🔍 Key Concepts

• Heat transfer in waste heat boilers (convection from hot gas to tube surface) • Effect of increasing surface area with fins on heat transfer • How gas velocity and flow direction relate to heat transfer and deposits

💭 Think About

• Ask yourself: What is the main reason engineers add fins to a heat‑transfer surface exposed to hot gases? • Consider which option matches the physical effect of adding more surface area to the outside of a tube. • Think about whether fins are primarily for changing gas speed/direction or for changing how much gas‑to‑metal contact area exists.

✅ Before You Answer

• Verify which choice directly relates to surface area and heat transfer rather than side effects like deposits. • Check whether slowing gases down would normally increase or decrease the heat transfer rate in a boiler gas path. • Confirm that fins are mounted on the fireside (gas side) of the tubes and what benefit that gives to the boiler’s thermal efficiency.