🔍 Key Concepts

• Overall heat transfer coefficient (U) and what affects it • Difference between metal tube wall and scale/deposit in terms of heat conduction • Effect of insulating layers on heat transfer in heat exchangers

💭 Think About

• Think about what scaling actually is physically on the inside of a tube. How does this new layer compare to the original metal in terms of conducting heat? • Which choice describes a fundamental change in the heat-transfer path itself, rather than a side effect like temperature or turbulence? • If you were to draw a cross-section of the tube wall plus scale, where would the main resistance to heat flow be?

✅ Before You Answer

• Identify which option talks about heat conduction through materials rather than just temperature changes or flow conditions • Consider whether scale typically has higher or lower thermal conductivity than metal tube material • Ask: does scaling usually make flow more or less turbulent, and would that normally increase or decrease heat transfer?