Microturbocharger with Air Foil Bearings for a 100-W Class Micro Power System and Improvement of Rotordynamic Performance

Abstract

This article presents the experimental investigation of a microturbocharger supported on bump-type air foil bearings (AFBs) for a 100-W power generation. The microturbocharger was designed via thermodynamic cycle analyses as well as rotordynamic analyses and constructed using a centrifugal compressor and turbine with tip diameter of 10 mm. The tests for AFBs at rotating speeds up to 410 krpm driven by air showed a large subsynchronous motion at 100 Hz. However, AFBs with an additional viscoelastic film eliminated the subsynchronous response due to increased damping by the viscoelastic film. The compressor performance was evaluated numerically and experimentally.

KEY WORDS:

• Micro Power System
• Air Foil Bearing
• Viscoelastic Foil Bearing
• Rotordynamics

Acknowledgements

This work was supported by grants from the KIST project “R&D on Power Generation and Energy Storage Technology for Tri-Gen System” and the KEMCO (Korea) project “The Development of a High-Speed Motor System.” The authors thank Meerex Co., KIST, and KEMCO.

Review led by Gregory Kostrzewsky

Notes

The cooling air bled from the compressor for the stator cooling is not considered in this design study.

The efficiency of a generator in the MGT was reported to be 0.78 by Isomura, et al. (21). In this study, in the proposed configuration the generator is inside the MGT and the foil structure is placed between the stator and rotor. Hence, considering a possible eddy current loss of the foil structure and a larger air gap between the stator and rotor, the efficiency of the generator is assumed to be 0.7.

The optimum compression ratio could be found by equating with zero a derivative of the net power ratio to the compressor inlet power with respect to the compression ratio:

RAPP/PUP is a linear rotordynamic software (Rotordynamics–Seal Research, Loomis, CA) used to predict rotordynamic behavior of a rotor–bearing system with bearing force coefficients, based on the finite element method.

Actually, the two rigid modes experienced vibration resonances at very low speeds, but the speed-up rate was fast enough that the resonance effects could be neglected.