Multi-Model VE Comparison for Reciprocating Compressors
It includes five models: Theoretical, Worthington, Cooper-Bessemer, and NGPSA (slow- and high-speed) correlations for reciprocating compressor flow prediction.
Volumetric efficiency is the ratio of actual gas delivered to the swept volume of the cylinder, affected by clearance volume, pressure ratio, and gas properties.
Use NGPSA Slow Speed for integral and low-speed separable units below 500 RPM, and NGPSA High Speed for separable units at 500 RPM and above. The High Speed model uses a doubled loss coefficient (0.02 vs 0.01) to account for greater valve flutter and gas inertia at speed.
Higher compression ratios reduce volumetric efficiency through two mechanisms: greater clearance gas re-expansion (the T = CL×(R^(1/k)-1) term) and increased mechanical losses from valve pressure drop and ring leakage. Spread between the five models also widens with increasing R, ranging from about 7% at R=1.5 to 12% at R=4.