🔍 Key Concepts

• Effect of scale (mineral deposits) on heat transfer surfaces in an evaporator • Relationship between heat transfer efficiency and freshwater production rate • How fouling affects vacuum, tube life, and distillate quality

💭 Think About

• Ask yourself: if there is a layer of scale on the heating surfaces, does heat flow become easier or harder, and what does that do to the rate of evaporation? • Consider which effects would be gradual versus immediate (for example, would tube failure or vacuum loss happen right away just from scale forming?). • Think about whether poorer heat transfer would normally make the distillate purer or less pure, and whether more heat or less heat reaches the seawater.

✅ Before You Answer

• Which option best matches a gradual reduction in heat transfer rather than a sudden catastrophic event? • Eliminate any choices that suggest an immediate drastic failure unless scale directly causes that in a short time. • Focus on the option that most directly reflects lower evaporation/production rate resulting from insulated heating surfaces.