What happens to cycle efficiency if the condenser vacuum is increased?

What happens to cycle efficiency if the condenser vacuum is increased?

• A. Increases cycle efficiency due to lower condenser pressure and greater turbine work
• B. Decreases cycle efficiency due to higher back pressure
• C. No change in cycle efficiency
• D. Increases only the condenser efficiency

Answer: (A)

The main idea is that cycle efficiency improves when the back pressure on the turbine is reduced. Increasing condenser vacuum lowers the condenser pressure, allowing the steam to expand more in the turbine. That bigger expansion produces more turbine work without needing more heat input from the boiler, so the net work rises while the heat added stays about the same. With a larger net work for roughly the same heat input, the efficiency goes up. In practice, this gain holds up to practical limits where pumping or condenser requirements don’t offset the benefit.

The main idea is that cycle efficiency improves when the back pressure on the turbine is reduced. Increasing condenser vacuum lowers the condenser pressure, allowing the steam to expand more in the turbine. That bigger expansion produces more turbine work without needing more heat input from the boiler, so the net work rises while the heat added stays about the same. With a larger net work for roughly the same heat input, the efficiency goes up. In practice, this gain holds up to practical limits where pumping or condenser requirements don’t offset the benefit.