🔍 Key Concepts

• Natural vs. forced circulation in water-tube boilers • How water density changes with temperature in boiler tubes • Flow path of water from drum → downcomers → generating tubes → drum

💭 Think About

• Think about what actually makes the water move inside the tubes once the boiler is firing, even if the feed pump stopped for a moment. • Consider what happens to water when it is heated in vertical tubes compared to cooler water in other parts of the boiler. • Ask yourself: which option would still cause circulation even without any moving mechanical parts?

✅ Before You Answer

• Verify which choice involves a difference in density due to heating. • Check which options describe something that would work only when a pump or flow device is running versus a passive effect. • Eliminate any option that suggests a siphon or shape effect that doesn’t depend on temperature and density changes.