What does maintaining a high vacuum in the condenser improve?

What does maintaining a high vacuum in the condenser improve?

• A. Condenser heat transfer coefficient
• B. Turbine work output and cycle efficiency
• C. Steam dryness
• D. Feedwater quality

Answer: (B)

The main idea is that a very low condenser pressure (a high vacuum) lowers the exhaust pressure that the turbine sees. In a steam power cycle, the turbine expands steam from boiler pressure down to the condenser pressure. If that exhaust pressure is reduced, the expansion ratio increases, so the specific work produced by the turbine goes up. With more work being generated for the same amount of heat added in the boiler, the overall cycle efficiency improves. This is the direct and primary benefit of maintaining a high vacuum in the condenser. The other aspects listed—steam dryness, feedwater quality, or the condenser’s heat transfer coefficient—are not the main effects of condenser vacuum. Dryness relates to the steam quality entering the turbine and moisture separation, feedwater quality to the water treatment and condensate return system, and the heat transfer coefficient to surface area, fouling, and temperature driving force rather than vacuum alone.

The main idea is that a very low condenser pressure (a high vacuum) lowers the exhaust pressure that the turbine sees. In a steam power cycle, the turbine expands steam from boiler pressure down to the condenser pressure. If that exhaust pressure is reduced, the expansion ratio increases, so the specific work produced by the turbine goes up. With more work being generated for the same amount of heat added in the boiler, the overall cycle efficiency improves.

This is the direct and primary benefit of maintaining a high vacuum in the condenser. The other aspects listed—steam dryness, feedwater quality, or the condenser’s heat transfer coefficient—are not the main effects of condenser vacuum. Dryness relates to the steam quality entering the turbine and moisture separation, feedwater quality to the water treatment and condensate return system, and the heat transfer coefficient to surface area, fouling, and temperature driving force rather than vacuum alone.