The scroll profile modification and the inlet port area regulation were proposed to improve power output and the pneumatic conversion efficiency of a scroll expander. The circle involute-line profile modification combining with the inlet port regulation was adopted to modify a scroll compressor with the circle arc line profile. The experiment results show that the whole efficiency of the modified scroll expander would be up to 53%. The power output increased with the supply pressure

reaching 780 W at the supply pressure of 550 kPa. Under the same condition

the power output increased by 100 W and the whole efficiency rose by10% when the inlet port area increased by 30%. These results confirm the feasibility of the improvement method. The present method may be useful for the structure design of scroll expanders.