🔍 Key Concepts

• Submerged tube evaporator operation and what creates/holds vacuum • Difference between a steady loss of vacuum and an unsteady (fluctuating) vacuum • Role of air ejectors/vents and how non‑condensable gases affect vacuum

💭 Think About

• Ask yourself: which condition would cause vacuum to swing up and down rather than stay low all the time? • Which option would most directly affect the amount of air/non‑condensables entering or being removed from the system? • Think about how a high water level or steam quality would usually show up in operation—would that make vacuum fluctuate, or just be consistently poor?

✅ Before You Answer

• Identify which choices mainly affect air/non‑condensable gas in the shell vs. those that mainly affect heat transfer or capacity • Decide which option would cause a variable introduction/removal of air, leading to unstable readings, rather than a constant condition • Mentally separate problems that cause constant low vacuum from those that cause surging or hunting vacuum and match that to the best choice