🔍 Key Concepts

• Heat transfer and insulation: How does scale on heat transfer surfaces affect the temperature of the shell and the vacuum inside the heater? • Vacuum and pressure relationship: In a condensing/evaporating system, what does an increase in absolute pressure mean for the vacuum? • System efficiency: Think about what happens to shell temperature and pressure when heat transfer becomes less efficient due to fouling or scale.

💭 Think About

• If scale acts like an insulator, would the shell metal temperature tend to go up or down as the inside surface gets coated? Why? • When heat transfer is reduced, how would that affect the amount of steam condensed and the vacuum level (absolute pressure) inside the shell? • Which combination of temperature change and pressure (vacuum) change shows that the unit is working harder but transferring heat less effectively?

✅ Before You Answer

• Be clear on the relationship: higher absolute pressure = lower vacuum, and lower absolute pressure = higher vacuum. • Ask yourself: with more scale, does the shell side look hotter or cooler from the outside, and does the system have better or worse vacuum? • Eliminate any choices where the pressure/vacuum change does not match what you’d expect from reduced heat transfer and poorer condensation.