We made the prototype of the scroll expander for CO_2 refrigerant, which had the high-pressure vessel. We also designed the new scroll profile to make use of "over-expansion" and control the axial force on the thrust bearing. These techniques realized that the orbiting scroll never separated form the stationary scroll when the operating condition changed dramatically. As the result, the high volumetric efficiency was achieved. We also calculated the oil-film pressure of the main and eccentric bearings, considering both the dynamic behavior of the shaft and the interaction between the orbiting and stationary scroll wraps. From the calculation results, we could control the radial force between the scroll wraps, which contributed to decrease the leakage loss in expansion process.
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