🔍 Key Concepts

• Natural circulation vs. forced circulation in boilers • How density changes when water is heated and partially turned into steam • The path of downcomers and generating tubes in a boiler

💭 Think About

• Ask yourself: what physical property of water changes most when it starts turning into steam, and how could that create movement without a pump? • Think about why the water in the cooler downcomer tubes moves one way and the hotter steam/water mixture in the generating tubes moves the opposite way. • Which of the options would create a continuous circulation even if the boiler were perfectly level and the tubes were all the same size?

✅ Before You Answer

• Identify which choice involves a basic physical property (not just geometry like length or angle). • Consider which factor would still work to move water if the boiler were installed on a ship that rolls and pitches (changing its angle). • Check which option explains why hot mixture rises and cooler water descends in the boiler circuit.