as a separate bank of larger tubes, which is typical for downcomers rather than thin generating/riser tubes • Confirm that the term you choose matches the direction of flow implied by its location: down toward the lower drum or up toward the steam drum