Condenser vacuum definition The actual vacuum in a condenser equals ________.

Introduction / Context:
Condenser performance in steam plants is often expressed in terms of “vacuum,” which indicates how far below atmospheric pressure the condenser operates. Understanding the correct definition prevents confusion when reading gauges and calculating turbine back pressure and overall plant efficiency.

Given Data / Assumptions:

• Barometric (atmospheric) pressure P_atm measured at site conditions.
• Absolute pressure in the condenser P_abs (sometimes called “actual pressure” in exam phrasing).
• Vacuum gauges are typically calibrated to read zero at atmosphere and positive toward lower-than-atmospheric absolute pressures.

Concept / Approach:
By definition, condenser vacuum (on an absolute basis) is the difference between the local barometric pressure and the absolute pressure existing in the condenser: Vacuum = P_atm − P_abs. A perfect vacuum would correspond to P_abs = 0, yielding Vacuum = P_atm. In practice, the vacuum is less due to non-condensable gases, air leakage, and heat load.

Step-by-Step Solution:
Measure local barometric pressure P_atm.Measure condenser absolute pressure P_abs (or convert from a compound gauge reading).Compute actual vacuum: Vacuum = P_atm − P_abs.Use this value to assess air removal and condenser effectiveness.

Verification / Alternative check:
Example: If P_atm = 1.013 bar and P_abs = 0.07 bar, vacuum = 0.943 bar (about 710 mmHg), consistent with typical surface condenser operation.

Why Other Options Are Wrong:
Adding pressures (a) is dimensionally incorrect for vacuum definition; (c) and (d) mix gauge and absolute systems improperly; (e) yields a negative value for normal operation.

Common Pitfalls:
Confusing gauge readings with absolute; forgetting that barometric pressure varies with altitude and weather, affecting reported vacuum.

Final Answer:
barometric pressure - actual pressure