Shell-and-tube is a heat exchanger type, not a compressor. The three actual compressor types used in vapor compression systems are: centrifugal (uses a rotating impeller to generate kinetic energy, converted to pressure via a diffuser), scroll (two intermeshing spirals compress refrigerant as vapor pockets decrease toward the center), and reciprocating (piston-cylinder mechanism driven by a crankshaft that compresses refrigerant on the upstroke).