Conceptual Design of Scroll Expander-Compressor for Stirling Engine
نویسندگان
چکیده
Conceptual design of scroll expander and scroll compressor for 10 kW-class Stirling engine utilizing solar energy as heat source has been carried out. CO2 was chosen as the working fluid, since it is nontoxic, inflammable and it has relatively higher density among probably usable gases. Gas temperature at the expander inlet was set at 700 C, and that at the compressor inlet was at 40°C. System efficiency and engine power output were calculated for the high side pressure ranging from 5 MPa to 8 MPa with the pressure ratio of 1.5~4. System efficiency reached maximum at the pressure ratio of about 2.5, and the peak efficiency increased with increasing high side pressure. Due to safety concern, the pressure condition of 6 MPa / 2.5 MPa was chosen as design condition. Orbiting scroll members for the expander and compressor were designed to have double-sided structure in order to reduce the overall scroll size and to cancel out the axial gas forces acting on the orbiting scroll base plate. Expander and compressor were connected by two common shafts. Timing belt were adopted to link these two shafts, functioning as anti-rotation device for the orbiting scroll members. Gear assembly was used to extract the net power output from the expander. By parametric study on the scroll profile, smaller possible size for the scroll members was obtained. With the shaft speed of 3600 rpm, the shaft output of the designed scroll expander was calculated to be 45.4 kW, while input power for the scroll compressor was 34.5 kW, yielding 10.9 kW for the output power of the Stirling engine. System efficiency was estimated to be about 7.3%, and overall efficiencies of the scroll expander and compressor were around 84.1% and 88.3%, respectively.
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