In order to investigate the design method of a micro centrifugal compressor, which is the most important component of an ultra micro gas turbine, impellers having the outer diameter of 20mm were manufactured and tested. The impellers were manufactured by a stereolithography method and a machining. The designed corrected rotational speed is N=500,000 rpm. As a result, the impeller made by the machining was chosen for the present study. The impeller was rotated at N=250,000 rpm. The experimental results with the vaned diffusers having two different divergence angles and the vaneless diffuser were compared. It was found that the vaned diffuser attained the higher flow rate than the vaneless diffuser at the maximum pressure ratio. In addition the maximum pressure ratio was higher for the diffuser having a larger diffuser divergence angle at the high flow rate.

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