🔍 Key Concepts

• Heat transfer in boilers (conduction through metal, convection in water/steam, effect of insulation or fouling layers) • Effects of scale and deposits on thermal conductivity and metal temperature • Difference between water chemistry control and heat transfer efficiency

💭 Think About

• Which option directly affects how easily heat can pass from the hot gases, through the metal, into the water? • Which options are mainly about preventing corrosion or chemical damage, rather than maximizing the rate of heat transfer? • Think about what happens to heat transfer if there is any extra layer between the metal tube and the boiler water.

✅ Before You Answer

• Identify which choice changes the thermal resistance between the metal heating surface and the boiler water. • Decide which items are primarily about corrosion control versus instantaneous heat transfer rate. • Recall that even if chemistry is perfect, any insulating layer on the waterside will reduce heat transfer.