Masaru Matsui

Axial and Radial Force Control for a CO2 Scroll Expander

In this study, the scroll profile of the scroll expander was designed for CO2 refrigerant in order to make use of overexpansion and to control the axial force on the thrust bearing. This approach realized that the orbiting scroll never separated from the stationary scroll even when the operating condition changed dramatically. From the analysis on the oil-film pressure forces of the main and eccentric bearings, the radial force between the scroll wraps could be controlled, which in turn contributed to a decrease in the leakage loss in the expansion process. Test results for a prototype of the scroll expander with high-pressure shell design demonstrated the volumetric efficiency as high as 96%.

Development of the High-Efficiency Technology of a CO2 Two-Stage Rotary Expander

To improve the coefficient of performance of a heat pump cycle by using carbon dioxide, an expander was developed that recovers rotation power from the large pressure difference in the cycle and uses the power to partially drive the cycle. In the cycle, a two-stage rotary expander was adopted, because the suction control mechanism is not necessary in it. A performance analysis model was developed by combining the dynamic mechanical analysis and the refrigerant pressure analysis in the expander and taking refrigerant leakage into consideration. After examining the impact of each design parameter on the performance of the two-stage rotary expander, an optimized design was determined. With this design, an expander efficiency of 54% could be achieved in a short period of time.