Experimental Characterization of Two Single-Screw Expander Configurations for Pressure-Energy Recovery Under Cold and Heated Supply Conditions

Single-screw expanders can recover pressure energy from compressed gas, but measured shaft output depends on both operating conditions and prototype geometry. This study compares two compressed-air prototypes with built-in volume ratios of 2.04 and 3.13 and documents heated-supply transients for the 2.04 prototype. Cold-state tests covered 1400–3000 r/min and nominal regulated pressures of 1.0–1.8 MPa, with direct prototype comparisons at 1.4–1.8 MPa. At 1.8 MPa, the 3.13 prototype produced 102.8–126.7 W at 1400 r/min and 170.1–202.7 W at 3000 r/min. Its recorded output exceeded that of the 2.04 prototype by 10.8–24.4% and 1.0–10.6%, respectively, across the reported source-pressure intervals. These differences concern complete configurations because casing thickness and exhaust-port dimensions also differed. Power increased less than proportionally to speed between the endpoints; normalized linear fits describe the 1.8 MPa data within the tested range. Instrument-only expanded power uncertainty was 0.21–1.00% across the cold-state matrix under the stated specification assumptions. Several 1.0 MPa records were non-monotonic, but their physical origin remains unresolved without repeatability statistics. Five heated-supply runs at nominal settings of 435–500 K showed delayed temperature rises and intermittent pressure fluctuations. Missing mass flow, synchronized hot-state shaft power, and complete uncertainty information preclude efficiency comparisons and quantification of the net benefit of heating.