Why volumetric efficiency of reciprocating compressors is below 100% Identify the principal reasons why the volumetric efficiency of a reciprocating air compressor is less than unity (less than 100%).

Introduction / Context:
Volumetric efficiency measures how much fresh charge actually enters the cylinder compared with the swept volume. In reciprocating compressors, several real effects reduce the volumetric efficiency below 100%.

Given Data / Assumptions:

• Conventional valve plates with finite pressure loss.
• Non-zero clearance volume to avoid piston-head contact.
• Some heating of incoming air and minor leakage paths.

Concept / Approach:
At the end of delivery, compressed air remains in the clearance volume at discharge pressure. During expansion at the start of the suction stroke, this residual air expands, occupying part of the swept volume and delaying fresh intake. Valve pressure drops and heating further reduce the mass taken in per cycle.

Step-by-Step Solution:
Clearance effect: residual high-pressure air expands during suction, reducing intake volume.Valve losses: pressure drop across suction valves lowers the cylinder pressure, diminishing mass flow.Superheating: higher inlet temperature increases specific volume, reducing mass per unit volume admitted.Leakages: blowby past rings/valves reduces net intake.

Verification / Alternative check:
Empirical correlations for volumetric efficiency include terms for clearance ratio, pressure ratio, temperature rise, and valve losses, matching observed performance.

Why Other Options Are Wrong:

• Any single cause alone (a, b, or c) is incomplete; multiple mechanisms act together.
• “None of these” contradicts standard compressor theory and practice.

Common Pitfalls:
Ignoring the dominant role of clearance; underestimating temperature effects when suction piping is hot or poorly cooled.

Final Answer:
all of these