Compressor Theoretical Displacement
The swept-volume pumping ceiling of a reciprocating compressor -- the figure the refrigerant-mass-flow tile names as a gap: displacement = (pi/4) x bore^2 x stroke x cylinders x RPM, divided by 1728 for CFM. A 2.0 in bore, 1.5 in stroke, 4-cylinder compressor at 1750 RPM sweeps 18.85 in^3/rev, or 19.1 CFM at 100% volumetric efficiency. The actual delivered volume is this times the volumetric efficiency, which falls as the compression ratio rises and the valves and rings leak, so a real machine moves less -- but this is the geometric number to compare two compressors on. Reciprocating positive-displacement only; the rated capacity at the operating condition governs.
Formula and source
displacement_cfm = (pi/4) x bore_in^2 x stroke_in x cylinders x rpm / 1728; displacement_cid_per_rev = (pi/4) x bore^2 x stroke x cylinders.
Reciprocating compressor theoretical (swept-volume) displacement (ASHRAE Refrigeration; positive-displacement compressor geometry), by name; the rated capacity at the operating condition governs.
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