In condensers operating under vacuum, what is removed by air ejectors or vacuum pumps?

• A. Noncondensable gases
• B. Condensate
• C. Steam
• D. Water

Answer: (A)

In a vacuum condenser, the goal is to keep the pressure as low as possible so steam will condense efficiently. Noncondensable gases—like air or other gases that do not condense at the condenser’s operating temperature—till the system and form a gas layer at the heat transfer surface. That gas layer raises the effective resistance to heat transfer and makes it harder to maintain the vacuum, reducing condensation efficiency.

Air ejectors or vacuum pumps are used to remove these noncondensable gases from the condenser. By continuously pulling them out, the vacuum is maintained and heat transfer remains effective, allowing steam to condense more readily.

The condensate and water are the liquid byproducts of the condensation process and are handled separately (drained from the hotwell or condensate return system). The ejector’s job is specifically to remove the noncondensable gases, not the condensate.