# 초임계 CO2 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험

• Lee, Donghyun (Dept. of System Dynamics, Korea Institute of Machinery and Material) ;
• Kim, Byungok (Dept. of System Dynamics, Korea Institute of Machinery and Material) ;
• Sun, Kyungho (Dept. of System Dynamics, Korea Institute of Machinery and Material) ;
• Lim, Hyungsoo (Dept. of Extreme Energy System, Korea Institute of Machinery and Materials)
• 이동현 (한국기계연구원 시스템다이나믹스 연구실) ;
• 김병옥 (한국기계연구원 시스템다이나믹스 연구실) ;
• 선경호 (한국기계연구원 시스템다이나믹스 연구실) ;
• 임형수 (한국기계연구원 극한에너지기계 연구실)
• Accepted : 2016.12.30
• Published : 2017.02.28

#### Abstract

This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical $CO_2$ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of $40^{\circ}C$ between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.

#### Acknowledgement

Supported by : 한국기계연구원

#### References

1. Dostal, V., A supercritical carbon dioxide cycle for next generation nuclear reactors, Doctoral Thesis, MASSACHUSETTS Institute of Technology, USA, 2004.
2. Turchi, C., Ma, Z., and Wagner, M., "Thermodynamic study of advanced supercritical carbon dioxide power cycles for concentrating solar power systems", J. of Sol. Energy Eng., Vol. 135, pp. 041007, 2013. https://doi.org/10.1115/1.4024030
3. Kus, B., and Neks, P., "Development of one-dimensional model for initial design and evaluation of oilfree CO2 turbo-compressor," Int. J. of Refrig., Vol. 134, pp. 2079-2090, 2013.
4. Pecnik, R., Rinaldi, E., and Colonna, P., "Computational fluid dynamics of radial compressor operating with supercritical $CO_2$", J. of Eng. Gas Turbines and Power, Vol. 134, pp.122301, 2013.
5. D.Lee, B.Kim, "Bearing and Rotordynamic Performance Analysis of a 250 kW Reduction Gear System", J. Korean Soc. Tribol. Lubr. Eng., Vol. 32, No. 4, pp. 107-112, 2016. https://doi.org/10.9725/kstle.2016.32.4.107
6. Ettles, C., "The analysis and performance of pivoted pad journal bearings considering thermal and elastic effects", J. of Lub. Tech., Vol. 102, pp.182-192, 1980. https://doi.org/10.1115/1.3251465
7. Desbordes, H., Fillon, M. "Dynamic analysis of tilting pad journal bearing - Influence of pad deformations", J. of Tribol., Vol. 116, pp. 621-628., 1994. https://doi.org/10.1115/1.2928890
8. Rouch, K. E., "Dynamics of pivoted-pad journal bearing, including pad translation and rotation effects", J. of Tribol., J. of Lub. Tech., Vol. 26, pp. 102-109., 1983.
9. Chen, W. J., Introduction to Dynamics of Rotor Bearing Systmes, Chap. 6, Eigen Technologies, USA, 2007.