Meaning of “air power” in compressor analysis The “air power” of a compressor refers to the theoretical power imparted to the air stream (e.g., isothermal or isentropic requirement), not the measured indicated or brake power. Which option best describes this?

Introduction / Context:
Different “powers” appear in compressor discussions: indicated power (from the cylinder indicator diagram), brake (shaft) power supplied by the driver, mechanical losses, and the theoretical power actually imparted to the air—often called air power. Distinguishing these terms helps avoid misinterpretation of efficiency metrics.

Given Data / Assumptions:

• Steady compressor operation with fixed inlet and discharge conditions.
• Air treated as a perfect gas for ideal calculations.

Concept / Approach:
Air power is the minimum theoretical power required to raise the air from suction to delivery conditions, based on a chosen ideal process (commonly isentropic or isothermal). Indicated power includes thermodynamic and valve-flow losses inside the machine; brake power further includes mechanical losses in bearings, seals, and drive. Therefore, air power is not identical to indicated or brake power; it is the ideal benchmark that appears in efficiency definitions.

Step-by-Step Solution:

Verification / Alternative check:
Efficiency relations: isentropic efficiency (compressor) = air power (isentropic) / brake or indicated power, depending on convention. This highlights that air power is a distinct theoretical quantity.

Why Other Options Are Wrong:

Indicated/brake/frictional powers are measurement categories, not the ideal minimum theoretical requirement.“Mechanical efficiency times brake power” is not a standard definition for air power.

Common Pitfalls:
Equating air power with indicated power because both are “about the air.” They are related but not identical; one is theoretical, the other is measured from the cycle within the cylinder.

Final Answer:

None of these