Steam condenser terminology — define the index for quality of vacuum In steam power plant practice, the ratio of the actual vacuum obtained in a condenser to the ideal vacuum (corresponding to saturation pressure at the condensing temperature) is called what?

Introduction / Context:
The performance of a surface condenser is often summarized by how closely its vacuum approaches the ideal value at the measured condensate temperature. This question probes the correct name of that ratio used in steam plant performance testing and troubleshooting.

Given Data / Assumptions:

• Condenser operates near steady state with measurable barometric pressure and condensate temperature.
• Ideal vacuum equals barometric pressure minus saturation pressure at condensate temperature (no air leakage).
• Actual vacuum is what is read on the vacuum gauge (subject to air leakage and non-condensables).

Concept / Approach:
Define the index as: vacuum efficiency = actual vacuum / ideal vacuum. It reflects the influence of air ingress, inadequate air extraction, or maldistribution of cooling water. It is different from condenser heat-transfer effectiveness or overall “condenser efficiency,” terms that sometimes cause confusion in practice.

Step-by-Step Solution:

Verification / Alternative check:
When air leakage increases, actual vacuum drops while ideal remains the same for a given temperature, causing the ratio (vacuum efficiency) to fall—exactly what operators observe.

Why Other Options Are Wrong:

• Condenser efficiency: loosely used for heat-transfer performance, not the vacuum ratio.
• Nozzle/boiler efficiency: unrelated components.
• Air pump efficiency: concerns machinery, not the vacuum index definition.

Common Pitfalls:
Mixing pressure units; forgetting barometric corrections; comparing actual gauge vacuum directly to saturation pressure without converting to the same basis.

Final Answer: